CuO, ZnO, and γ-FeO nanoparticles modified the underground biomass and rhizosphere microbial community of Salvia miltiorrhiza (Bge.) after 165-day exposure.

To investigate whether metal oxide nanoparticles exhibit toxicity or positive effects on medicinal plants, CuO, ZnO, and γ-FeO nanoparticles (NPs), at concentrations of 100 and 700 mg kg were introduced into the cultivation of Salvia miltiorrhiza (Bge.). Metal elemental contents, chemical constituents, biomass and the structure of the rhizosphere microbial community was used to estimate this effect. The results indicated CuO NPs increased the Cu content and ZnO NPs increased the Zn content significantly as exposure increased, γ-FeO NPs had no significant effect on Fe content in S. miltiorrhiza roots, while 100 mg kg ZnO and CuO NPs significantly decreased the Fe content in roots. Additionally, ZnO and γ-FeO NPs increased the underground biomass, and diameter of S. miltiorrhiza roots. However, these three metal oxide nanoparticles had no significant effect on total tanshinones, while the 700 mg kg γ-FeO NPs treatment increased salvianolic acid B content by 36.46%. High-throughput sequencing indicated at 700 mg kg ZnO NPs, the relative abundance of Humicola (Zn superoxide dismutase producer), was notably increased by 97.46%, and that of Arenimonas, Thiobacillus and Methylobacillus (taxa related to heavy metal tolerance) was significantly increased by 297.14%, 220.26% and 107.00%. The 700 mg kg CuO NPs exposure caused a significant increase in the relative abundances of Sphingomonas (a copper-resistant and N-fixing genus) and Flavisolibacter (stripe rust biocontrol bacteria) by 127.32% and 118.33%. To our best knowledge, this is the first study to examine the potential impact of NPs on the growth and rhizosphere microorganisms of S. miltiorrhiza.