Mechanisms of growth-promotion and Se-enrichment in Brassica chinensis L. by selenium nanomaterials: beneficial rhizosphere microorganisms, nutrient availability, and photosynthesis

Maintaining a proper content of selenium (Se) in food is particularly important for human health. However, the mechanisms of uptake and enrichment of Se ENMs in crops are still unclear. Herein, Se engineered nanomaterials (Se ENMs) (size 62.3 ± 14.6 nm and surface charge −34.4 ± 1.4 mV) were synthesized and used as nanofertilizers for Se-fortified vegetables. The results demonstrated the Se content and yield were increased by 338.0% and 19.8% respectively in Brassica chinensis L. through soil application of Se ENMs (0.5 mg‧kg–1). The content of Se in vegetables increased up to 32.8 μg/100 g (7.5 μg/100 g for the control), which could provide the daily recommended Se intake (55–400 μg/day) for human. Amendments of the slightly alkaline soil with the Se ENMs improved beneficial rhizosphere microbiomes (Pseudomonas and Bacillus), and resulted in the plants accumulating more low molecular weight compounds (betaine, proline, glycine, norleucine, urocanic acid and indole-3-acrylic acid) with increases in the Se content of the plant by 264.9%. Moreover, the nutrient accumulation in leaves promoted the photosynthesis (16.7%) and increased carbohydrate content (6.5%). Also, the expression of carbohydrate transport-related genes (BnSUC1,1, BnSUC1,4, and BnSWEET10,2) were up-regulated by 52.2, 53.2 and 76.3-fold, respectively, promoting root growth, improving rhizosphere microbiome and nutrient availability. Therefore, such mutual benefits between leaves and roots using ENMs could provide an alternative model for cultivating Se-enriched crops.