Effects Of Nitrogen Deposition Background Rainfall Changes On Root Exudates And Rhizosphere Microorganisms In Typical Grasslands Of Inner Mongolia

In this study,we sampled grassland on the south bank of Hulun Lake and selected a naturally occurring water gradient zone to simulate the change of global precipitation pattern and the response of soil microorganisms after climate change.In the process of designing experiments,the influence of human disturbance and grazing disturbances were eliminated.The next step is to plan sampling along the lake again in other locations of Hulun Lake,taking into account the influence of human disturbance,land use methods,grazing intensity,etc.The influence mechanism of soil microbial community provides basic data for subsequent scientific research.The increasing global change will lead to significant impacts of biogeochemical processes in terrestrial ecosystems,including organic matter decomposition,soil respiration and nutrient cycling.Grassland is one of the most extensive terrestrial ecosystems.Understanding the response of grassland ecosystems to climate change is crucial for the successful development of effective climate change mitigation and adaptation strategies.Precipitation change and nitrogen deposition are two major characteristics of global climate change,which have a far-reaching impact on the growth of soil,and are also important limiting factors for plants and soil microorganisms.As two important components of the biological cycle of underground ecosystem,plant root exudates and rhizosphere microorganisms have been studied only for a long time,coupled with the recent high-throughput sequencing and other research There have been some new technological breakthroughs,so it is necessary to use the latest technology to carry out systematic research.It is also helpful for us to determine the influence mechanism of environmental factors on the underground biological cycle of typical steppe in Inner Mongolia,and provide more ecological basis for the study of the process of underground biological cycle of typical steppe in China under the background of climate change in the future.From June to October 2018,30 different types of sample plots were established in Hulun Lake Reserve Grassland Ecological Research Station,Minzu University of China,with three water increasing and decreasing gradients and two nitrogen application gradients.Stipa krylovii Roshev.and Allium polyrhizum Turcz.were selected as representative plants,and their root exudates,rhizosphere microorganisms and soil physical and chemical properties were systematically studied.The main conclusions are as follows:(1)The increase of nitrogen deposition and precipitation changed soil water content,and aboveground and belowground biomass.Increasing nitrogen deposition and precipitation significantly increased soil water content,aboveground and belowground biomass.(2)This study found that nitrogen deposition significantly increased the carbon rate and nitrogen rate of root exudates,while the increase of precipitation reduced the yield of root exudates.Although species and seasons had a significant impact on the yield of root exudates,the interaction between these factors is only reflected in the carbon rate of root exudates,but not obvious in the nitrogen rate.(3)The increase of nitrogen deposition and precipitation increased the biomass of soil microorganisms,and led to the change of microbial community structure to a certain extent.Compared with fungi,bacteria were more sensitive to environmental changes.(4)There was an interaction between root exudates and rhizosphere microorganisms.When root exudates increased,rhizosphere microorganisms also showed the same trend.At the same time,rhizosphere microorganisms used more nutrients in root exudates for their own use under the condition of low nitrogen.