Carbon isotope discrimination and salt tolerance of rice genotypes

Abstract

Rice genotypes were evaluated for salt tolerance in a greenhouse based upon stable carbon isotope analysis under salt stress (EC = 8 dSm−1) and non-stressed (1 dSm−1) conditions. Ten seedlings from each replicate and genotype were randomly sampled at 25 or 33 days after sowing (DAS). Values for carbon isotope discrimination (A) were obtained from dried and homogenized seedling tissue of twelve genotypes. Rice genotypes were ranked from high to low salt tolerance based on whole plant average maximum A of these two salt levels at these two early growth stages. Differences in fractionation among genotypes were observed at 25 and 33 DAS. Fractionation effects of salinity stress on A were significantly different among genotypes at 33 DAS, but not at 25 DAS. The salt tolerant cultivar maintained significantly higher average flag leaf tissue A than did the sensitive cultivar. Flag leaves of salt stressed rice maintained higher A than predicted for these two genotypes based a theoretical A value. The lack of greater reductions in leaf tissue A of salt stressed rice genotypes may the result of an increased contribution of respired carbon to the total carbon budget of rice leaves.