Silicon Nanoparticle Seed Priming Modulates Germination, Early Seedling Growth, and Biochemical Responses of Soybean Under PEG-Induced Drought Stress

Drought stress during germination and early seedling growth can impair soybean performance, while silicon nanoparticle (SiNP) seed priming may modulate early stress responses. This study aimed to evaluate the effects of SiNP seed priming on the germination, early seedling growth, and biochemical responses of 11 soybean (Glycine max (L.) Merr.) genotypes under non-stressed conditions and two levels of PEG-induced drought stress (5% and 10% PEG 6000), and to assess how these responses varied with stress intensity and genotype. Seeds were untreated, hydroprimed, or primed with SiO2 nanoparticles at 500 or 1000 mg L−1. Across genotypes and stress levels, priming generally increased germination energy and total germination and reduced non-germinated seeds, with similar improvements observed following hydropriming and SiNP priming, whereas normal seedling development was not consistently improved. Increasing stress strongly inhibited shoot elongation and seedling fresh mass, whereas root growth was comparatively maintained. SiNP priming generally resulted in higher seedling fresh mass, with SiNPs 500 producing higher values than the untreated control in most genotypes under mild stress and all genotypes under severe stress. SiNP priming also increased proline accumulation and total amylolytic activity, with SiNPs 1000 showing the highest values under mild and severe stress. Overall, SiNP seed priming most consistently improved soybean germination under PEG-induced drought stress, whereas its effects on early seedling growth and biochemical responses varied with nanoparticle concentration, genotype, and stress intensity.