# Drought and Shrub Encroachment Accelerate Peatland Carbon Loss Under Climate Warming

## TL;DR

Drought and shrub encroachment increase carbon loss from peatlands under warming, with deep and dry peat being most sensitive.

## Contribution

New insights into how peat decomposition and temperature sensitivity vary with depth and plant litter under climate stressors.

## Key findings

- Drought and Betula leaves increased CO2 emissions in both shallow and deep peat layers.
- Deep peat with Betula showed higher temperature sensitivity (Q10) than shallow peat.
- Sphagnum moss only affected shallow peat, and its effect disappeared under drought conditions.

## Abstract

Peatlands store substantial amounts of carbon (C) in the form of peat, but are increasingly threatened by drought and shrub encroachment under climate warming. However, how peat decomposition and its temperature sensitivity (Q10) vary with depth and plant litter input under these stressors remains poorly understood. We incubated peat from two depths with different degrees of decomposition, either alone or incubated with Sphagnum divinum shoots or Betula ovalifolia leaves, under five temperature levels and two moisture conditions in growth chambers. We found that drought and Betula addition increased CO2 emissions in both peat layers, while Sphagnum affected only shallow peat. Deep peat alone or with Betula exhibited higher Q10 than pure shallow peat. Drought increased the Q10 of both depths’ peat, but this effect disappeared with fresh litter addition. The CO2 production rate showed a positive but marginal correlation with microbial biomass carbon, and it displayed a rather similar responsive trend to warming as the microbial metabolism quotient. These results indicate that both deep and dry peat are more sensitive to warming, highlighting the importance of keeping deep peat buried and waterlogged to conserve existing carbon storage. Additionally, they further emphasize the necessity of Sphagnum moss recovery following vascular plant encroachment in restoring carbon sink function in peatlands.