Differences In The Properties Of Soil Organic Carbon Components In Different Grassland Types Of Qilian Mountain

Grassland ecosystems are widely distributed,covering about 30% of the global terrestrial ecosystem area and storing a large amount of soil carbon.Grassland ecosystem is very sensitive to climate change,and the retention mechanism and turnover of soil carbon and nitrogen have become one of the hotspots in the study of global change.At present,the research on soil organic carbon and its components is mainly focused on the turnover and response mechanism,but the storage and stability of soil organic carbon is not clear.Yeniugou area of Qilian Mountain is located in the northern edge of Qinghai-Tibet Plateau,which is a typical alpine area.Under the scenario of global warming and permafrost degradation,affected by altitude,grassland ecosystem soil organic carbon has great decomposition potential.In this study,samples of different grassland types(alpine swamp meadow,alpine steppe and alpine meadow)were selected to determine the contents of carbon and nitrogen,physical and chemical properties,heavy fraction carbon(Heavy fraction organic carbon,HFOC),light fraction carbon(Light fraction organic carbon,LFOC),soil water soluble organic carbon(Water soluble organic carbon,WSOC),soil microbial biomass carbon(Microbial biomass carbon,MBC)and soil microbial biomass nitrogen(Microbial biomass nitrogen,MBN)in 0～10cm,10～20cm,20～30cm,30～40cm and 40～50cm soils.The purpose of this study was to explore the storage and stability of soil organic carbon and its components in different grassland types in alpine areas.It is analyzed and discussed.The main results are as follows:(1)The content of soil carbon and nitrogen in alpine area is affected by grassland type and soil depth.There were significant differences in aboveground and underground biomass among alpine swamp meadow,alpine steppe and alpine meadow,and the order of soil carbon and nitrogen content in different grassland types was as follows: alpine swamp meadow > alpine meadow > alpine steppe.The contents of TC,SOC and TN in different soil layers in different grassland types changed vertically with soil layer,and the carbon and nitrogen content in surface soil was significantly higher than that in bottom soil.The value of C/N in alpine swamp meadow soil was higher than that in other regions,but there was no significant difference among different soil layers.(2)Soil carbon and nitrogen content in alpine area is affected by soil p H,soil moisture content and soil silt content.Alkaline environment can promote the decomposition of SOC,and the range of soil moisture content in different grassland types is 7.04%～82.47%.There is a high correlation between TC,SOC,TN content and C/N value and soil p H and soil moisture content in alpine swamp meadow,alpine steppe and alpine meadow.Soil electrical conductivity has no effect on soil carbon and nitrogen content,and there is a significant positive correlation between soil silt content and total carbon content.(3)There were obvious vertical changes in soil heavy and light material quality and soil HFOC and LFOC content in alpine swamp meadow,alpine steppe and alpine meadow area.The LFOC/SOC value of alpine meadow had obvious vertical change among soil layers,the LFOC/SOC value of alpine swamp meadow and alpine steppe did not reach a significant level between soil layers,and the WSOC content of alpine meadow and alpine steppe showed significant vertical change.Different grassland types had different effects on the content and distribution of LFOC and WSOC in different soil layers.LFOC can well predict the long-term change of total SOC,and the order of soil organic carbon pool stability of 0～50cm in each region is alpine meadow>alpine steppe>alpine swamp meadow.(4)The changes of grassland type,plant biomass,soil physical and chemical properties and environmental variables all affect the stability of soil organic carbon pool in alpine area,while soil p H,moisture content,TC,SOC,TN content and C/N value are the main factors affecting the composition and stability of soil organic carbon pool in grassland ecosystem.(5)The higher the microbial biomass concentration in the soil and the more unstable the microbial community structure,the stronger the ability to promote the carbon and nitrogen cycle and vegetation growth of the ecosystem.The order of plant biomass providing energy for soil microbial activities in different grassland types is alpine swamp meadow>alpine meadow>alpine steppe,and the contribution rate of soil microbial biomass carbon to soil organic carbon pool is as follows: alpine meadow>alpine steppe>alpine swamp meadow.(6)Soil carbon and nitrogen play a key role in regulating energy flow and material circulation in soil,and there is a very significant positive correlation between MBC and MBN content and TC,SOC,TN and WSOC;soil microbial activity increases with the increase of soil p H value,and MBN content is significantly negatively correlated with p H;MBC and MBN content in each region has obvious vertical variation in 0～50cm soil layer,and has a very significant positive correlation with soil moisture content.The range of MBC/MBN is from0.49 to 5.87,that is,the bacterial community is relatively dominant in each regional soil community.To sum up,this paper selects different grassland types in Yeniugou area of Qilian Mountain,collects soil samples of different grassland types,and reveals the spatial distribution characteristics of soil carbon and nitrogen content and physical and chemical properties through indoor analysis and data analysis.the composition,stability and influencing factors of organic carbon pool were clarified,and the distribution of soil microbial biomass carbon and nitrogen and their influencing factors were explored.The results of this paper provide a scientific basis for clarifying the composition and sustainable utilization of soil carbon pool in alpine grassland in Qilian Mountain area.