Woody plants reduce the sensitivity of soil extracellular enzyme activity to nutrient enrichment in wetlands: A meta-analysis

Greater deposition of nitrogen (N) and phosphorus (P) is expected to increase decomposition of soil organic carbon (C) in wetlands. Soil extracellular enzyme activities (EEAs) are sensitive indicators of soil biogeochemical processes, but their response to N and/or P enrichment in wetlands needs to be assessed on a global scale. We conducted a meta-analysis with peer-reviewed papers from Web of Science and China National Knowledge Infrastructure on soil EEAs after N and/or P enrichment in wetlands. Seven soil EEAs and five soil chemical properties in the 0-20 cm depth from 31 studies analyzing N and/or P enrichment were collated, from studies that described vegetation composition in wetland. Soil EEAs were classified into C-, N-, and P- acquiring function categories. To examine influence of vegetation types on soil EEAs, we further defined two categories of wetlands with different vegetation types: moss/sedge-dominated non-woody and shrub/tree-dominated woody wetlands. We showed that soil EEAs in moss/sedge-dominated wetlands were more susceptible to nutrient enrichments than those in shrub/tree-dominated wetlands. Nitrogen enrichment increased C- and P-acquiring EEAs in both categories of wetlands. However, for P enrichment, significant responses of soil EEAs were observed in moss/sedge-dominated wetlands only: β-1,4-glucosidase activity increased 76% but phosphatase activity decreased 78%, on average. Soil EEAs in both wetland categories remained unchanged when N and P were supplied together. Woody plants may override microbial response to nutrient enrichment and mitigate the negative effect of nutrient enrichment on soil organic C stock. Further studies are needed to consider the effect of plant physiology and vegetation dynamics on soil EEAs, and integrate wetland soil EEAs modules into process-based biogeochemical model to better understand the feedback of wetland ecosystems with global change.