Comparative gas exchange and growth responses of C3 and C4 beach species grown at different salinities.

Comparative laboratory gas exchange and relative growth rate experiments were conducted on three native California coastal strand species at four salinity treatment levels. Relative mesophyll conductance sensitivities to salinity of Atriplex leucophylla (Moq.) D. Dietr. (C4) and Atriplex californica Moq. in D.C. (C3) were nearly identical. Mesophyll conductances of both species were stimulated by moderate levels of salinity. Mesophyll conductances of Abronia maritima Nutt. ex Wats. (C3) were highest in the absence of salinity and depressed by increasing levels of salinity. Increasing levels of salinity generally decreased net photosynthesis and leaf conductances but increased water use efficiencies. The C4 species, Atriplex leucophylla, had higher mesophyll conductances and water use efficiencies at all salinity levels than the C3 species. The effects of salinity on relative growth and net assimilation rates of greenhouse grown plants were not directly correlated with the effects on net photosynthesis measured in the laboratory. Growth of Abronia maritima was greatly stimulated by low levels of salinity whereas photosynthesis was substantially inhibited. The possible significance of C4 photosynthesis in relation to salinity is discussed.