Effect of repeated drying-rewetting cycles on soil extracellular enzyme activities and microbial community composition in arid and semi-arid ecosystems

Climate change is predicted to alter precipitation patterns, which may have profound consequences on soil microbial communities and functions in arid and semi-arid ecosystems. However, it is uncertain if the direction and magnitude of soil microbial function and community responses to repeated drying and rewetting (DRW) events differ in diverse arid and semi-arid ecosystems. We collected surface soils in forest, farmland, grassland, and desert ecosystems from the Chinese Ecosystem Research Network (CERN) with mean annual precipitation ranged from 164 to 600 mm. Soils were then exposed to 0, 2, 5, 7 and 14 DRW cycles with variable drought periods at 20 degrees C. Soil respiration was measured in the rewetting phases of each DRW cycle. We also measured microbial biomass carbon (C), dissolved organic C, inorganic nitrogen, activities of four C-acquisition extracellular enzymes (beta-glucosidase, cellobiohydrolase, phenol oxidase, and peroxidase), and microbial community structure after the last DRW cycle. Results showed that repeated DRW cycles significantly affected most microbial parameters in our study. Specifically, repeated DRW cycles increased activities of beta-glucosidase and cellobiohydrolase. Lower DRW frequencies with longer drought periods had higher soil respiration, microbial biomass C, and the relative abundance of fungi. The responses of soil enzyme activities to repeated DRW were similar in the four ecosystems. However, soil microbial biomass and community composition were generally more resistant to repeated DRW cycles in the forest soil, while they were more vulnerable to repeated DRW stress in the desert soil, suggesting that altered precipitation patterns may have a greater impact on soil microbial communities in more arid ecosystems.