Organic phosphorus mediates the preservation of peat carbon by woody plants during water-table decline
摘要
Peatlands store large amounts of carbon but are vulnerable to vegetation and hydrological changes. The mechanisms by which lower groundwater drives woody plant expansion and affects carbon stock remain unclear. Here we combine long-term drainage, fertilization, and pot experiments in a northern peatland to identify processes linking hydrology, nutrients, and vegetation. We show that lower groundwater stimulates phytase that mineralizes organic phosphorus in the acrotelm (surface peat) and mesotelm (seasonally waterlogged peat), increasing plant-available phosphorus and promoting woody plant growth. Woody plants alter carbon dynamics with depth: in the acrotelm, woody litter releases phenolics that slow decomposition; in the mesotelm, increased fresh carbon inputs offset decomposition losses so carbon stocks remain stable; in the catotelm (permanently waterlogged peat), woody plants have little effect and waterlogging continues to preserve carbon stocks. These findings clarify mechanisms of woody expansion under declining groundwater on carbon stocks and inform resilience strategies for future climates.