Stimulation of methane emission by carbon dioxide enrichment of marsh vegetation

Abstract

THERE is substantial evidence that many plants respond to increased concentrations of atmospheric carbon dioxide by increasing their productivity1–4. This observation has led to the suggestion that, by taking up CO2, the terrestrial biosphere might mitigate the potential greenhouse warming associated with anthro-pogenic CO2 emissions5. Whiting and Chanton6 have found, how-ever, that for wetlands of varying productivity around the world, higher net primary production is associated with higher emissions of methane—another important greenhouse gas. Here we present measurements of methane emissions from a marsh that has been exposed to twice the present ambient concentration of atmospheric CO2. We find that over a one-week period, the CO2-enriched sites had significantly higher emissions of methane than the control sites. Our results suggest that future increases in atmospheric CO2 concentration may lead to significant increases in methane emis-sions from wetlands.