Root exudate-induced priming of CO2 and CH4 in a thawing permafrost peatland

Abstract Arctic permafrost faces multiple interactive changes in thaw, drainage, and vegetation shift due to climate warming. Thaw-induced waterlogging can shift vegetation from shrubs to graminoids, altering greenhouse gas emissions. This study aims to quantify and mechanistically explain how vegetation-specific root exudates amplify or dampen greenhouse gas emissions from Arctic permafrost during thaw and drainage transitions. Using field observations and soil incubations, we show that environmentally relevant concentrations of root organic exudates (15% of dissolved organic carbon), obtained from thaw stage-specific plants, altered greenhouse gas fluxes under site-realistic redox conditions. Graminoid exudates were richer in sugars and carboxylates, whereas shrub exudates were richer in amino acids. In thawed, anoxic permafrost soil incubations, graminoid exudates stimulated the emission of 51% more CO 2 and 83% more CH 4 compared to the absence of exudates. In intact, drained permafrost soil, shrub exudates stimulated 14% more CO 2 and negligible CH 4 compared to untreated soils. Geochemical and microbial analyses revealed that soil, including their hydrology, and exudate differences drove exudate and soil organic matter decomposition. These soil incubation findings were supported by field measurements: Bare locations per soil-habitat provided baseline greenhouse gas fluxes in relation to each soil’s properties of moisture and geochemistry. Vegetation by graminoids increased greenhouse gas emissions from thawed permafrost soils significantly while shrubs barely affected greenhouse gas emissions from drained permafrost soils. Collectively, this study shows that thaw-specific vegetation shapes greenhouse gas fluxes, indicating that vegetation shifts can intensify radiative forcing beyond the known direct effect of permafrost thaw and associated hydrological transitions. Clarifying the context-dependence and mechanisms underlying these distinct exudate effects may improve projections of Arctic terrestrial climate feedback. • Root exudates from thaw-stage plants altered permafrost CO 2 and CH 4 emissions • Graminoid exudates increased thawed permafrost soil CO 2 by 51% and CH 4 by 83% • Shrub exudates increased drained permafrost soil CO 2 by 14% with negligible shifts in CH 4 • Field data confirmed soil incubation data: plant shifts amplify GHG emissions beyond thaw alone