Under elevated carbon dioxide levels, wetland plants can absorb up to 32 percent more carbon than they do at current levels, according to a 19-year study published in Global Change Biology from the Smithsonian Environmental Research Center in Edgewater, Md. With atmospheric CO2 passing the 400 parts-per-million milestone this year, the findings offer hope that wetlands could help soften the blow of climate change.
Back then, most scientists thought plants would gradually stop responding to rising CO2. Whether or not terrestrial ecosystems could assimilate additional carbon—and act as powerful carbon sinks—was not known. This study tracked not only how much CO2 wetlands absorb, but also the impact of rising temperature and sea level, changing rainfall and plant type.
To simulate a high-CO2 world, Drake’s team surrounded marsh plots with open-top Mylar chambers. For this study they left half of the chambers exposed to today’s atmosphere. In the other half they added CO2 and raised the level to 700 ppm, roughly doubling the CO2 concentration as it was in 1987. Other plots of land were left without chambers. They compared the levels of CO2 going in and CO2 going out to determine the carbon exchange between the wetland and the atmosphere.
Two types of plants populate most of the world, and the experiment tested both. C3 plants—which include more than 95 percent of the plant species on earth, including trees—form molecules of three carbon atoms during photosynthesis, and they tend to photosynthesize more as atmospheric CO2 rises. C4 plants form molecules of four carbon atoms.