氮添加对黄土丘陵区草地土壤微生物养分限制特征的影响OA北大核心

Increasing atmospheric nitrogen deposition is affecting the soil nutrient balance.This may result in decreased nutrient availability to soil microbes.However,the effect of nitrogen deposition on the characteristics of nutrient limitation for soil microbes in grassland in the Loess Hilly Region is still unclear.The objective of this study was to investigate the effects of nitrogen deposition on soil microbial nutrient limitation in this region.A field-based controlled experiment simulating nitrogen deposition was conducted,and the soil microbial biomass,nutrient-transforming enzyme activities,and soil physicochemical properties were determined.This allowed us to elucidate the characteristics of nutrient limitation for grassland soil microorganisms,and its influencing factors,under different nitrogen addition levels.The results showed that nitrogen addition led to a decrease in soil pH,and altered the soil nutrient balance.More specifically,nitrogen addition increased the soil organic carbon and total nitrogen contents,but did not significantly affect the total phosphorus content.In addition,nitrogen addition enhanced the contents of soil available nutrients,with a greater increase in the available phosphorus content than in the soluble carbon and mineral nitrogen contents.This resulted in a relative shortage of carbon and nitrogen as available nutrients.Notably,the soil microbial biomass and extracellular enzyme activities decreased under low nitrogen addition but increased under high nitrogen addition.Further analyses using an enzyme stoichiometric model indicated that with increasing amounts of nitrogen addition,nitrogen limitation for soil microorganisms was intensified,while carbon limitation was alleviated.Microbial carbon limitation also affected the microbial carbon utilization efficiency.The imbalance of soil total and available nutrients caused by nitrogen addition jointly affected the characteristics of nutrient limitation for soil microorganisms by regulating microbial biomass and enzyme activity.In conclusion,these findings provide new information about the characteristics of soil nutrient cycling in grassland as affected by increasing nitrogen deposition.