Separate and Combined Effects of Silicic and Salicylic Acids On Growth and N2-Fixation in Lentil Plants Under Water Stress

Both silicic and salicylic acids have been reported to be effective in mitigating the harmful effects of environmental stresses. The effects of silicic acid (Si), salicylic acid (SA), and their combination on dry matter yield (DM), nitrogen yield (NY) and N₂-fixation (Ndfa) in lentil grown under varying levels of water stress (high I1, mild I2 and well-watered I3) were assessed in a pot experiment in which Si (150 mg L⁻¹) and/or SA (10⁻⁵mol L⁻¹) were applied as foliar spraying. The ¹⁵N isotope dilution method was employed for estimating Ndfa using barley as a reference crop. A significant decline in the DM, NY and Ndfa of lentil plants was observed due to water stress. However, the exogenous application of Si and/or SA significantly enhanced the overall growth performance particularly under high water stress (I1). Among spraying treatments, the solely applied Si in I1 showed better DM and NY yields as compared to the other treatments, particularly in root growth enhancement. Positive and significant impacts on N₂ fixed in response to Si and/or SA were generally observed in plants grown under high water stress.. Decrease in soil N uptake by lentil plants in Si+SA treatment was associated with a higher amount of N₂-fixation. These findings may illustrate the importance of dual application of Si+SA in saving irrigation water and alleviating water stress influences to ensure higher N₂-fixation and lower consumption of soil nitrogen. Overall, response to Si and/or SA was expressed more clearly when lentil plants were exposed to water stress. The co-application of these two compounds may be considered as important environmentally friendly and sound agricultural practice inputs for improving the symbiotic performance of N₂-fixing plants by mitigating the adverse effects of water stress influences.