Characteristics And Stability Mechanism Of Soil Organic Carbon Accumulation During The Primary Succession Of Forests In Southeast Tibet

Forest succession is a basic ecological process of land plant growth,in which both biological and abiotic characteristics show systematic changes,including plant community structure,productivity and soil carbon pool.Previous studies have mostly explored the influence of vegetation succession on soil organic carbon cycle from aboveground plant communities and soil physicochemical properties.For example,in the process of vegetation succession and restoration,the increase of surface vegetation communities and underground biomass leads to changes in soil carbon pool,and natural vegetation succession can promote the accumulation and stability of soil organic carbon(SOC).In the context of global climate change,vegetation succession is of great significance to improve soil carbon sink function,maintain the stability and balance of soil carbon pool,and mitigate climate change.Soil can be physically or biochemically protected to reduce the availability of substrates,thereby inhibiting the decomposition of microorganisms and enhancing the stability of SOC.However,there are relatively few studies on the accumulation characteristics and stabilization mechanisms of microbial-mediated SOC in forest ecosystems during native succession,especially in high-altitude cold regions that are extremely sensitive to global change.The complete primary succession sequence formed by the glacier retreat site of Hailuogou is a natural research site to explore the formation and stability of SOC during the process of forest native succession.Taking the retreat site of Hailuogou glacier as the study area,seven forest stands with different primary succession stages were selected(FS1,10 a;FS2,30 a;FS3,40 a;FS4,50 aa;FS5,60 a;FS6,90 a;FS7,130 a),collecting forest topsoil at different succession stages.The physical and chemical properties,carbon composition,carbon residual carbon of microbial residues and structural characteristics of microbial communities of soil were determined,and the results were compared and analyzed to explore the accumulation and stability mechanism of stand SOC in the process of primary succession.The main results are as follows:(1)Forest soil organic carbon(SOC)gradually accumulates with the advancement of forest succession.Based on the determination of the soil moisture content(SMC)and SOC content of the top soil in seven different succession stages,the results showed that the water regulation capacity of the forset soil showed an increasing trend,and the physicobiochemical characteristics of soils gradually improved with the advancement of forest succession.From the perspective of soil carbon sequestration capacity,the retreat of Hailuogou glacier reached the cclimax community of the community after 90 years of succession.Before reached the cclimax community,the average annual accumulation rate was 0.46 g·kg-1·a-1,the accumulation rate in the early stage of succession was relatively fast,and the accumulation rate in the later stage of succession gradually decreased,and after the formation of the top level of the community,the soil organic carbon concentration of the stand no longer increased.SOC is significantly related to the physicochemical properties of soil,and forest stands at different succession stages mainly affect soil phy si cochemistry,thereby directly or indirectly affecting the accumulation and sequestration of SOC.(2)Particulate organic carbon(POC)and mineral-associated organic carbon(MAOC)respond differently to the advancement of forest succession.With the advancement of forest succession,the concentrations of POC and MAOC in forset soil increased,among which POC was the main component of soil organic carbon pool,and the change trend of POC was closer to SOC,and the accumulation rate of SOC was mainly regulated by POC.MAOC is one of the stable carbon pool,MAOC accumulation is faster than POC along the forest primary succession,and the contribution to the whole soil organic carbon is increasing,and the stability of SOC is mainly regulated by MAOC.(3)With the advancement of forest succession,the contribution of microbial necromass carbon(MNC)to the soil carbon pool gradually increased.In addition,the biomass of fungi and bacteria increased during succession,but fungi grew faster,fungal OTUs showed an upward trend,and bacteria,on the contrary,showed a downward trend of OTUs,that is,the dominant microbial flora changed from bacteria to fungi;The abundance of dominant ascomycetes(eutrophicious)in stand soils decreased significantly with succession,while the abundance of basidiomycetes and acid anhydride(oligotrophic)showed an upward trend,that is,the way of nutrient acquisition by the flora changed from eutrophication to oligonutrient,in which the cell walls of fungi and bacteria were relatively more difficult to degrade.The increase in microbial biomass,the transition from bacterial communities to fungal communities,and the transition from eutrophicious flora to oligoinfluence may all be responsible for the accumulation of MNC.During forest succession,soil microorganisms increase the accumulation of MNC through the increase of biomass and the transformation of community composition,and MNC is a stable SOC component,and the change of microbial characteristics during succession characterizes the enhancement of SOC stability.In summary,SOC continue to accumulate during the process of forest native succession,and the stability is gradually enhanced by the transformation of physical components and microbial communities.Studying the soil organic carbon accumulation and stability mechanism in the process of native succession of forests in the retreat area of Hailuogou glacier can provide important theoretical support and scientific basis for forest restoration and management.