Hydrological influences on soil enzyme activities in contrasting peatland treatments

Peatland restoration through rewetting is widely used to recover ecosystem functioning and promote carbon storage yet its effect on extracellular enzyme activities (EEAs) involved in peat decomposition remains insufficiently resolved. However, there is uncertainty whether rewetting uniformly suppresses microbial decomposition or selectively constrains oxidative pathways associated with phenolic degradation. This study investigated EEAs across contrasting peatland treatments representing rewetted, drained, afforested, and open moorland conditions. Monthly soil samples were collected over one year and analysed for hydrolytic enzymes involved in carbon, nitrogen, and phosphorus cycling (acid phosphatase, α-glucosidase, β-glucosidase, N-acetylglucosaminidase, and leucine aminopeptidase) together with oxidative enzymes (polyphenol oxidase and peroxidase). Soil moisture content (SMC) and pH were also assessed to evaluate their relationships with enzyme activity patterns. The key results showed that EEA responses varied among functional groups. Among the hydrolytic enzymes, only β-glucosidase (βG) and N-acetylglucosaminidase (NAG) exhibited significant treatment differences, with greater activities generally observed under rewetted conditions, whereas acid phosphatase (AP), α-glucosidase (αG), and leucine aminopeptidase (LAP) showed no significant treatment effects despite displaying similar directional trends. In contrast, polyphenol oxidase activity declined significantly with increasing SMC, whereas peroxidase showed no significant relationship with SMC. These findings provide partial support for the enzyme latch hypothesis. Principal component analysis (PCA) revealed distinct extracellular enzyme activity patterns across the various peatland treatments, with PC1 and PC2 mainly driven by hydrolase and oxidase, respectively. Redundancy analysis showed that environmental variables explained 28.28% of enzyme activity variation, with soil moisture content and pH structuring the primary and secondary constrained gradients, respectively. Overall, peatland rewetting restructured extracellular enzyme functioning by suppressing oxidative decomposition while maintaining aspects of hydrolytic activity. These enzyme patterns indicate functional recovery following restoration and highlight extracellular enzyme activities as sensitive indicators of peatland restoration trajectories and hydrological controls on carbon cycling.