Meta-Analysis of Nanoparticles in Plant Drought Responses: Functional Shifts Across Stress Intensities...

Drought is one of the most critical abiotic stresses limiting global crop productivity, and nanoparticles (NPs) have recently emerged as promising tools to enhance plant stress tolerance. However, how strongly and in what ways NPs influence plant performance is not yet well established, particularly in relation to drought intensity and nanoparticle identity. We conducted a comprehensive meta-analysis of studies assessing physiological and biochemical traits, comparing plant responses with and without nanoparticle application under well-watered, moderate, and severe drought conditions, and identifying particle-specific effects through subgroup analyses. The results revealed that application of NPs consistently improved plant performance in a stress-dependent manner. Chlorophyll content effect size increased up to 44% under moderate drought, while oxidative stress markers (MDA, H₂O₂) declined more than twofold under both moderate and severe drought. Under severe drought, nanoparticles markedly enhanced antioxidant activities: CAT, SOD, and POD effect size increased by about 30%-35% relative to controls. Particle-specific responses evidenced that titanium NPs produced the highest yield gains (effect size = 11.1), whereas iron-based NPs had negligible effects. Under well-watered conditions, titanium, zinc, and silicon-based NPs promoted chlorophyll accumulation and yield stability. Under moderate drought, zinc, silicon, and selenium-based NPs improved yield and pigments, while titanium NPs supported osmotic balance. Under severe drought, copper, cerium, and titanium-based NPs showed strong osmotic and enzymatic protection. Overall, this meta-analysis shows that NPs improved plant performance across both optimal and drought conditions, with responses varying according to drought severity and nanoparticle identity.