Effect of grazing on soil enzyme activities in grassland ecosystems: A meta-analysis

Grazing causes major disturbances to grassland ecosystems and may alter soil enzyme activity. However, the mechanism by which grazing intensity, livestock type, grazing duration and environmental (e.g., climate and soil) factors affect the response of soil enzymes to grazing is currently unknown. This meta-analysis investigated the response of soil enzymes to grazing and the underlying intrinsic mechanisms based on 443 observations collected from 38 studies. Overall, grazing had a negative effect on soil enzyme activity, especially the activities of beta-glucosidase, sucrase, urease and alkaline phosphatase. Activity in response to grazing varied depending on the grazing intensity, grazing animals and grazing duration. Negative effects increased with increasing grazing intensity, as both moderate and heavy grazing significantly reduced activity by 10.08% and 20.06%, respectively. All levels of grazing intensity significantly reduced carbon-cycle-related sucrase but there were no significant effects on N-acetyl-beta-D glucosaminidase or leucine aminopeptidase, two enzymes involved in the nitrogen cycle. Among grazing animals, sheep, cattle and mixed grazing all significantly reduced activity, with the exception of the positive effects of cattle grazing on the activities of beta-glucosidase and protease, both of which participate in the carbon cycle, and N-acetyl-beta-D glucosaminidase, involved in the nitrogen cycle. However, while short-term (<5 years) and medium-term (5-10 years) grazing significantly reduced activity, the negative effects were ameliorated as the number of grazing years increased, such that long-term grazing (>10 years) had no significant effects. The interactions between climate, soil and other factors and grazing in terms of the impact on soil enzyme activity varied. Because soil enzymes mediate nutrient cycling, maintaining soil health requires that decision-makers appropriately reduce grazing intensity while increasing grazing duration.