[Effects of Topography, Tree Species and Soil Properties on Soil Enzyme Activity in Karst Regions]

Soil extracellular enzymes are crucial in biogeochemical cycle and ecosystem functioning. Yet uncertainty exists in terms of major determinants on soil extracellular enzyme activity (EEA), especially at calcareous areas. In this study, soil samples (0-15 cm) were collected from different topographic conditions (different slope positions and aspects) and different tree species (Cryptocarya concinna and Eurycorymbus cavaleriei) in a forest located at Mulun natural reserve, a typical karst area. Six hydrolytic enzymes, related to carbon, nitrogen or phosphorus cycling, and soil physiochemical properties were investigated. The effects of topography, tree species and soil properties on soil enzyme activities were analyzed by multi-response permutation procedures (MRPP), redundancy analysis (RDA) and variation partitioning. The enzyme profiles were significantly (P<0.05) separated among the four slope positions but not significantly separated between the two aspects or two tree species according to multi-response permutation procedure (MRPP) analysis. Variation partitioning indicated that topography, tree species and soil properties together explained 55.3% of EEA variation. Soil property was the key factor influencing EEA variation, which explained 44.2% of EEA variation. The result of redundancy analysis (RDA) showed that soil pH, total nitrogen and inorganic nitrogen were the most important variables among the nine soil properties for EEA variation. This study first quantified the effects of small-scale topographic, tree species, and soil properties on soil enzyme activity variation in karst areas. Our results suggest that EEA variation can be well explained by soil properties at a small scale in the karst area.