Characteristics Of Plant Communities And Soil Organic Carbon Mineralization In Desert Steppe Of Western Inner Mongolia

Grassland is an important part of terrestrial ecosystem,which is particularly important for maintaining regional ecological balance.Desert steppe,as a transition zone between desert and steppe,is sensitive to climate change,especially mean annual temperature and mean annual precipitation.In recent years,with the increase of temperature and the irregular change of precipitation,the plant composition and soil characteristics of desert steppe in western Inner Mongolia have changed.Therefore,it is very important to study the response of desert steppe ecosystem to mean annual temperature and mean annual precipitation in western Inner Mongolia.In this study,the desert steppe ecosystem in western Inner Mongolia was selected as the research object to investigate the effects of mean annual temperature and mean annual precipitation on plant community characteristics and soil characteristics.Soil temperature and moisture are the main regulatory factors affecting soil organic carbon mineralization.The effects of temperature and moisture on the rate and amount of soil organic carbon mineralization were explored through laboratory culture experiments.Finally,structural equation model was used to explore the relationship between temperature and precipitation,plant community characteristics,soil characteristics and soil organic carbon mineralization.The results show that:（1）Mean annual temperature（MAT）and mean annual precipitation（MAP）had no significant effects on plant diversity,while C4 plants were more adaptable to drought and less rainfall environment.The increase of MAP can promote the increase of the relative biomass of perennial herbs（PEH）and decrease the relative biomass ratio of shrubs（SHR）.MAT had no significant effect on the relative biomass of plant functional groups.MAT can reduce above-ground biomass,below-ground biomass and litter biomass,and has a significant negative correlation with below-ground biomass（5-10 cm）.MAP increased above-ground biomass,below-ground biomass and litter biomass,and had a significant positive correlation with below-ground biomass（5-10 cm）.（2）The increase of MAT can reduce soil organic carbon（SOC）and total nitrogen（TN）contents,while MAP can increase SOC and TN contents,and there is a significant positive correlation with SOC.MAT can significantly reduce soil carbon-nitrogen ratio（C:N）,increase soil p H,reduce microbial biomass carbon（MBC）and fungal bacteria ratio（F:B）,and reduce soil particle composition of gravel（>0.25 mm）content percentage,increase the content percentage of sand particles（0.002-0.25 mm）.However,the relationship between MAP and these soil factors is opposite to MAT.（3）Under the condition of controlled culture in laboratory,the mineralization rate of soil organic carbon was significantly different at different points and different soil layers.The rate and amount of mineralization in 0-5 cm soil layer are higher than those in 5-10cm and 10-20 cm soil layer.Both temperature and moisture can promote soil organic carbon mineralization.At most sampling sites,CO₂release at 25℃and 35℃was significantly greater than that at 5℃and 15℃.CO₂release also increased with the increase of soil water content,especially when the soil pore water content（WFPS）was60%and 90%.（4）SEM analysis results showed that ecological factors in soil and microorganisms had a negative regulatory effect on organic carbon mineralization,plant community biomass had a positive regulatory effect on organic carbon mineralization,soil ecological factors had a negative regulatory effect on microbial ecological factors,and climate factors had a positive regulatory effect on plant community biomass.In this study,the effects of temperature and precipitation on plant community characteristics and soil characteristics,as well as the effects of temperature and moisture on the mineralization rate and amount of soil organic carbon were explored by combining field transect investigation and indoor culture experiment.Finally,the relationship between climate,plant community characteristics,soil characteristics and soil organic carbon mineralization was analyzed by structural equation model.