Recovery of microbial ecophysiology and carbon accrual functions in peatlands under restoration

Peatlands are water-logged ecosystems that limit microbial decomposition making them effective carbon sinks. However, drainage or erosion removes these constraints on decomposition, switching them to carbon sources. Restoration aims to reverse these trends. Microbial ecophysiology influences carbon fluxes but how it responds to peatland degradation and restoration is poorly understood. Here we used metagenomics to study microbial functions and quantified growth rates using isotope labelling across seven sites in Britain, each with restored, degraded, and near-natural peatlands. We found that growth rates in restored treatments were comparable to the near-natural, but were significantly higher in degraded. This growth rate reduction in restored peatlands was dependent on the scale of degradation and the length of restoration, and was underpinned by a shift towards energetically less favourable metabolic pathways such as anaerobic respiration, fermentation, and carbon fixation. A peatland ecosystem health index estimated based on measurements of peat moisture, oxygen, pH, organic matter chemistry, and moss cover, explained a significant amount of variation in microbial ecophysiology across the gradient. We demonstrate that microbial ecophysiology changes with peatland ecosystem health in a predictable manner. This knowledge can inform restoration targets and monitoring of recovery to maximise the return of carbon accrual functions of peatlands.