Characteristics Of Soil Labile Organic Carbon Fractions In Different Communities Of Desert Steppe

The desert steppe in the eastern part of Ningxia is a typical ecological fragile area in China,as it affected by geographical location and climatic conditions,which result in poor soil and rare vegetation diversity.The process of soil material cycling and energy flowing in grassland ecosystem is largely affected by the balance of soil carbon pool,therefore,the study of soil carbon pool,especially soil labile organic carbon and its components,have a great significance in evaluating the benefits of vegetation restoration and promoting regional ecological balance.This study selected four different communities as the research object,to study the soil organic carbon and its active components,soil physical and chemical properties and soil enzyme activities in different habitats and different soil types.The relationship between soil organic carbon and its active components and enzyme activity was studied by canonical correlation analysis and simple correlation analysis.The main conclusions are as follows:(1)The different type communities soil physical properties in different habitats(crown,shrub)and different soil layers(0-5,5-10,10-15cm)did not show significant difference,while the soil chemical properties(nitrogen,total phosphorus and available nutrient index)was gradually decreased with the increase of soil depth,which show its obvious "Surface aggregation".The Physicochemical properties of soil in the same soil layer showed in different habitats in the community:under the canopy,which reflect the contribution of the special spatial structure characteristics of plant communities to the accumulation of soil nutrients.(2)The distribution characteristics of soil organic carbon(SOC)and its active components in different communities were different in different habitats and different soil depths;The soil organic carbon(SOC),microbial biomass carbon(MBC)and easily oxidized organic carbon(EOC)in shrub(Caragana Korshinskii,Artemisia ordosica)community in the same depth as follows:under the canopy>interspace,and with the increase of the soil depth decreased,while in the herb(Stipa breviflora and Agropyron mongolicum)showed a tendency of "V" shape with the increase of soil depth,and the content of dissolved organic carbon(DOC)in different communities was different.(3)Different community types of soil microbial biomass in shrub(Caragana Korshinskii,Artemisia ordosica)community under canopy significantly(P<0.05)higher than under interspace,and decreased with the increasing of soil depth in the two habitats;The shrub communities soil organic carbon activity in two habitats with soil depth increased,and the canopy>interspace.While however,soil organic carbon activity of herb(Stipa breviflora and Agropyron mongolicum)communities under the canopy show a trend of "V" shape,but decreased with the increase of soil depth in interspace.The soil organic carbon activity of different community types range from 0.05 to 0.147,significantly lower than the national level,which is related to the low content of active organic carbon in desert steppe,and the relatively low conversion rate.(4)The distribution characteristics of soil invertase activity in different habitats were consistent in the two habitats(canopy,interspace),which decreased with the increasing of soil depth.The soil urease activity in different habitats shown as canopy>interspace.The soil alkaline phosphatase of Artemisia ordosica,Stipa breviflora and Agropyron mongolicum community in two habitats increased significantly(P<0.05)with soil depth decreasing,which is the opposite to Caragana Korshinskii community.The distinction between different communities soil enzyme activity under different habitats and in different soil layers may illustrate the soil enzymes are sensitive to the changes of soil micro-environment.(5)The canonical analysis of soil labile organic carbon,enzyme activity and soil properties showed that the activities of catalase,urease and invertase were affected by the content of MBC and DOC,while affected by EOC is not obvious;The content of total phosphorus and available P significantly affected the activity of alkaline phosphatase.The Simple correlation analysis showed that soil labile organic carbon is affected by the physical and chemical properties and soil enzyme activity greatly,and kinds of changes in soil nutrient effects on enzyme activity and nutrient level is related to the size,but the nutrient and enzyme activity were significantly correlated.