Spatial Variability Of Soil Organic Carbon And Its Influencing Factors In Plateau Grassland Transect

Soil organic carbon pool of plateau grassland is a key component of geochemical carbon cycle,which is closely related to global climate change.The active component of soil organic carbon in grassland is an important index to study the response of soil carbon pool to climate change.The inert component of soil carbon is related to soil carbon fixation,adsorption and cation exchange capacity.At present,the research on spatial variability of soil organic carbon in grassland is focused on structure and randomness,while the research on biological and abiotic factors on spatial variability of soil organic carbon is relatively weak.In this study,the spatial distribution of soil organic carbon(SOC)in the natural grassland of the three plateaus(Mongolian Plateau,Tibetan Plateau and loess plateau)was studied by chemical analysis,physical extraction,redundancy analysis and structural equation analysis in order to find out the spatial variation mechanism of soil organic carbon under biotic and abiotic conditions.The related research results can provide theoretical support for better protecting the ecological environment and improving the soil quality of plateau grassland in China,as follows:1.The results show that there are significant spatial variability of organic carbon and particulate organic carbon in the Mongolian Plateau,Tibetan Plateau and Loess Plateau under different climatic conditions,and the distribution of organic carbon and particulate organic carbon is as follows: Tibetan Plateau > Mongolia Plateau > Loess Plateau.The contents of particulate organic carbon and organic carbon were 0.89-17.07 g / kg and 2.20-52.68 g / kg,respectively.In general,the content of organic carbon in Tibet Plateau is the highest,followed by Mongolia and Loess Plateau.The distribution pattern of organic carbon and particulate organic carbon in different grassland types in three large plateaus is: meadow grassland > typical grassland > desert grassland.The results showed that the contents of soil readily oxidizable organic carbon and water-soluble organic carbon had significant regional differences under multi-scale conditions,and the distribution was as follows: Tibetan Plateau > Mongolia Plateau > Loess Plateau.We found that the soil water-soluble organic carbon content of the three plateaus grassland is low,the water-soluble organic carbon content of the Mongolian Plateau is between 0.07-0.51 g / kg,the Tibetan Plateau is between 0.02-0.49 g / kg,and the Loess Plateau is between 0.01-0.11 g / kg.The variation coefficient of organic carbon and active organic carbon is the same,which is Loess plateau ? Mongolia Plateau ? Tibetan Plateau.2.There were significant differences in the composition of inert organic carbon among the three plateaus.With the change of spatial location and grassland type,the components of inert organic carbon showed significant spatial variability among different plateau transects.The contents of humus carbon,humic acid carbon and fulvic acid carbon in grassland soil of Mongolian Plateau were 5.23-13.10g/kg,2.36-5.92g/kg and 2.77-7.18g/kg,respectively.The distribution of inert organic carbon in Tibetan Plateau is 4.54-23.22 g / kg,2.07-11.25 g / kg and2.22-11.99 g / kg.The contents of inert organic carbon in the Loess Plateau are 0.38-8.28 g / kg,1.12-2.95 g / kg and 0.67-5.54 g / kg,respectively.The variation coefficient of inert organic carbon in grassland transect is the same: Mongolia Plateau < Loess Plateau < Tibetan Plateau.3.Soil organic carbon and particulate organic carbon were positively correlated with annual average temperature,annual average precipitation,soil microorganisms(bacteria and fungi)and aboveground plant biomass,and negatively correlated with total radiation,soil p H and soil bulk density.Soil particle size and soil p H are the main factors affecting the spatial variability of particulate organic carbon in the Mongolian Plateau,while total radiation is the main factor affecting the spatial variability of particulate organic carbon in the Loess Plateau,and soil p H is the main factor affecting the spatial variability of particulate organic carbon in the Tibetan Plateau transect.The structural equation showed that the spatial variability of particulate organic carbon in the plateau grassland transect was the result of the indirect effect of abiotic factors on biological factors.The soil bulk density is the main factor affecting the spatial variability of the inert organic carbon in the Mongolian Plateau,the annual precipitation is the main factor affecting the spatial variability of the inert organic carbon in the Loess Plateau,and the soil p H is the main factor affecting the spatial variability of the inert organic carbon in the Tibetan plateau transect.The results of structural equation showed that the spatial variability of inert carbon was determined by both biotic and abiotic factors.