Growth, nitrogen uptake and carbon isotope discrimination in barley genotypes grown under saline conditions

The effect of different salinity levels of irrigation water (ECw range 1-12 dS/m) on dry matter yield, nitrogen uptake, fertilizer nitrogen use efficiency (%NUE), stomatal conductance and carbon isotope discrimination (Δ13C‰) in three barley genotypes originating from different geographic areas (Arabi.Abiad, Syria; Pk-30-136, Pakistan and WI-2291, Australia) was investigated in a pot experiment. An increase in salinity resulted in a decrease in Δ13C in all the genotypes. Increasing salinity reduced leaf stomatal conductance which was less pronounced in WI-2291 comparing to other genotypes. At high salinity level, the reduction in Δ13C corresponded to a considerable decrease in the ratio (Ci/Ca) of intercellular (Ci) and atmospheric (Ca) partial pressures of CO2 in all the genotypes indicating that such a decrease was mainly due to the stomatal closure. Moreover, since the reduction in dry matter yield in all the genotypes grown at 12 dS/m did not exceed 50% in comparison with their controls, the photosynthetic apparatus of all studied genotypes seemed to be quit tolerant to salinity. At the moderate salinity level (8dS/m), the enhancement of leaf dry matter yield in the WI2291 genotype might have been due to positive nutritional effects of the salt as indicated by a significant increase in nitrogen uptake and NUE. Thus, the lower Ci/Ca ratio could result mainly from higher rates of photosynthetic capacity rather than stomatal closure. On the other hand, relationships between dry matter yield or NUE and Δ13C seemed to be depending on plant genotype, plant organ and salinity level. Based on growth, nutritional and Δ13C data, selection of barley genotypes for saline environments was affected by salinity level. Therefore, such a selection must be achieved for each salinity level under which the plants have been grown.