Effects of the freeze-thaw cycle on soil enzyme activities in a sub-alpine forest in western Sichuan

Research on soil enzyme activities is beneficial to identify relationships between plants, microbes, and soil organic matter. Freeze-thaw cycles will change resource allocations for the production of soil extracellular enzymes, which affects organic matter decomposition processes in the soil. Based on the pre-recognition of sub-alpine seasonal freeze-thaw cycles and considering typical coniferous-broadleaf mixed forest, coniferous forest, and broadleaf forest soil in the sub-alpine region of western Sichuan, we controlled the freeze-thaw environment and analyzed the effects of freeze-thaw cycles on enzyme activities in the soil, including carbon, nitrogen, and phosphorus. According to the results, the freeze-thaw cycles had a significant impact on β-N-acetylglucosidase and phosphatase activities associated with soil N and P. The activity of β-N-acetylglucosidase was elevated at the beginning of freeze-thaw period and then decreased with an increase in freeze-thaw frequency. The phosphatase activity increased significantly in the later portion of the freeze-thaw cycle. However, the freeze-thaw cycle had no significant effect on C-related soil enzyme activities. The changes in C-related soil enzyme activities in this study were more determined by litter decomposition processes and forest types. Among them, cellulase and β-glucosidase activities were significantly correlated with the decomposition process of organic matter. The limiting factors of peroxidase and polyphenol oxidase and low temperature and low oxygen were still present in this test, so the activities of these two enzymes did not change significantly. On the other hand, the effect of forest types on cellulase, peroxidase and phosphatase activities was significant. The soil cellulase activity of broadleaf forest was significantly lower than that of coniferous forest. The peroxidase activity of broadleaf forest soil was significantly lower than that of coniferous-broadleaf mixed forest and coniferous forest. The soil phosphatase activity of coniferous forest soil was significantly higher than that of coniferous-broadleaf mixed forest and broadleaf forest. Our results indicate that the effects of the freeze-thaw cycles on extracellular enzyme activities in the soil vary in this area. Freeze-thaw cycles that result from climate change will further influence the organic matter decomposition processes of the soil ecology system in the sub-alpine forest in western Sichuan.