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植被物候对极端气候响应及机制

花匠小妙招
2024-09-28 16:44

1 引言

气候变化导致全球极端气候事件频发，生态系统面临的风险日益增加[1-2]。IPCC第六次工作报告指出，未来持续增温会引起愈加频繁和强烈的极端温度、降水和干旱事件[3-4]。目前关于极端气候事件的定义不尽相同，IPCC报告将极端气候事件定义为天气或气候变量的值高于或低于某个阈值[5]，气候变化检测与极端气候事件指标专家组（ETCCDI）推荐了27个极端气候核心指标，并被广泛用于极端气候变化研究[4,6 -7]。高温热浪、极端干旱、暴雨洪涝和寒潮等极端气候事件具有突发性强、破坏性大和难以预测等特征，当植物不能适应气候异常变化时会抑制植物光合作用，导致生产力降低，影响陆地生态系统结构和功能[8⇓⇓-11]。因此，认识植被动态对极端气候事件的响应及其机制，对于深刻理解陆地生态系统对气候变化与极端气候的响应具有重要意义。

植被物候是植被对气候变化响应最敏感的生物学指标之一，中国著名地理学家竺可桢曾依据物候绘制了中国近五千年来的温度变化曲线[12]。植被物候变化对陆地生态系统碳水循环和能量平衡具有重要的控制作用[13]。温度是影响植被物候的重要因素[14⇓⇓-17]，之前的研究主要关注植被物候对平均温度的响应，如日均温升高导致植被返青期提前、枯黄期推迟[18⇓⇓⇓⇓⇓-24]。除温度外，降水对植被物候也有很强的控制作用，生长季开始前1~3个月降水不仅可以直接影响植被物候[25⇓-27]，还可以通过调节辐射和热量需求间接影响植被物候，在干旱半干旱地区尤为显著。近年来，一些学者研究了植被生长与植被物候对极端气候事件的响应[28]，发现春季极端高温导致植被返青期提前、极端复合干旱减缓地球变绿[29]，生长季极端干旱和高热胁迫导致植被枯黄期提前[6]。与气候平均态相比，极端气候事件对植被物候的影响更加明显[19,30⇓⇓⇓⇓⇓ -36]，如极端干旱发生年份植被返青期与多年平均返青期相比延迟了6~34 d，枯黄期提前了约12 d，远远超过气候平均态的影响[37⇓-39]。但是目前植被物候对极端气候事件响应研究依旧较少，响应机制仍不清楚。因此，本文从气候冷热干湿性质出发，以极端温度（高温和低温）、极端干旱、极端降水等常见极端气候事件为例，系统梳理植被物候对极端气候事件的响应及其潜在机制（图1），并针对目前研究的不足对未来研究方向提出展望。

图1 植被物候对极端气候事件响应示意图注：在表示植被物候对极端气候事件的响应时，“＋”代表植被返青期、枯黄期推迟，“－”代表植被返青期、枯黄期提前。在表示极端气候事件对植被死亡、光合作用、蒸腾作用和固碳能力影响时，“＋”代表促进作用，“－”代表抑制作用。

Fig. 1 Schematic diagram of response of vegetation phenology to extreme climatic events

Full size|PPT slide

2 植被物候对极端温度的响应及机制

温度是影响植被物候的关键因素[18,40⇓ -42]，植物生长存在最适温度范围，温度过高或过低超出适宜植物生长的温度阈值，会影响植物正常的生理代谢，改变植被返青期和枯黄期。以往研究关于极端高温和极端低温的定义大多采用固定阈值法（如日最高气温超过35 ℃）与百分位阈值法[43-44]，或者根据ETCCDI推荐的极端气候指数进行计算[45-46]，极端高温指数如暖昼日数、冷昼日数、年最大（小）日最高气温以及持续暖日日数等指标，极端低温指数如冷昼日数、冷夜日数、年最大（小）日最低气温以及持续冷日日数等指标。

2.1 植被物候对极端高温的响应及机制

随着全球变暖，极端高温天气的发生频率、强度和空间范围大幅增加[3]。研究表明，春季极端高温显著影响北半球温带和寒带森林的冠层发育[47]，导致欧洲和北美洲温带森林返青期提前了3~40 d[48-49]，实验研究也发现了相似的结果[50]。但是，一些研究得到了相反的结果，例如冬季多重极端变暖事件导致亚北极欧石楠地优势矮灌木返青期推迟了一周[11]。与植被返青期相比，植被枯黄期对极端高温的响应更为复杂。秋季极端高温（如暖昼日数、中热胁迫和暖夜日数）导致北半球高纬度植被枯黄期延迟[7]，比如极端高温导致欧洲高纬度地区常绿针叶林、落叶阔叶林和针阔混交林的枯黄期延迟了5~15 d[51]。同时，极端气温暖极值（年最大日最低气温、年最大日最高气温、暖昼日数和暖夜日数等）升高也广泛推迟了中国温带草地枯黄期[34,52]。但是，生长季极端高温也会缩短植被生长季长度，如极端高温导致中国高寒草原、新英格兰温带落叶林、阿尔卑斯山草地枯黄期提前[53⇓-55]，进而导致生长季变短。不同区域植被枯黄期对极端高温指数的响应存在差异，如内蒙古植被枯黄期主要受到春夏暖昼日数和暖夜日数影响[56]，而中亚植被枯黄期除了受到暖昼日数的影响外，还受到冷昼日数和年均日最高气温的影响[57]。

极端高温可能导致植被返青期和枯黄期提前或者推迟，植被物候对极端高温的响应机制在不同区域不同植被类型存在较大差异。在较寒冷或较湿润地区，早春极端高温可以提高植物酶的活性，加快植被生长，导致植被返青期提前[58⇓-60]。但由于热需求、冷激、降水以及光周期对植被返青期存在复杂相互作用[25,61⇓ -63]，冬季极端高温也可能导致植物因无法满足解除休眠的低温刺激而推迟植被返青期。植被返青期对极端高温事件的响应因植被类型而异，如祁连山草地返青期比森林和灌木对极端高温的响应更敏感[37]，这可能与区域干旱严重程度和海拔高度有关。对于植被枯黄期，高热胁迫能够催化植物蛋白质降解，进而促使植被提前枯黄[64-65]，但是发生在较寒冷地区的极端高温事件却能够促进光合作用，维持植物的生理活动，延缓植被枯黄期。不同类型植被枯黄期对极端高温事件的响应也存在差异。以内蒙古草地为例，荒漠草原、森林草原和典型草原西部的枯黄期主要受春夏季暖昼日数的影响，而森林和典型草原东部枯黄期主要受春夏季暖夜日数的影响[56]，且不同类型草地枯黄期受到极端高温的影响程度存在差异[34,52,55]，这可能与区域干旱程度有关。

2.2 植被物候对极端低温的响应及机制

除极端高温事件，极端低温事件对植被物候也具有重要影响。春季极端低温导致植被返青期延迟，如2007年春季霜冻导致大部分美国温带落叶林树种返青延迟16~34 d[66]。植被返青期对不同强度的极端温度事件的响应存在差异，如季前的年最大日最高气温与年最小日最高气温，以及年最小日最低气温均与中国温带植被返青期之前存在显著负相关关系，但季前的年最大日最低气温却与返青期存在显著正相关关系[67]。不同类型植被返青期对极端低温事件的响应程度也不相同，如在中国温带植被区域，草地和植被稀疏区域的返青期与季前霜冻日数的显著相关系数明显大于混交林[67]。对于植被枯黄期，秋季霜冻通常导致植被枯黄期提前，如霜冻日数、冷夜日数和冷昼日数等低温胁迫导致北半球中高纬度植被枯黄期平均每年提前0.02~0.59 d，且随纬度降低极端低温对植被枯黄期的提前效应减弱[7]。此外，中国内蒙古沙地和草原沙漠的植被枯黄期主要受到春夏季冷夜日数和冷昼日数的影响[56]。

与极端高温类似，植被物候对极端低温的响应机制也较为复杂，极端低温可能导致植被返青期推迟、枯黄期发生提前或者推迟现象。气候变暖导致植被返青提前，增加花叶暴露在极端低温环境中的可能性[68⇓⇓-71]，研究发现，晚春霜冻使温带树种生长速度减慢[72]，导致植物叶片脱落、冠层发育迟缓甚至死亡，严重影响生态系统生产力[73]。总的来说，极端低温推迟植被返青期主要有两方面原因：一是当极端低温发生在早春时，极端寒冷会减缓季前热量的积累，会延迟植被返青期；二是当极端低温发生在晚春时，霜冻可能使植被叶芽受损，需要植物重新发芽展叶，导致植被返青期延迟。对于植被枯黄期，由于晚秋霜冻时间发生频率较高，植物通过自身的进化机制，为了避免遭受霜冻损害提前枯黄期。当生长季霜冻导致植被叶片受损时[70,74 -75]，植物会通过推迟秋季衰老补偿生长亏损[76]，这可能是极端低温导致植被枯黄期推迟的主要原因。此外，不同类型植被枯黄期对极端低温事件的响应不同，如高寒草原、高寒草甸、典型草原和荒漠草原与极端低温之间以负相关为主，而草甸草原与极端低温之间则以正相关为主[55]，这可能与植被所在区域干旱严重程度有关，草甸草原所在区域较为干旱。

2.3 植被物候对其他极端温度事件的响应及机制

除了极端高温和极端低温事件，昼夜不对称增温也会影响植被物候，而且存在明显的区域差异。白天升温导致北半球中高纬度植被返青期提前，其效应大于夜晚升温和日均温升高[41]。而对于青藏高原和中国东部样带，植被返青期对夜晚升温的响应大于白天升温，这可能与低温约束有关，春季夜晚升温加快了植被返青所需热量累积进而提前返青[77-78]。植被返青期对昼夜不对称增温的响应还存在季节性差异，中国温带草原返青期在冬季主要受白天升温影响、在春季主要受夜晚升温影响[79]。昼夜增温对植被返青期还会出现相反作用[80]，冬季白天升温促进热量积累提前植被返青期，而冬季夜晚升温减少冷激延迟植被返青期[81]。植被枯黄期对昼夜不对称增温的响应与水分胁迫有关[82]，白天和夜晚升温分别导致湿润地区植被枯黄期推迟和提前、干旱地区植被枯黄期提前和推迟。除昼夜不对称增温外，北半球中高纬度植被返青期也对温度日较差响应敏感，但在温度季节性较强的地区，植被返青期对季前温度日较差的敏感性较小，这可能与植被热耐受性增强有关[83]。

3 植被物候对极端降水的响应及机制

植被物候对极端降水的响应比对极端温度的响应更为复杂。极端降水事件的定义也常采用固定阈值法（如日降水量超过1 mm）与百分位阈值法[84-85]，或者使用ETCCDI推荐的极端气候指数进行计算[86]，如极端大雨日数、持续湿润日数、1 d最大降水量、连续5 d最大降雨量以及极端强降水总量等指标。已有研究表明春季极端降水对植被返青期存在推迟作用，如频繁的极端降雨减慢了美国大陆春季植被返青的速度[87]，1 d最大降雨量和连续5 d最大降雨量减少导致中亚中西部植被返青期推迟[57]，连续5 d最大降雨量增加导致中国西南地区植被返青期推迟[88]。然而干旱半干旱区的极端降水事件导致植被返青期提前[26,89]，如降雨频率的减少提前了北方生态系统植被返青期[90]。也有研究表明，植被返青期还会受到降水持续时间和降水强度的影响[91]，如在1982—2015年中国温带植被返青期与生长季前强降水总量、1 d最大降雨量之间呈显著正相关，与极端强降水总量、连续5 d最大降雨量之间则呈显著负相关[67]。植被枯黄期对极端降水事件的响应与极端降水的发生强度和研究区域有关。尽管不同强度的生长季极端降水都提前了北半球高纬度植被枯黄期[7,54]，但是植被枯黄期对低强度降水和高强度降水响应的主要时间段为季前1~2个月，而中等强度降水为季前2~3个月[7]。

极端降水可能导致植被返青期和枯黄期发生提前或者推迟现象。植被物候对极端降水的响应机制随研究区域和植被类型而异。在暴雨、洪涝等极端降水发生时，土壤水分急剧增加，降低植物的水分和养分吸收效率，严重者破坏植物根系，导致植物生长受阻、萎蔫甚至死亡[92-93]，这就会导致植被返青期推迟，特别是在水资源丰富的区域该影响更加明显。但是，发生在干旱半干旱区的极端降水事件，可以对水资源亏缺区域进行一定的补给，进而产生更适宜植被生长的环境，有利于植被提前返青。此外，不同植被类型返青期对极端降水的响应存在一定的差异，如祁连山地区灌丛和森林返青期对极端降水事件响应大于草地，并以低灌木为主的亚高山地区影响最大，造成这种格局的原因可能是以高寒草甸为主的高海拔地区气候寒冷潮湿，而以森林和灌木为主的低海拔地区气候相对温暖干燥[37]。对于植被枯黄期，由于极端降水会造成植被根系产生厌氧环境，从而会加速枯黄期的到来[94]。但是在干旱半干旱区，极端降水可以缓解土壤水分胁迫，进而推迟植被枯黄期[34,95]。对于不同植被类型，极端降水导致中国荒漠草原枯黄期提前，却导致高寒草甸枯黄期推迟，这主要是因为极端降水有效补充了荒漠草原的土壤含水量[55]。也有研究表明极端降水减少对水分限制区域植被枯黄期的趋势变化没有显著影响，这可能是因为中亚地区植被已经适应了干旱环境[57]。

4 植被物候对极端干旱的响应及机制

随着气候变暖，极端干旱的发生频率和强度显著增加[96-97]，当干旱发生强度超过植物对干旱的耐受阈值时，轻则抑制植被生长，重则使植被损伤甚至死亡[9,98⇓ -100]（表1）。极端干旱事件的定义除表1所述外，ETCCDI推荐的极端气候指数中的持续干旱指数也可以用于表征极端干旱[55]。极端干旱对植被物候也产生了重要影响[101-102]。研究表明，春季干旱导致欧洲西南部和中国北方干旱半干旱区植被返青期延迟了7~40 d[37,103⇓⇓⇓ -107]。但是，春冬季干旱导致北美洲、欧亚边界以及亚洲东北部植被返青期提前[107]，控制实验中也发现一致结果[108]。植被枯黄期对干旱的响应因地理位置和干旱发生时间而异。季前干旱胁迫导致中国温带草地干旱区域、北方半干旱区草地和稀疏植被以及青藏高原等干旱区和半干旱区植被枯黄期平均每10 a提前约2 d[6,103,109]。但是极端干旱导致欧洲和中国云贵高原植被枯黄期延迟[110-111]。植被枯黄期对干旱不同发生时间也可能产生相反的响应，例如夏季前的干旱导致云贵高原植被枯黄期延迟，夏季干旱导致云贵高原植被枯黄期提前[110]。

