The Seasonal Dynamics Of Soil Microbial Biomass And Enzyme Activities In Permafrost Regions And Seasonal Frozen Ground Of Maxian Mountain

Permafrost is one of the main components of the cryosphere,which plays an important role in ecosystems,global carbon cycle,hydrological processes and waterresources,Permafrost is also closely related with engineering construction and economy development in cold regions.Permafrost is a product of cold weather thus is very sensitive to climate change.Maxian mountain is located on the eastern edge of the Qinghai-Tibet Plateau,underlying with permafrost,with a typical land cover of meadow.The dominant species are Kobresia,Carex,Deschampsia caespitosa(Linn.)Beauv,Saussurea stella Maxim andother alpine meadow,The ecosystem on the Maxian Mountain is similar with that on the permafrost regions on Qinghai-Tibet Plateau permafrost,and thus provides us a good opportunity to study the mountain permafrost ecosystem.To investigate the differences of seasonal dynamics of soil microbial biomass and enzyme activities between permafrost areas and seasonal frozen ground areas,the permafrost area,seasonal frozen ground and the boundary area of permafrost and seasonal frozen ground in Maxian mountain were selected.Invertase,Urease,Neutral Phosphatase,Amylase,Catalase,and Polyphenol Oxidase activities,as well as the microbial biomass C and N in 0-30 cm soil layers were analyzed.In addition,this study discussed the seasonal variation of soil light fraction organic carbon(LFOC)and heavy fraction organic carbon(HFOC)in permafrost and non-permafrost regions.The main conclusions are as follows:(1)The highest values of soil microbial biomass carbon and nitrogen in the permafrost and seasonal frozen soils appeared in the surface(0-10cm),and gradually decreased with the deepening of the soil.The soil microbial biomass C and N of permafrost and seasonal frozen soils in Maxian mountain showed similar seasonal changes,but the variation law was different in different soil layers.The seasonal variation of microbial biomass carbon and nitrogen ratios showed different pattems among different soil layers and sites,The ratio of carbon to nitrogen ranged from 4 to 18.(2)Six enzymes in different sampling areas had different seasonal changes.The enzyme activities showed a decrease in soil enzyme activity except for the catalase and polyphenol oxidase.The change of enzyme activity is related to its own metabolic process.The contents of total nitrogen,total phosphorus,total organic carbon and microbial biomass carbon are the main controlling factors of soil enzyme activity.(3)In addition to dissolved organic carbon(DOC),the contents of total soil carbon(TC),total organic carbon(TOC),light fraction organic carbon(LFOC)and heavy fraction organiccarbon(HFOC)in permafrost soil were significantly higher than those in non-permafrost.During the whole growing season,the dissolved organic carbon(DOC)in each study area showed the first relatively stable from July began to significantly increase the trend in October to reach the highest..The total organic carbon(TOC)and total carbon(TC)in the permafrost regions were increased from April to June and then decreased,reaching the lowest in July and increasing in August In the non-permafrost region increased slightly in June but overall relatively stable.While light fraction organic carbon(LFOC)showed a decrease of 4-7months in each sampling area,reached the lowest in July and began to rise in August.The heavy fraction organic carbon(HFOC)showed a decrease from April to May in each sampling area,reached the lowest in July and increased in August..There was no significant correlation among light fraction organic carbon(LFOC)and heavy fraction organic carbon(HFOC).surface temperature,humidity,pH value,total carbon(TC)and microbial biomass carbon(MBC)(P> 0.05),indicating that the soil environment were not the determinants seasonal variations of light fraction organic carbon(LFOC)and heavy fraction organic carbon(HFOC).This study shows that,as a typical high temperature permafrost region,the microbial biomass carbon and nitrogen contents in the permafrost regions are comparable to non-permafrost regions in Maxian Mountain.The vegetation geochemical and soil organic carbon contents in the permafrost region were significantly higher than those in the non-permafrost regions.Therefore,the bio-geochemical cycle intensity of soil carbon or unit soil was higher in non-permafrost regions.This suggests that the degradation of permafrost leads to an increase in soil bio-cycling intensity due to soil microbes and enzymes involved,leading to the decomposition of soil carbon library strengthen,ecosystem degradation and the decrease of soil nutrients.