Salinity is a major detrimental abiotic factor for plant growth. The main purpose of this study was to analyze the effects of different NaCl concentrations on growth and some physiological parameters related to gas exchanges and water relations in amaranth (Amaranthus cruentus) plants. Three weeks old amaranth plants from the cultivar ‘Locale’ were exposed in nutrient solution to 0, 30 or 90 mM NaCl (electrical conductivities of 1.915; 4.815 and 11.70 dS.m-1 respectively) in phytotron conditions. Shoot elongation as well as fresh and dry masses of shoot and root were determined after two weeks of stress exposure. Net photosynthesis (A), intercellular CO2 concentration (Ci), instantaneous transpiration (E), stomatal conductance (gs), osmotic potential (Ψs) as well as the efficiency of the instantaneous carboxylation (A/Ci), intrinsic (A/gs) and instantaneous (A/E) water use efficiency were estimated. Results reveal that salt stress induced a significant reduction in growth of aerial part as well as net photosynthesis, instantaneous transpiration, stomatal conductance and leaf and root osmotic potentials. In contrast, no significant reductions were recorded for root growth, shoot water content, intercellular CO2 concentration and instantaneous carboxylation efficiency. However, a significant increase was observed for intrinsic (A/gs) and instantaneous (A/E) water use efficiency. The plant growth reduction observed hinges upon a drop in photosynthetic activity due mainly to stomatal closure. These data suggest that photosynthetic activity may be used as a reliable criterion for physiological estimation of salt-tolerance in A. cruentus cultivars.
Key words: Saline stress, net photosynthesis, stomatal conductance, osmotic potential, water use efficiency.
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