Growth, gas exchange, chlorophyll fluorescence, and ion content of naked oat in response to salinity

Understanding of the physiological responses of crop plants to salinity stress is of paramount importance for selection of genotypes with improved tolerance to salt stress. Two naked oat (Avena sativa L.) genotypes, 'VAO-7' and 'VAO-24', were subjected to different salt concentrations (0, 50, 100, 150, 200, and 250 mM NaCl) to determine the effects of salt levels and stress duration on seedling growth, ion content and photosynthetic productivity. Relative growth rate (RGR) and leaf chlorophyll were determined at weekly intervals after salinity was imposed. Total leaf area, plant dry weight, photosynthetic parameters, and plant tissue ion concentrations were determined at 25 d after salinity application. Under salt stress conditions, germination rates varied greatly among the genotypes. The differences between VAO-7 and VAO-24 for most parameters measured were significant after 2 wk of stress introduction at 200 and 250 mM NaCl. Salt stress at the lowest level (50 mA) reduced total leaf area by 35% and plant dry matter by 52%. At 25 d after salt stress, plants treated with the 250 mM NaCl accumulated 36-fold more Na+, 79% more Ca2+, and 2.4-fold less K+ than the control. Salt treatment resulted in the reduction of almost all the growth parameters and coincident increases in plant Na+ and Ca2+ concentrations. Our results indicate that there is great variability for salt tolerance among naked oat germplasms, and greater photosynthesis capacity, higher RGR, and relatively lower tissue Na+ accumulation at high salt concentrations appeared to he associated with salt tolerance in naked oats.