Effect of NaCl salinity on Atriplex nummularia (L.) with special emphasis on carbon and nitrogen metabolism

Abstract

The present study aimed to uncover the interconnected mechanisms underlying salt tolerance of Atriplex nummularia, a potential fodder plant for saline agriculture. The plants were grown in gravel/hydroponic quick check system in the greenhouse and irrigated with various seawater salinities (sws) (0, 25, 50, 100 and 150 %). Raising NaCl salinity stimulated the plant growth, which was highest at 50 % sws. Growth stimulation was mainly due to positive water balance, bestowed by plant ability to adjust osmotically and to minimize water loss via transpiration. Osmotic adjustment was mainly achieved by substantial accumulation of Na+ and Cl−. This was associated concurrently with sharp decrease in K+ and NO3− concentrations, resulting into ion imbalance. However, the plants were able to maintain adequate ion ratios in their roots and juvenile leaves, where the metabolic activities are expected to be highest. Salt-induced reduction in transpiration rates was coincided with progressive decrease in net photosynthesis (PN). This reduction was proportionally higher than those observed for photosynthesis, leading to improve photosynthetic water use efficiency (PWUE). Reduction in NO3− concentration may contribute to the overall reduction in total soluble protein (TSP), total N content and hence net photosynthetic rates. However, photosynthetic nitrogen use efficiency (PNUE) and nitrogen use efficiency (NUE) were transiently increased, peaked at moderate salinities, indicating that the plants could effectively regulate nitrogen utilization for C-assimilation machinery. Thus, plant’s ability to maintain carbon and nitrogen assimilation in equilibrium through well-coordinated regulatory mechanisms could be considered as a key determinant for salt tolerance in A. nummularia.