Silica Nanomaterials Promote Rice Tillering and Yield by Regulating Rhizosphere Processes, Nitrogen Uptake, and Hormone Pathways

Nanotechnology has attracted worldwide attention as an effective method for sustainable crop production. Herein, silica nanomaterials (SiO2 NMs) with different sizes and concentrations were applied in paddy soils to explore their effects on rice seedlings. SiO2 NMs of 8 nm size at 50 mg·kg–1 exhibited the best performance to increase rice growth as compared with the control and conventional Si fertilizer (sodium silicate, Na2SiO3). SiO2 NMs could be a slow-release Si fertilizer to enhance the availability of monosilicic acid in rhizosphere. More interestingly, SiO2 NMs significantly enhanced the rice tiller number by 100% over the control, while Na2SiO3 showed little effects. The promotion mechanisms of rice tillering by SiO2 NMs are as follows: SiO2 NMs enhanced the N content by 109.8 and 21.2% in shoots and roots, respectively, by optimizing root exudates and rhizosphere soil bacterial community; SiO2 NMs increased the content ratio of cytokinin/auxin by 140.8% and decreased the content of GA1 and GA4 (GA = gibberellic acid) by 38.4 and 58.3%; and SiO2 NMs up-regulated the tillering-related gene expressions (e.g., OsMOC, OsFON, and OsTB) by 50.6–282.8%. In addition, the SiO2 NM treatment significantly elevated the rice grain yield after the whole growth period. The findings highlight the promising potential of SiO2 NMs for sustainable crop production.