Legacy of peatland erosion shapes microbial communities during recovery.

Human degradation has caused many peatlands worldwide to shift from long-term carbon sinks to net sources. In upland blanket peatlands, erosion disrupts plant-derived carbon input and exposes deep peat, accelerating oxidation of old carbon. The efficacy of restoration in preventing carbon loss and recovering ecosystem function depends on microbial responses to both water table manipulation and renewed litter input. Yet it is unclear how these factors alter the microbial communities that ultimately control carbon storage and emissions. Here we show that microbial community composition in the eroded Waun Fignen Felen peatland, South Wales, was governed primarily by organic matter bioavailability rather than water-table position. Long-term erosion leaves a legacy of highly decomposed organic matter, unaltered by re-wetting. Where plant litter accumulation is renewed on formerly eroded peat surfaces, the influx of bioavailable organic input supports a distinct prokaryote community with a greater bacterial population size, and evidence of elevated respiration.