Climatic and Vegetation Controls on Peatland CO2 Fluxes in Alaska: Early Response to Ecosystem-Scale Drought and Soil Warming Manipulations

Peatlands store 30% of the world's terrestrial soil carbon (C) and are located primarily at northern latitudes, where they are expected to experience severe climate warming. We monitored growing season carbon dioxide (CO2) fluxes across a factorial design of in situ water table drawdown (i.e., drought) and soil warming treatments for 2 years in a rich fen located just outside the Bonanza Creek Experimental Forest in interior Alaska. We hypothesized that the sensitivity of microbial activity and decomposition rates to soil environmental change would lead to large changes in ecosystem respiration (ER) and net ecosystem exchange (NEE) across our experimental treatments. Our results showed that the lowered water table treatment did not alter ER of CO2, but did lower gross primary production (GPP) and increase NEE relative to the control treatment, making this plot more of an atmospheric source relative to the control. Surface soil warming increased ER and GPP by 16% compared to un-warmed plots, with no evidence of water table x soil warming interactions. Nonlinear modeling showed that both hydroclimate (water table position, soil temperature) and vegetation (seasonality of LAI) were important controls on of CO2 fluxes. Overall, our initial results suggest that drought will impact CO2 fluxes in northern rich fens by reducing ecosystem C storage due to plant stress.