表1 干旱等级划分

Tab. 1 Classification of drought

分类 SPEI或SPI PDSI 危害程度基本正常 -0.49~0.49 -0.99~0.99 无危害轻旱 -0.99~-0.50 -1.99~-1.00 轻微危害中旱 -1.49~-1.00 -2.99~-2.00 中等危害重旱 -1.99~-1.50 -3.99~-3.00 严重危害特旱 ≤-2.00 ≤-4.00 特重危害注：干旱事件识别一般采用固定阈值法与百分位阈值法，前者如表中使用的标准化降水蒸散指数（SPEI）[112]、帕尔默干旱强度指数（PDSI）[113]、标准化降水指数（SPI）[114]等常见干旱指标的阈值划分干旱等级；后者定义干旱阈值为多年升序排列数据分布的十百分位[107,115]。

极端干旱可能通过不同的机制导致植被返青期和枯黄期发生提前或者推迟现象，其差异可能在于区域水分盈亏程度。植被对干旱胁迫的生理响应机制发挥重要作用，植被通过增加根系吸水能力、关闭部分气孔以及调节组织渗透性以积极维持生理水分平衡[116]，例如干旱区和湿润区植被能够快速响应干旱，前者更能迅速适应干旱胁迫，后者则适应性较差，而半干旱区和半湿润区植被对水分亏缺的承受能力较强、对干旱的反应时间更长[117]。极端干旱导致植被返青期提前的响应机制可能有两个主要解释，一是气候变暖对植被返青期的提前作用大于干旱胁迫的抑制作用，二是气候变暖导致的冰雪或冻土融化可以补充土壤水分，进而缓解了干旱胁迫。但是，极端干旱也会导致植被返青期推迟，这主要是由于季前干旱能够降低土壤含水量，进一步加剧水分胁迫，进而导致植被返青期推迟，特别是在干旱区和半干旱区。对于植被枯黄期，干旱促使植物关闭气孔降低蒸散和光合速率，同时维持更高呼吸速率加速碳分解，导致植被枯黄期提前。但是在湿润区和半湿润区，干旱胁迫对植被枯黄期的影响可能不会抵消气候变暖对植被枯黄期的延迟作用，最终导致枯黄期推迟。此外，不同类型植被物候对极端干旱的响应存在明显差异，如在祁连山与澳大利亚的中等海拔灌木的返青期对干旱的响应大于更缺水的低海拔森林或草原[37,39]；持续干旱指数与高寒草原枯黄期之间以正相关为主，却与荒漠草原枯黄期之间主要存在负相关关系[55]，这都可能与区域干旱程度与海拔高度有关。

5 植被物候对其他极端气候事件的响应及机制

除了极端温度、降水和干旱事件，植被物候对复合极端气候事件、野火等其他极端气候事件也存在响应。复合极端气候事件是指多个极端气候事件同时发生、并发影响植被生长动态，比单个极端气候事件对生态系统的影响更加剧烈[118]，如在极端温暖和极端湿润年份祁连山植被返青期分别提前6.4 d、5.1 d，但在极端暖湿年份其返青期提前了13.2 d[37]，这可能是因为极端变暖与极端降水的综合影响是通过某种更为复杂的优化协同机制来调控植被物候变化[37]。复合冷干事件对北半球植被生产力的抑制作用也超过单一冷干事件[119]。近年来，复合高温干旱频发[120]，比单一极端气候事件对植被造成的影响更为严重。控制实验表明，极端干旱和高温复合事件导致大量叶片死亡、提前植被衰老，其影响远远超过了单独的极端干旱或高温事件[121]。例如，复合高温干旱胁迫导致鹅耳枥和樱桃树枯黄期比多年平均枯黄期分别提前了5 d和16 d[122]。这主要是由于频繁的高温天气加快土壤水分蒸发，进一步加重干旱程度，从而加剧了对植被物候的影响。

随着高温干旱复合事件增多，森林火灾更加频繁，进而影响植被物候。科罗拉多州海曼森林大火使植被返青期由延迟趋势转变为提前趋势，火烧痕迹区比缓冲区的植被返青期更早，并在漫长恢复期内对植被返青期产生持续影响[123]。旱季和雨季的交替时间异常也会影响叶片脱落与生长时间[124]。此外，异常风速也会对植被物候产生影响，如春季大风导致北方生态系统植被返青期延迟[125]，秋季风速减弱推迟了北半球高纬度区域的植被枯黄期，且植被枯黄期对风的响应高于温度和降水[126]。关于植被物候对其他极端气候事件的响应研究相对较少，且这些极端气候事件发生原因更为复杂，目前尚无较为统一的响应机制来解释它们对植被物候的影响。

6 植被物候响应极端气候研究展望

综上所述，全球极端气候频发对植被物候产生了深刻影响。本文基于当前植被物候对极端气候事件响应机制研究进展，概述了当前研究中存在的问题并对未来可能的研究方向提出了展望，主要包括3个方面：① 植被物候对（复合）极端气候事件的响应与反馈机制仍存在较大的不确定性；② 缺乏多时间尺度下植被物候对极端气候变化响应的滞后效应研究；③ 耦合极端气候事件到植被物候模型的研究不够全面。

6.1 植被物候对极端气候的响应与反馈机制

目前，植被物候对极端气候事件的响应机制不够清楚，这主要是因为不同频率、强度、空间区域的极端气候事件对植被物候存在复杂影响。极端高温、低温、降水与干旱事件均可能导致植被物候提前或推迟，且响应机制并不一致，这可能与研究区域（包括不同水热条件、气候特征等）、研究对象、研究方法（控制实验、遥感、再分析等手段）、以及极端气候指标选择（极端气候事件发生频率以及严重程度）等方面有关。不同生态系统植被物候对各极端气候事件的响应不同[34,56,106,127]，例如在中亚不同生态分区，大多为草地覆盖的生态区枯黄期主要受到暖昼日数的影响，而在以裸地或稀疏植被为主的生态区植被枯黄期主要受到冷昼日数的影响[57]。而且，植被物候对极端温度和极端降水的响应程度也存在不同，例如在生长阶段极端降水对青藏高原干旱半干旱区草地枯黄期的影响远大于极端温度[34]。不同树种对极端气候的抵抗力和恢复力也存在差别[128]。此外，随着高温热浪与干旱并发事件增加[120]，热胁迫和干旱复合胁迫影响了植被物候的各个阶段[129]。为深刻理解植被物候对极端气候事件，特别是复合极端气候事件的响应机制，需要加强基于野外观测、控制实验、遥感反演及模型模拟等多源数据、多尺度、多方法、多过程的集成耦合研究。植被物候不仅会响应气候变化与极端气候事件，植被物候还通过改变陆气系统的碳水循环、能量交换等生物物理化学过程对气候系统产生影响[130-131]。因此，关注极端气候条件下植被物候变化对气候系统的反馈效应，需要综合观测、模拟和实验等方法，从不同的尺度和层面开展研究，以便更好地理解和应对气候变化。

6.2 植被物候对极端气候响应的滞后效应

植被生长和物候变化对气候变化与极端气候变化存在显著滞后和积累效应，并存在明显的空间异质性[107,132⇓⇓⇓ -136]，在气候变化—植被生长模型中考虑气候因子的累积作用显著提高了植被生长的拟合效果[137]。植被物候与其生长相似，不仅对极端气候事件产生萎蔫甚至死亡等即时响应，也存在明显的滞后效应和累积效应，这对于植被物候对极端气候的响应过程与机制的理解增加了难度。不同植被物候期对极端气候事件响应最敏感的滞后时间也不同[106,127]。以干旱事件为例，干旱胁迫对全球地表物候具有显著的累积和滞后效应[107,135]，在中国东北过渡带的西北部区域，植被返青期对1~3个月时间尺度干旱的响应最敏感[106]。北半球植被枯黄期对季前干旱响应的主要时间尺度为累积1~4个月、滞后2~6个月，且干旱对草地、稀树草原和灌木的影响超过森林[127]。植被在干旱发生后需要一段时间修复受损根系以恢复到正常生长状态，恢复时间长短取决于生长环境和植被类型[127,137]，同时植被动态也会通过直接或间接生物物理反馈影响旱后恢复[138]。以往研究多探讨植被物候对月、季或年尺度干旱等极端气候变化的响应[139]，植被物候对多时间尺度极端气候变化的时滞和累积效应的综合研究亟待增加。因此，未来的研究可以通过综合运用生态学、气象学、植物学等多学科的知识和方法，深入探究植被物候对极端气候事件响应的滞后效应及其在植被恢复过程中的调控作用，以此提高极端气候对生态系统功能和恢复力影响的预测能力。

6.3 耦合极端气候事件的植被物候模型

在极端气候下，植被物候模型将面临更大的挑战，其模拟结果准确性有待进一步提高。目前常用的植被物候模型包括积温模型、冷度日模型、温度与光周期模型等[140-141]，随着植被物候对极端气候响应研究的开展，其响应机制在植被物候模型构建中也被考虑。例如，对于北半球植被枯黄期，耦合干旱的秋季物候模型模拟精度平均提升了约12%[142]；对于青藏高原，引入多个极端气候指数模拟植被物候的精度明显提升[6]；耦合温度日较差到冷度日模型模拟的欧洲植被枯黄期具有更高的预测精度[143]。植被物候对极端气候事件的响应机制探究仍然有限，多驱动因子相互作用与极端气候事件的偶然发生使植被物候模型模拟与预测难度加大。随着新技术的进步，可以考虑在机器学习等算法中耦合极端气候事件来预测植被物候[140]。因此，综合考虑不同极端气候事件对植被物候的影响及其差异，有利于准确模拟历史和未来植被物候的演变特征，为气候变化下生态系统经营与管理以及脆弱性评价提供科学参考。

7 结论

综上所述，极端气候事件对植被生长干扰更剧烈，对植被物候影响更大。植被物候对极端气候事件的响应及其机制与平均气候相比更加复杂，且存在明显的空间异质性和不确定性，并随植被类型差异具有较大的差异。同时，极端气候事件的表征指标在各研究中不尽相同，在探究植被物候对极端气候的响应时应予以注意。随着气候变暖，复合极端气候事件的发生频率和强度增加，其影响程度和范围往往更大，虽然植被物候对极端气候事件响应机制的研究在逐步增多，但植被物候对复合极端气候事件响应的认识依旧受到限制，缺乏对其机制的综合理解。因此，亟需加强植被物候对各极端气候事件响应机制的认识，并从水热条件、气候分区、植被类型与季节阶段等多角度深入剖析其复杂性，同时推进耦合极端气候事件的植被物候模型研究，为全球动态植被模型提供更可靠的理论和技术支撑。

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摘要

As an important compartment of the Earth's surface, terrestrial ecosystems act as a vital harbor for human survival and development. Climate change significantly increased the frequency, intensity and duration of drought since the 21st century, which have marked impact on ecosystems, leading to serious restriction or even threat on the sustainable development of human beings. Therefore, developing integrative research on effects of drought on terrestrial ecosystems and assessing the associated ecological risk are impressive in global change field. This study reviewed the effects of drought on plant physiological and ecological processes, biogeochemical cycles, biodiversity, and ecosystem structure and functions in terrestrial ecosystems, and discussed current hotspot issues in this field as well as deeply analyzing the existing problems and the potential development direction. This study aims to provide some suggestions for the future observation, manipulative experiments, and modeling prediction on effects of drought on terrestrial ecosystems, and offer new insights to enhance risk assessment and management under drought.

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{{custom_citationIndex}3}https://doi.org/{{custom_citationIndex}1}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_ref.citationList}9}{{custom_ref.citationList}7}本文引用 [{{custom_ref.citationList}2}]摘要{{custom_ref.citationList}1}[11]Xu C G

McDowell N G

Fisher R A

, et al. Increasing impacts of extreme droughts on vegetation productivity under climate change. Nature Climate Change, 2019, 9(12): 948-953.

. A preliminary study on the climatic fluctuations during the last 5000 years in China. Scientia Sinica, 1973, 3(2): 226-256.

[竺可桢. 中国近五千年来气候变迁的初步研究. 中国科学, 1973, 3(2): 226-256.]

Liu Q

Chen A P

, et al. Plant phenology and global climate change: Current progresses and challenges. Global Change Biology, 2019, 25(6): 1922-1940.

Plant phenology, the annually recurring sequence of plant developmental stages, is important for plant functioning and ecosystem services and their biophysical and biogeochemical feedbacks to the climate system. Plant phenology depends on temperature, and the current rapid climate change has revived interest in understanding and modeling the responses of plant phenology to the warming trend and the consequences thereof for ecosystems. Here, we review recent progresses in plant phenology and its interactions with climate change. Focusing on the start (leaf unfolding) and end (leaf coloring) of plant growing seasons, we show that the recent rapid expansion in ground- and remote sensing- based phenology data acquisition has been highly beneficial and has supported major advances in plant phenology research. Studies using multiple data sources and methods generally agree on the trends of advanced leaf unfolding and delayed leaf coloring due to climate change, yet these trends appear to have decelerated or even reversed in recent years. Our understanding of the mechanisms underlying the plant phenology responses to climate warming is still limited. The interactions between multiple drivers complicate the modeling and prediction of plant phenology changes. Furthermore, changes in plant phenology have important implications for ecosystem carbon cycles and ecosystem feedbacks to climate, yet the quantification of such impacts remains challenging. We suggest that future studies should primarily focus on using new observation tools to improve the understanding of tropical plant phenology, on improving process-based phenology modeling, and on the scaling of phenology from species to landscape-level.© 2019 John Wiley & Sons Ltd.

. Effects of global warming on plant phenological events in China. Acta Geographica Sinica, 1995, 50(5): 402-410.

摘要

In this paper, effects of global warming on phenological events of China are discussed.First, it is demonstrated that atmospheric temperature is the most important factor influencing plant phenophase: 1. the integral regresseion method is used to analyse the relationship between meteorological factors and phenophase of trees in spring in Beijing. The calculated results show that the relation between meteorological factors and phenophase is close. But the most important factor which influence the phenophase of trees in spring is temperature and their correlation coefficient is more than 0. 7. The sunshine and precipitation are not important factors. If precipitation and sunshine are similar to those in normal years. they may be analysed in three intervals:pre-winter、winter and spring. The effect of spring temperature on phenophase is the most important. At that time. the higher the temperature is. the earlier the phenophase occurs. The temperature effect in pre-winter period is similar to that in spring, but the intensity of the effects is smaller. The low temperature in winter also affects the phenophase in spring. but the higher the temperature in that time. the later the phenophase. It is shown that low temperature in winter is also an essential condition for the phenophases occurs. Secondary. the correlation coefficient between phenophase and annual mean temperature is calculated and the value is higher.Because atmospheric temperature is the most important factor on phenophase. a linear model contains only phenophase and annual mean temperature factors are established by the author. Finally, we apply this model to evaluate changes of the phenological events in China for future global warming scenario. The calculated results are as follows:1. Assuming a 2℃ rise of annual mean temperature. trees phenological events of spring in China will occur about 3-4 days earlier, but may be postponed for 3-4 days in autumn. The greenleaf stage will be prolonged for 6-8 days.2. Assuming the scenario of a doubled CO2 content on the next century which caddses a 1. 0- 1. 8℃ rise in the annual mean temperature in China, phenological events in China will be 4-6 days earlier in spring, but will be postponed 4-6 day in autumn. The green-leaf stage is prolonged for 10-12 days. The mature date of fruits and seeds may be earlier. Moreover. the number of days in the changes of phenological events in the nothern part of China will be more than those in the southern part.

