Silica nanomaterials and earthworms synergistically regulate maize root metabolite profiles via promoting soil Si bioavailability

Abstract

Silicon (Si) acquisition by plants is stimulated by root-associated rhizosphere processes which are usually mediated by nanomaterials and soil fauna. In this study, 10 mg kg⁻¹ silica nanomaterials (SiO₂ NMs) and an equivalent dose of conventional silicate fertilizer (sodium silicate) were added to maize-planted soils in the absence or presence of earthworms for 20 days. The effects of SiO₂ NMs, earthworms, and their interactions on silicate solubilizing bacteria (SSB) abundance, Si bioavailability in the rhizosphere and drilosphere and maize root metabolite profiles were investigated. The results showed that SiO₂ NMs in the presence of earthworms increased the SSB abundance in the rhizosphere and drilosphere soils by 48.6% and 55.8%, respectively. Correspondingly, the combined addition of SiO₂ NMs and earthworms increased the concentration of silicic acid in the rhizosphere and drilosphere soils by 11.5% and 5.3%, respectively. Moreover, soil SiO₂ NM addition up-regulated the expression of Si transporter genes ZmLsi1, ZmLsi2, and ZmLsi6 in the presence of earthworms by 1.6, 1.7, and 1.8-fold, respectively, as compared to untreated plants, which resulted in higher Si accumulation in maize leaves and increased maize growth. Particularly, SiO₂ NMs induced higher upregulation of the relative abundance of root metabolites including sugars (maltose and fructose), amino acids (phenylalanine and glutamic acid), and small molecular organic acids (fumaric acid and caffeic acid) in the presence of earthworms. Most root metabolites (phenylalanine, malic acid, histidine, etc.) were positively correlated with the rhizosphere silicic acid content. Altogether, our results provide novel insights into understanding the synergistic regulation effect of SiO₂ NMs and earthworms on maize growth and root metabolite profiles via altering rhizosphere Si bioavailability and could promote the application of SiO₂ NMs as nanofertilizers in earthworm-worked agricultural fields.