江西官山不同海拔常绿阔叶林土壤活性氮组分特征

Characteristics of soil active nitrogen fractions in evergreen broad-leaved forests at different altitudes in Guanshan mountain of eastern China

【目的】研究海拔梯度对常绿阔叶林土壤氮有效性的影响,揭示常绿阔叶林土壤活性氮组分的海拔差异性,为保护区内常绿阔叶林生态系统可持续经营提供科学依据。【方法】以江西官山国家级自然保护区内5个海拔梯度(400、600、800、1000、1200 m)的常绿阔叶林为研究对象,采集0~10、10~20、20~40 cm土壤样品,测定土壤全氮、无机氮(铵态氮和硝态氮)、微生物生物量氮、可溶性有机氮含量,分析海拔梯度与土壤活性氮组分的关系。【结果】土壤全氮、微生物生物量氮和可溶性有机氮含量随土层的加深而下降,随海拔的上升呈先增加后下降的趋势,1000 m海拔均显著高于400、600和1200 m海拔。随着海拔的上升,表层土壤铵态氮(0~20 cm)和硝态氮(10~20 cm)含量显著降低,而深层土壤铵态氮和硝态氮(20~40 cm)含量则先在600 m海拔显著增加后快速下降。土壤总活性氮占全氮的比例随海拔的升高出现先降后增的趋势,微生物生物量氮占全氮的比例显著高于其他氮组分所占的比例。海拔与土壤铵态氮呈显著负相关,而与可溶性有机氮呈显著正相关。土壤各活性氮组分与土壤湿度、微生物生物量碳、有机碳均呈显著正相关。【结论】海拔梯度对常绿阔叶林土壤氮的有效性具有显著影响,土壤水分、微生物生物量碳和总有机碳的变化是引起不同海拔高度上土壤活性氮组分变化的重要因子。

【Objective】In this study the effect of altitudinal gradient on soil nitrogen availability was investigated in evergreen broadleaved forests,in order to reveal the altitude distribution in soil active nitrogen components and finally provide scientific basis for sustainable management of evergreen broad-leaved forest ecosystem in nature reserve.【Method】Evergreen broad-leaved forests were selected at five different altitudes(400,600,800,1000,1200,and 1600 m)in Guanshan National Nature Reserve,Jiangxi province,from which soil samples were collected in the depths of 0-10,10-20,and 20-40 cm.The contents of soil total nitrogen(TN),inorganic nitrogen(DIN)including ammonium(NH_(4)^(+)-N)and nitrate(NO_(3)^(-)-N)nitrogen,microbial biomass nitrogen(MBN),and soluble organic nitrogen(SON)were determined to analyze the relationships between altitude and soil active nitrogen.【Result】Soil TN,MBN and SON contents decreased with soil depth while firstly increased and then decreased with altitude increasing,being significantly higher at 1000 m than those at 400,600 and 1200 m.With the increase of altitude,soil NH_(4)^(+)-N and NO_(3)^(-)-N contents in the surface layer significantly decreased,while these contents in the deep soil layer(20-40 cm)increased with a peak at 600 m and then decreased significantly.The proportions of total soil active nitrogen to TN showed a decrease and then an increase tendency with the elevation of altitude,further the proportions of MBN to TN were significantly higher than those in other nitrogen fractions.Altitude was negatively correlated with soil NH_(4)^(+)-N but had a significantly positive relationship with soil SON.In addition,soil active nitrogen fractions showed positively correlation with soil moisture,total organic carbon,and microbial biomass carbon.【Conclusion】Our results suggest that altitude,to some extent,significantly influences soil nitrogen availability in evergreen broad-leaved forests,and the changes in soil moisture,microbial biomass carbon and total organic carbon may be the important factors explaining the distribution differences in soil active nitrogen fractions along altitude.