[张福春. 气候变化对中国木本植物物候的可能影响. 地理学报, 1995, 50(5): 402-410.]

本文根据我国近３０年的物候资料和气候资料的统计分析，论证了气温是影响中国木本植物物候的主要因子，在此基础上建立了物候与年平均气温的线性统计模式，又利用此模式分别计算了未来全球年平均气温升高０．５－２．０℃和未来大气中ＣＯ<sub>２</sub>浓度倍增而增暖情况下，我国主要木本植物物候期的大致变幅。

Bai Hongying

Gao Shan

, et al. Comprehensive effect of climatic factors on plant phenology in Qinling Mountains region during 1964-2015. Acta Geographica Sinica, 2018, 73(5): 917-931.

摘要

Based on the data of phenological observation and daily meteorological records during 1964-2015, we studied the relationship between plant phenology variation and climate change in the Qinling Mountains region by using correlation and Partial Least Squares (PLS) regression analysis. The results showed that: (1) In the past 52 years, the climate of the study region presented a warming-drying trend at the start and the end of plant phenophase, and the warming trend at the start of phenophase is more significant than that at the end of phenophase, especially after the phenophase abrupt change around 1985. (2) The responses of the start and the end of phenophase to the change of climatic factors such as temperature, precipitation and sunshine varied differently. Before the period of phenophase abrupt change, the responses of phenophases were not significant to all the climatic factors except for the daily mean temperature. However, after the period of phenophase abrupt change, the response of phenophases was significant to all the climatic factors. The start of phenophase advanced by 3 d and the end of phenophase delayed by 12 d with the increase of the daily mean temperature by 1℃. The start of phenophase advanced by 1.3 d with the decrease of the accumulated precipitation by 1 mm, and the end of phenophase delayed by 1 d with the increase of the accumulated precipitation by 1 mm. The start of phenophase advanced by 4.3 d and the end of phenophase delayed by 18.3 d with the increase of daily mean sunshine hours by 1 h, respectively. (3) There is a lag effect for the responses of the start and the end of phenophase to climate change. The time-lag was about 1-2 months for air temperature and about 1-3 months for the pre-period accumulated precipitation at the start of phenophase, respectively. No lag effect on the start of phenophase was observed for the sunshine hours. As related to the end of phenophase, the time-lag was about 1-3 months for the air temperature and about 1-2 months for the sunshine hours, respectively. No lag effect on the end of phenophase was found for the precipitation. (4) Both the start and the end of phenophase were jointly affected by the climatic factors, in which the air temperature was the predominant factor. Especially, the rise of the daily mean temperature plays a dominant role in advancing the start of phenophase and delaying the end of phenology.

[邓晨晖, 白红英, 高山, 等. 1964—2015年气候因子对秦岭地区植物物候的综合影响效应. 地理学报, 2018, 73(5): 917-931.]

以1964-2015年物候观测数据和逐日气象资料为基础,运用相关分析和PLS回归法,研究了秦岭地区植物物候变化与气候变化的响应关系。结果表明：① 1964-2015年,秦岭地区物候始末期的气候均呈干暖化趋势,且始期的暖化趋势较末期显著,物候突变后（1985年之后）尤为显著。② 就单一因素而言,物候始末期对气温、降水、日照等气候因子的响应程度存在差异,突变前（1985年之前）,除物候始期的日均温外,其他气候因子对物候的影响均不显著,但突变后影响显著,始期与末期的日均温每升高1 ℃,始期提前3.0 d,末期推迟12.0 d;始期的累积降水每减少1 mm始期提前1.3 d,末期的每增加1 mm末期推迟1.0 d;始期与末期的日均日照时数每增加1 h,始期提前4.3 d,末期推迟18.3 d。③ 气候因子对物候始末期的影响存在滞后效应,物候始期,气温影响的滞后时效约1~2个月,降水的滞后时效约1~3个月,而日照几乎无滞后效应;物候末期,气温的滞后时效约1~3个月,降水几乎无滞后效应,而日照影响的滞后时效约1~2个月。④ 物候始期与末期均受气温、日照、降水的综合影响,气温是影响物候变化最重要的因素,特别是同期日均温的升高对物候始期的提前及末期的推迟具有主导控制作用。

Zhang Ziyan

Lei Xiaoyu

, et al. Monte Carlo survival analysis on the influencing factors of forest phenology in Northeast China. Acta Geographica Sinica, 2019, 74(3): 490-503.

摘要

Quantitative analysis of the influencing factors of vegetation phenology is not only helpful to accurate assessment of impacts of climate change on vegetation but also has great importance in the improvement of regional climate models, as well as accurate estimation of vegetation net primary productivity and carbon balance. Vegetation phenology monitoring based on remote sensing data has made great progress, however, few studies have focused on analyses of the influencing factors of vegetation phenology based on large-scale and time series remote sensing data. The use of the linear regression model in some existing studies has certain limitations due to the nonlinearity of vegetation phenology. In this paper, we propose a Monte Carlo based survival analysis method, which was applied to the forest regions of Northeast China. Start of season (SOS), end of season (EOS) and growing season length (GSL) were firstly extracted from time series AVHRR GIMMS NDVI data of the study area in the period of 1982-2009, using the double logistic curve fitting method. And then the survival analysis model of vegetation phenological influencing factors based on Monte Carlo estimation was constructed. Finally, the proposed method was applied to the forest regions in Northeast China to investigate possible influencing factors of vegetation phenology in the rejuvenation period and deciduous period. Results show that temperature, precipitation, and wind can influence phenology of the forest in the region, with temperature being the primary influencing factor for both start and end of seasons. Long-term changes of average temperature have more significant impacts on the forest phenology, compared with short-term temperature variations. The increase of wind speed before the EOS may lead to an early EOS. In addition to environmental factors, EOS tends to be later if SOS is early. The results also prove that the proposed survival analysis method can provide a good scheme to quantitatively analyze the influencing factors of the phenological periods.

[卓莉, 张子彦, 雷小雨, 等. 基于蒙特卡洛生存分析探究东北森林物候的影响因素. 地理学报, 2019, 74(3): 490-503.]

植被是生态环境变化的指示器,分析植被物候的影响因素不仅有助于气候变化分析,提高区域气候模式的模拟精度,而且对于准确评估植被生长趋势、生产力以及全球碳收支均具有重要意义。基于遥感的植物物候监测已取得了长足的发展和进步,但当前利用大范围、长时间序列的遥感数据分析植被物候影响因素的研究尚不多,采用线性回归模型对非线性的植被物候影响因素进行分析可能存在偏误。因此,本文提出一种基于蒙特卡洛模拟的生存分析方法,对东北森林物候的影响因素进行量化分析。首先利用东北森林地区1982-2009年间AVHRR GIMMS NDVI数据,应用双Logistic曲线拟合方法对植被春季返青期（SOS）、秋季落叶期（EOS）及植被生长期（GSL）进行提取;然后基于蒙特卡洛模拟和生存分析构建植被物候影响因素分析模型;最后运用所构建模型探讨了东北森林区春季返青期、秋季落叶期的可能影响因素。结果发现：温度、降水和风力对中国东北森林关键物候期有一定影响,其中温度是春季返青期和秋季落叶期的最主要驱动因素,长期平均温度比短期内的温度突变对物候影响更显著,落叶期前的风速增加有可能使落叶时间提前;除了环境因素,春季返青早的年间秋季落叶倾向于更晚。研究表明,结合蒙特卡洛方法的生存分析可以较好地对物候期的影响因素进行定量分析,可为物候现象的归因分析提供一种新的方法。

Wu Z F

Gong Y F

, et al. Larger responses of trees' leaf senescence to cooling than warming: Results from a climate manipulation experiment. Agricultural and Forest Meteorology, 2023, 339: 109568. DOI: 10.1016/j.agrformet.2023.109568.

Fabian P

. Growing season extended in Europe. Nature, 1999, 397: 659. DOI: 10.1038/17709.

Fang J Y

Zhou L M

, et al. Variations in satellite-derived phenology in China's temperate vegetation. Global Change Biology, 2006, 12(4): 672-685.

Xu L

. Temperature controls on the spatial pattern of tree phenology in China's temperate zone. Agricultural and Forest Meteorology, 2012, 154-155: 195-202.

Piao S L

Delpierre N

, et al. Larger temperature response of autumn leaf senescence than spring leaf-out phenology. Global Change Biology, 2018, 24(5): 2159-2168.

Climate warming is substantially shifting the leaf phenological events of plants, and thereby impacting on their individual fitness and also on the structure and functioning of ecosystems. Previous studies have largely focused on the climate impact on spring phenology, and to date the processes underlying leaf senescence and their associated environmental drivers remain poorly understood. In this study, experiments with temperature gradients imposed during the summer and autumn were conducted on saplings of European beech to explore the temperature responses of leaf senescence. An additional warming experiment during winter enabled us to assess the differences in temperature responses of spring leaf-out and autumn leaf senescence. We found that warming significantly delayed the dates of leaf senescence both during summer and autumn warming, with similar temperature sensitivities (6-8 days delay per °C warming), suggesting that, in the absence of water and nutrient limitation, temperature may be a dominant factor controlling the leaf senescence in European beech. Interestingly, we found a significantly larger temperature response of autumn leaf senescence than of spring leaf-out. This suggests a possible larger contribution of delays in autumn senescence, than of the advancement in spring leaf-out, to extending the growing season under future warmer conditions.© 2017 John Wiley & Sons Ltd.

Zhang Jing

Wu Zhaofei

, et al. Vegetation phenology response to climate change in China. Journal of Beijing Normal University: Natural Science, 2022, 58(3): 424-433.

[付永硕, 张晶, 吴兆飞, 等. 中国植被物候研究进展及展望. 北京师范大学学报: 自然科学版, 2022, 58(3): 424-433.]

Zhang Qiang

Huang Wenlin

, et al. Vegetation phenology change in Tibetan Plateau from 1982 to 2013 and its related meteorological factors. Acta Geographica Sinica, 2017, 72(1): 39-52.

摘要

Using NDVI3g vegetation index, we defined 18 phenological metrics to investigate phenology change in the Tibetan Plateau (TP). Considering heterogeneity of vegetation phenology, we divided TP into 8 vegetation clusters according to 1:1000000 vegetation cluster map. Using partial least regression (PLS) method, we investigated impacts of climate variables such as temperature, precipitation and solar radiation on vegetation phenology. Results indicated that: (1) Turning points of the date of the start of growing season (SOS) metrics are mainly observed during 1997-2000, before which SOS advanced 2-3 d/a. Turning points of the date of the end of growing season (EOS) and length of growing season (LOS) metrics are found during 2005 and 2004-2007, respectively. Before the turning point, EOS has a delayed tendency of 1-2 d/10a, and LOS has a lengthening tendency of 1-2 d/10a. After the turning point, the tendency of SOS and EOS metrics is questionable. Meanwhile, lengthening of LOS is not statistically significant; (2) Alpine meadows and alpine shrub meadows are subject to the most remarkable changes. Lengthening LOS of alpine meadow is mainly due to advanced SOS and delayed EOS. Nevertheless, lengthening LOS of alpine shrub meadow is attributed mainly to advanced SOS; (3) Using PLS method, we quantified impacts of meteorological variables such as temperature, precipitation and solar radiation on phenology changes of alpine meadows and alpine shrub meadows, indicating that temperature is the dominant meteorological factor affecting vegetation phenology. In these two regions, autumn of last year and early winter temperature of last year have a positive effect on SOS. Firstly, increased temperature in this period would postpone last year's EOS, and hence indirectly delay SOS of the current year; Secondly, warming autumn and early winter have the potential to negatively impact fulfilment of chilling requirements, leading to delay of SOS. Except summer, minimum temperature has a similar effect on vegetation phenology, when compared to average and maximum temperature. Furthermore, precipitation effects on phenology fluctuate widely across different months. Precipitation of the autumn and winter/spring of the last year has a negative/positive effect on SOS. Besides, precipitation acts as the key driver constraining vegetation growth in August, during which precipitation has a positive impact on EOS. Therefore, solar radiation can exert impacts on vegetation phenology mainly during summer and early fall. Our research will provide a scientific support for the improvement of vegetation phenology model.

[孔冬冬, 张强, 黄文琳, 等. 1982—2013年青藏高原植被物候变化及气象因素影响. 地理学报, 2017, 72(1): 39-52.]

根据NDVI3g数据,本文定义了18种植被物候指标研究植被物候变化情况。根据1:100万植被区划,把青藏高原划分为8个植被区分。对物候变化比较显著的区域,采用最高温度、最低温度、平均温度、降水、太阳辐射数据,运用偏最小二乘法回归（PLS）研究物候变化的气候成因。结果表明：① 青藏高原生长季初期物候指标,转折发生在1997-2000年,转折前初期物候指标平均提前2~3 d/10a;青藏高原末期物候指标转折发生在2004-2007年左右,生长季长度物候指标突变发生在2005年左右,转折前末期物候指标平均延迟1~2 d/10a、生长季长度平均延长1~2 d/10a;转折之后生长季初期物候指标推迟趋势的显著性水平仅为0.1,生长季末期物候指标、生长季长度指标趋势不显著。② 高寒草甸与高寒灌木草甸是青藏高原物候变化最剧烈的植被分区。高寒草甸区生长季长度的延长主要是由生长季初期物候指标提前导致的。高寒灌木草甸区生长季长度的延长主要是由于初期物候指标的提前,以及末期物候指标的推迟共同作用导致的。③ 采用PLS进一步分析气象因素对高寒草甸与高寒灌木草甸物候剧烈变化的影响。表明,温度对物候的影响占主导地位,两植被分区均显示上年秋季、冬初温度对生长季初期物候具有正的影响,该时段温度一方面会导致上年末期物候指标推迟,间接推迟生长季开始时间;另一方面高温不利用冬季休眠。除夏季外,其余月份最小温度对植被物候的影响与平均温度、最高温度的影响类似。降水对植被物候的影响不同月份波动较大,上年秋冬季节降水对初期物候指标具有负的影响,春初降水对初期物候指标具有正的影响。8月份限制植被生长季的主要因素是降水,此时降水与末期物候指标模型系数为正。太阳辐射对植被物候的影响主要在夏季与秋初。PLS方法在物候变化研究中具有较好的效果,本文研究结果将会对植被物候模型改进,提供有力的科学依据。

Li L H

Zhang Y L

, et al. Start of vegetation growing season on the Tibetan Plateau inferred from multiple methods based on GIMMS and SPOT NDVI data. Journal of Geographical Sciences, 2015, 25(2): 131-148.

