Bioavailability of selenium nanoparticles in soil and plant: the role of particle size

Abstract

The application of selenium nanoparticles (Se NPs) in agriculture has garnered significant attention, yet there remains a knowledge gap regarding the correlation between the size of Se NPs and their availability in soil. To address this gap, adsorption experiments, soil column experiments, and pot experiments were conducted to investigate the relationship between the availability in soil of Se NPs and their particle size. The results showed that the adsorption capacities of Se NPs with various sizes (30, 50, 80, 110 nm) to fulvic acid (FA) was decreased with increasing particle sizes and pH. Small sized Se NPs (30 nm) are more stable because they adsorb more organic matter, which significantly decreases aggregation. Moreover, the mobility of Se NPs was decreased by increasing clay content in soil and particle size. These results demonstrated that small-sized Se NPs have higher bioavailability than large-sized Se NPs. The Se content in rhizosphere soil and Brassica chinensis shoot was significantly increased by 319.4% and 220.2% upon exposure to Se NPs (30 nm), higher than that for others (50, 80, 110 nm and 2 µm). The reason is that small-sized Se NPs are more stable in the soil, more easily migrate from the non-rhizosphere to the rhizosphere and interact with crop roots, leading to increased root exudations. These interactions recruit beneficial microorganisms in the rhizosphere. In turn, the improved root exudations and the presence of these microorganisms enhance the bioavailability of Se NPs. Linear regression analysis indicated that the size of soil-applied Se NPs should fall within the range of 11–631 nm, as those outside of this range may not meet the standard for Se-enriched food. Besides, the nutrient accumulation in leaves promoted photosynthesis (81.1%) and increased the yield (113.1%) of Brassica chinensis by small-sized Se NPs (30 nm). Therefore, these information highlights the critical role of Se NPs size in crop Se biofortification for agriculture production.