A comparative study of above‐ground productivity of dominant U.S. Gulf Coast marsh species

Above‐ground productivity of dominant freshwater, brackish, and salt‐marsh species from the U.S. Gulf Coast was evaluated using both gas exchange techniques and harvest methods. Both techniques showed significant differences in productivity among the study species which represent major components of their respective communities. Estimates of net aerial primary productivity using the harvest method yielded 3683 g dw (dry weight) m −2 yr −1 for Spartina alterniflora (tall), 2008 g dw m −2 yr −1 for S. alterniflora (short), 3677 g dw m − yr −1 for S. patens and 1641 g dwm − yr −1 for Panicum hemitomon. Carbon balance estimated from gas exchange calculation yielded values approximately equivalent to a biomass accumulation of 6024 g dw m −2 yr −1 for S. alterniflora (tall), 3047 g dw m − yr −1 for S. alterniflora (short), 5702 g dw m − yr −1 for S. patens , and 2912 g dm − yr −1 for P. hemitomon. The net aerial primary production was estimated to be approximately 61% of total productivity in S. alterniflora (tall‐form) and 66%o of total productivity in short‐form, 64% in S. patens and 56%) in P. hemitomon. The assimilation data also indicated that Spartina alterniflora and S. patens continue carbon fixation throughout the year while assimilation in Panicum hemitomon is absent due to lack of live leaves during the winter. Various aspects of harvest and gas exchange techniques are discussed.