Response Of Soil Enzyme Activities And Stoichiometry To Ecological Restoration In Yuanjiang Dry-hot Valley

The decomposition proces of soil macromolecule organic matter dominated by soil enzymes is the key and core of the carbon,nitrogen,and phosphorus cycles in the soil,and its stoichiometric ratio is an important indicator for evaluating the limitation of soil nutrient resources.Deeper understanding of soil enzyme activity and its stoichiometric ratio is of great significance for understanding the chemical matters cycle process in the soil.Dry-hot valleys are characterized by prominent water-heat contradictions and serious soil erosion.They are a typical fragile ecosystem in my country,and the ecological restoration pressure of degraded ecosystems is extremely high.Since 2003,Our country has implemented a series of ecological restoration projects represented by "returning farmland to forests",but the restoration effect is not good.This may be due to insufficient understanding of the material circulation process in the soil in the process of ecological restoration in the region.In this study,the dry-hot valley of Yuanjiang River was used as the research area and agricultural land was used as control.Grassland（early restoration）,shrubland（mid-restoration）and woodland（end-restoration）were selected as the research objects to monitor the activity of soil enzymes in different stages and explore The response of soil enzyme activity and its stoichiometry to ecological restoration.Redundant analysis,single factor analysis of variance,random forest and other statistical methods were used to analyze the important soil factors of soil extracellular enzyme activity and its stoichiometric ratio in the process of ecological restoration in dry and hot valleys.Two vectors were further constructed to explore the limitation of microbial resources in the process of ecological restoration in dry-hot valleys.The main conclusions are as follows:（1）With ecological restoration,soil total phosphorus and nitrate nitrogen content gradually decrease,while total nitrogen,p H,and ammonium nitrogen content gradually increase.Generally,soil fertility increases with ecological restoration.（2）With ecological restoration,soil enzyme activities continue to increase.Redundancy analysis results showed that soil factors can explain 87.9% of the changes in soil enzyme activity,and the key influencing factors are total nitrogen,p H,organic carbon and exchangeable magnesium ions.（3）The stoichiometric ratio of soil enzyme C:N:P in the dry and hot valley is1:1.23:0.32,which deviates from the global scale of 1:1:1,indicating that the microbial resources in Yuanjiang dry-hot valley may be limited by nitrogen and carbon.Further through the analysis of the construction vector,it is concluded that as the ecological restoration of the microbial resource carbon limit slows,the microbial resource nitrogen limit increases,and it is not restricted by the phosphorus.Random forest results show that total nitrogen is the main factor affecting the stoichiometric ratio of soil enzymes in dry and hot valleys.Therefore,artificial addition of nitrogen and carbon can be considered in the ecological restoration of the Yuanjiang dry-hot valley to increase soil enzyme activity and alleviate the nitrogen and carbon limitations during the ecological restoration of the dry-hot valley.