Carbon Isotope Composition of the Halophyte Disphyma clavellatum (Haw.) Chinnock (Aizoaceae), as Affected by Salinity

Abstract

The δ¹³C values of the leaves of Disphyma clavellatum (Aizoaceae) systematically became less negative as the salinity in the root environment increased from 0 to 500 mol m^-3 NaCl. The maximum shift of δ¹³C was from -26.1‰ to -20.0‰. Similar increases in salinity did not, however, result either in a change in the diurnal pattern of net CO₂ assimilation or in an appreciable increase in the fluctuations of titratable acidity. It is suggested that salinity induced the observed shift in δ¹³C values, not by effecting change in the mode of carboxylation towards that of crassulacean acid metabolism (CAM), but by affecting the degree of limitation of CO₂ assimilation by diffusion processes. It is concluded therefore that, in D. clavellatum, CAM is not induced by salinity, as it is in Mesembryanthemum crystallinum.