Copper-Based Materials as an Effective Strategy for Improving Drought Resistance in Soybean (Glycine max) at the Reproductive Stage

Drought is among the most damaging climatic hazards affecting crop productivity and nutritional quality. Here, we investigated the influence of Cu-based materials at mitigating drought stress in soybeans (Glycine max) during the reproductive stage in order to elucidate effects on productivity. Commercial copper oxide (CuO) nanoparticles (NPs), in-house synthesized copper sulfide (CuS) NPs, and copper sulfate (CuSO₄) were foliar applied at 10 mg Cu/L daily for 1 week to soybean that were exposed to water deficit at the onset of flowering, and plants were harvested 5 days after exposure. Drought inhibited flower production by 27% compared to the nondrought treatment. Notably, both CuS NPs and ionic Cu mitigated the drought-induced inhibition of flower production, showing 41.7 and 33.3% improvement. CuS NPs exhibited the most positive impact on restoring shoot biomass, pod biomass, and shoot moisture content, increasing values by 53, 96, and 10%, respectively, compared to the drought control plants. The Cu-based materials maintained photosynthetic parameters under drought conditions and modulated oxidative damage by enhancing reactive oxygen species-scavenging enzyme activities. Furthermore, CuO NP treatment increased shoot and pod Cu levels by 624 and 54%, respectively, compared to the drought control plants. Taken together, these findings suggest that Cu-based materials modulate plant protective mechanisms against drought stress during the flowering stage, offering a potentially important nanoenabled strategy to promote biofortified climate resilient crops.