Effects Of Simulated Warming On Soil Enzyme Activity And Microbial Community Structure In An Alpine Treeline

Soil microorganisms and soil enzymes play an important role in the formation,mineralization and transfer of soil organic matter and regulating greenhouse gas fluxes between soil and atmosphere.Understanding the effects of climate warming on the decomposition of soil organic matter is crucial to global soil carbon stocks.The effects of climate change on the degradation of organic matter and nutrient release depend on how soil microorganisms and soil extracellular enzymes response to the changes in temperature.At present,there are many studies on the effects of simulated warming on soil microbes and soil enzyme activities,but the results are not all the same.Will climate warming cause changes in soil microorganisms and soil enzyme activities in the high-altitude and high-latitude regions and will they affect the microbial nutrient limits associated with soil carbon,nitrogen and phosphorus?There is still a lot of uncertainty about the current research.Therefore,in this study,the effect of simulated warming on soil microbial biomass,microbial community structure,soil enzyme activity and microbial nutrient limitation was investigated systematically through field experiment of simulated warming.It will provide valuable information on global patterns on the changes of soil microorganisms and soil enzymes and their potential mechanisms under the background of global warming.Through two years of simulated warming experiment,we found that the warming effect is as follows:air temperature 0.97?>temperature in soil organic matter layer?OL?0.6?>temperature in mineral soil layer?ML?0.37?.Moreover,there are significant differences in warming effects between different growing seasons,with early growing season?EGS?>later growing season?LGS?>non-growing season?NGS?.Simulated warming significantly affected the activities of?-glucosidase?BG?and peroxidase?POD?.Soil warming did not significantly affected the activities of cellobiohydrolase?CBH?,leucine aminopeptidase?LAP?and phenol oxidase?PPO?.The effects of simulated warming on the activities of acid phosphatase?AP?and N-acetylglucosidase?NAG?in the ML were greater than those in the OL and mainly exhibited as simulated warming reduced the activities of AP and NAG.In summary,simulated warming typically decreased soil enzyme activity.Soil warming did not significantly affected the ecoenzymatic stoichiometry and microbial nutrient limitation in the OL,while significantly affected ratios of C:N_EEAEA and N:P_EEAEA and microbial relative C limitation in the ML.The ratios of C:N_EEAEA and microbial relative C limitation were mainly reduced with simulated warming,during EGS1 and NGS2.In the OL,simulated warming had significant effect on soil gram-negative?G^-?bacteria and significantly reduced gram-negative?G^-?bacteria during EGS1 and EGS2.In the ML,simulated warming had significant effect on fungal biomass?TF?and significantly reduced fungal biomass?TF?during EGS2.Warming treatment have little effect on total microbial biomass,bacterial biomass?TB?and the ratios of fungi to bacteria?F/B?and gram-negative to gram-positive bacteria?G^-/G⁺?.Simulated warming had similar effects on gram-positive?G⁺?and gram-negative?G^-?bacteria.During EGS1 and EGS2,G^-and G⁺bacteria were reduced with simulated warming in the OL.Soil temperature,soil moisture content and soil pH were the three main factors affecting soil enzyme activity,soil enzyme stoichiometry and microbial community in the study area.Soil temperature,soil water content and pH were positively correlated with most enzyme activities.In addition,soil organic carbon?SOC?and soil total nitrogen?TN?were negatively correlated with most enzyme activities.Soil temperature and soil C:N_EEA,C:P_EEAEA and microbial relative carbon limitation were positively correlated,and soil temperature was negatively correlated with N and P limitation and soil N:P_EEA.RDA analysis showed that soil temperature,soil moisture content and soil pH significantly affected the microbial community structure.In summary,simulated warming decreased soil enzyme activity during some sampling periods;simulated warming had little effect on soil microbial biomass and soil microbial community structure,and bacteria were more sensitive to simulated warming than fungi.Seasonal changes have a stronger effect on soil enzyme activity and microorganisms than simulated climate change.Soil temperature,soil moisture and pH were the three main factors affecting soil enzyme activity,soil enzyme stoichiometry and microbial community in this study area.These results will provide important information for understanding the processes of soil ecosystems in alpine forests in the context of global warming.