Combined effects of zinc oxide nanoparticles and arbuscular mycorrhizal fungi on soybean yield, oil quality, and biochemical responses under drought stress

The increasing frequency and intensity of drought stress, exacerbated by climate change, pose significant threats to agricultural productivity and food security. In this context, this study investigates the effects of zinc oxide nanoparticles (ZnONPs) and Myco-Root-a proprietary blend of three distinct mycorrhizal fungal species-on the yield and oil quality of soybean (Glycine max) under drought stress. By exploring innovative strategies, this research aims to enhance agricultural resilience and promote sustainable food production in challenging environmental conditions. Utilizing a randomized complete block design over two years (2021–2022), the experiment included 12 treatments with three levels of drought stress (optimal irrigation (MAD₂₀), moderate water deficit (MAD₅₀), and severe water deficit (MAD₈₀)) and four fertilizer management strategies (control, ZnONPs (200 mg L⁻¹), arbuscular mycorrhizal fungi (AMF), and a combination of both). The results showed that drought stress reduced colonization, whereas the combined application of ZnONPs+AMF enhanced colonization by 10 % relative to AMF alone. Additionally, under MAD₂₀ conditions, the combined treatment of ZnONPs+AMF significantly increased nitrogen, phosphorus, potassium, and zinc uptake by 82.61 %, 100.49 %, 94.78 %, and 143.11 %, respectively, compared to severe drought stress conditions without fertilization. This treatment also increased proline and soluble carbohydrates under severe drought conditions by 77.29 % and 58.75 %, respectively, compared to the control. Furthermore, the activity of antioxidant enzymes such as ascorbate peroxidase, guaiacol peroxidase, and catalase increased by 85.92 %, 111.18 %, and 80.13 respectively, reducing oxidative stress markers such as malondialdehyde (51.27 %) and hydrogen peroxide (63.44 %) compared to untreated conditions. In terms of both oil quantity and quality, the combined treatment of ZnONPs+AMF under MAD₂₀ conditions increased linoleic and linolenic acid concentrations by 60.75 % and 43.91 %, respectively, while decreasing palmitic and stearic acid concentrations by 50.45 % and 24.88 %, respectively. These changes resulted in a 145.47 % increase in seed yield and an 24.32 % increase in oil content compared to MAD₈₀ conditions without treatment. Additionally, when compared to severe drought stress without fertilization, the application of ZnONPs+AMF under MAD₂₀ enhanced the iodine value by 9.7 %, while the saponification number under MAD₈₀ without fertilization increased by 3.2 % relative to the control. Furthermore, the combined application of ZnONPs+AMF under optimal irrigation conditions resulted in an 41.04 % reduction in the acid value compared to drought stress without fertilizer application. Overall, these findings suggest that the combined use of ZnONPs and AMF can serve as an effective strategy to improve crop performance and oil quality under drought stress conditions. This approach enhances plant resilience to climate change, improves agricultural productivity, promotes food security, and supports the sustainability of agricultural systems.