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不同森林经营模式对土壤氮含量及酶活性的影响

花匠小妙招
2024-12-21 05:06

摘要：

【目的】探讨不同森林经营模式对土壤氮含量及相关酶活性的影响,为太湖沿岸防护林模式构建提供依据。【方法】在江苏省宜兴市周铁镇选取林龄相同的杨树纯林、杨树石楠混交林以及杨树女贞混交林3种森林经营模式,挖取1 m深的土壤剖面采集土壤样品,测定各模式下春季土壤的氮含量及相关酶活性,并分析其与土壤理化性质之间的关系。【结果】①试验地土壤全氮含量为0.17~1.35 g/kg,各森林经营模式之间土壤全氮含量存在显著差异(df=2,F=102.820,P<0.05),与杨树纯林相比,杨树女贞混交林和杨树石楠混交林土壤全氮含量分别增加了21.8%、69.7%;随着土层深度增加,2种混交林土壤全氮含量逐渐降低,各土层之间差异显著(df=3,F=108.289,P<0.05);土壤硝态氮、铵态氮含量分别为5.67~9.79、3.22~12.43 mg/kg,各森林经营模式之间差异显著(df=2,F=18.764,P<0.05;df=2,F=9.655,P<0.05),杨树女贞混交林和杨树石楠混交林土壤硝态氮含量相比杨树纯林分别降低了11.8%、27.3%,而杨树女贞混交林和杨树石楠混交林的土壤铵态氮含量在≥20~40、≥40~60和≥60~80 cm土层显著增加(df=3,F=106.230,P<0.05;df=3,F=119.794,P<0.05);随着土层深度的增加,3种经营模式土壤硝态氮和铵态氮含量逐渐降低;土壤微生物生物量氮含量为6.04~9.52 mg/kg,与杨树纯林相比,杨树女贞混交林土壤微生物生物量氮含量增加了7.5%;②土壤脲酶活性、硝酸还原酶活性和亚硝酸还原酶活性分别为3.43~9.16、0.16~1.04、0.15~0.25 mg/(g·d),与杨树纯林相比,杨树女贞混交林土壤脲酶活性在各土层均显著增加(df=2,F=19.600,P<0.05),而土壤硝酸还原酶活性在土壤表层则显著降低(df=3,F=43.637,P<0.05);杨树石楠混交林土壤脲酶活性在各土层均显著降低(df=3,F=17.825,P<0.05),而土壤硝酸还原酶活性则相反;3种森林经营模式下土壤亚硝酸还原酶活性无显著差异。表明脲酶和硝酸还原酶对经营模式的响应更敏感,可作为土壤氮变化的指标。此外,不同森林经营模式下土壤氮含量及酶活性与含水量、pH密切相关。【结论】与杨树纯林相比,杨树女贞混交林和杨树石楠混交林提高了土壤速效养分,有效吸收并削减土壤中的硝态氮含量,降低硝酸盐向土壤深层淋溶导致污染浅层地下水的风险。同时,土壤微生物量氮和酶活性变化加速了土壤氮转化和养分循环。建议在太湖沿岸防护林构建过程中,推广乔灌复层混交林。

关键词: 杨树, 经营模式, 土壤, 氮含量, 酶活性, 防护林, 江苏宜兴

Abstract:

【Objective】This study investigated the effects of three forest management modes on soil nitrogen content and related enzyme activities associated with the construction of shelterbelts surrounding the shore of Taihu Lake.【Method】Poplar plantations that have been standardized and aged, with three management modes, i.e., Populus euramericana cv. 35 (poplar) pure plantation (PPP), Populus euramericana cv. 35-Ligustrum lucidum(poplar-ligustrum) mixed plantation (LMP), and Populus euramericana cv. 35-Photinia serrulata (poplar-photinia) mixed plantation (PMP), were selected in Zhoutie Town of Yixing City in Jiangsu Province, China. Soil samples were collected from a one meter-deep soil profile to measure the soil nitrogen content, the activities of related enzymes in spring, and the relationship among them. The physical and chemical properties of the soil were also analyzed.【Result】① The levels of total nitrogen (TN) content were about 0.17-1.35 g/kg and were significantly (df=2, F=102.820, P<0.05) affected by the applied forest management modes. Compared with the content of TN in PPP, those in LMP and PMP increased by 21.8% and 69.7%, respectively. Along the soil profiles, the TN content decreased with increasing soil depth in the two mixed plantations and was significantly different among layers (df=3, F=108.289, P<0.05). The levels of nitrate nitrogen (N O-3 -N) and ammonium nitrogen (N H+4 -N) contents were 5.67 to 9.79 mg/kg and 3.22 to 12.43 mg/kg, respectively. They were also significantly affected by management modes (df=2, F=18.764, P<0.05; df=2, F=9.655, P<0.05). The content of N O-3 -N in LMP and PMP decreased by 11.8% and 27.3%, respectively, compared with that in PPP; while the content of N H+4 -N was significantly increased in the layers of ≥20-40, ≥40-60, and ≥60-80 cm when compared with those in PPP (df=3, F=106.230, P<0.05; df=3, F=119.794, P<0.05). Along the soil profiles, N O-3 -N and N H+4 -N contents generally decreased with increasing soil depth in the three forest management modes. The level of microbial biomass nitrogen (MBN) was about 6.04-9.52 mg/kg and the mean value of MBN in the LMP was 7.5% higher than that in PPP. ② The activities of soil urease (UE), nitrate reductase (NR), and nitrite reductase (NiR) were 3.43-9.16, 0.16-1.04, and 0.15-0.25 mg/(g·d), respectively. Compared with PPP, the activity of the UE in LMP was significantly increased in all soil layers (df=2, F=19.600, P<0.05), while the activity of NR in topsoil was significantly decreased (df=3, F=43.637, P<0.05). In PMP, however, the activity of UE was significantly decreased (df=3, F=17.825, P<0.05), but the activity the of NR was increased in comparison to those in the PPP. Moreover, there was no significant difference in soil NiR activity among the three forest management modes.These results indicate that UE and NR are more sensitive to management modes and could serve as indicators of soil nitrogen dynamics. In addition, soil nitrogen content and enzyme activities were closely correlated with water content and pH value.【Conclusion】The LMP and PMP management modes can improve the soil available nutrients, efficiently absorbing and decreasing N O-3 -N in the soil, when compared with the PPP. In this way, the risks of nitrate leaching into the deep soil layer and that of polluting shallow groundwater are reduced. At the same time, the change in microbial biomass nitrogen and enzyme activity in the soil accelerated the soil nitrogen transformation and nutrient cycling. This suggests that multi-layer mixed forest management modes should be introduced and applied in the process of constructing shelterbelt forests surrounding the shore the Taihu Lake.

Key words: poplar, management mode, soil, nitrogen content, enzymatic activity, shelterbelts, Yixing City,Jiangsu Province

中图分类号:

S718

S715