In this study, we have used four methods to investigate the start of the growing season (SGS) on the Tibetan Plateau (TP) from 1982 to 2012, using Normalized Difference Vegetation Index (NDVI) data obtained from Global Inventory Modeling and Mapping Studies (GIMSS, 1982-2006) and SPOT VEGETATION (SPOT-VGT, 1999-2012). SGS values estimated using the four methods show similar spatial patterns along latitudinal or altitudinal gradients, but with significant variations in the SGS dates. The largest discrepancies are mainly found in the regions with the highest or the lowest vegetation coverage. Between 1982 and 1998, the SGS values derived from the four methods all display an advancing trend, however, according to the more recent SPOT VGT data (1999-2012), there is no continuously advancing trend of SGS on the TP. Analysis of the correlation between the SGS values derived from GIMMS and SPOT between 1999 and 2006 demonstrates consistency in the tendency with regard both to the data sources and to the four analysis methods used. Compared with other methods, the greatest consistency between the in situ data and the SGS values retrieved is obtained with Method 3 (Threshold of NDVI ratio). To avoid error, in a vast region with diverse vegetation types and physical environments, it is critical to know the seasonal change characteristics of the different vegetation types, particularly in areas with sparse grassland or evergreen forest.

Piao S L

Zhao H F

, et al. Unexpected role of winter precipitation in determining heat requirement for spring vegetation green-up at northern middle and high latitudes. Global Change Biology, 2014, 20(12): 3743-3755.

Heat requirement, expressed in growing degree days (GDD), is a widely used method to assess and predict the effect of temperature on plant development. Until recently, the analysis of spatial patterns of GDD requirement for spring vegetation green-up onset was limited to local and regional scales, mainly because of the sparse and aggregated spatial availability of ground phenology data. Taking advantage of the large temporal and spatial scales of remote sensing-based green-up onset data, we studied the spatial patterns of GDD requirement for vegetation green-up at northern middle and high latitudes. We further explored the correlations between GDD requirement for vegetation green-up and previous winter season chilling temperatures and precipitation, using spatial partial correlations. We showed that GDD requirement for vegetation green-up onset declines towards the north at a mean rate of 18.8 °C-days per degree latitude between 35°N and 70°N, and vary significantly among different vegetation types. Our results confirmed that the GDD requirement for vegetation green-up is negatively correlated with previous winter chilling, which was defined as the number of chilling days from the day when the land surface froze in the previous autumn to the day of green-up onset. This negative correlation is a well-known phenomenon from local studies. Interestingly, irrespective of the vegetation type, we also found a positive correlation between the GDD requirement and previous winter season precipitation, which was defined as the sum of the precipitation of the month when green-up onset occur and the precipitation that occurred during the previous 2 months. Our study suggests that GDD requirement, chilling and precipitation may have complex interactions in their effects on spring vegetation green-up phenology. These findings have important implications for improving phenology models and could therefore advance our understanding of the interplay between spring phenology and carbon fluxes. © 2014 John Wiley & Sons Ltd.

Fu Y H

Chen S Z

, et al. Increasing importance of precipitation in spring phenology with decreasing latitudes in subtropical forest area in China. Agricultural and Forest Meteorology, 2021, 304-305: 108427. DOI: 10.1016/j.agrformet.2021.108427.

Fu Y H

Zeng Z Z

, et al. Temperature, precipitation, and insolation effects on autumn vegetation phenology in temperate China. Global Change Biology, 2016, 22(2): 644-655.

Autumn phenology plays a critical role in regulating climate-biosphere interactions. However, the climatic drivers of autumn phenology remain unclear. In this study, we applied four methods to estimate the date of the end of the growing season (EOS) across China's temperate biomes based on a 30-year normalized difference vegetation index (NDVI) dataset from Global Inventory Modeling and Mapping Studies (GIMMS). We investigated the relationships of EOS with temperature, precipitation sum, and insolation sum over the preseason periods by computing temporal partial correlation coefficients. The results showed that the EOS date was delayed in temperate China by an average rate at 0.12 ± 0.01 days per year over the time period of 1982-2011. EOS of dry grassland in Inner Mongolia was advanced. Temporal trends of EOS determined across the four methods were similar in sign, but different in magnitude. Consistent with previous studies, we observed positive correlations between temperature and EOS. Interestingly, the sum of precipitation and insolation during the preseason was also associated with EOS, but their effects were biome dependent. For the forest biomes, except for evergreen needle-leaf forests, the EOS dates were positively associated with insolation sum over the preseason, whereas for dry grassland, the precipitation over the preseason was more dominant. Our results confirmed the importance of temperature on phenological processes in autumn, and further suggested that both precipitation and insolation should be considered to improve the performance of autumn phenology models.© 2015 John Wiley & Sons Ltd.

Kreyling J

Gellesch E

, et al. Recurring weather extremes alter the flowering phenology of two common temperate shrubs. International Journal of Biometeorology, 2013, 57(4): 579-588.

The aim of this study is to explore the effects of heavy rain and drought on the flowering phenology of two shrub species Genista tinctoria and Calluna vulgaris. We conducted a field experiment over five consecutive years in Central Europe, applying annually recurring extreme drought and heavy rain events on constructed shrubland communities and recorded the flowering status. Further, we correlated spring temperature and precipitation with the onset of flowering. Both species showed a response to extreme weather events: drought delayed the mid flowering date of Genista tinctoria in 3 of 5 years by about 1 month and in 1 year advanced the mid flowering date by 10 days, but did not affect the length of flowering. Mid flowering date of Calluna vulgaris was not affected by drought, but the length of flowering was extended in 2 years by 6 and 10 days. For C. vulgaris the closer the drought occurred to the time of flowering, the larger the impact on the flowering length. Heavy rainfall advanced mid flowering date and reduced the length of flowering of Genista tinctoria by about 2 months in 1 year. Mid flowering date of Calluna vulgaris was not affected by heavy rain, but the length of flowering was reduced in 1 year by 4 days. Our data suggest that extreme weather events, including alterations to the precipitation regime, induce phenological shifts of plant species of a substantial magnitude. Thus, the impacts of climate extremes on plant life cycles may be as influential as gradual warming. Particularly, the variability in the timing of precipitation events appears to have a greater influence on flowering dynamics than the magnitude of the precipitation.

Sun G P

Fu Z

, et al. Compound droughts slow down the greening of the Earth. Global Change Biology, 2023, 29: 3072-3084.

Vegetation response to soil and atmospheric drought has raised extensively controversy, however, the relative contributions of soil drought, atmospheric drought and their compound droughts on global vegetation growth remain unclear. Combining the changes in soil moisture (SM), vapor pressure deficit (VPD) and vegetation growth (NDVI) during 1982-2015, here we evaluated the trends of these three drought types and quantified their impacts on global NDVI. We found that global VPD has increased 0.22±0.05 kPa·decade during 1982-2015, and this trend was doubled after 1996 (0.32±0.16 kPa·decade ) than before 1996 (0.16±0.15 kPa·decade ). Regions with large increase in VPD trend generally accompanied with decreasing trend in SM, leading to a widespread increasing trend in compound droughts across 37.62% land areas. We further found compound droughts dominated the vegetation browning since late 1990s, contributing to a declined NDVI of 64.56%. Earth system models agree with the dominant role of compound droughts on vegetation growth, but their negative magnitudes are considerably underestimated, with half of the observed results (34.48%). Our results provided the evidence of compound droughts induced global vegetation browning, highlighting the importance of correctly simulating the ecosystem-scale response to the under-appreciated exposure to compound droughts as it will increase with climate change.This article is protected by copyright. All rights reserved.

Kreyling J

Boettcher-Treschkow J

, et al. Beyond gradual warming: extreme weather events alter flower phenology of European grassland and heath species. Global Change Biology, 2009, 15(4): 837-849.

Sibley A

Ivan Ortiz-Monasterio J

. Extreme heat effects on wheat senescence in India. Nature Climate Change, 2012, 2(3): 186-189.

Fu Y H

Zhu Z C

, et al. Delayed autumn phenology in the Northern Hemisphere is related to change in both climate and spring phenology. Global Change Biology, 2016, 22(11): 3702-3711.

The timing of the end of the vegetation growing season (EOS) plays a key role in terrestrial ecosystem carbon and nutrient cycles. Autumn phenology is, however, still poorly understood, and previous studies generally focused on few species or were very limited in scale. In this study, we applied four methods to extract EOS dates from NDVI records between 1982 and 2011 for the Northern Hemisphere, and determined the temporal correlations between EOS and environmental factors (i.e., temperature, precipitation and insolation), as well as the correlation between spring and autumn phenology, using partial correlation analyses. Overall, we observed a trend toward later EOS in ~70% of the pixels in Northern Hemisphere, with a mean rate of 0.18 ± 0.38 days yr. Warming preseason temperature was positively associated with the rate of EOS in most of our study area, except for arid/semi-arid regions, where the precipitation sum played a dominant positive role. Interestingly, increased preseason insolation sum might also lead to a later date of EOS. In addition to the climatic effects on EOS, we found an influence of spring vegetation green-up dates on EOS, albeit biome dependent. Our study, therefore, suggests that both environmental factors and spring phenology should be included in the modeling of EOS to improve the predictions of autumn phenology as well as our understanding of the global carbon and nutrient balances.© 2016 John Wiley & Sons Ltd.

Zhou X C

Li X X

, et al. Decreasing control of precipitation on grassland spring phenology in temperate China. Global Ecology and Biogeography, 2021, 30(2): 490-499.

Adu B

Li C B

, et al. Diverse responses of phenology in multi-grassland to environmental factors on Qinghai-Tibetan Plateau in China. Theoretical and Applied Climatology, 2022, 148(3): 931-942.

Wang S P

Jiang N

, et al. Plant phenology changes and drivers on the Qinghai-Tibetan Plateau. Nature Reviews Earth & Environment, 2022, 3(10): 633-651.

Chen S Z

Wu Z F

, et al. Review of vegetation phenology trends in China in a changing climate. Progress in Physical Geography: Earth and Environment, 2022, 46(6): 829-845.

Vegetation phenology is sensitive to climate change and has been defined as the footprint of ongoing climate change. Previous studies have shown that the spatial difference in China’s vegetation phenology varies substantially in both spring and autumn. Here, we reviewed phenological dynamics at the national and the regional scale of China over the period 1982−2020 using a remote sensing-based dataset and meta-analysis from phenological studies in China. We also explored the underlying mechanisms of both spring and autumn phenology and discussed potential phenological studies under future climate conditions. We found that, over the past four decades, the spring phenology advanced at a rate of 0.23 ± 0.47 days/year, while the autumn phenology was delayed at a rate of 0.17 ± 0.46 days/year. This led to an extended vegetation growth season of approximately 5 days per decade. The trends in the spring and autumn phenology were spatially specific in the Northern region, Northwest region, Qinghai–Tibet region, and Southern region: the change in spring phenology was −0.16, −0.46, −0.18, and −0.13 days/year, respectively, while the change in autumn phenology was 0.02, 0.32, 0.09, and 0.28 days/year, respectively. We also explored the dominant climatic drivers of regional phenological changes. We found that temperature was the dominant factor for spring phenology in cold regions, while precipitation, radiation, and temperature co-determined spring phenology in warm regions. The autumn phenology was affected by all three environmental cues but the effect of temperature was larger than that of radiation and precipitation across all regions. In future climate warming conditions, we recommend that studies focus on the phenological feedback mechanisms, such as the climatic and hydrological effects of vegetation changes, and agricultural phenology to investigate its fundamental role in crop productivity, especially under extreme climate events, to ensure national food security and ecological security.

Du J

Chen L F

, et al. Impacts of recent climate extremes on spring phenology in arid-mountain ecosystems in China. Agricultural and Forest Meteorology, 2018, 260-261: 31-40.

Li Y

Feng K

, et al. Monitoring responses of vegetation phenology and productivity to extreme climatic conditions using remote sensing across different sub-regions of China. Environmental Science and Pollution Research, 2021, 28(3): 3644-3659.

Huete A

Moran S S

, et al. Abrupt shifts in phenology and vegetation productivity under climate extremes. Journal of Geophysical Research: Biogeosciences, 2015, 120(10): 2036-2052.

Basler D

. Phenology under global warming. Science, 2010, 327(5972): 1461-1462.

In most temperate tree species, phenological events such as flowering and autumnal cessation of growth are not primarily controlled by temperature.

Tan J G

Chen A P

, et al. Leaf onset in the Northern Hemisphere triggered by daytime temperature. Nature Communications, 2015, 6: 6911. DOI: 10.1038/ncomms7911.

Piao, Shilong; Shen, Miaogen Chinese Acad Sci, Inst Tibetan Plateau Res, Ctr Excellence Tibetan Earth Sci, Key Lab Alpine Ecol & Biodivers, Beijing 100085, Peoples R China. Piao, Shilong Chinese Acad Sci, CAS Ctr Excellence Tibetan Plateau Earth Sci, Beijing 100085, Peoples R China. Piao, Shilong; Tan, Jianguang; Fu, Yongshuo H.; Liu, Qiang; Zeng, Zhenzhong; Li, Yue; Peng, Shushi Peking Univ, Sino French Inst Earth Syst Sci, Coll Urban & Environm Sci, Beijing 100871, Peoples R China. Chen, Anping Princeton Univ, Dept Ecol & Evolutionary Biol, Princeton, NJ 08544 USA. Fu, Yongshuo H.; Janssens, Ivan A.; Vicca, Sara Univ Antwerp, Dept Biol, B-2610 Antwerp, Belgium. Ciais, Philippe; Peng, Shushi UMR CEA CNRS, LSCE, F-91191 Gif Sur Yvette, France. Jeong, Su-Jong CALTECH, Jet Prop Lab, Pasadena, CA 91011 USA. Myneni, Ranga B. Boston Univ, Dept Earth & Environm, Boston, MA 02215 USA. Penuelas, Josep CREAF, Barcelona 08193, Spain. Penuelas, Josep CREAF CSIC UAB, Global Ecol Unit, Barcelona 08193, Spain.

Wang Y Y

Zhang Z X

, et al. The variations of land surface phenology in Northeast China and its responses to climate change from 1982 to 2013. Remote Sensing, 2016, 8(5): 400. DOI: 10.3390/rs8050400.

Chen Q L

Zhang J Y

, et al. Trends in extreme high temperature at different altitudes of Southwest China during 1961-2014. Atmospheric and Oceanic Science Letters, 2020, 13(5): 417-425.

Wang G F

. Assessment of the hazard of extreme low-temperature events over China in 2021. Advances in Climate Change Research, 2022, 13(6): 811-818.

Liu Y J

Ding Y H

. Identification of winter long-lasting regional extreme low-temperature events in Eurasia and their variation during 1948-2017. Advances in Climate Change Research, 2021, 12(3): 353-362.

Zhang Y

Gao X J

, et al. Evaluation and ensemble projection of extreme high and low temperature events in China from four dynamical downscaling simulations. International Journal of Climatology, 2021, 41 (Suppl.1): E1252-E1269.

Jeong S J

Ho C H

, et al. Nonlinear response of vegetation green-up to local temperature variations in temperate and boreal forests in the Northern Hemisphere. Remote Sensing of Environment, 2015, 165: 100-108.

Verger A

Descals A

, et al. Monitoring the responses of deciduous forest phenology to 2000-2018 climatic anomalies in the Northern Hemisphere. Remote Sensing, 2021, 13(14): 2806. DOI: 10.3390/rs13142806.

