Effects Of Drought And Nitrogen Deposition On Soil Properties Of Typical Steppe In Inner Mongolia

Under the background of global climate change,the frequency of extreme climate in arid and semi-arid areas is increasing,and atmospheric nitrogen deposition is becoming increasingly significant.The typical grassland area is facing more and more severe environmental challenge.In this study,drought and nitrogen addition simulation experiments were carried out in the typical grassland ecosystem of Inner Mongolia.According to different drought scenarios that may be faced in the future,the treatment modes of natural rainfall,half rainfall reduction,rainfall frequency reduction and extreme drought period were set.The effects of different drought patterns and their interaction with nitrogen on soil physical and chemical properties(soil water content,soil pH,soil trace elements,soil available nitrogen,available phosphorus,total carbon,total nitrogen),soil enzymes(acid phosphomonoesterase,?-Glucosidase),soil microbial biomass(soil microbial biomass carbon,soil microbial biomass nitrogen)and their mutual influence were studied.The main conclusions are as follows:1.The results showed that the soil water content was significantly reduced under drought treatment,and the lowest under half rainfall treatment.Nitrogen deposition had no significant effect on soil water content.Soil pH value decreased year by year,and there was no significant difference under different drought scenarios and their interaction with nitrogen deposition,but the response was significant under the interaction of nitrogen deposition and interannual change.The contents of K,CA,Na,Mg,Fe,Mn,Cu,Zn in soil were significantly different with the change of years,and Fe,Mn,Cu,Zn were increased with time.The interannual variation of ammonium nitrogen was significant,and increased significantly under the interaction of reducing rainfall and nitrogen deposition.There was no significant response to the reduction of rainfall frequency,extreme drought treatment and the interaction between ammonium nitrogen and nitrogen deposition.The interannual variation of nitrate nitrogen was significant,which increased significantly under the interaction of extreme drought and nitrogen application,and the interaction of reducing rainfall and nitrogen application.The interaction of reducing rainfall frequency and nitrogen application had no significant effect on nitrate nitrogen.Under the interaction of reducing rainfall and nitrogen deposition,available phosphorus decreased significantly.The response of soil total carbon and nitrogen to drought and nitrogen deposition was not significant.2.Drought and nitrogen deposition significantly changed soil biological characteristics.Microbial biomass carbon and microbial biomass nitrogen changed significantly with months,and responded significantly to each drought treatment scenario and its interaction with nitrogen deposition.Microbial biomass carbon and biomass nitrogen increased significantly under nitrogen deposition,while microbial biomass carbon and microbial biomass nitrogen decreased significantly under drought stress.The difference of soil enzyme activitiesbetween months and years was significant.In 2019,the response of soil enzyme activity to drought treatment,nitrogen deposition and their interaction was significant.But in 2020,the response to each treatment was not significant.With the passage of treatment time,soil enzyme activity first decreased and then increased.3.The results of correlation analysis showed that there was a significant positive correlation between microbial biomass carbon,microbial biomass nitrogen and soil water content,and a significant positive correlation between soil enzymes and soil water content.There was a significant negative correlation between microbial biomass carbon and microbial biomass nitrogen and soil enzymes.Soil microbial biomass nitrogen was positively correlated with aboveground productivity,coverage and plant diversity.The decrease of available phosphorus stimulated the increase of acid phosphomonoesterase.Relationship between soil pH value and soil ?-Glucosidase was a significant negative correlation.In conclusion,drought and nitrogen deposition and their interaction have an important impact on soil characteristics of typical grassland.This study clarified the response of soil characteristics of typical grassland ecosystem to drought and nitrogen deposition,which will help to understand the ecological consequences of global change and improve the measures to deal with future climate change.