森林表层土壤微生物碳氮库对大气氮沉降增加的响应

摘要

Soil microbial carbon (C) and nitrogen (N) pools play importance roles in C and N cycle of forest soil ecosystem. In order to investigate the effects of increasing N deposition to soil microbial C and N pools in forest surface soil, we carried out a field-based observation experiment in a temperature broad-leaved mixed forest during growth season (from May to October), and N deposition was implemented in forms of NH4Cl and KNO3 with dose as 40 kg·hm-1·y-1. The results indicated that the concentrations of soil dissolved organic C and soil inorganic N were not affected by N deposition in forest surface soil;N deposition in forms of NH4Cl induced significant decrease in soil pH value, i.e. the soil pH value decreased by 0.2 units, and resulted in significant decrease by 18%and 32%in soil microbial biomass C and N pools respectively, as contrast to Control. In current study condition, N deposition in forms of KNO3 did not affect the soil microbial biomass C and N pools. The correlation coefficient of soil C and N pools with those of soil microorganism under different forms of N deposition showed that the relationship between soil active C pools and soil microbial biomass C and N pools were increased by N deposition in form of KNO3, but not in those of NH4Cl form. Moreover, the possible mechanism which N deposition affect the forest soil C and N pools was discussed, our study emphasized that it is important to pay attention to the different effects of N forms in research of atmospheric N deposition.%土壤微生物碳氮库是森林土壤生态系统碳氮循环的重要组成部分，为了探索氮沉降增加对森林表层土壤微生物碳氮库的影响，本研究以长白山温带阔叶红松（Pinus koraiensis）混交原始林为研究对象，在2009年生长季节（5月至10月）开展了人工模拟大气氮沉降增加的野外试验，氮沉降处理采用NH4Cl和KNO3两种形态，处理剂量为喷施氮素40 kg·hm-2·a-1。研究结果显示，人工模拟氮沉降增加对森林表层土壤的溶解性有机碳及无机氮素含量未产生显著性影响；在观测期间NH4Cl形态氮沉降处理导致森林表层土壤的pH值降低0.2个单位（p<0.05），而且其土壤微生物量碳、氮含量比对照处理分别减少了18%（p<0.05）和32%（p<0.05）。在本研究的观测期间，KNO3形态的氮沉降增加对土壤微生物碳、氮库未产生显著性影响。通过分析不同形态氮沉降处理条件下土壤及其微生碳氮库之间的相关性，研究发现KNO3态氮沉降处理增强了土壤活性碳库与土壤微生物量碳、氮库间的关联性，而 NH4Cl 态氮沉降处理降低了这种关联性。此外，研究还探讨了不同形态的氮干扰影响森林土壤微生物碳、氮库的可能性机制，研究结果强调了在大气氮沉降研究中不应忽视氮素的形态效应。