Effects of different inundation periods on soil enzyme activity in riparian zones in Lijiang

The most important environmental processes in riparian zones are the release of carbon, nitrogen, and phosphorus from various organic compounds. The extracellular enzymes of soil microorganisms are involved in the biogeochemical cycling of organic matter nutrients and may be important for regulating water quality. The objectives of the present study were to determine whether the activities of soil enzymes were affected by different inundation periods in the riparian zone and to identify major factors that influence soil enzyme activity. We subjected three study plots to different inundation conditions (long inundation, moderate inundation, and rare inundation) within the transects perpendicular to the river flow at three sites (Weijiadu, Lijiaocun, and Daxu) in Lijiang, Guilin City, China. Soil physicochemical properties, dissolved nutrient composition, and soil enzyme activities were analyzed. The activity of acid phosphatase, alkaline phosphatase, and arylsulfatase significantly increased as the inundation frequency decreased, whereas the activity of glucosidase, β-N-acetylglucosaminidase, glycine aminopeptidase, l-leucine aminopeptidase, and dehydrogenase were significantly higher in study plots that received long inundation than in those subjected to moderate or rare inundation. Linear regression indicated that most hydrolase and dehydrogenase activities were affected by soil clay content, soil organic matter, and soil water content, among other factors. NO3−-N limited the activity of acid phosphatase, l-leucine aminopeptidase, and glycine aminopeptidase. Polyphenol oxidase activity was constrained by soil water content and available potassium but promoted by NO3−-N. Our study demonstrated that imposing longer inundation periods can increase soil enzyme activities. To maintain microbial activity and to minimize water pollution, it is important to reduce high NO3−-N loads.