Oxygen priming induced by elevated CO2 reduces carbon accumulation and methane emissions in coastal wetlands

Warming temperatures and elevated CO2 are inextricably linked global change phenomena, but they are rarely manipulated together in field experiments. As a result, ecosystem-level responses to these interacting facets of global change remain poorly understood. Here we report on a four-year field manipulation of warming and elevated CO2 in a coastal wetland. Contrary to our expectations, elevated CO2 combined with warming reduced the rate of carbon accumulation due to increases in plant-mediated oxygen flux that stimulated aerobic decomposition via oxygen priming. Evidence supporting this interpretation includes an increase in soil redox potential and a decrease in the nominal oxidation state of the dissolved organic carbon pool. While warming alone stimulated methane (CH4) emissions, we found that elevated CO2 combined with warming reduced net CH4 flux due to plant-microbe feedbacks. Together, these results demonstrate that ecosystem responses to interacting facets of global change are mediated by plant traits that regulate the redox state of the soil environment. Thus, plant responses are critical for predicting future ecosystem survival and climate feedbacks.