title: Gas exchange responses of Chesapeake Bay tidal marsh species under field and laboratory conditions.
abstract: Laboratory and field gas exchange measurements were made on C3(Scirpus olneyi Gray) and C4(Spartina patens (Ait.) Mahl., Distichlis spicata (L.) Green) species from an irregularly flooded tidal marsh on the Chesapeake Bay. Laboratory measurements were made on plants grown from root stocks that were transplanted to a greenhouse and grown under high light and high nutrient conditions. The two C4species were similar in their laboratory gas exchange characteristics: both had higher net carbon exchange rates, higher mesophyll conductances, higher photosynthetic temperature optima and lower leaf conductances than the C3species. The laboratory photosynthetic water use efficiency of the C4species was approximately three times that of the C3species.Field gas exchange responses of the above species were measured in situ a Chesapeake Bay tidal marsh. Despite differences in biological potential measured in the laboratory, all three species had similar in situ carbon exchange rates on a leaf area basis. On a dry weight basis, leaves of the two C4species had about 1.4 times higher light saturated CO2assimilation rates than the C3species. Light saturation of CO2exchange occurred at photosynthetic photon flux densities of 80 n Einstein cm-2s-1, compared with 160 n Einstein cm-2s-1in the laboratory grown plants. Spartina patens and Scirpus olneyi had similar daily CO2assimilation rates, but the daily transpiration rate of the C3species was almost twice that of the C4species. Spartina patens showed greater seasonal decrease in photosynthesis than Distichlis spicata and Scirpus olneyi. The two C4grass species maintained higher mesophyll conductances and photosynthetic water use efficiencies than the C4sedge.
authors.affiliation: Smithsonian Radiation Biology Laboratory, 12441 Parklawn Drive, 29852, Rockville, MD, USA.|Department of Botany, University of California, 95616, Davis, CA, USA.
authors.forename: T M
authors.initials: TM
authors.lastname: DeJong
authors.affiliation: Smithsonian Radiation Biology Laboratory, 12441 Parklawn Drive, 29852, Rockville, MD, USA.
authors.forename: B G
authors.initials: BG
authors.lastname: Drake
authors.affiliation: Department of Botany, University of California, 95616, Davis, CA, USA.
authors.forename: R W
authors.initials: RW
authors.lastname: Pearcy