A FIELD-STUDY OF THE EFFECTS OF ELEVATED CO2 ON ECOSYSTEM PROCESSES IN A CHESAPEAKE BAY WETLAND

Open top chambers are being used in a long-term project to determine the effects of elevated CO2 on ecosystem processes on a Chesapeake Bay wetland. Three communities are studied: mono-specific stands of the C3 sedge, Scirpus olneyi, and the C4 grass, Spartina patens, and a mixed community of these two species and the C4 grass, Distichlis spicata. Treatment began in the spring of 1987 and will continue through the 1994 growing season. During the first 4 years of exposure, elevated CO2 had the following effects on mono-specific stands of the C3 sedge, Scirpus olneyi: increased quantum yield and photosynthetic capacity, reduced dark respiration, increased numbers of shoots, roots and rhizomes, reduced nitrogen concentration of all tissues, increased nitrogen fixation and increased ecosystem carbon accumulation. In a mixed community of the sedge and C4 grass species, Spartina patens and Distichlis spicata, biomass of the C3 component increased over 100% and this was accompanied by decreased biomass in the C4 component of the community. Elevated CO2 reduced water loss, increased water potential and delayed senescence in all three species. Many factors contributed to CO2 stimulated carbon accumulation in the plant community dominated by the C3 sedge, Scirpus olneyi, including: sustained high photosynthetic capacity, decreased respiration, delayed senescence, and allocation of the additional carbon to roots and rhizomes. The complex interaction of these diverse responses suggests that the rising atmospheric CO2 may have a significant impact on ecosystem processes.