ABSTRACT: Soil salinization-alkalization is a widespread abiotic stress globally, severely impairing crop growth and environmental ecology. Nanomaterials hold significant potential for application in regulating plant stress tolerance due to their unique physical and chemical properties. In this study, the sol-gel method was optimized to synthesize a type of spherical, monodisperse, amorphous mesoporous silica nanoparticles (MSNs) with an average particle size of 40-50 nm and a positive surface charge of 35 mV. A 20 mg/L MSN solution was foliarly applied to two soybean cultivars, Hefeng 50 (HF50) and Henong 95 (HN95), in a pot experiment at the R1 stage to investigate its effects on plant growth and yield-related traits under saline-alkali stress (pH 9.2). MSNs treatment significantly alleviated the growth inhibition induced by saline-alkali stress. Specifically, MSNs significantly increased the plant height, leaf area, root volume, and root surface area of soybean plants under saline-alkali stress. MSNs also increased the dry matter accumulation of plant shoots and roots, improved root activity, and increased the number of pods and seeds per plant. MSNs enhanced cell mechanical strength by activating the synthesis of cuticle and epidermal wax, and maintained intracellular metabolic homeostasis by activating the antioxidant defense system and suppressing the excessive activation of pathways such as the mitogen-activated protein kinase (MAPK) pathway. Additionally, MSNs increased the content of photosynthetic pigments in soybean leaves, thereby enhancing light energy absorption and utilization efficiency, and elevating carbohydrate levels. MSNs promoted the directed translocation of photosynthates to sink organs such as seeds and roots by regulating the activity of carbon metabolism enzymes and source-sink allocation. Taken together, these cumulative effects improved soybean saline-alkali stress tolerance, and ultimately increasing the number of pods per plant, seeds per plant, 100-seed weight, and total yield per plant. The study provides theoretical basis and technical support for the development of nanomaterial-based cultivation practices to improve crop saline-alkali tolerance.
