Salicylic Acid Modulates Morphophysiological Responses of Paubrasilia echinata Seedlings Irrigated with Saline Water

Rising salt concentration in water induces osmotic stress and ionic toxicity, compromising photosynthesis, growth, and survival of threatened species such as Paubrasilia echinata and highlighting the need for stress-mitigating compounds such as salicylic acid. This study evaluated the effect of salicylic acid on the morphophysiological responses of P. echinata seedlings irrigated with saline water. Treatments were arranged in a 2 × 3 factorial scheme, with two electrical conductivity levels of irrigation water (0.5 and 6.0 dS m−1) and three salicylic acid concentrations (0, 2, and 3 mM), randomized across 24 experimental plots containing five plants each in a randomized complete block design. Analyses included growth, relative water content, chlorophyll indices and fluorescence of seedlings. Irrigation water with an electrical conductivity of 6.0 dS m−1 reduced leaf number by 9.09% and PSII efficiency by 26.94%. Under saline conditions, salicylic acid at 2 and 3 mM increased root dry matter by 49.28% and 60.29%, respectively. The highest total chlorophyll index (79.03) was obtained at 2 mM, whereas leaf area peaked at 734.74 cm2 per plant at 3 mM. Salicylic acid enhances salt tolerance in P. echinata. At 2 mM, it improves seedling morphophysiological traits and may support restoration in salinized sites.