Study On The Carbon And Nitrogen Characteristics Of Community And Soil For L. Chinensis Grassland Under Different Utilization Ways In Xilingol Steppe

As one of the most important types of typical steppe ecosystem,L.chinensis grassland is a representative type of studying typical steppe ecosystem that responses to human disturbance.This paper studies the characteristics of community and soil carbon and nitrogen and their interaction under the different ways of using(enclosure,mowing,grazing,mowing and grazing mixed)in L.chinensis grassland in Xilingol steppe,which aims to explore the effects of human activities on the characteristics of carbon and nitrogen.The main results are as follows:1)Under the ways of enclosure,mowing and grazing mixed use,sample plots maintains higher species diversity and evenness.Patrick richness index is the highest in mowing plot,taking second place in enclosed plot,which is the lowest in grazing plot,which are significant differences among them.2)With the increasing of utilization intensity to pasture(enclosure without utilization?mowing utilization?mowing and grazing mixed utilization?continuous grazing throughout the year for many years,the same below),the height,coverage and density of plant community show a obvious downward trend;root crown ratio shows a obvious rising trend;Leguminosae and Compositae show a downward trend in species composition..3)Under different utilization ways to pasture,there are significant differences among living plants,litter and root biomass,and all sample plots are characterized by root biomass>living plants biomass>litter biomass.The spatial distribution of root biomass for all sample plots are the"T"type,concentrating in 0~20 cm soil layer(account for 55%~75%of total amount),accounting for only about 8%in 40~50 cm soil layer.4)Under different ways of using to pasture,there are significant differences between living plants and litter for organic carbon content among sample plots,and no significant difference for root.There are significant differences among living plants,litter and root for organic carbon content in the same sample plot,being characterized by living plant>litter>root.With the increasing of utilization intensity to pasture,total nitrogen content of living plants generally shows a trend of gradual increase,being relatively stable for litter and root.5)With the increasing of utilization intensity to pasture,carbon nitrogen ratio of living plants generally show a trend of gradual decline.Compared with the litter and root,carbon nitrogen ratio of living plants has a tendency to become lower.6)Vegetation total organic carbon density is 542.0~900.2 g/m~2,including root accounted for 79.5%~91.2%.The organic carbon density is to the highest in enclosed sample plot,being 30.76%~66.09%higher than other sample plots.With the increasing of utilization intensity to pasture,the changes of organic carbon density of vegetation presents a parabolic curve in the remaining 6 sample plots.7)The vertical distribution of soil organic carbon,total nitrogen and available nitrogen content have law of diminishing with the depth of the soil layer.The 0~20 cm soil layer of soil organic carbon,total nitrogen and available nitrogen content accounts for about 50%of 0~50 cm soil layer;the surface effect is more obvious.The organic carbon,total nitrogen content in mowing without grazing sample plots for many years are less than the same soil layer in other sample plots;this kind of utilization must be noticed.With the increasing of utilization intensity,the ratio of soil C:N has a trend of unimodal curve that is first rise and then fall.8)With the increasing of utilization intensity to pasture,the total organic carbon and total nitrogen in the vegetation-soil system generally shows a trend of increasing first and then decreasing.Soil is the largest source of organic carbon and total nitrogen that accounts for 56.50%~65.44%and 74.49%~82.43%.9)Soil total nitrogen has extremely significant positive correlation with soil organic carbon;soil available nitrogen has significant negative correlation with plant organic carbon.Total nitrogen of root has significantly positively correlated with litter organic carbon and total nitrogen.