Effects Of Nitrogen And Litter Input On Microbial Community In Songnen Grassland

Nitrogen deposition is one of the important phenomena of global change.A series of ecological problems caused by the gradual increase of nitrogen deposition have become the focus of attention.Grassland,as the main body of terrestrial ecosystems,is seriously affected by human factors and climate change.Litter is an important part of grassland ecosystem.It plays an important role in connecting the aboveground and underground ecological processes and regulating the normal functioning of ecosystem functions.The circulation and distribution of nutrients in litter are inseparable from the role of decomposers-soil microbes.Soil microbes are the main participants in maintaining ecosystem functions,as well as an important component of regulating ecological processes.It plays an important role in decomposition of organic matter,cycling of plant nutrients,flow and transformation of energy,and formation of soil fertility.Nitrogen deposition as a global climate change can affect soil microbial activity and growth through direct or indirect effects.However,the study of litter on soil microbial community under the background of nitrogen deposition is relatively less.This study was conducted on the local scale of Songnen grassland,by controlling the addition and removal of the litter,to explore the influence of two main microbial communities-soil fungi and bacteria under nitrogen deposition.Analysis the changes of soil microbial numbers,microbial biomass,diversity and community composition and main influence factors based on the Illumina Hi Seq sequencing and real-time PCR technology which under the different nitrogen treatment and different level of litter.The main results and conclusions are obtained:(1)Soil bacterial community plays a dominant role in the research region and is a main dominant group in the microbial community.Nitrogen addition under remove litter treatment significantly reduces the number of soil bacteria.The effect of nitrogen on the soil fungi number under the remove litter and natural litter treatment was significantly inhibited,and the number of fungi was sensitive to the addition of litter.The number of bacteria and the number of fungi showed significant positive correlation with the soil ammonium content.It is indicated that the available N of soil is the main factor driving the change of microbial numbers.(2)In the case of nitrogen application,the addition of litter has a significant positive effect on soil microbial biomass carbon.Soil microbial biomass carbon was positively correlated with soil water content,soil organic carbon content,soil nitrate nitrogen content and soil total nitrogen content.It is indicated that the input of litter increases the content of soil organic matter,and thus increases the amount of carbon source that microorganisms can use.The organic matter in soil is the key factor affecting microbial biomass.In addition,soil microbial biomass carbon and plant diversity(plant species richness and Shannon-Wiener index)showed significant positive correlation.(3)The analysis of structural equation model shows that the treatment of nitrogen and litter can directly affect the diversity of bacteria.The treatment of litter can directly affect the physical and chemical properties of the soil and indirectly affect the diversity of bacterial communities.The litter can play a positive role in promoting the maintenance of bacterial community diversity by adjusting the main nutrients such as ammonium nitrogen,soil nitrate,soil total nitrogen and soil organic carbon content.The application of nitrogen treatment has a direct effect on fungal community diversity.(4)The main dominant groups in the bacterial community were Proteobacteria,Acidobacteria and Actinobacteria,which relative abundance were 42.97%,19.31% and 18.46%.The main dominant group in the fungal community was Ascomycota which relative abundance was 86.46%.Changes in the relative abundance of bacterial and fungal communities did not respond significantly to the treatment of nitrogen and litter.The community composition of fungi and bacteria is not sensitive to plant community index and soil physicochemical index.Means that under the nitrogen deposition and litter input,to some extent,to strengthen the soil bacteria and fungi community's ability to maintain its community structure stability,presumably,in the small scale of litter add may weaken or obscures the nitrogen deposition in grassland ecosystem caused some adverse effects.In conclusion,based on the global change of nitrogen deposition,this study analyzed the effects of different treatment levels of nitrogen and litter on soil microbial community.The mechanism and main ways of influencing soil microbial community were revealed.At the same time,the response of the above-ground and below-ground biome to the input of litter in the background of nitrogen deposition is discussed.The change regularity and influence way of soil microbial community were clarified.The treatment of nitrogen and litter can significantly affect bacterial and fungal communities.And the microbial number and soil microorganism biomass of soil microorganisms have different driving factors.The effects of nitrogen and litter on soil microbial community diversity are both direct and indirect.On a small scale,the change of environment caused by human or natural factors can enhance the stability of bacterial and fungal communities to maintain their community structure to a certain extent.In the context of global change,this study explored the sensitive changes of soil microbial community and the development of grassland ecosystem.It helps to explore the relationship between plants,soil and microbes under external stress.It provides a theoretical reference for the study of the relationship between the multi trophic level of the grassland ecosystem.It also provides the basis for the assessment of the above-ground and below-ground ecosystem.It is of great significance to explore its methods and measures to maintain the normal ecosystem structure and function.It will provide scientific reference for scientific management and sustainable development of grassland.