Effects of Spraying Mn3O4 Nanozymes at Different Concentrations on the Physiological Characteristics and Yield of Wheat Flag Leaves Under High-Temperature Stress During the Filling Stage
Abstract
Climate change-driven high-temperature stress has become a major threat to global wheat production, and developing effective strategies to ensure heat-resilient, stable-yield cultivation is an urgent scientific priority. Mn3O4 nanozymes, a newly developed type of nanozyme, have not yet been tested for improving wheat heat tolerance. This study investigated the physiological mechanisms by which Mn3O4 nanozymes alleviate high-temperature stress during wheat grain filling. A polyethylene film greenhouse simulated a high-temperature environment, increasing the average canopy temperature of wheat by 2–3 °C. Under stress, plants were sprayed with distilled water (M0) or with Mn3O4 nanozymes at 100 (M1), 150 (M2), or 200 mg·L−1 (M3), while an additional control (CK) was sprayed with distilled water under natural conditions. Compared with the CK, high-temperature stress significantly disrupted chloroplast structure, altered stomatal morphology, and reduced SPAD values, flag leaf area, and photosynthetic parameters in flag leaves, ultimately leading to a decrease in thousand-kernel weight (down 4.86%) and wheat yield (down 21.24%); in contrast, under high-temperature stress, Mn3O4 nanozyme treatment resulted in milder damage to chloroplast membrane structure; the thylakoid membrane system exhibited a slightly relaxed state overall, and stomatal aperture remained favorable. This treatment slowed the decline in photosynthetic capacity and significantly enhanced antioxidant enzyme activity, thereby mitigating the impact on yield. Among these, the M1 treatment yielded the best results, with thousand-kernel weight and yield increasing by an average of 2.62% and 18.26%, respectively, compared to M0; however, this mitigating effect diminished as the concentration rose. Compared with the M0 treatment, M2 and M3 treatments produced average yield increases of 9.04% and 5.34%, respectively. Therefore, Mn3O4 nanozymes at an appropriate concentration can mitigate the adverse effects of high-temperature stress on wheat at multiple levels, thereby effectively alleviating yield losses during the grain-filling stage.