Photosynthesis of six barley genotypes as affected by water stress

The effect of water stress on plant water status and net photosynthetic gas exchange (P-N) in Six barley genotypes (Hordeum vulgare L.) differing in productivity and drought tolerance was studied in a controlled growth chamber. Osmotic adjustment (OA), P-N, Stomatal conductance (g(s)), and the ratio intercellular/ambient CO2 concentration (C-i/C-a) were evaluated at four different levels of soil water availability, corresponding to 75, 35, 25 and 15 % of total available water, Variability in OA capacity was observed between genotypes: the drought tolerant genotypes Albacete and Alpha showed higher OA than drought susceptible genotypes Express and Mogador. The genotype Albacete exhibited also higher P-N than the others at low water potential (Psi). The ratios of P-N/g(s) and C-i/C-a showed that differences in photosynthetic inhibition betweeen genotypes at low Psi were probably due to nonstomatal effects. In Tichedrett, a landrace genotype with a very extensive root development, OA was not observed, however, it exhibited a capacity to maintain its photosynthetic activity under water stress.