Effect of Salinity on Leaf Gas Exchange in Two Populations of a C₄ Nonhalophyte

Abstract

Gas exchange measurements were made on plants from two natural populations differing in salt tolerance of Axdropogon glomeratus, a C4 nonhalophyte, to examine the effect of salinity on components responsible for differences in photosynthetic capacity. Net CO2 uptake and stomatal conductance decreased with increasing salinity in both populations, but to a greater extent in the inland (nontolerant) population. The intercellular CO2 concentrations increased with increasing salinity in the inland population, but decreased in the marsh (tolerant) population. Water use efficiency decreased as salinity increased in the inland population, and remained unchanged in the marsh population. Carboxylation efficiency decreased and CO2 compensation points increased with increasing salinity in both populations, but to a lesser extent in the marsh population. Carboxylation efficiencies were higher with 2% relative to 21% atmospheric 02 in salt stressed plants, suggesting that a decrease in the carboxylation:oxygenation ratio of ribulose 1,5-bisphosphate carboxylase/oxygenase was partly responsible for the decrease in photosynthetic capacity. Populational differences in photosynthetic capacity were the result of greater salinity-induced changes in carboxylation efficiency in the inland population, and not due to differences in the stomatal limitation to C02 diffusion.Photosynthetic inhibition due to salinity stress has been described in both salt-tolerant and salt-sensitive species (2,3,5,15,19,22,23,28,29). Decreases in photosynthetic CO2 uptake with increasing salinity have been ascribed to lower stomatal conductance (15, 22, 28), a depression of biochemical capacity for carbon uptake and reduction (2,3,5,19,23), a decrease in photochemical capacity (1), or some combination of these. Enzymatic sensitivity to salinity under uniform conditions is thought to be the same for halophytes, species native to saline habitats, and nonhalophytes, species potentially inhabiting marginally saline areas, but which are more widespread geographically in nonsaline habitats (9,10,12,17,26). Genetic differentiation in the response to salinity between natural populations has been described for a number of species, yet the sensitivity of CO2 uptake to salinity in populations differing in salt tolerance has not been addressed.Examination of the effect of salinity on gas exchange parameters in populations which have evolved under different salinity regimes would yield important information toward understanding photosynthetic inhibition in nonhalophytes. Andropogon glomeratus Walter B.S.P. is a widespread nonhalophyte found in ' Supported by PhytoResources Research Inc., the Duke University Botany Department, a Sigma-Xi grant-in-aid of research, and NSF dissertation improvement award BSR 861-2381. the higher elevations of salt marshes and in nonsaline habitats in the coastal plain of the southeastern United States. The purpose of this study was to examine the influence of salinity on characteristics of gas exchange in plants of two natural pop...

Water relations and leaf gas exchange properties in some elite canola (Brassica napus) lines under salt stress

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