Effects Of Warming And Nitrogen Addition On Soil Aggregate Nutrients And Enzyme Activities

Due to the intensification of human activities,global warming and increased atmospheric nitrogen deposition have become important driving factors for global change.The effects of climate warming and the increase of atmospheric nitrogen deposition on soil nutrients are increasingly significant,but the response mechanisms of the physicochemical properties and enzyme activities of desert steppe soils and aggregates to the dual effects of climate warming and nitrogen deposition are unclear.In order to understand the effects of long-term warming and nitrogen application on the physicochemical properties and enzyme activities of soils and aggregates,taking the light chestnut calcareous soil of Stipa breviflora desert steppe in Inner Mongolia as the research object,infrared radiation was used to simulate wanning,and ammonium nitrate(NH4NO3)was used as a nitrogen source for nitrogen addition treatment,and the effects of warming and nitrogen addition on the physicochemical properties and enzyme activity of grassland soil and aggregates were measured.The purpose was to reveal the nutrient content and enzyme activity of soil and aggregates in the desert steppe of Inner Mongolia.The response to long-term warming and nitrogen addition provides parameters for global change models to more accurately predict and assess the impact of climate change on soil nutrient cycling.The conclusion is as follows:(1)In 2018,nitrogen addition and warming+nitrogen addition significantly reduced soil pH(P<0.0001),and had no significant effect on soil conductivity and water content(P>0.05).The depth of the soil layer has a significant effect on soil pH,electrical conductivity,and water content(P<0.01).In the agglomerates,nitrogen addition significantly reduced the pH of the agglomerates(P<0.0001)and had no significant effect on soil conductivity and water content(P>0.05).The size of aggregates had a significant effect on soil pH(P<0.05)and a very significant effect on soil water content(P<0.01),but had no significant effect on soil conductivity(P>0.05).There were no significantly effects on soil pH,electrical conductivity,and water content of warming the whole soil and aggregates between warming and no warming(P>0.05).In 2019,nitrogen addition significantly reduced soil pH(P<0.01),significantly increased soil conductivity(P<0.01),and had no significant effect on soil moisture content(P>0.05).The depth of the soil layer has a significant effect on soil pH,electrical conductivity,and water content(P<0.01).In the agglomerates,warming had a significant effect on soil water content(P<0.05),and had no significant effect on soil pH and conductivity values(P>0.05).The size of aggregates has a very significant effect on soil pH and electrical conductivity(P<0.001)and a significant effect on soil water content(P<0.05).(2)In 2018,warming and nitrogen addition only significantly increased the content of nitrate nitrogen in the soil(P<0.01),and had no significant effect on other soil nutrient contents(P>0.05).The depth of soil layer had a significant effect on the contents of organic carbon,total nitrogen,total phosphorus and nitrate nitrogen(P<0.001),but had no significant effect on the content of soil ammonium nitrogen and available phosphorus(P>0.05).In the agglomerates,warming significantly reduced the total nitrogen,organic carbon,and available phosphorus content in the agglomerates(P<0.05),and nitrogen addition significantly increased the nitrate nitrogen content in the agglomerates(P<0.05),which significantly increased The content of ammonium nitrogen in the agglomerates(P<0.01),while the size of the agglomerates only was of a significant effect on the content of ammonium nitrogen and available phosphorus in the agglomerates(P<0.01),and had no significant effect on other soil nutrient contents(P>0.05).In 2019,nitrogen addition significantly increased soil ammonium and nitrate nitrogen contents(P<0.01).The depth of the soil layer affected soil organic carbon,total nitrogen,total phosphorus,ammonium nitrogen,and nitrate nitrogen contents.It is of significant effect(P<0.01),and the warming is of no significant effect on the soil nutrient index content(P>0.05).In the agglomerates,the warming significantly reduced the organic carbon content in the agglomerates,and the nitrogen addition significantly increased the ammonium and nitrate nitrogen contents in the agglomerates,and the size of the agglomerates was of a significant effect on the ammonium and nitrate nitrogen contents in the agglomerates(P<0.0001),there is a significant difference in total nitrogen and organic carbon content in the aggregates(P<0.05).(3)In 2018,nitrogen addition significantly increased soil dehydrogenase activity(P<0.01),and soil depth significantly affected soil urease,?-glucosidase,phosphatase,and dehydrogenase activities(P<0.0001).In the agglomerates,the warming significantly reduced the soil urease and phosphatase activities in the agglomerates(P<0.05),and nitrogen addition significantly reduced the urease and(3-glucosidase activities in the agglomerates(P<0.05).Body size was of a very significant difference in urease and?-glucosidase activity within the aggregates(P<0.01).In 2019,only the soil depth was of a very significant difference in the four soil enzyme activities(P<0.0001),and the effects of warming,nitrogen addition,and their interactions on soil enzyme activities were not significant(P>0.05).In the agglomerates,the warming significantly reduced the urease activity in the agglomerates(P<0.01),and nitrogen addition significantly reduced the ?-glucosidase activity in the agglomerates(P<0.05).The size of aggregates was of a very significant effect on soil urease activity(P<0.01)and a significant effect on phosphatase and dehydrogenase activities(P<0.05).Soil physicochemical properties and enzyme activities of desert grassland are not greatly affected by temperature,and nitrogen addition is of a greater impact on soil physicochemical properties and enzyme activities.But at the same time,the large difference in soil water content during the two years of the experiment is also the main factor that causes the two years to fluctuate greatly,indicating that in the semi-arid desert steppe,changes in soil nutrient characteristics are also affected by water content.At the same time,studying the response of nutrient content and enzyme activity in different aggregates to changes in warming and nitrogen adddition can help understand the stability characteristics of different soil carbon pools,and can better help us predict the ecosystem's resistance to global climate changes.