Abstract
Experiments were conducted to investigate the role of silicon (Si, 2 mM potassium silicate - K2SiO3) in ameliorating the salinity (200 mM NaCl) triggered growth retardation, photosynthetic inhibition and the oxidative damage in Talh trees (Acacia gerrardii Benth). Salinity stress reduced length and dry biomass accumulation of root and shoot which were significantly improved by Si supplementation. Application of Si enhanced the synthesis of photosynthetic pigments including chlorophyll a, chlorophyll b, total chlorophylls and carotenoids resulting in greater photosynthetic activity measured in terms of net CO2 assimilation. Stomatal conductance and transpiration rate were declined due to NaCl treatment and supplementation of Si ameliorated the negative impact of NaCl on these attributes and was significantly improved when applied to normal grown plants. Further, lipid peroxidation was more in NaCl stressed plants without Si as compared to those supplemented with Si. Si protected Talh trees from NaCl induced oxidative damage by improving the activity of antioxidant enzymes (SOD, POD, CAT, APX and GR) and the content of ascorbic acid. Accumulation of compatible osmolytes including proline and glycine betaine was increased due to Si supplementation leading to improved growth under saline conditions in addition Si supplementation mitigated the deleterious effects of NaCl on flavonoid content. More importantly Si supplementation prevented excess uptake of Na and also protected the ill effects of excess Na on the uptake and accumulation of K and Ca resulting in significant decline in Na/K ratio. In conclusion, Si mitigates the negative effects of NaCl in A. gerrardii by modifying nutrient uptake, osmolytes accumulation and up-regulating antioxidant system.