Responses Of Vegetation Communities And Soil Microbial Nutrient Utilization Characteristics To Precipitation And Nitrogen Deposition In Typical Steppe On The Loess Plateau

Precipitation change and increased nitrogen deposition are two important aspects of global change,which have important effects on grassland ecosystem structure and function.Typical Steppe is one of the main vegetation types on the Loess Plateau,which is extremely sensitive to global changes with fragile ecological environment.Some scholars have carried out research on the effects of precipitation or nitrogen deposition on plant community characteristics,soil physicochemical properties and microbial characteristics in this area,but there are few studies on the effects of the interaction between precipitation and nitrogen deposition on the ecosystem of the Loess Plateau.Therefore,we conducted a two-factor manipulation experiment of precipitation change（W-,reduce 30%natural precipitation,W0,natural precipitation,W+,increase 30%natural precipitation）and N addition(N0,N1,N2,nitrogen addition levels are 0,2.3,9.2 g m^-2 y^-1,respectively)in typical steppe of the Loess Plateau.This experiment explored the response of vegetation community and soil microbial nutrient utilization characteristics to precipitation,nitrogen deposition and their interactions in typical steppe on the Loess Plateau,aiming to deeply understand the influence of precipitation and nitrogen deposition on the structure and function of typical steppe ecosystems,and to provide a scientific basis for the scientific assessment and prediction of the main ecological and environmental effects on the Loess Plateau under the combined action of precipitation changes and atmospheric nitrogen deposition.The main results are as follows:1.Precipitation change played a leading role in changes in vegetation community diversity and biomass of typical steppe on the Loess Plateau.Decreased precipitation significantly decreased vegetation community diversity,cover and biomass,while increased precipitation significantly improved vegetation cover and biomass;nitrogen addition significantly increased above-ground biomass,belowground biomass and total biomass excluding legumes,low N addition（N1）significantly increased the vegetation cover.N addition promoted the positive response of aboveground biomass to increased precipitation,alleviated the inhibition of decreased precipitation on total biomass,and aggravates the limitation of decreased precipitation on total grassland cover.Vegetation community stability significantly decreased under precipitation change and N addition.Vegetation community diversity,productivity and stability were significantly positively correlated with soil water content（SWC）,soil organic carbon（SOC）,dissolved organic nutrients.2.Except for soil ammonium nitrogen（NH₄⁺-N）and nitrate nitrogen（NO₃^--N）,decreased precipitation generally inhibited soil dissolved organic carbon,nitrogen,phosphorus（DOC,DON,DOP）and microbial biomass carbon,nitrogen,phosphorus（MBC,MBN,MBP）.Increased precipitation increased SWC,SOC,MBC,MBN,MBP and carbon（C）,nitrogen（N）,phosphorus（P）acquisition enzyme activities.N addition significantly reduced SWC,DOC and N,P acquisition enzyme activities,alleviated soil N deficiency,and increased total nitrogen（TN）,DON,MBN.Nitrogen addition inhibited the positive effect of increasing precipitation on SWC,and aggravated the negative effect of decreased precipitation on DOC,DON,and MBN;decreased precipitation increased the positive effect of nitrogen addition on NH₄⁺-N,and increased precipitation promoted nitrogen addition on MBC,MBN,MBP.Soil microbial biomass and soil enzyme activities were significantly positively correlated with SWC,DOC and SOC.3.Decreased precipitation significantly reduced soil C:P and N:P imbalances,while increased precipitation decreased C:P imbalances;N addition significantly reduced C:N and C:P imbalances and increased N:P imbalances.Microbes maintained their own stoichiometric homeostasis by regulating soil extracellular enzyme production and element threshold ratios in response to stoichiometric imbalances caused by precipitation and nitrogen addition and their interactions.4.Precipitation,N addition and their interactions affected soil microbial biomass and extracellular enzyme activities through affecting soil water content and soil dissolved organic nutrients,and changed the characteristics of typical steppe vegetation communities and microbial nutrient utilization.