Growth and production of water-stress indicators modified by zinc oxide nanoparticles as nanofertilizers under water-regulated conditions on tomatoes (Solanum lycopersicum L.)

Abstract

Vegetables play a vital role in ensuring food security, but their production has declined significantly due to unfavorable climatic conditions, soil nutrient depletion, and the plants' limited ability to adapt. This study investigates the impact of varying concentrations of zinc oxide nanoparticles (ZnONPs) on the growth and production of selected water-stress indicators in Solanum lycopersicum. Varying concentrations (1, 2, 3, and 4 g ZnONPs per Litre distilled water) were sprayed once daily on the plants at 100 mL per potted plant, while different controls were sprayed with either 100 mL distilled water daily (0¹) or weekly (0²). The functional groups of ZnONPs were determined, while morphological, optical and biochemical parameters were characterized. Their effects on morphological traits (plant height, number of leaves), leaf-related growth components, reactive oxygen species, and antioxidants, were further evaluated. Elemental analysis revealed that zinc (60.24 %, 53.30 %) was the predominant element in ZnONPs, while silica (50.0 %) was the primary component in cassava peel extract (CPE). Structural analysis revealed crystalline structures in cassava peel extract (CPE) and sharp peaks in zinc oxide nanoparticles (ZnONPs). The 4 g/L ZnONPs significantly enhanced vegetable growth, with increased: Height (48.33 cm), number of leaves (18.67), leaf area (82.33 cm), specific leaf area (6531.57 cm²/g) and relative growth rate (0.07 g/g/day) compared with other treatments. In contrast, control group 0¹ exhibited notable leaf area index (0.47 m²/g), net assimilatory rate (2.39 g/m²/day) and leaf area ratio (0.21(m²/g). However, control group 0² showed higher levels of oxidative stress markers (malondialdehyde 23.24 nmol/g) and hydrogen peroxide (43.11 µmol/g) in roots). Conversely, catalase (2568.06 µmol/g), ascorbate peroxidase (30.35µmol/g) and superoxide dismutase (1.48µmol/g) were substantially higher in the leaves of 0² and roots compared with 4 g/L ZnOPs. The 4 g/L ZnONPs treatment also yielded significant quantities of ascorbic acid (148.71 mg/g), glutathione (8.31 µmol/g) and total soluble sugars (21.53 mg/g) in the leaves and roots of the vegetables. The ZnONPs exhibited beneficial functional groups, making them suitable for tomato cultivation. Notably, the 4 g/L ZnONPs treatment enhanced agronomic characters, whereas the 0² treatment reduced these characters but triggered increased production of water-stress indicators. These findings suggest that ZnONPs, as a nanofertilizer, have great potential for improving tomato production and should be encouraged.