Comparison of plant litter and peat decomposition changes with permafrost thaw in a subarctic peatland

Abstract

Organic matter decomposition in response to thawing permafrost has critical implications for carbon release. This study examined how thaw induced plant community and environmental changes influenced litter and peat decomposition in a subarctic peatland. We conducted laboratory incubations under current site pre-thaw (dry and large oxic peat layer) and thawed (wet and small oxic peat layer) conditions, and mimiced pond thaw conditions (water saturated and anoxic) at 4 and 22 °C. Carbon dioxide (CO2) and methane (CH4) releases from ground surface plant litter and top 1 m peat samples at permafrost area (Palsa) and wet thawed lawn (WL) were quantified under current site conditions. Dissolved organic carbon (DOC) released from litter was additionally quantified under pond thaw conditions. Plant litter mass significantly increased from Palsa to WL. Under current site conditions, litter in WL had significantly higher CO2 and CH4 production rates than litter in Palsa. Pond thaw conditions changed litter carbon loss partitioning into lower CO2 but higher DOC and CH4 production, and increased total carbon release. Whole peat decomposition was restricted from Palsa to WL with thaw. Estimated growing season gas carbon loss (CO2 and CH4) in WL was greater than that in Palsa due to significantly increased litter carbon loss after thaw. Changes in organic matter decomposition, especially litter decomposition, enlarged carbon losses from this subarctic peatland with permafrost thaw.