Green zinc oxide nanoparticles improve zinc bioavailability and mitigate high temperature stress in rice

To address the rising global demand for food, the development of sustainable technologies that can increase agricultural productivity while minimizing environmental impact is essential. This study reports on the green synthesis of zinc oxide nanoparticles (ZnO NPs) and evaluates their application in mitigating the adverse effects of elevated temperatures on rice. An experiment was conducted on rice PB-1121 during the kharif seasons of 2021 and 2022, utilizing synthesized green ZnO NPs (30 nm) compared to ZnSO₄ under a Free Air Temperature Enrichment (FATE) system. The temperature of FATE was higher by ~ 1.5 °C compared to the ambient temperature throughout the crop growing period. The incorporation of ZnO NPs into the soil increased the photosynthetic rate (Pn) by 17.8%, stomatal conductance (gs) by 16.2%, and chlorophyll concentration by 4.3% compared to the control under FATE (CKET). In contrast, Pn, gs, chlorophyll, and carotenoids decreased by 9.2-18.6% in the control under FATE compared to the ambient control (CK). Moreover, protein, proline, catalase (CAT), and superoxide dismutase (SOD) activities improved by 6.8-12.8% under ZnO NPs soil manipulation compared to ZnSO₄ under FATE. Soil treated with ZnO NPs also significantly enhanced (p < 0.05) the number of productive tillers, filled grains (p < 0.05), and overall grain yield (p < 0.001) compared to control under CKET. Additionally, root length, root surface area, and root diameter were significantly (p < 0.05) greater in soil amended with ZnO NPs than in the control under FATE. Zinc (Zn) concentration in grains was higher (p < 0.001) in ZnO NPs, while phytic acid (PA) concentration decreased by 25.8-31.1%. The bioavailability of Zn was also significantly (p < 0.05) increased in the treatments using ZnO NPs. This study investigates how NPs interact with plants, demonstrating their potential to enhance agricultural sustainability, particularly during periods of extreme weather. Future studies should elucidate the molecular bases underlying the observed enhancement of Zn uptake, translocation, and high temperature stress tolerance in rice with ZnO NPs application.