Response Of Rhizosphere Soil Hydrolase Activities Of Seven Plants To Nitrogen Addition And Rainfall Change In Songnen Grassland

Global changes are profoundly affecting the structure and function of terrestrial ecosystems.In recent years,climate changes such as nitrogen deposition and changing precipitation patterns have become the hotspot of ecological research.Soil hydrolase is an important active catalyst to accelerate the degradation of soil organic matter in the terrestrial ecosystem.It is mainly produced by microorganisms and can indirectly represent the nutritional needs of microorganism and plants and the changes of microbial community structure,so as to understand the energy flow and nutrient cycling of the terrestrial ecosystem.However,it is not clear how the rhizosphere soil enzyme activities of different plant species respond to global changes.In this experiment,seven kinds of common plants in Songnen grassland?Leymus chinensis?Trin.?Nevski,Setaria viridis?L.?Beauv.,Chloris virgata Sw.,Vicia amoena Fisch.,Lespedeza daurica?Laxm.?Schindl.var.Daurica Fisch.,Medicago ruthenica?L.?Trautv.,Kochia sieversiana?Pall.?C.A.M?are selected as experimental materials?and a factor?,which are planted singly in mesocosm in our experimental greenhouse.When simulating nitrogen deposition and precipitation change,we set three nitrogen addition and water addition gradients respectively:N0(0 g N m^-2a^-1),N1(5 g N m^-2a^-1)and N2(10 g N m^-2a^-1);W0?average rainfall?,W1?increased rainfall by 30%?and W2?decreased rainfall by 30%?.The nitrogen addition and water addition are not interactive factors,and we use average rainfall addition for the nitrogen treatment experiment.In September 2017,seven plant rhizosphere soil samples are tested,in which we measured seven types of soil hydrolase activity,namely?-glucosidase??G?,?-glucosidase??G?,?-xylosidase??X?,Cellobiohydrolase?CBH?,N-acetylglucosaminidase?NAG?,Leucine aminopeptidase?LAP?and scid phosphatases?aP?.We also measured many edaphic indicators,plant underground biomass and soil microbial biomass carbon to analyze the specific reasons affecting soil hydrolase activity.To answer the following scientific questions:?1?How do rhizosphere soil hydrolase activities of different plant species respond to nitrogen addition and rainfall change??2?Is there a specific relationship between plant species and rhizosphere soil hydrolases??3?How do soil indexes respond to nitrogen addition and rainfall change??4?What are the main environmental factors that lead to the change of soil hydrolase activity in the interactive effects of nitrogen addition and rainfall change with plant species respectively?The main conclusions are as follows:?1?Nitrogen addition increases the hydrolase activities closely related to the cycle of carbon??G,?G,?X,CBH?and phosphorus?aP?,but to some extent inhibits the soil hydrolase activities closely related to the cycle of nitrogen?NAG,LAP?.Compared with normal rainfall,increased or decreased rainfall generally reduces the activity of soil hydrolase.?2?The effect of plant species on the activity of soil hydrolase reaches an extremely significant level,regardless of nitrogen addition or rainfall change.There is an obvious specific relationship between the activity of soil hydrolase and plant species.In addition,the soil enzyme activities of these seven grassland plants also show a specific response to plant functional groups and the soil hydrolase activities of poaceae plants are higher than those of leguminous plants and weeds.?3?Nitrogen addition has the most significant effect on available nitrogen?AN?and pH in soil,while rainfall change has the most significant effect on pH in soil.In terms of the influence on soil physical and chemical characteristics,the effect of plant species is significantly higher than that of nitrogen addition and rainfall change.It is predicted that plant species specificity will be the key factor to determine the rhizosphere hydrolase activity of plants in Songnen grassland under the global climate change scenario of intensified nitrogen deposition and rainfall change.In this experiment,we conducted single planting of seven common plants in Songnen grassland and the simulated treatment of nitrogen addition and rainfall change to investigate the effects of nitrogen deposition and rainfall pattern change on the activity of rhizosphere soil hydrolase.Our results emphasize that plant species-specificity plays a critical role in the response of rhizosphere soil hydrolase activities to global changes.This is of great significance for the understanding of the functional uniqueness of plant species in grassland plant communities and even ecosystems.