[Responses of soil extracellular enzyme activities to the anthropogenic transition from desert grassland to shrubland in eastern Ningxia, China].

To understand the responses of soil extracellular enzyme activities to the desert grassland-shrubland anthropogenic transition, we examined soil properties and six extracellular enzyme activities, in soil under vegetation patches and bare interspaces in desert grassland, grassland edge, shrubland edge, shrubland in a typical anthropogenic desert grassland-shrubland mosaic in desert steppe of eastern Ningxia, China. The six measured enzymes included cellobiohydrolase, β-1,4-xylosidase, β-1,4-glucosidase, β-1,4-N-acetylglucosaminidase, leucine aminopeptidase and alkaline phosphatase. We found that soil moisture, soil organic carbon, total nitrogen, total phosphorus, microbial biomass carbon and microbial biomass nitrogen decreased significantly by 26.0%-88.5% with the process of the desert grassland-shrubland anthropogenic transition. All soil properties, except soil organic carbon and soil moisture in grassland edge site, were 3.9%-82.3% higher under vegetation patches than those in bare interspaces in each site. The six extracellular enzyme activities also decreased by 22.1%-82.4% in the transition process, especially for leucine aminopeptidase and alkaline phosphatase, showing significant decrease by 82.4% and 75.5%, respectively. All extracellular enzyme activities but β-1,4-N-acetylglucosaminidase in shrubland were significantly higher by 10.7%-42.7% under vegetation patches than those in bare interspaces in each site. The activities of six extracellular enzymes were all positively correlated with each other. All of them were positively correlated with soil properties. Moreover, activities of these soil extracellular enzymes responded more positively to the changes of microbial biomass carbon, microbial biomass nitrogen, and total nitrogen in the process of anthropogenic transition.