Growth and N2fixation in Saline and/or Water Stressed Sesbania aculeata Plants in Response to Silicon Application

This study aimed at investigating the effects of silicon (Si) on dry matter yield (DM), N uptake and N2-fixation in Sesbania aculeata grown under water stress and/or salt stress using 15N. Irrigation regime had two levels, well watered (I1) and water stress (I2), and was made either with saline (Salt+) or with non saline water (Salt-). Silicon had positive impacts on DM of sesbania grown under water stress. Only root DM increased as a result of Si addition in well watered plants grown under salt stress or under both stress conditions. Moreover, root/shoot ratio was higher in Si-fed plants, under stresses, than those of non-fertilized plants. N yield significantly increased in salt stressed sesbania plant grown under well watering regime. However, the positive effect of Si in plants subjected to both stresses was only occurred in roots. In addition, Si application enhanced soil (Ndfs), fertilizer (Ndff) and N2-fixation (Ndfa) under salt and/or water stress conditions. The beneficial effect of Si on the amount of Ndfa was more pronounced under stress conditions. In the whole plant, significant effects of Si were obtained in water-stressed, salt-stressed and both water and salt-stressed treatments, where amounts of Ndfa increased by 8, 39 and 39%, respectively, as compared to their controls. Overall, response to Si was expressed more clearly when sesbania plants were subjected to stresses. Silicon may be considered as an important element for the symbiotic performance in legumes by mitigating the adverse effects of abiotic stresses.