Drainage alters bacterial co-occurrence networks and net nitrogen mineralization rate in peatlands under different forest management regimes

Peatlands are crucial for maintaining ecological balance, supporting biodiversity, and regulating hydrological and biogeochemical cycles. However, extensive drainage for forestry and forest management practices has severely altered their carbon and nitrogen dynamics and microbial communities. This study evaluated the effects of peatland drainage and three forest management practices—clear-cutting, even-aged forest, and continuous cover forestry—on microbial biomass, soil nutrients and bacterial community structure. The results showed that soil microbial biomass carbon was unaffected by forest management or water table depth. However, in pristine peatland, soil microbial biomass nitrogen was influenced by water table depth. Compared with a low water table (-30 cm below the soil surface), the net nitrogen mineralization rate was significantly higher under a high water table (-10 cm below the soil surface). Bacterial diversity was influenced by forest management practices but unaffected by water table depth, with the highest diversity observed in pristine peatland. High water table enhanced the connectivity and complexity of bacterial co-occurrence networks. Soil characteristics (NH₄⁺–N, DOC, MBN, net N mineralization rate, and MBC) collectively explained 56.9% of the observed variation in bacterial community structure. Furthermore, bacterial community assembly processes shifted from stochastic processes in high-water-table peatland to deterministic processes in drained sites. This indicates that environmental filtering is intensified, potentially reducing ecosystem stability. These findings highlight the effects of forest management and hydrology on microbial biodiversity and function, providing a key scientific basis for the ecological restoration of degraded peatlands and sustainable forest management.