Synergistic effects of zinc and silicon dioxide nanoparticles improve cucumber (Cucumis sativus L) drought tolerance

Water scarcity significantly threatens agricultural productivity because of changing precipitation patterns and increasing competition for water use. Nanotechnology presents a sustainable and cost-effective strategy to improve water use efficiency, particularly through the application of silicon dioxide nanoparticles (nSiO₂) and zinc (Zn), as they alleviate water stress by enhancing plant water relationships. This study assessed the effects of nSiO₂ alone or in combination with zinc oxide (ZnO) at concentrations of 1.5 % and 3.0 %, applied at 150 mg L⁻¹ , on cucumber plants under water stress. The results indicated that nSiO₂ and nSiO₂ + ZnO_1.5 % significantly increased fruit yield by 52.7 % (5134.3 g), whereas water stress reduced yield by 31.1 % (2449.7 g). These treatments, nSiO₂ and nSiO₂ + ZnO_1.5 %, helped recover fruit production under drought conditions, with yields reaching levels comparable to those of well-irrigated control plants. Moreover, they reduced fruit abortion by 27.1 % and 25.2 %, respectively. The application of nSiO₂ + ZnO_1.5 % and nSiO₂ + ZnO_3.0 % increased the root biomass under both normal and deficit irrigation and increased the root-to-shoot ratio, indicating adaptive biomass allocation to optimize water uptake. The net photosynthesis rate improved in drought-stressed plants treated with nSiO₂ alone, whereas under regular irrigation, the combination with ZnO_1.5 % was more effective. The mesophyll conductance decreased in drought-stressed plants treated with nSiO₂ + ZnO_1.5 %, which was associated with increased intrinsic water use efficiency (iWUE). The combination also increased leaf Zn levels and improved stomatal conductance, although nSiO₂ alone reduced the leaf silicon content, suggesting that the cultivar is not a silicon accumulator. The combination of nSiO₂ and ZnO_1.5 % is a promising approach to increase drought tolerance in cucumbers by improving yield, water use efficiency, and physiological responses under water-limited conditions