Effects of salinity on chlorophyll fluorescence and photosynthesis of barley (Hordeum vulgare L.) grown under a triple-line-source sprinkler system in the field

In flag leaves of four cultivars of barley (Hordeum vulgare L.) grown in th e field under a triple-line-source sprinkler system, that produces a linear soil salinity gradient, a decrease in net carbon dioxide assimilation rate (P-N) and stomatal conductance for water vapour (g(s)) was found. These ch anges were related to salinity tolerance at moderate salinity. With increas ing salinity, P-N was saturated at low irradiances and stomatal frequencies increased. A decrease in photosystem 2 (PS2) efficiency was not found in t he field after dark adaptation even at high salinity. Salinity induced only small decreases in the actual PS2 efficiency at midday steady-state photos ynthesis, indicating that the photosynthetic electron transport was little affected by salinity. Therefore, using PS2 efficiency estimates in attached leaves is probably not a useful tool to screen barley genotypes grown unde r saline conditions in the field for salinity tolerance. In contrast, excis ed flag leaves from high salinity plots, once in the laboratory, exhibited a decrease in the variable to maximum chlorophyll fluorescence ratio as com pared to excised leaves from control plants. On the other hand, the P-N rat e might allow for a good discrimination between tolerant and non-tolerant c ultivars.