A comparative analysis of the CO 2 and water vapor responses of two Spartina species from Georgia coastal marshes

Abstract

CO 2 and water vapor exchange of intact plants of Spartina cynosuroides and Spartina alterniflora were monitored in marshes on the Georgia coast during early spring. The CO 2 response under 21% and low oxygen conditions suggest that S. cynosuroides has the C 4 metabolic pathway. S. alterniflora which dominates the Georgia salt marshes, is also a C 4 plant. Characteristics of the CO 2 response of photosynthesis and the temperature response of leaf conductance to water vapor indicate that photosynthesis of S. cynosuroides is controlled more by stomatal activity than by internal components of the CO 2 movement pathway. In contrast, photosynthetic response of S. alterniflora is controlled by internal factors. Maximum rates of photosynthesis, temperature optima and photosynthetic light response suggest that both species efficiently utilize the high light and high temperature regimes of south-eastern U.S. marshes. These physiological characteristics provide a basis for the high annual biomass production of these species.