Silicon reduces oxidative stress under zinc deficiency in a species-dependent manner in rice and soybean

BACKGROUND: Zinc (Zn) deficiency is a common nutritional limitation in agricultural systems and is directly associated with redox imbalance, impacting crop growth. Silicon (Si) has been highlighted for its potential to improve plant tolerance to abiotic stresses; however, there is limited evidence regarding its effectiveness in mitigating Zn deficiency, particularly in species with contrasting Si accumulation capacities under different application methods. This study investigated the effects of foliar and root Si application on Si and Zn accumulation, oxidative metabolism, antioxidant responses, and dry matter production in rice (Oryza sativa L.), a known Si accumulator, and soybean (Glycine max L.), a non-accumulating species, grown under Zn-sufficient and Zn-deficient conditions. RESULTS: Silicon supplementation significantly increased Si concentration and accumulation in both crops, irrespective of species or application method, and improved Zn accumulation and Zn use efficiency under Zn deficiency. Zinc deprivation induced oxidative stress, characterized by elevated H₂O₂ and MDA levels and alterations in antioxidant enzyme activities. Both foliar and root Si supply reduced oxidative damage markers in rice and soybean, although regulatory responses differed between species. In Zn-deficient rice plants, both root and foliar Si application enhanced ascorbate peroxidase (APX) and catalase (CAT) activity. In soybean Zn-deficient plants, foliar Si selectively increased APX activity, while CAT activity was less responsive. These physiological adjustments translated into increased biomass accumulation in both crops compared with untreated Zn-deficient plants, demonstrating the functional relevance of Si-induced biochemical modulation. Notably, responses were not restricted to stress scenarios, as Si also improved antioxidant coordination and nutrient efficiency under adequate Zn supply, suggesting a priming effect. CONCLUSION: Si supplementation supported oxidative homeostasis, improved nutrient dynamics, and enhanced plant performance under Zn deficiency, with effectiveness modulated by species physiology and Si delivery route. These results demonstrate for the first time that foliar or root Si represents a promising agronomic strategy to mitigate Zn deficiency in Si-accumulating and non-Si-accumulating crops.