Carbon dioxide assimilation by a wetland sedge canopy exposed to ambient and elevated CO

1. The wetland sedge Scirpus olneyi Gray displays fast rates of CO 2 assimilation and responds positively to increased atmospheric CO 2 concentration. The present study was aimed at identifying the ecophysiological traits specific to S. olneyi that drive these CO 2 -assimilation patterns under ambient and elevated CO 2 conditions. 2. The net ecosystem exchange (NEE) of CO 2 between S. olneyi communities and the atmosphere was measured in open-top chambers. 3. We developed a new mechanistic model for S. olneyi communities based on published ecophysiological data and additional measurements of photosynthetic parameters. 4. Our NEE measurements confirmed that S. olneyi communities have a high rate of summertime CO 2 assimilation, with noontime peaks reaching 40 μ mol CO 2 m − 2