Gas exchange characteristics of Gulf of Mexico coastal marsh macrophytes

Abstract

Gas exchange characteristics of three major Louisiana Mississippi River deltaic plain marsh species, Spartina patens (Ait.) Muhl., Spartina altemiflora Lois., and Panicum hemitomon Shult., was studied under controlled environment conditions. The optimum temperature for maximum photosynthesis was ≈ 36 °C for S. patens, 27 °C for S. alterniflora, and 28 °C for rP. hemitomon. Net photosynthesis rates at optimum temperature averaged 20.1 μmol · m t-2 · s t-1 in S. patens, 22.8 μmol · m −2 · s −1 in S. alterniflora, and 11.4 μmol · m −2 · s −1 in P. hemitomon. Photosynthetic light saturation occurred ≈720, 530, and 750 μmol · m −2 · s −1 in S. patens, S. alterniflora, and P. hemitomon, respectively. Only S. patens had a midday depression of stomatal conductance, but net photosynthesis was not reduced by the depression. Maximum stomatal conductances were 285 mmol · m −2 · s −1 in S. patens, 238 mmol · m −2 · s −1 in S. alterniflora, and 335 mmol · m −2 · s −1 in P. hemitomon. In contract, net photosynthesis values were lower in P. hemitomon compared with the Spartina species, indicating a greater degree of water use efficiency of photosynthesis for both Spartina species.