Microbial Mechanism Of Soil Aggregate Organic Carbon Pool Stability In Alpine Grassland Under Long-term Enclosure

Enclosure is an effective method for grassland soil degradation restoration in semi-arid areas,which can not only improve soil ecological function but also improve grassland productivity.As the basic structure of soil,aggregates not only provide a habitat for microbial survival,but also determines the soil productivity.At present,there is a lack of systematic research on the mechanism of ecological function in grassland soil aggregates.Taking Bayinbulak alpine grassland soil as the research object,this study screened the aggregates of air dried and fresh soil respectively,analyzed the changes of carbon pool,microbial structure,function and diversity in alpine meadow,alpine meadow steppe and alpine steppe soil aggregates,and explored the microbial mechanism of the stability of organic carbon pool of Bayinbulak Alpine grassland soil aggregates under long-term enclosure conditions on a spatial scale,It provides a theoretical basis for the restoration and utilization of alpine grassland.The main results are as follows:(1)Under each treatment,the mass percentage of LMA(large macroaggregates,>2 mm)was significantly higher than that of other particle sizes,and the highest was 61.5% under GE treatment of alpine meadow 47%;The mass percentage of SMA(small macroaggregates,2～0.25 mm)is the lowest.After 36 years of long-term enclosure,MWD(mean weight diameter)and GMD(geometric mean diameter)of all types of grass under underground GE treatment are greater than those under FG treatment;MWD(3.94 mm)and GMD(2.17 mm)were the largest in GE treatment of alpine meadow.(2)Enclosure is beneficial to the accumulation of SOC(Soil organic carbon)in soil aggregates of alpine meadow and alpine steppe.There is no significant difference in SOC content between GE and FG treatments in alpine meadow steppe.The soil carbon pool of Bayinbulak alpine grassland is dominated by F1(extremely unstable organic carbon)and F4(inert organic carbon).The stability index of organic carbon in soil aggregates of each particle size under GE treatment of all types of grassland is greater than 1,indicating that the stable organic carbon component is dominant in the treatment.(3)The bacterial community diversity of LMA and SMA soil aggregates in alpine meadow and alpine meadow steppe is less than that of MIA(microaggregates,<0.25 mm),indicating that the soil bacterial community tends to be multipolar.Under the GE treatment,the bacterial communities in soil aggregates are mainly Acidobacteria,Proteobacteria,Chloroflexi,Gemmatimonadetes and Actinobacteria.The function of bacterial community was predicted by FAPROTAX tool.It was detected that the functional groups related to the participation of alpine grassland in carbon cycle were chemoheterotrophy,aerobic＿chemoheterotrophy,predatory＿or＿exoparasitic and photoheterotrophy.(4)The dominant communities of fungi in grassland soil aggregates under enclosure treatment are Ascomycota,Mortierellomycotaand Basidiomycota.Moreover,most of the genus level biomarkers of enclosure treatment belong to Ascomycota.Through the prediction of the function of soil fungi community by Fungild,it is found that the functional groups of soil fungi in Bayinbulak alpine grassland are mainly Undefined Saprotroph,Wood Saprotroph and Plant Saprotroph-Wood Saprotroph.(5)By constructing the random forest model of soil aggregate bacteria and fungi OTU and soil organic carbon stability coefficient,the bacteria and fungi out of top 30 can be obtained,and then the corresponding door can be found.The main bacterial phyla are Proteobacteria,Actinobacteria,Planctomycetes,Acidobacteria,Chloroflex,Gemmatimonadetes,Bacteroidetes,Verrucomicrobia and Rokubacteria;The main fungi phyla are Ascomycota,Basidiomycota,unclassified,Chytridiomycota,Mortierellomycota and Rozellomycota.This study found that F4,SOC and AP(Available phosphorus)are the main factors driving bacteria in LMA and SMA soil aggregates,.The changes of fungi community structure such as Ascomycota,Basidiomycota and Chytridiomycota can accelerate the accumulation of soil active and inert organic carbon components,promote the formation of microaggregates and large aggregates in soil.