Abstract: Wetland is characterized by permanent or seasonal inundation, whose structure and function are directly influenced by the changes of flooding conditions. To investigate the effects of flooding conditions on soil enzyme activities and identify the driving factors, we used three kinds of plots with different flooding conditions (longterm flooded wetlands, periodically flooded wetlands and seldom flooded wetlands) in the Bird Island of Qinghai Lake. Soil chemical properties, soil microbial biomass carbon and nitrogen, and soil enzyme activities were analyzed. The results showed that, compared to the long-term flooded wetland, the activities of β-glucosidase, cellobiase, and glycine aminopeptidase in the periodically flooded wetland decreased by 24.01%, 18.80% and 2.96%, respectively. The activities of those enzymes decreased by 33.65%, 18.84%, and 63.47% in the seldom flooded wetlands, compared with the periodically flooded wetland, respectively. The activities of N-acetylglucosaminidase and leucine aminopeptidase were significantly higher in periodically flooded wetland and long-flooded wetland than in the seldom flooded wetlands. However, the activities of alkaline phosphatase and phenol oxidase were the highest in the seldom flooded wetlands. Results of redundancy analysis showed that readily oxidizable carbon, total nitrogen, organic carbon, microbial biomass carbon and nitrogen, and dissolved organic nitrogen were significantly correlated with the changes of soil enzyme activities. Among them, soil organic carbon was responsible for the variability in cellobiase activity, whereas the activities of β-glucosidase, N-acetylglucosaminidase and glycine aminopeptidase were well explained by readily oxidizable carbon. Our results indicate that imposing flood was more conducive to the accumulation of carbon and nitrogen, and thus increased the activities of several hydrolases.

Key words: Cutting, Lolium perenne, Trifolium repens, Regrowth