Peatlands at Southernmost Permafrost Edge: Rapid Carbon Accumulation but High Vulnerability to Drying

ABSTRACT Permafrost‐affected peatlands are climate‐sensitive carbon pools, yet their response to recent warming remains unclear. Here, we analyzed carbon dynamics and their environmental controls over recent centuries using two well‐dated peat cores from a mountaintop permafrost peatland in Northeast China at 47.37° N, one of the southernmost regions of circum‐Arctic permafrost distribution. The peatland initiated during the cold Little Ice Age, with high organic matter (85%) and low bulk density (< 0.1 g cm −3 ) in basal layers immediately above the underlying bedrock, indicating that cold‐induced decomposition suppression was a dominant preservation mechanism during initial peat formation. Apparent carbon accumulation rates (CAR) averaged 101.7 g C m −2 year −1 , substantially exceeding most other northern peatlands. Moisture variability primarily controlled CAR on multidecadal scales, with moisture deficit inhibiting carbon accumulation. The recent high apparent CAR at Motianling reflects the combined effects of relatively high peat production inputs, associated with higher PAR at this low‐latitude permafrost margin, and low decay rates under permafrost‐affected conditions. Data synthesis from permafrost‐affected peatland records showed that modelled production input was positively related to both photosynthetically active radiation (PAR) and growing degree days above 0°C (GDD0), whereas CAR showed a clearer positive relationship with PAR than with GDD0. While carbon‐rich, these southern marginal permafrost‐affected peatlands are highly vulnerable to drying, implying accelerated carbon loss under the ongoing warming and drying trend.