Silicon nanoparticle morphology and aggregation state modulate plant antioxidant responses under abiotic stress: a meta-analysis

Abstract Drought, salinity, and heavy metal toxicity collectively reduce global crop yields by more than 50% and share a common biochemical outcome: excessive reactive oxygen species (ROS) accumulation. Silicon dioxide nanoparticles (SiO 2 NPs) have attracted growing interest as a means of bolstering plant antioxidant defences against these stresses, yet the factors governing their efficacy remain poorly defined. Following PRISMA 2020 guidelines, we synthesised data from 31 studies encompassing 313 effect sizes across 11 plant species and three stress categories. Random-effects meta-analysis (restricted maximum likelihood, REML; Paule-Mandel I 2 correction) revealed significant enhancements of catalase (CAT; + 49%), glutathione reductase (GR; + 53%), ascorbate peroxidase (APX; + 29%), and superoxide dismutase (SOD; + 39%), with concomitant reductions in malondialdehyde (MDA; − 32.3%) and hydrogen peroxide (H 2 O 2 ; − 32.2%). Effects were strongest under drought (CAT + 77%) and heavy metal stress (GR + 70%). High heterogeneity (I 2 † ≥ 89% for all variables) was substantially explained by nanoparticle morphology: hollow and porous SiO 2 NPs release up to 14-fold more silicic acid than solid particles, associated with correspondingly larger antioxidant responses. The DLS/TEM hydrodynamic ratio served as a significant negative moderator of efficacy (β = − 0.087; p = 0.042), suggesting that aggregation in suspension reduces nanoparticle bioavailability. Critically, 76% of included studies did not report dynamic light scattering characterization, leaving aggregation state unknown for the majority of the literature. P-curve analysis confirmed genuine biological effects rather than selective-reporting artefacts. What emerges from this synthesis is that NP architecture and dispersibility, rather than dose or species identity, are the variables most worth engineering in next-generation nano-Si crop protection formulations.