Cultivar-Specific Hormesis Effects of Silver Nanoparticles on Maize Growth are Linked to Rhizosphere Microbial Mommunities of two Maize Cultivars
摘要
Purpose: Silver nanoparticles (AgNPs) are becoming emerging contaminants, raising increasing interests and concerns regarding their effects on plants and soil microbes. Understanding these effects from a cultivar-specific perspective is crucial for ensuring crop production and food safety. Methods: Pot experiments were performed to evaluate the effects of AgNPs (1.0 mg kg− 1, 10.0 mg kg− 1, and 50.0 mg kg− 1) on the growth, Ag accumulation, and rhizosphere microbial community of two maize cultivars: waxy maize and sweet maize. Results: AgNPs exerted hormetic effects on plant growth of waxy maize and sweet maize. Low concentrations (1.0 and/or 10.0 mg kg− 1) increased plant shoot, root and total biomass as well as chlorophyll content but increased superoxide dismutase (SOD) activity and hydrogen peroxide (H2O2) contents, whereas high concentrations (50.0 mg kg− 1) decreased plant shoot, total biomass, chlorophyll content, and increased malondialdehyde (MDA) content. The stimulatory effect occurred at 1.0 and 10.0 mg kg− 1 AgNPs for waxy maize but only at 10.0 mg kg− 1 for sweet maize, indicating that waxy maize might respond more positively to AgNPs. Additionally, with increasing AgNP doses, waxy maize seedlings accumulated lower Ag in leaves, stems, and roots relative to sweet maize. The waxy maize rhizosphere was enriched with Proteobacteria (Sphigomonas) and Actinobacteria (Arthrobacter) under lower doses (1.0 and 10.0 mg kg− 1) of AgNPs, especially under 10.0 mg kg− 1 AgNPs, which could increase plants resistance and adsorb Ag in soil, respectively. In contrast, the sweet maize rhizosphere contained comparable Actinobacteria and Proteobacteria under control and lower doses (1.0 and 10.0 mg kg− 1) of AgNPs. Soil Ag content and plant biomass were found to be highly correlated with bacterial community composition in the maize rhizosphere. Conclusions: Taken together, these findings suggest that the hormetic effects of AgNPs on maize growth are cultivar-dependent, which may be closely linked to the differential shifts in rhizosphere microbial communities.