The Influence of Cuprous Oxide Nanoparticles on Photosynthetic Efficiency, Antioxidant Responses and Grain Quality throughout the Soybean Life Cycle

The widespread application of nanoparticles (NPs) in agriculture has not only enhanced the efficiency of agrochemical use but also introduced environmental pollution, potentially impacting human health through absorption and accumulation in edible plants. The purpose of this study was to evaluate the toxic effects and ecological risks of Cu[sub.2]O nanoparticles (nCu[sub.2]O) in the life cycle of soybean, and to provide a theoretical basis for the safe application of NPs in agriculture. Soybeans were grown in natural soil modified with nCu[sub.2]O, bulk cuprous oxide (bCu[sub.2]O) and copper sulfate (CuSO[sub.4]) at concentrations of 0, 50, 200, and 800 mg/kg. Samples and grains from treated soybeans were collected at the flowering, podding, and seed-filling stages for analysis. The results indicated that treatments with nCu[sub.2]O, bCu[sub.2]O, and Cu[sup.2+] reduced the chlorophyll content in soybean leaves, thereby affecting photosynthesis. Significant reductions were observed in the net photosynthetic rate (Pn), the transpiration rate (Tr), stomatal conductance (Gs), the quantum yield of photosystem II (Y(II)), photochemical quenching (qP), and the electron transport rate (ETR) at high concentrations. However, the toxicity of nCu[sub.2]O to photosynthesis recovers as the plant grows. Almost all treatments increased the levels of antioxidant enzymes (SOD, POD, CAT) and reduced oxidative stress. In the nCu[sub.2]O and bCu[sub.2]O treatments, grain protein content was significantly reduced, while fat and water content increased. Phosphorus (P) content decreased, whereas sulfur (S), potassium (K), magnesium (Mg) and calcium (Ca) contents increased. The accumulation of copper in plants followed the order nCu[sub.2]O > bCu[sub.2]O > Cu[sup.2+], with the bCu[sub.2]O treatment being slightly more toxic than the nCu[sub.2]O treatment, and both being more toxic than the Cu[sup.2+] treatment. The above data indicated that nCu[sub.2]O had a dose-dependent effect, which significantly inhibited soybean growth and changed grain quality at high concentrations.