氮沉降对米槠天然林土壤有机碳及微生物群落结构的影响

Effects of Nitrogen Deposition on Soil Organic Carbon and Soil Microbial Communities in a Natural Castanopsis carlesii Forest

[目的]研究氮(N)沉降对亚热带常绿阔叶天然林土壤有机碳和微生物群落结构的影响,为亚热带森林生态系统碳循环过程的研究提供依据。[方法]选取中亚热带典型米槠天然林为研究对象,采用随机区组试验设计,设3个N沉降水平:对照(CK,0kg·hm^(-2)·a^(-1))、低N(LN,40kg·hm^(-2)·a^(-1))和高N(HN,80kg·hm^(-2)·a^(-1))。[结果]在0~10 cm土层,与对照相比,高N和低N处理总微生物生物量显著增加,低N处理土壤有机碳含量增加27.4%,而高N对土壤有机碳无显著影响;在10~20 cm土层,N沉降(低N和高N处理)对土层有机碳含量和总微生物及各类群生物量均无显著影响。相关分析和随机森林模型结果分析表明,N沉降导致土壤可溶性有机碳(DOC)、全氮(TN)、C/N和微生物生物量增加是驱动表层土壤有机碳累积的关键因子;主成分分析表明,N沉降显著改变0~10 cm土层土壤微生物群落结构,而对10~20 cm土层土壤微生物群落结构无显著影响。[结论]在亚热带常绿阔叶天然林中,短期低N沉降增加能够提高土壤碳储量,但长期N沉降对土壤碳吸存的影响仍不清楚。

[Objective] To study the effects of N deposition on soil organic carbon and microbial community structure in subtropical evergreen broadleaved natural forest-in order to better understand the response of forest ecosystem to future N deposition and develop effective mitigation strategies.[Method] An N addition experiment was designed to evaluate the effect of N deposition on soil carbon(C) and soil microbial communities in a natural Castanopsis carlesii forest in subtropical China.In this study,randomized block design was adopted with three-levels of N addition,viz.control(CK,0 kg·hm^(-2)·a^(-1)),low N(LN,40 kg·hm^(-2)·a^(-1)) and high N(HN,80 kg·hm^(-2)·a^(-1)).[Result] Compared with the CK,the total microbial biomass examined by phospholipid fatty acid analysis(PLFA) were insignificantly increased in LN and HN treatment.The SOC concentration in LN treatment was 27.4% higher than that in CK treatment in 0-10 cm depth,while no significant effect being observed in HN.There were no significant effects of N addition on SOC concentration at the 10-20 cm soil depth in both LN and HN treatment.LN treatment significantly increased the total biomass and the biomass of each microbial component,while there was no significant effect in HN treatment at the 0-10 cm soil depth.Correlation analysis and random forest model analysis showed that increased dissolved organic carbon(DOC) concentration,total nitrogen(TN) concentration,C/N ratio and the increase of total microbial biomass under N deposition are the key factors driving soil organic C accumulation.Principal component analysis showed that N deposition significantly changed the microbial community at the 0-10 cm soil depth while not in the 10-20 cm depth.[Conclusion] Short term elevated atmospheric N inputs can increase forest soil C storage by increasing DOC concentration and microbial biomass in subtropical natural forest,while the long-term effects of N deposition on soil C sequestration remains unknown.