Effects Of N Deposition On Plant Community Structure And Soil Microbial Nutrient Utilization In Typical Steppe On Loess Plateau

In order to understand plant community structure,productivity and the influence as well as the mechanism of soil microbial drive nutrient carbon and nitrogen cycle under long-time nitrogen deposition which can give scientific basis of grassland productivity and nutrient apply management.This study mainly focused on typical grassland in Loess Plateau where located on Lanzhou Province,concerning nitrogen addition as air nitrogen deposition with 10 years nitrogen addition study area since 2009 and selected 4 treatments as this research group,they are 0,2.3,4.6 and 9.2 g N m^-2yr^-1respectively marked as N0?N2.3?N4.6 and N9.2.Unveiling the plant community structure and soil microbial nutrient utilization mechanism,we got the following conclusions:1.Long-time nitrogen addition significantly increase the total plant biomass and grasses biomass while nitrogen fixation and no-nitrogen fixation grasses ratio are highest in the N2.3treatment and richness is lowest in N9.2.2.Analyses from soil solubility nutrient showed weakly relationship with soil microbial stoichiometry imbalance to resource,however,under the same nitrogen addition full-grass stage had huge difference with dry-yellow period;N addition had Carbon,Nitrogen and Phosphorus homeostasis in different plant phenological periods;Full-grass stage microbial utilization efficiency increased with the nitrogen addition,but microbial utilization efficiency in dry-yellow period explored no differences with Nitrogen treatments.What's more,only microbial utilization efficiency in full-grass stage with N0 and N9.2 had higher results in same N concentration.3.Soil microbial extracellular enzyme activity stoichiometry had unchanged pattern with plant phenological periods,but in full-grass stage and dry-yellow period extracellular enzyme activity showed significantly differences in same N concentration.