Monitoring the phenological responses of deciduous forests to climate is important, due to the increasing frequency and intensity of extreme climatic events associated with climate change and global warming, which will in turn affect vegetation seasonality. We investigated the spatiotemporal patterns of the response of deciduous forests to climatic anomalies in the Northern Hemisphere, using satellite-derived phenological metrics from the Copernicus Global Land Service Leaf Area Index, and multisource climatic datasets for 2000–2018 at resolutions of 0.1°. Thereafter, we assessed the impact of extreme heatwaves and droughts on this deciduous forest phenology. We assumed that changes in the deciduous forest phenology in the Northern Hemisphere for the period 2000–2018 were monotonic, and that temperature and precipitation were the main climatic drivers. Analyses of partial correlations of phenological metrics with the timing of the start of the season (SoS), end of the season (EoS), and climatic variables indicated that changes in preseason temperature played a stronger role than precipitation in affecting the interannual variability of SoS anomalies: the higher the temperature, the earlier the SoS in most deciduous forests in the Northern Hemisphere (mean correlation coefficient of −0.31). Correlations between the SoS and temperature were significantly negative in 57% of the forests, and significantly positive in 15% of the forests (p < 0.05). Both temperature and precipitation contributed to the advance and delay of the EoS. A later EoS was significantly correlated with a positive Standardized Precipitation Evapotranspiration Index (SPEI) at the regional scale (~30% of deciduous forests). The timings of the EoS and SoS shifted by >20 d in response to heatwaves throughout most of Europe in 2003, and in the United States of America in 2012. This study contributes to improve our understanding of the phenological responses of deciduous forests in the Northern Hemisphere to climate change and extreme climate events.

Tang X G

Gu Q

, et al. Climatic anomaly and its impact on vegetation phenology, carbon sequestration and water-use efficiency at a humid temperate forest. Journal of Hydrology, 2018, 565: 150-159.

Chandler J L

Guiden P W

, et al. Extreme winter warm event causes exceptionally early bud break for many woody species. Ecosphere, 2019, 10(1): e02542. DOI: 10.1002/ecs2.2542.

In many ecosystems, climate is changing faster during winter compared to other seasons. However, we lack basic information about the responses of many species to winter climate change, including extreme warm events. Extreme warm events may have particularly strong influences at the end of winter, when some species begin to break dormancy while the risk of freezing remains high. Here, we monitored bud burst of 101 temperate woody species following an extreme warm event during winter to investigate species responses to this anomalous event and determine whether functional traits predicted species responses. Following six consecutive days of extreme warm temperatures in winter, nearly half the surveyed tree and shrub species had an advanced stage of bud phenology. Responding species were most likely to be shade‐intolerant, phylogenetically related, and have weaker dormancy requirements. Based on established species response thresholds to spring temperatures in the region, species were expected to be unresponsive to warm temperatures this early in the year, yet many species broke dormancy. Species responses to this extreme winter warm event highlighted how climate change can alter well‐established species–climate associations. In an era of increasing climate change creating novel winter conditions, continued monitoring both long‐term and following extreme events is needed to understand new species–climate dynamics.

Dash J

Rodriguez-Galiano V F

, et al. Extreme warm temperatures alter forest phenology and productivity in Europe. Science of the Total Environment, 2016, 563/564: 486-495.

Zhao Lin

Li Xinxin

, et al. Diverse responses of end of growing season to extreme climate events in different grasslands in temperate China during 1982-2015. Acta Ecologica Sinica, 2023, 43(14): 6015-6032.

[袁沫汐, 赵林, 李鑫鑫, 等. 1982—2015年中国温带不同草地植被枯黄期对极端气候事件的响应. 生态学报, 2023, 43(14): 6015-6032.]

Filippa G

Galvagno M

, et al. Heat wave hinders green wave: The impact of climate extreme on the phenology of a mountain grassland. Agricultural and Forest Meteorology, 2017, 247: 320-330.

Wang X J

Silander J A

. Deciduous forest responses to temperature, precipitation, and drought imply complex climate change impacts. PNAS, 2015, 112(44): 13585-13590.

Changes in spring and autumn phenology of temperate plants in recent decades have become iconic bio-indicators of rapid climate change. These changes have substantial ecological and economic impacts. However, autumn phenology remains surprisingly little studied. Although the effects of unfavorable environmental conditions (e.g., frost, heat, wetness, and drought) on autumn phenology have been observed for over 60 y, how these factors interact to influence autumn phenological events remain poorly understood. Using remotely sensed phenology data from 2001 to 2012, this study identified and quantified significant effects of a suite of environmental factors on the timing of fall dormancy of deciduous forest communities in New England, United States. Cold, frost, and wet conditions, and high heat-stress tended to induce earlier dormancy of deciduous forests, whereas moderate heat- and drought-stress delayed dormancy. Deciduous forests in two eco-regions showed contrasting, nonlinear responses to variation in these explanatory factors. Based on future climate projection over two periods (2041-2050 and 2090-2099), later dormancy dates were predicted in northern areas. However, in coastal areas earlier dormancy dates were predicted. Our models suggest that besides warming in climate change, changes in frost and moisture conditions as well as extreme weather events (e.g., drought- and heat-stress, and flooding), should also be considered in future predictions of autumn phenology in temperate deciduous forests. This study improves our understanding of how multiple environmental variables interact to affect autumn phenology in temperate deciduous forest ecosystems, and points the way to building more mechanistic and predictive models.

Wang X Y

Li R J

, et al. Impacts of climate extremes on autumn phenology in contrasting temperate and alpine grasslands in China. Agricultural and Forest Meteorology, 2023, 336: 109495. DOI: 10.1016/j.agrformet.2023.109495.

Zhang H Y

Zhao J J

, et al. Effects of spring and summer extreme climate events on the autumn phenology of different vegetation types of Inner Mongolia, China, from 1982 to 2015. Ecological Indicators, 2020, 111: 105974. DOI: 10.1016/j.ecolind.2019.105974.

Zhao C Y

Li J Y

, et al. Impact of extreme climates on land surface phenology in Central Asia. Ecological Indicators, 2023, 146: 109832. DOI: 10.1016/j.ecolind.2022.109832.

Ho C H

Gim H J

, et al. Phenology shifts at start vs. end of growing season in temperate vegetation over the Northern Hemisphere for the period 1982-2008. Global Change Biology, 2011, 17(7): 2385-2399.

Zhao J J

Wang Y Q

, et al. Comparison of land surface phenology in the Northern Hemisphere based on AVHRR GIMMS3g and MODIS datasets. ISPRS Journal of Photogrammetry and Remote Sensing, 2020, 169: 1-16.

Zhang H Y

Zhang Z X

, et al. Spatial and temporal changes in vegetation phenology at middle and high latitudes of the Northern Hemisphere over the past three decades. Remote Sensing, 2015, 7(8): 10973-10995.

Wu Z F

Gong Y F

, et al. Climate warming shifts the time interval between flowering and leaf unfolding depending on the warming period. Science China Life Sciences, 2022, 65(11): 2316-2324.

Lin C F

Wang S X

, et al. The sensitivity of ginkgo leaf unfolding to the temperature and photoperiod decreases with increasing elevation. Agricultural and Forest Meteorology, 2022, 315: 108840. DOI: 10.1016/j.agrformet.2022.108840.

Wu Zhaofei

Fu Yongshuo

, et al. Effects of climate change on spring budburst of typical tree species in Beijing based on manipulative experiments. Acta Ecologica Sinica., 2023, 43(5): 1948-1958.

[龚玉凤, 吴兆飞, 付永硕, 等. 气候变化对北京常见树种春季萌芽的影响: 基于控制实验研究. 生态学报, 2023, 43(5): 1948-1958.]

{{custom_citation.annotation}4}https://doi.org/{{custom_citation.annotation}2}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_citation.annotation}0}{{custom_ref.label}8}本文引用 [{{custom_ref.label}3}]摘要{{custom_ref.label}2}[64]Gulen H

Eris A

. Effect of heat stress on peroxidase activity and total protein content in strawberry plants. Plant Science, 2004, 166(3): 739-744.

{{custom_ref.label}1}https://doi.org/{{custom_citation.content}9}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_citation.content}7}{{custom_citation.content}5}本文引用 [{{custom_citation.content}0}]摘要{{custom_citation.doi}9}[65]He Y L

Liu X Z

Huang B R

. Changes in protein content, protease activity, and amino acid content associated with heat injury in creeping bentgrass. Journal of the American Society for Horticultural Science, 2005, 130(6): 842-847.

Various physiological processes may deteriorate in response to increasing temperatures, contributing to the decline in turf quality for cool-season turfgrasses during heat stress. This study was performed to investigate metabolic changes (membrane lipid peroxidation, total protein content, amino acid content, and protease activity) associated with turf quality decline for creeping bentgrass (Agrostis stolonifera Huds.) in response to gradually increasing temperatures for a short duration and prolonged exposure to lethally high temperature. Plants were subjected to increasing temperatures of 20, 25, 30, 35, and 40 °C for 7 days at each level of temperature [gradual heat stress (GHS)] or exposed to high temperature of 40 °C for 28 days [prolonged heat stress (PHS)] in growth chambers. During the GHS treatment, significant decline in turf quality occurred when plants were exposed to 30 °C for 7 days; simultaneously, malondialdehyde (MDA) content increased and total protein content in shoots decreased significantly compared to those at 20 °C. Protease activity increased at 25 °C and then decreased as temperature was elevated from 30 to 40 °C during the GHS treatment. Amino acid content decreased under GHS, beginning at 25 °C. Under the PHS treatment, turf quality declined and MDA content increased significantly, beginning at 14 days of PHS, while total protein content decreased at 7 days of PHS. Protease activity and amino acid content increased at 7 days of PHS, and then declined with longer stress duration. Our results indicated that protease activity, and amino acid and total protein content were more responsive to GHS or PHS than that of lipid peroxidation and turf quality. Changes in metabolic parameters of protease activity, amino acid and total protein content, and lipid peroxidation may contribute to leaf senescence and poor turf performance under severe or prolonged heat stress conditions for creeping bentgrass.

. Spring 2007 warmth and frost: Phenology, damage and refoliation in a temperate deciduous forest. Functional Ecology, 2009, 23(6): 1031-1039.

{{custom_citation.doi}5}https://doi.org/{{custom_citation.doi}3}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_citation.doi}1}{{custom_citation.pmid}9}本文引用 [{{custom_citation.pmid}4}]摘要{{custom_citation.pmid}3}[67]Mo Y H

Zhang X

Liu Z C

, et al. Effects of climate extremes on spring phenology of temperate vegetation in China. Remote Sensing, 2023, 15(3): 686. DOI: 10.3390/rs15030686.

The response of vegetation spring phenology to climate warming has received extensive attention. However, there are few studies on the response of vegetation spring phenology to extreme climate events. In this study, we determined the start of the growing season (SOS) for three vegetation types in temperate China from 1982 to 2015 using the Global Inventory Modeling and Mapping Study’s third-generation normalized difference vegetation index and estimated 25 extreme climate events. We analyzed the temporal trends of the SOS and extreme climate events and quantified the relationships between the SOS and extreme climate events using all-subsets regression methods. We found that the SOS was significantly advanced, with an average rate of 0.97 days per decade in China over the study period. Interestingly, we found that the SOS was mainly associated with temperature extremes rather than extreme precipitation events. The SOS was mainly influenced by the frost days (FD, r = 0.83) and mean daily minimum temperature (TMINMEAN, r = 0.34) for all three vegetation types. However, the dominant influencing factors were vegetation-type-specific. For mixed forests, the SOS was most influenced by TMINMEAN (r = 0.32), while for grasslands and barren or sparsely vegetated land, the SOS was most influenced by FD (r > 0.8). Our results show that spring phenology was substantially affected by extreme climate events but mainly by extreme temperature events rather than precipitation events, and that low temperature extremes likely drive spring phenology.

{{custom_citation.pmid}2}https://doi.org/{{custom_citation.pmid}0}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_citation.pmid}8}{{custom_citation.pmid}6}本文引用 [{{custom_citation.pmid}1}]摘要{{custom_citation.pmid}0}[68]Cannell M G R

Smith R I

. Climatic warming, spring budburst and forest damage on trees. Journal of Applied Ecology, 1986, 23(1): 177. DOI: 10.2307/2403090.

{{custom_citation.url}9}https://doi.org/{{custom_citation.url}7}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_citation.url}5}{{custom_citation.url}3}本文引用 [{{custom_citation.url}8}]摘要{{custom_citation.url}7}[69]Gu L H

Hanson P J

Post W M

, et al. The 2007 Eastern US Spring Freeze: Increased cold damage in a warming world? BioScience, 2008, 58(3): 253-262.

{{custom_citation.url}6}https://doi.org/{{custom_citation.url}4}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_citation.url}2}{{custom_citation.url}0}本文引用 [{{custom_ref.citedCount>0}5}]摘要{{custom_ref.citedCount>0}4}[70]Liu Q

Piao S L

Janssens I A

, et al. Extension of the growing season increases vegetation exposure to frost. Nature Communications, 2018, 9: 426. DOI: 10.1038/s41467-017-02690-y.

While climate warming reduces the occurrence of frost events, the warming-induced lengthening of the growing season of plants in the Northern Hemisphere may actually induce more frequent frost days during the growing season (GSFDs, days with minimum temperature < 0 degrees C). Direct evidence of this hypothesis, however, is limited. Here we investigate the change in the number of GSFDs at latitudes greater than 30 degrees N using remotely-sensed and in situ phenological records and three minimum temperature (T-min) data sets from 1982 to 2012. While decreased GSFDs are found in northern Siberia, the Tibetan Plateau, and northwestern North America (mainly in autumn), similar to 43% of the hemisphere, especially in Europe, experienced a significant increase in GSFDs between 1982 and 2012 (mainly during spring). Overall, regions with larger increases in growing season length exhibit larger increases in GSFDs. Climate warming thus reduces the total number of frost days per year, but GSFDs nonetheless increase in many areas.

{{custom_ref.citedCount>0}3}https://doi.org/{{custom_ref.citedCount>0}1}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_citationIndex}9}{{custom_citationIndex}7}本文引用 [{{custom_citationIndex}2}]摘要{{custom_citationIndex}1}[71]Zohner C M

Mo L D

Sebald V

, et al. Leaf-out in northern ecotypes of wide-ranging trees requires less spring warming, enhancing the risk of spring frost damage at cold range limits. Global Ecology and Biogeography, 2020, 29(6): 1065-1072.

{{custom_citationIndex}0}https://doi.org/{{custom_ref.citationList}8}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_ref.citationList}6}{{custom_ref.citationList}4}本文引用 [{{custom_ref.id}9}]摘要{{custom_ref.id}8}[72]Lamichhane J R

. Rising risks of late-spring frosts in a changing climate. Nature Climate Change, 2021, 11(7): 554-555.

{{custom_ref.id}7}https://doi.org/{{custom_ref.id}5}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_ref.id}3}{{custom_ref.id}1}本文引用 [{{custom_ref.citedCount}6}]摘要{{custom_ref.citedCount}5}[73]Hufkens K

Friedl M A

Keenan T F

, et al. Ecological impacts of a widespread frost event following early spring leaf-out. Global Change Biology, 2012, 18(7): 2365-2377.

