氮磷添加对色季拉山高寒草地土壤酶活性和化学计量比的影响OA

Due to intensified human activities and industrial development,the input of reactive nitrogen(N)and phosphorus(P)has been continuously increasing.However,there is a lack of studies on soil physicochemical properties under N and P enrichment in the alpine grassland of Sejila Mountain,and little attention has been paid to the interactive effects of N and P.This study examined the response mechanisms of soil enzyme activities and stoichiometric ratios to nutrient addition using a field-control experiment of N and P addition in the alpine grassland of Sejila Mountain.Results showed that:1)compared with the control,the activities of β-1,4-glucosidase and cellobiohydrolase increased by 71.3%and 62.0%,respectively,under combined N and P addition(p<0.05).Nitrogen-acquiring enzymes displayed heterogeneous responses:β-1,4-N-acetylglucosaminidase increased by 90.6%and 59.8%under P addition and combined N-P addition,respectively,but decreased by 43.8%under N addition.Leucine aminopeptidase increased by 111.2%only under combined N-P addition.Alkaline phosphatase increased by 55.2%under combined N-P addition(p<0.05).2)Enzyme stoichiometry and vector analysis showed that the soil microorganisms were predominantly limited by P,as the vector angles under all treatments exceeded 45°.Although N and P addition elevated the metabolic upper limit of the microbial community,the dominant limitation still tended to be P.3)Correlation analysis and redundancy analysis indicated that exogenous N,P,and their combined addition jointly regulated soil enzyme activities and their stoichiometric structure by altering soil C꞉N ratio,available phosphorus,microbial biomass carbon,and dissolved organic carbon.Under P addition and combined N-P addition,available phosphorus increased markedly by 103.1%and 427.2%,respectively;microbial biomass carbon declined by 32.9%under combined N-P addition;and dissolved organic carbon decreased by 8.2%under combined N-P addition.The sampling sites were distinctly separated along the gradient of"available phosphorus-carbon-nitrogen ratio"(p<0.05).In summary,this study demonstrates the characteristics of"stoichiometric rebalancing-metabolic threshold"of alpine grasslands under N and P enrichment:single-factor addition modifies enzymatic investment at specific sites,whereas combined addition enhances the overall metabolic potential without shifting P from its role as the dominant limiting nutrient.