Abstract
We examined the effects of elevated atmospheric CO 2 on soil carbon decomposition in an experimental anaerobic wetland system. Pots containing either bare C 4 ‐derived soil or the C 3 sedge Scirpus olneyi planted in C 4 ‐derived soil were incubated in greenhouse chambers at either ambient or twice‐ambient atmospheric CO 2 . We measured CO 2 flux from each pot, quantified soil organic matter (SOM) mineralization using δ 13 C, and determined root and shoot biomass. SOM mineralization increased in response to elevated CO 2 by 83–218% ( P P = 0.003). Our results (1) show that there is a positive feedback between elevated atmospheric CO 2 concentrations and wetland SOM decomposition and (2) suggest that this process is mediated by the release of oxygen from the roots of wetland plants. Because this feedback may occur in any wetland system, including peatlands, these results suggest a limitation on the size of the carbon sink presented by anaerobic wetland soils in a future elevated‐CO 2 atmosphere.