{{custom_ref.citedCount}4}https://doi.org/{{custom_ref.citedCount}2}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_ref.citedCount}0}{{custom_citation.annotation}8}本文引用 [{{custom_citation.annotation}3}]摘要{{custom_citation.annotation}2}[74]Bennie J

Kubin E

Wiltshire A

, et al. Predicting spatial and temporal patterns of bud-burst and spring frost risk in north-west Europe: The implications of local adaptation to climate. Global Change Biology, 2010, 16(5): 1503-1514.

{{custom_citation.annotation}1}https://doi.org/{{custom_fund}9}https://www.ncbi.nlm.nih.gov/pubmed/{{custom_fund}7}{{custom_fund}5}本文引用 [{{custom_fund}0}]摘要{{custom_citation.annotation}}[75]Vitasse Y

Lenz A

Körner C

. The interaction between freezing tolerance and phenology in temperate deciduous trees. Frontiers in Plant Science, 2014, 5: 541. DOI: 10.3389/fpls.2014.00541.

Temperate climates are defined by distinct temperature seasonality with large and often unpredictable weather during any of the four seasons. To thrive in such climates, trees have to withstand a cold winter and the stochastic occurrence of freeze events during any time of the year. The physiological mechanisms trees adopt to escape, avoid, and tolerate freezing temperatures include a cold acclimation in autumn, a dormancy period during winter (leafless in deciduous trees), and the maintenance of a certain freezing tolerance during dehardening in early spring. The change from one phase to the next is mediated by complex interactions between temperature and photoperiod. This review aims at providing an overview of the interplay between phenology of leaves and species-specific freezing resistance. First, we address the long-term evolutionary responses that enabled temperate trees to tolerate certain low temperature extremes. We provide evidence that short term acclimation of freezing resistance plays a crucial role both in dormant and active buds, including re-acclimation to cold conditions following warm spells. This ability declines to almost zero during leaf emergence. Second, we show that the risk that native temperate trees encounter freeze injuries is low and is confined to spring and underline that this risk might be altered by climate warming depending on species-specific phenological responses to environmental cues.

Rockinger A

Renner S S

. Increased autumn productivity permits temperate trees to compensate for spring frost damage. New Phytologist, 2019, 221(2): 789-795.

Climate warming is leading to earlier budburst and therefore an increased risk of spring frost injury to young leaves. But to what extent are second-cohort leaves, which trees put out after leaf-killing frosts, able to compensate incurred losses? To investigate whether second-cohort leaves behave differently from first-cohort leaves, we exposed saplings of beech (Fagus sylvatica), oak (Quercus robur), and honeysuckle (Lonicera xylosteum) to experimental treatments mimicking either a warm spring or a warm spring with a leaf-killing frost. Refoliation took 48, 43, and 36 d for beech, oak and honeysuckle, respectively. In beech and oak, autumn Chl content and photosynthesis rates were higher in second- than in first-cohort leaves, senescence in second-cohort leaves occurred c. 2-wk-later, and autumn bud growth in beech was elevated 66% in frost-damaged plants compared with the warm spring treatment. No differences in autumn phenology and growth were observed for honeysuckle. Overall, in beech and oak, delayed Chl breakdown in second-cohort leaves mitigated 31% and 25%, respectively, of the deficit in growing-season length incurred by spring frost damage. These results reveal an unexpected ability of second-cohort leaves of beech and oak to compensate for spring frost damage, and demonstrate that long-lived trees vary their autumnal phenology depending on preceding productivity.© 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

Piao S L

Chen X Q

, et al. Strong impacts of daily minimum temperature on the green-up date and summer greenness of the Tibetan Plateau. Global Change Biology, 2016, 22(9): 3057-3066.

Understanding vegetation responses to climate change on the Tibetan Plateau (TP) helps in elucidating the land-atmosphere energy exchange, which affects air mass movement over and around the TP. Although the TP is one of the world's most sensitive regions in terms of climatic warming, little is known about how the vegetation responds. Here, we focus on how spring phenology and summertime greenness respond to the asymmetric warming, that is, stronger warming during nighttime than during daytime. Using both in situ and satellite observations, we found that vegetation green-up date showed a stronger negative partial correlation with daily minimum temperature (Tmin ) than with maximum temperature (Tmax ) before the growing season ('preseason' henceforth). Summer vegetation greenness was strongly positively correlated with summer Tmin, but negatively with Tmax. A 1-K increase in preseason Tmin advanced green-up date by 4 days (P < 0.05) and in summer enhanced greenness by 3.6% relative to the mean greenness during 2000-2004 (P < 0.01). In contrast, increases in preseason Tmax did not advance green-up date (P > 0.10) and higher summer Tmax even reduced greenness by 2.6% K(-1) (P < 0.05). The stimulating effects of increasing Tmin were likely caused by reduced low temperature constraints, and the apparent negative effects of higher Tmax on greenness were probably due to the accompanying decline in water availability. The dominant enhancing effect of nighttime warming indicates that climatic warming will probably have stronger impact on TP ecosystems than on apparently similar Arctic ecosystems where vegetation is controlled mainly by Tmax. Our results are crucial for future improvements of dynamic vegetation models embedded in the Earth System Models which are being used to describe the behavior of the Asian monsoon. The results are significant because the state of the vegetation on the TP plays an important role in steering the monsoon.© 2016 John Wiley & Sons Ltd.

Gao Q

Wang C

, et al. Spatiotemporal patterns of vegetation phenology change and relationships with climate in the two transects of East China. Global Ecology and Conservation, 2017, 10: 206-219.

Liu B H

Henderson M

, et al. Asymmetric effects of daytime and nighttime warming on spring phenology in the temperate grasslands of China. Agricultural and Forest Meteorology, 2018, 259: 240-249.

Zhou Y Y

Li X C

, et al. Divergent responses of spring phenology to daytime and nighttime warming. Agricultural and Forest Meteorology, 2020, 281: 107832. DOI: 10.1016/j.agrformet.2019.107832.

Zhang L R

Zhang Z H

, et al. Opposite effects of winter day and night temperature changes on early phenophases. Ecology, 2019, 100(9): e02775. DOI: 10.1002/ecy.2775.

Changes in day (maximum temperature, TMAX) and night temperature (minimum temperature, TMIN) in the preseason (e.g., winter and spring) may have opposite effects on early phenophases (e.g., leafing and flowering) due to changing requirements of chilling accumulations (CAC) and heating accumulations (HAC), which could cause advance, delay or no change in early phenophases. However, their relative effects on phenology are largely unexplored, especially on the Tibetan Plateau. Here, observations were performed using a warming and cooling experiment in situ through reciprocal transplantation (2008–2010) on the Tibetan Plateau. We found that winter minimum temperature (TMIN) warming significantly delayed mean early phenophases by 8.60 d/°C, but winter maximum temperature (TMAX) warming advanced them by 12.06 d/°C across six common species. Thus, winter mean temperature warming resulted in a net advance of 3.46 d/°C in early phenophases. In contrast, winter TMIN cooling, on average, significantly advanced early phenophases by 5.12 d/°C, but winter TMAX cooling delayed them by 7.40 d/°C across six common species, resulting in a net delay of 2.28 d/°C for winter mean temperature cooling. The opposing effects of TMAX and TMIN warming on the early phenophases may be mainly caused by decreased CAC due to TMIN warming (5.29 times greater than TMAX) and increased HAC due to TMAX warming (3.25 times greater than TMIN), and similar processes apply to TMAX and TMIN cooling. Therefore, our study provides another insight into why some plant phenophases remain unchanged or delayed under climate change.

Wang X Y

Wang H J

, et al. Contrasting responses of autumn-leaf senescence to daytime and night-time warming. Nature Climate Change, 2018, 8(12): 1092-1096.

Jiang N

Shen M G

, et al. Effect of preseason diurnal temperature range on the start of vegetation growing season in the Northern Hemisphere. Ecological Indicators, 2020, 112: 106161. DOI: 10.1016/j.ecolind.2020.106161.

Alterskjær K

Stjern C W

, et al. Frequency of extreme precipitation increases extensively with event rareness under global warming. Scientific Reports, 2019, 9(1): 16063. DOI: 10.1038/s41598-019-52277-4.

The intensity of the heaviest extreme precipitation events is known to increase with global warming. How often such events occur in a warmer world is however less well established, and the combined effect of changes in frequency and intensity on the total amount of rain falling as extreme precipitation is much less explored, in spite of potentially large societal impacts. Here, we employ observations and climate model simulations to document strong increases in the frequencies of extreme precipitation events occurring on decadal timescales. Based on observations we find that the total precipitation from these intense events almost doubles per degree of warming, mainly due to changes in frequency, while the intensity changes are relatively weak, in accordance to previous studies. This shift towards stronger total precipitation from extreme events is seen in observations and climate models, and increases with the strength - and hence the rareness - of the event. Based on these results, we project that if historical trends continue, the most intense precipitation events observed today are likely to almost double in occurrence for each degree of further global warming. Changes to extreme precipitation of this magnitude are dramatically stronger than the more widely communicated changes to global mean precipitation.

Huang A N

Wu P L

, et al. Drivers of summer extreme precipitation events over East China. Geophysical Research Letters, 2021, 48(11): e2021GL093670. DOI: 10.1029/2021GL093670.

Sorí R

Vázquez M

, et al. Extreme precipitation events. WIREs Water, 2022, 9(6): e1611. DOI: 10.1002/wat2.1611.

The effect of increased populations concentrated in urban areas, coupled with the ongoing threat of climate change, means that society is becoming increasingly vulnerable to the effects of extreme precipitation. The study of these events is therefore a key topic in climate research, in their physical basis, in the study of their impacts, and in our adaptation to them. From a meteorological perspective, the main questions are related to the definition of extreme events, changes in their distribution and intensity both globally and regionally, the dependence on large‐scale phenomena including the role of moisture transport, and changes in their behavior due to anthropogenic pressures. In this review article, we address all these points and propose a set of challenges for future research.

Song C H

Clark J S

, et al. Understanding the continuous phenological development at daily time step with a Bayesian hierarchical space-time model: Impacts of climate change and extreme weather events. Remote Sensing of Environment, 2020, 247: 111956. DOI: 10.1016/j.rse.2020.111956.

Qin G X

Li C B

, et al. Grassland phenology's sensitivity to extreme climate indices in the Sichuan province, western China. Atmosphere, 2021, 12(12): 1650. DOI: 10.3390/atmos12121650.

Depending on the vegetation type, extreme climate and drought events have a greater impact on the end of the season (EOS) and start of the season (SOS). This study investigated the spatial and temporal distribution characteristics of grassland phenology and its responses to seasonal and extreme climate changes in Sichuan Province from 2001 to 2020. Based on the data from 38 meteorological stations in Sichuan Province, this study calculated the 15 extreme climate indices recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI). The results showed that SOS was concentrated in mid-March to mid-May (80–140 d), and 61.83% of the area showed a significant advancing trend, with a rate of 0–1.5 d/a. The EOS was concentrated between 270–330 d, from late September to late November, and 71.32% showed a delayed trend. SOS was strongly influenced by the diurnal temperature range (DTR), yearly maximum consecutive five-day precipitation (RX5), and the temperature vegetation dryness index (TVDI), while EOS was most influenced by the yearly minimum daily temperature (TNN), yearly mean temperature (TEMP_MEAN), and TVDI. The RX5 day index showed an overall positive sensitivity coefficient for SOS. TNN index showed a positive sensitivity coefficient for EOS. TVDI showed positive and negative sensitivities for SOS and EOS, respectively. This suggests that extreme climate change, if it causes an increase in vegetation SOS, may also cause an increase in vegetation EOS. This research can provide a scientific basis for developing regional vegetation restoration and disaster prediction strategies in Sichuan Province.

Shen M G

Jiang N

, et al. Spatial variations in the response of spring onset of photosynthesis of evergreen vegetation to climate factors across the Tibetan Plateau: The roles of interactions between temperature, precipitation, and solar radiation. Agricultural and Forest Meteorology, 2023, 335: 109440. DOI: 10.1016/j.agrformet.2023.109440.

Liu D S

Ciais P

, et al. Decreasing rainfall frequency contributes to earlier leaf onset in northern ecosystems. Nature Climate Change, 2022, 12(4): 386-392.

Wang T

Nan H J

, et al. Changes in satellite-derived spring vegetation green-up date and its linkage to climate in China from 1982 to 2010: A multimethod analysis. Global Change Biology, 2013, 19(3): 881-891.

The change in spring phenology is recognized to exert a major influence on carbon balance dynamics in temperate ecosystems. Over the past several decades, several studies focused on shifts in spring phenology; however, large uncertainties still exist, and one understudied source could be the method implemented in retrieving satellite-derived spring phenology. To account for this potential uncertainty, we conducted a multimethod investigation to quantify changes in vegetation green-up date from 1982 to 2010 over temperate China, and to characterize climatic controls on spring phenology. Over temperate China, the five methods estimated that the vegetation green-up onset date advanced, on average, at a rate of 1.3 ± 0.6 days per decade (ranging from 0.4 to 1.9 days per decade) over the last 29 years. Moreover, the sign of the trends in vegetation green-up date derived from the five methods were broadly consistent spatially and for different vegetation types, but with large differences in the magnitude of the trend. The large intermethod variance was notably observed in arid and semiarid vegetation types. Our results also showed that change in vegetation green-up date is more closely correlated with temperature than with precipitation. However, the temperature sensitivity of spring vegetation green-up date became higher as precipitation increased, implying that precipitation is an important regulator of the response of vegetation spring phenology to change in temperature. This intricate linkage between spring phenology and precipitation must be taken into account in current phenological models which are mostly driven by temperature.© 2012 Blackwell Publishing Ltd.

Blair J M

Kelly E F

, et al. Contingent productivity responses to more extreme rainfall regimes across a grassland biome. Global Change Biology, 2009, 15(12): 2894-2904.

Zhu Jianjun

Liu Huamin

, et al. Effects of extreme rainfall and drought events on grassland ecosystems. Chinese Journal of Plant Ecology, 2014, 38(9): 1008-1018.

摘要

Global atmospheric circulations are greatly affected by anthropogenic activities. Several atmospheric circulation models predict that the frequencies of extreme rainfall events and extreme droughts will increase in the future. Water is one of the most limiting resources for growth and development of plants in arid and semi-arid ecosystems. Furthermore, grassland ecosystems have been proven to be very sensitive to changing precipitation regimes. However, our understanding on the effects of extreme climatic events on the structure and functioning of grassland ecosystems is inadequate. By far, the definitions of extreme climatic events are still inconsistent. Therefore, based on analyses of the definitions of extreme climatic events and research methods in literature, we synthesize the effects of extreme rainfall events and extreme droughts on soil water and nutrient availability, individual plant development and physiological characteristics, community structure, ecosystem productivity and carbon cycling. In addition, we put forward five scientific questions on research concerning the impacts of extreme climatic events and identify two key issues on manipulative precipitation experiments to help with understanding the mechanisms on how grassland ecosystems respond to extreme climatic events in the context of global change.

