Growth and senescence in plant communities exposed to elevated CO concentrations on an estuarine marsh.

Three high marsh communities on the Chesapeake Bay were exposed to a doubling in ambient CO concentration for one growing season. Open-top chambers were used to raise CO concentrations ca. 340 ppm above ambient over monospecific communities of Scirpus olneyi (C) and Spartina patens (C), and a mixed community of S. olneyi, S. patens, and Distichlis spicata (C). Plant growth and senescence were monitored by serial, nondestructive censuses. Elevated CO resulted in increased shoot densities and delayed sensecence in the C species. This resulted in an increase in primary productivity in S. olneyi growing in both the pure and mixed communities. There was no effect of CO on growth in the C species. These results demonstrate that elevated atmospheric CO can cause increased aboveground production in a mature, unmanaged ecosystem.