[张彬, 朱建军, 刘华民, 等. 极端降水和极端干旱事件对草原生态系统的影响. 植物生态学报, 2014, 38(9): 1008-1018.]

当前人类活动的加剧显著地影响着全球大气循环的格局。大气循环的多个模型均预测未来全球气候变化的显著特征是极端降水事件和极端干旱事件发生的频率会显著增加。水分是干旱、半干旱区草原植物生长发育的限制性资源, 而草原生态系统是陆地生态系统中对降水格局变化非常敏感的系统。但是, 关于极端降水事件和极端干旱事件对草原生态系统结构和功能的影响还是以分散的个案研究为主, 甚至关于极端气候事件的定义迄今也不尽相同。为此, 该文在分析极端气候事件定义及其研究方法的基础上, 总结了极端降水事件和极端干旱事件对草原生态系统土壤水分和养分状况、植物生长发育和生理特性、群落结构、生产力和碳循环过程的影响, 并提出了未来极端气候事件研究中应重点关注的5个重要方向, 以及控制试验研究的2个关键科学问题, 对开展全球变化背景下草原生态系统对极端气候事件响应机制的研究具有指导意义。

Peres C A

. Tree phenology in adjacent Amazonian flooded and unflooded forests. Biotropica, 2005, 37(4): 620-630.

Ji Z X

Chen Y

, et al. The sensitivity of vegetation phenology to extreme climate indices in the Loess Plateau, China. Sustainability, 2021, 13(14): 7623. DOI: 10.3390/su13147623.

Climate changes, especially increased temperatures, and precipitation changes, have significant impacts on vegetation phenology. However, the response of vegetation phenology to the extreme climate in the Loess Plateau in Northwest China remains poorly quantified. The research described here analyzed the spatial change in vegetation phenology and the response of vegetation phenology to climate change in the Loess Plateau from 2001 to 2018, using data from seven extreme climate indices based on the ridge regression method. The results showed that extreme climate indexes, TNn (yearly minimum value of the daily minimum temperature), TXx (yearly maximum value of the daily maximum temperature), and RX5day (yearly maximum consecutive five-day precipitation) progressively increased from 2001 to 2018 in the Loess Plateau region, but decrease trend was found in DRT (diurnal temperature range). The start of the growing season (SOS) of vegetation gradually advanced with precipitation from northwest to southeast, and the rate was +0.38 d/a. The overall vegetation end of the growing season (EOS) was delayed, and the trend was −2.83 d/a. The sensitivity of the different vegetation phenology to different extreme weather indices showed obvious spatial differences, the sensitivity coefficient of SOS being mainly positive in the region, whereas the sensitivity coefficient of EOS was negative generally. More sensitivity was found in the EOS to extreme climate indexes than in the SOS. Forest, shrubland and grassland have similar responses to DRT and TNn; namely, both SOS and EOS are advanced with the increase in DRT and delayed with the increase in TNn (the sensitivity coefficient is quite different) but have different responses to RX5day and TXx. These results reveal that extreme climate events have a greater impact on vegetation EOS than on vegetation SOS, with these effects varying with vegetation types. This research can provide a scientific basis for formulating a scientific basis for regional vegetation restoration strategies and disaster prediction on the Loess Plateau.

. Increasing drought under global warming in observations and models. Nature Climate Change, 2013, 3(1): 52-58.

Dai A G

van der Schrier G

, et al. Global warming and changes in drought. Nature Climate Change, 2014, 4(1): 17-22.

Brodribb T J

Brodersen C R

, et al. Triggers of tree mortality under drought. Nature, 2018, 558(7711): 531-539.

Sthultz C M

Bowker M A

, et al. Mortality gradients within and among dominant plant populations as barometers of ecosystem change during extreme drought. Conservation Biology, 2006, 20(5): 1477-1486.

Understanding patterns of plant population mortality during extreme weather events is important to conservation planners because the frequency of such events is expected to increase, creating the need to integrate climatic uncertainty into management. Dominant plants provide habitat and ecosystem structure, so changes in their distribution can be expected to have cascading effects on entire communities. Observing areas that respond quickly to climate fluctuations provides foresight into future ecological changes and will help prioritize conservation efforts. We investigated patterns of mortality in six dominant plant species during a drought in the southwestern United States. We quantified population mortality for each species across its regional distribution and tested hypotheses to identify ecological stress gradients for each species. Our results revealed three major patterns: (1) dominant species from diverse habitat types (i.e., riparian, chaparral, and low- to high-elevation forests) exhibited significant mortality, indicating that the effects of drought were widespread; (2) average mortality differed among dominant species (one-seed juniper[Juniperus monosperma (Engelm.) Sarg.] 3.3%; manzanita[Arctostaphylos pungens Kunth], 14.6%; quaking aspen[Populus tremuloides Michx.], 15.4%; ponderosa pine[Pinus ponderosa P. & C. Lawson], 15.9%; Fremont cottonwood[Populus fremontii S. Wats.], 20.7%; and pinyon pine[Pinus edulis Engelm.], 41.4%); (3) all dominant species showed localized patterns of very high mortality (24-100%) consistent with water stress gradients. Land managers should plan for climatic uncertainty by promoting tree recruitment in rare habitat types, alleviating unnatural levels of competition on dominant plants, and conserving sites across water stress gradients. High-stress sites, such as those we examined, have conservation value as barometers of change and because they may harbor genotypes that are adapted to climatic extremes.

Piao S L

Huntingford C

, et al. Global variations in critical drought thresholds that impact vegetation. National Science Review, 2023, 10(5): nwad049. DOI: 10.1093/nsr/nwad049.

Identifying the thresholds of drought that, if crossed, suppress vegetation functioning is vital for accurate quantification of how land ecosystems respond to climate variability and change. We present a globally applicable framework to identify drought thresholds for vegetation responses to different levels of known soil-moisture deficits using four remotely sensed vegetation proxies spanning 2001–2018. The thresholds identified represent critical inflection points for changing vegetation responses from highly resistant to highly vulnerable in response to drought stress, and as a warning signal for substantial vegetation impacts. Drought thresholds varied geographically, with much lower percentiles of soil-moisture anomalies in vegetated areas covered by more forests, corresponding to a comparably stronger capacity to mitigate soil water deficit stress in forested ecosystems. Generally, those lower thresholds are detected in more humid climates. State-of-the-art land models, however, overestimated thresholds of soil moisture (i.e. overestimating drought impacts), especially in more humid areas with higher forest covers and arid areas with few forest covers. Based on climate model projections, we predict that the risk of vegetation damage will increase by the end of the twenty-first century in some hotspots like East Asia, Europe, Amazon, southern Australia and eastern and southern Africa. Our data-based results will inform projections on future drought impacts on terrestrial ecosystems and provide an effective tool for drought management.

Kojima M

Gepstein A

, et al. Delayed leaf senescence induces extreme drought tolerance in a flowering plant. PNAS, 2007, 104(49): 19631-19636.

Drought, the most prominent threat to agricultural production worldwide, accelerates leaf senescence, leading to a decrease in canopy size, loss in photosynthesis and reduced yields. On the basis of the assumption that senescence is a type of cell death program that could be inappropriately activated during drought, we hypothesized that it may be possible to enhance drought tolerance by delaying drought-induced leaf senescence. We generated transgenic plants expressing an isopentenyltransferase gene driven by a stress- and maturation-induced promoter. Remarkably, the suppression of drought-induced leaf senescence resulted in outstanding drought tolerance as shown by, among other responses, vigorous growth after a long drought period that killed the control plants. The transgenic plants maintained high water contents and retained photosynthetic activity (albeit at a reduced level) during the drought. Moreover, the transgenic plants displayed minimal yield loss when watered with only 30% of the amount of water used under control conditions. The production of drought-tolerant crops able to grow under restricted water regimes without diminution of yield would minimize drought-related losses and ensure food production in water-limited lands.

Estiarte M

Peñuelas J

. Drought advances spring growth phenology of the Mediterranean shrub Erica multiflora. Plant Biology, 2011, 13(2): 252-257.

Current climate projections predict drier and warmer conditions in the Mediterranean basin over the next century. While advanced spring growth due to warming has been described in the literature, few data are available on the effects of drought on phenology. Hence, the phenology and growth of two Mediterranean shrubs, Erica multiflora and Globularia alypum, was studied in a rainfall exclusion field experiment to simulate spring drought in a natural shrubland. We estimated the onset of growth in spring by monitoring the appearance of new stems, and the end of growth in summer by following the elongation of stems. Drought treatment caused earlier onset of the spring growing season in E. multiflora, whereas no advance was observed in G. alypum. However, growth cessation was not affected in E. multiflora. Drought reduced the growth of both shrubs, as reflected in less stem elongation. The results show that a drier climate might affect not only growth but also spring phenology of some Mediterranean species. We suggest that a reduction in the cooling effect of transpiration may have analogous effects to warming and might advance the start of growth in E. multiflora, a species whose phenology has been described as warming-sensitive. The lengthening of the growing season resulting from advanced growth did not imply higher productivity, as growth was restricted by drought.© 2010 German Botanical Society and The Royal Botanical Society of the Netherlands.

Wang T

Liu S L

. The response of vegetation phenology and productivity to drought in semi-arid regions of northern China. Remote Sensing, 2018, 10(5): 727. DOI: 10.3390/rs10050727.

Zhao J J

Zhang H Y

, et al. Preseason drought controls on patterns of spring phenology in grasslands of the Mongolian Plateau. Science of the Total Environment, 2022, 838: 156018. DOI: 10.1016/j.scitotenv.2022.156018.

Yokozawa M

Zhang Z

, et al. Land surface phenology dynamics and climate variations in the North East China Transect (NECT), 1982-2000. International Journal of Remote Sensing, 2008, 29(19): 5461-5478.

Zhao L

Lin A W

, et al. Impacts of preseason drought on vegetation spring phenology across the Northeast China Transect. Science of the Total Environment, 2020, 738: 140297. DOI: 10.1016/j.scitotenv.2020.140297.

Wu W X

Ge Q S

, et al. Legacy effects of spring phenology on vegetation growth under Preseason meteorological drought in the Northern Hemisphere. Agricultural and Forest Meteorology, 2021, 310: 108630. DOI: 10.1016/j.agrformet.2021.108630.

Sun Geng

Luo Peng

, et al. Flowering responses of alpine meadow plant in the Qinghai-Tibetan Plateau to lowering responses of alpine meadow plant in the Qinghai-Tibetan Plateau to extreme drought imposed in different periods. Chinese Journal of Applied & Environmental Biology, 2013, 19(2): 272-279.

[牟成香, 孙庚, 罗鹏, 等. 青藏高原高寒草甸植物开花物候对极端干旱的响应. 应用与环境生物学报, 2013, 19(2): 272-279.]

Tong S Q

Bao G

, et al. Spatiotemporal variation of autumn phenology responses to preseason drought and temperature in alpine and temperate grasslands in China. Science of the Total Environment, 2023, 859: 160373. DOI: 10.1016/j.scitotenv.2022.160373.

Han J Q

Zhang D J

, et al. Divergent impacts of droughts on vegetation phenology and productivity in the Yungui Plateau, southwest China. Ecological Indicators, 2021, 127: 107743. DOI: 10.1016/j.ecolind.2021.107743.

Sever K

Pflug E

, et al. Seasonal photosynthetic response of European beech to severe summer drought: Limitation, recovery and post-drought stimulation. Agricultural and Forest Meteorology, 2016, 220: 83-89.

Yusop Z

Yusof F

. Drought analysis and water resource availability using standardised precipitation evapotranspiration index. Atmospheric Research, 2018, 201: 102-115.

Doesken N J

Kleist J

. The relationship of drought frequency and duration to time scales//American Meteorological Society. Proceedings of the 8th Conference on Applied Climatology. Boston, 1993: 17-22.

Piao S L

Wang K

, et al. Temporal trade-off between gymnosperm resistance and resilience increases forest sensitivity to extreme drought. Nature Ecology & Evolution, 2020, 4(8): 1075-1083.

Rico-Medina A

Caño-Delgado A I

. The physiology of plant responses to drought. Science, 2020, 368(6488): 266-269.

Drought alone causes more annual loss in crop yield than all pathogens combined. To adapt to moisture gradients in soil, plants alter their physiology, modify root growth and architecture, and close stomata on their aboveground segments. These tissue-specific responses modify the flux of cellular signals, resulting in early flowering or stunted growth and, often, reduced yield. Physiological and molecular analyses of the model plant have identified phytohormone signaling as key for regulating the response to drought or water insufficiency. Here we discuss how engineering hormone signaling in specific cells and cellular domains can facilitate improved plant responses to drought. We explore current knowledge and future questions central to the quest to produce high-yield, drought-resistant crops.Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Gouveia C

Camarero J J

, et al. Response of vegetation to drought time-scales across global land biomes. PNAS, 2013, 110(1): 52-57.

We evaluated the response of the Earth land biomes to drought by correlating a drought index with three global indicators of vegetation activity and growth: vegetation indices from satellite imagery, tree-ring growth series, and Aboveground Net Primary Production (ANPP) records. Arid and humid biomes are both affected by drought, and we suggest that the persistence of the water deficit (i.e., the drought time-scale) could be playing a key role in determining the sensitivity of land biomes to drought. We found that arid biomes respond to drought at short time-scales; that is, there is a rapid vegetation reaction as soon as water deficits below normal conditions occur. This may be due to the fact that plant species of arid regions have mechanisms allowing them to rapidly adapt to changing water availability. Humid biomes also respond to drought at short time-scales, but in this case the physiological mechanisms likely differ from those operating in arid biomes, as plants usually have a poor adaptability to water shortage. On the contrary, semiarid and subhumid biomes respond to drought at long time-scales, probably because plants are able to withstand water deficits, but they lack the rapid response of arid biomes to drought. These results are consistent among three vegetation parameters analyzed and across different land biomes, showing that the response of vegetation to drought depends on characteristic drought time-scales for each biome. Understanding the dominant time-scales at which drought most influences vegetation might help assessing the resistance and resilience of vegetation and improving our knowledge of vegetation vulnerability to climate change.

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Bevacqua E

Chen C

, et al. Regional asymmetry in the response of global vegetation growth to springtime compound climate events. Communications Earth & Environment, 2022, 3: 123. DOI: 10.1038/s43247-022-00455-0.

AghaKouchak A

. Substantial increase in concurrent droughts and heatwaves in the United States. PNAS, 2015, 112(37): 11484-11489.

A combination of climate events (e.g., low precipitation and high temperatures) may cause a significant impact on the ecosystem and society, although individual events involved may not be severe extremes themselves. Analyzing historical changes in concurrent climate extremes is critical to preparing for and mitigating the negative effects of climatic change and variability. This study focuses on the changes in concurrences of heatwaves and meteorological droughts from 1960 to 2010. Despite an apparent hiatus in rising temperature and no significant trend in droughts, we show a substantial increase in concurrent droughts and heatwaves across most parts of the United States, and a statistically significant shift in the distribution of concurrent extremes. Although commonly used trend analysis methods do not show any trend in concurrent droughts and heatwaves, a unique statistical approach discussed in this study exhibits a statistically significant change in the distribution of the data.

De Boeck H J

Janssens I A

, et al. Do successive climate extremes weaken the resistance of plant communities? An experimental study using plant assemblages. Biogeosciences, 2014, 11(1): 109-121.

. The probability that plant communities undergo successive climate extremes increases under climate change. Exposure to an extreme event might elicit acclimatory responses and thereby greater resistance to a subsequent event, but might also reduce resistance if the recovery period is too short or resilience too low. Using experimental herbaceous plant assemblages, we compared the effects of two successive extremes occurring in one growing season (either two drought extremes, two heat extremes or two drought + heat extremes) to those of assemblages being exposed only to the second extreme. Additionally, the recovery period between the successive extremes was varied (2, 3.5 or 6 weeks). Among the different types of climate extremes, combined heat + drought extremes induced substantial leaf mortality and plant senescence, while the effects of drought and heat extremes were smaller. Preceding drought + heat extremes lowered the resistance in terms of leaf survival to a subsequent drought + heat extreme if the recovery period was two weeks, even though the leaves had completely recovered during that interval. No reduced resistance to subsequent extremes was recorded with longer recovery times or with drought or heat extremes. Despite the substantial mortality on the short term, the drought + heat and the heat extremes increased the end-of-season aboveground biomass independent of the number of extreme events or the duration of the recovery period. These results show that recurrent climate extremes with short time intervals can weaken the resistance of herbaceous plant assemblages. This negative effect in the short term can, however, be compensated in the longer term through rapid recovery and secondary positive effects.

Babálová D

Valach J

, et al. Impact of temperature and wetness of summer months on autumn vegetative phenological phases of selected species in Fageto-Quercetum in the years 2011-2015. Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, 2017, 65(3): 939-946.

Zhang X Y

. Impacts of wildfires on interannual trends in land surface phenology: An investigation of the Hayman Fire. Environmental Research Letters, 2017, 12(5): 054008. DOI: 10.1088/1748-9326/aa6ad9.

Rivera G

Hagnauer W

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Wu C Y

Wang X Y

, et al. Satellite observed delaying effects of increased winds on spring green-up dates. Remote Sensing of Environment, 2023, 284: 113363. DOI: 10.1016/j.rse.2022.113363.

Wang J

Ciais P

, et al. Widespread decline in winds delayed autumn foliar senescence over high latitudes. PNAS, 2021, 118(16): e2015821118. DOI: 10.1073/pnas.2015821118.

Decline in winds over past decades were observed over high northern latitudes (>50°), yet its influence on the date of autumn leaf senescence (DFS) remains unknown. Using ground observations, flux measurements, and remote sensing imagery, here we show that decline in winds significantly extended DFS over high latitudes at a magnitude comparable with the temperature and precipitation effects. We found that decline in winds reduces evapotranspiration, causes fewer damaging effects, and also results in decreased cooling effect. Our results therefore are of great significance for carbon cycle modeling because an improved algorithm based on these findings projected overall widespread earlier DFS by the end of this century, contributing potentially to a positive feedback to climate.

Wu C Y

Zhang X Y

, et al. Satellite detection of cumulative and lagged effects of drought on autumn leaf senescence over the Northern Hemisphere. Global Change Biology, 2019, 25(6): 2174-2188.

Climate change has substantial influences on autumn leaf senescence, that is, the end of the growing season (EOS). Relative to the impacts of temperature and precipitation on EOS, the influence of drought is not well understood, especially considering that there are apparent cumulative and lagged effects of drought on plant growth. Here, we investigated the cumulative and lagged effects of drought (in terms of the Standardized Precipitation-Evapotranspiration Index, SPEI) on EOS derived from the normalized difference vegetation index (NDVI3g) data over the Northern Hemisphere extra-tropical ecosystems (>30°N) during 1982-2015. The cumulative effect was determined by the number of antecedent months at which SPEI showed the maximum correlation with EOS (i.e., R ) while the lag effect was determined by a month during which the maximum correlation between 1-month SPEI and EOS occurred (i.e., R ). We found cumulative effect of drought on EOS for 27.2% and lagged effect for 46.2% of the vegetated land area. For the dominant time scales where the R and R occurred, we observed 1-4 accumulated months for the cumulative effect and 2-6 lagged months for the lagged effect. At the biome level, drought had stronger impacts on EOS in grasslands, savannas, and shrubs than in forests, which may be related to the different root functional traits among vegetation types. Considering hydrological conditions, the mean values of both R and R decreased along the gradients of annual SPEI and its slope, suggesting stronger cumulative and lagged effects in drier regions as well as in areas with decreasing water availability. Furthermore, the average accumulated and lagged months tended to decline along the annual SPEI gradient but increase with increasing annual SPEI. Our results revealed that drought has strong cumulative and lagged effects on autumn phenology, and considering these effects could provide valuable information on the vegetation response to a changing climate.© 2019 John Wiley & Sons Ltd.

Bottero A

Cailleret M

, et al. Contrasting resistance and resilience to extreme drought and late spring frost in five major European tree species. Global Change Biology, 2019, 25(11): 3781-3792.

Extreme climate events (ECEs) such as severe droughts, heat waves, and late spring frosts are rare but exert a paramount role in shaping tree species distributions. The frequency of such ECEs is expected to increase with climate warming, threatening the sustainability of temperate forests. Here, we analyzed 2,844 tree-ring width series of five dominant European tree species from 104 Swiss sites ranging from 400 to 2,200 m a.s.l. for the period 1930-2016. We found that (a) the broadleaved oak and beech are sensitive to late frosts that strongly reduce current year growth; however, tree growth is highly resilient and fully recovers within 2 years; (b) radial growth of the conifers larch and spruce is strongly and enduringly reduced by spring droughts-these species are the least resistant and resilient to droughts; (c) oak, silver fir, and to a lower extent beech, show higher resistance and resilience to spring droughts and seem therefore better adapted to the future climate. Our results allow a robust comparison of the tree growth responses to drought and spring frost across large climatic gradients and provide striking evidence that the growth of some of the most abundant and economically important European tree species will be increasingly limited by climate warming. These results could serve for supporting species selection to maintain the sustainability of forest ecosystem services under the expected increase in ECEs.© 2019 John Wiley & Sons Ltd.

Hejjaoui K

El-Baouchi A

, et al. Heat and drought stress impact on phenology, grain yield, and nutritional quality of lentil (Lens culinaris Medikus). Frontiers in Nutrition, 2020, 7: 596307. DOI: 10.3389/fnut.2020.596307.

Lentil (Lens culinaris Medikus) is a protein-rich cool-season food legume with an excellent source of protein, prebiotic carbohydrates, minerals, and vitamins. With climate change, heat, and drought stresses have become more frequent and intense in lentil growing areas with a strong influence on phenology, grain yield, and nutritional quality. This study aimed to assess the impact of heat and drought stresses on phenology, grain yield, and nutritional quality of lentil. For this purpose, 100 lentil genotypes from the global collection were evaluated under normal, heat, and combined heat-drought conditions. Analysis of variance revealed significant differences (p &lt; 0.001) among lentil genotypes for phenological traits, yield components, and grain quality traits. Under no stress conditions, mineral concentrations among lentil genotypes varied from 48 to 109 mg kg−1 for iron (Fe) and from 31 to 65 mg kg−1 for zinc (Zn), while crude protein content ranged from 22.5 to 32.0%. Iron, zinc, and crude protein content were significantly reduced under stress conditions, and the effect of combined heat-drought stress was more severe than heat stress alone. A significant positive correlation was observed between iron and zinc concentrations under both no stress and stress conditions. Based on grain yield, crude protein, and iron and zinc concentrations, lentil genotypes were grouped into three clusters following the hierarchical cluster analysis. Promising lentil genotypes with high micronutrient contents, crude protein, and grain yield with the least effect of heat and drought stress were identified as the potential donors for biofortification in the lentil breeding program.

Rutishauser T

Filella I

. Phenology feedbacks on climate change. Science, 2009, 324(5929): 887-888.

Chen Ying

Shi Wenjiao

, et al. Influences of agricultural phenology dynamics on land surface biophysical processes and climate feedback: A review. Acta Geographica Sinica, 2017, 72(7): 1139-1150.

摘要

The response and feedback of land surface processes to climate change constitute a research priority in the field of geosciences. Previous studies have focused on the impacts of global climate change on land surface processes; however, the feedback of land surface processes to climate change remains unknown. It has become increasingly meaningful under the framework of Earth system science to understand systematically the relationships between agricultural phenology dynamics and biophysical processes, as well as their feedback to climate change. This study summarized research progress in this field, including agricultural phenology change, parameterization of phenology dynamics in land surface process models, and the influence of agricultural phenology dynamics on biophysical processes, as well as its feedback to climate. The results showed that the agricultural phenophase, represented by paramount phenological phases such as sowing, flowering, and maturity, has shifted significantly because of the impacts of climate change and agronomic management. Digital expressions of dynamic land surface processes, as well as biophysical and atmospheric processes, have been improved by coupling phenology dynamics in land surface models. Agricultural phenology dynamics influence net radiation, latent heat, sensible heat, the albedo, temperature, precipitation, and circulation, thus, play an important role in surface energy partitioning and climate feedback. Considering the importance of agricultural phenology dynamics in land surface biophysical processes and climate feedback, the following research priorities have been identified: (1) interactions between climate change and land surface phenology dynamics, (2) relationships between agricultural phenology dynamics and different land surface reflectivity spectra, (3) contributions of changes in crop physiological characteristics to land surface biophysical processes, and (4) regional differences of climate feedback from phenology dynamics in different climatic zones. This review will be helpful in accelerating the understanding of the role of agricultural phenology dynamics in land surface processes and climate feedback.

[刘凤山, 陈莹, 史文娇, 等. 农业物候动态对地表生物物理过程及气候的反馈研究进展. 地理学报, 2017, 72(7): 1139-1150.]

地表过程对全球变化的响应和反馈是地球系统科学研究的核心课题之一,目前的研究多关注全球变化对地表过程的影响,而地表动态过程对地表生物物理过程及气候的反馈研究较少。系统认识地表物候动态对生物物理过程及气候的反馈对深化地球系统科学研究有着重要的意义。本文从农业物候动态的事实、农业物候动态在陆面过程模型中的参数化表达、农业物候动态对地表生物物理过程及气候的反馈等方面进行综述,发现在气候变化和管理措施影响下,以种植期和灌浆期为代表的农业物候期发生了显著的规律性变化;耦合农业物候动态,改善了模型对地表动态过程、生物物理过程和大气过程的数字化表达;农业物候变化对地表净辐射、潜热、感热、反照率和气温、降水、环流等过程产生了影响,并表现出以地表能量分配为主的气候反馈机理。针对农业物候动态对地表生物物理过程及气候效应的时空重要性,需要继续开展以下方面的工作：① 加强全球变化对地表物候动态的影响及其反馈的综合研究;② 不同光谱波段地表反射率与农业物候动态的关系研究;③ 农业物候动态引起的作物生理学特征变化在地表生物物理过程中的贡献;④ 重视不同气候区物候动态对气候反馈效应的差异。

Wang J

Hu R C

, et al. Relationship between vegetation change and extreme climate indices on the Inner Mongolia Plateau, China, from 1982 to 2013. Ecological Indicators, 2018, 89: 101-109.

Li Z

Peng S Z

. Global analysis of time-lag and -accumulation effects of climate on vegetation growth. International Journal of Applied Earth Observation and Geoinformation, 2020, 92: 102179. DOI: 10.1016/j.jag.2020.102179.

Yu Q Y

Feng L L

, et al. Evaluating the cumulative and time-lag effects of drought on grassland vegetation: A case study in the Chinese Loess Plateau. Journal of Environmental Management, 2020, 261: 110214. DOI: 10.1016/j.jenvman.2020.110214.

Liu Y Y

Cui M Y

, et al. Global assessment of cumulative and time-lag effects of drought on land surface phenology. GIScience & Remote Sensing, 2022, 59(1): 1918-1937.

Zhang Qiang

Kong Dongdong

, et al. Response of vegetation phenology to drought in Inner Mongolia from 1982 to 2013. Acta Ecologica Sinica, 2019, 39(13): 4953-4965.

[黄文琳, 张强, 孔冬冬, 等. 1982—2013年内蒙古地区植被物候对干旱变化的响应. 生态学报, 2019, 39(13): 4953-4965.]

Liu X P

Xin Q C

, et al. Cumulative effects of climatic factors on terrestrial vegetation growth. Journal of Geophysical Research: Biogeosciences, 2019, 124(4): 789-806.

Extensive studies have focused on instantaneous and time-lag impacts of climatic factors on vegetation growth; however, the chronical and accumulative indirect impacts of antecedent climatic factors carrying over for a period of time on vegetation growth, defined as cumulative effects, are less investigated. Here we aimed to disentangle the cumulative effects of climatic factors on vegetation growth by using vegetation indexes and accumulated meteorological data. First, we investigated the explanation and fit of climate changes on vegetation variations by applying stepwise multiple linear regression with Akaike information criterion. Then, we obtained the correlation coefficients and lagged time of climatic factors on vegetation growth whereby partial correlation and time-lag effect analyses. Results showed that (i) consideration of cumulative climate effects increased the explanation and fit of climate changes on vegetation dynamics for more than 77% of vegetated surface with an average global explanation of 68.33%, which was approximately 3.35% higher than the scenario when only time-lag effects were considered; (ii) big differences exhibited in the correlation coefficients and lagged times under the scenarios with cumulative climate effects considered or not; and (iii) positive accumulated temperature (accumulated solar radiation) effects with zero (three-month) time lag dominates most mid-high latitude ecosystems, and negative accumulated temperature effects with three-month delay dominates the temperate arid and semiarid regions and tropical dry ecosystems. By comparison, accumulated precipitation had relatively complex cumulative effects on vegetation growth. We concluded that climatic factors had significant cumulative effects on vegetation growth; consideration of the cumulative effects helps us better understand the climate-vegetation interactions.

. Spring phenology alters vegetation drought recovery. Nature Climate Change, 2023, 13: 123-124.

Sun S

Yao R

, et al. Long-term vegetation phenology changes and response to multi-scale meteorological drought on the Loess Plateau, China. Journal of Hydrology, 2022, 614: 128605. DOI: 10.1016/j.jhydrol.2022.128605.

Li X X

Zhou X C

, et al. Progress in plant phenology modeling under global climate change. Science China Earth Sciences, 2020, 63(9): 1237-1247.

Song Xingyang

Zhou Mengzi

, et al. Advances in influencing mechanism and model of total climatic production factors of plant phenology change. Scientia Sinica Vitae, 2023, 53(3): 380-389.

[周广胜, 宋兴阳, 周梦子, 等. 植物物候变化的全气候生产要素影响机制与模型研究. 中国科学: 生命科学, 2023, 53(3): 380-389.]

Peng J

Ciais P

, et al. Increased drought effects on the phenology of autumn leaf senescence. Nature Climate Change, 2022, 12: 943-949.

Liu D S

. Larger diurnal temperature range undermined later autumn leaf senescence with warming in Europe. Global Ecology and Biogeography, 2023, 32(5): 734-746.

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