Impact of Zinc Oxide Nanoparticles Amended Organic Manure on Arachis hypogaea Growth Response and Rhizosphere Bacterial Community

The effect of zinc oxide nanoparticle-organic manure amended ultisol and loam soils on plant growth response and rhizosphere bacterial community of peanut (Arachis hypogaea) was evaluated using standard methods under greenhouse conditions. Results indicate germination rates ranged between 30 and 100% in the amended soils compared to 50 and 70% in the controls. ZnO nanoparticles exerted concentration-dependent and varying effects on the plant root and shoot lengths, weights, nodules and pod formation in the two soil types. Heterotrophic bacterial counts ranged from 7.21 ± 0.51 to 7.38 ± 0.5 Log10CFUg-1 in the amended ultisol and 6.99 ± 0.55 Log10CFUg-1 in the control with a log reduction to 6.70 ± 0.39 Log10CFUg-1 in 500 mgkg⁻¹ ZnO spiked soil. Counts in the amended loam soil ranged between 6.59 ± 0.48 and 7.22 ± 0.41 Log10CFUg-1 relative to 6.80 ± 0.58 Log10CFUg-1 in the control. ZnO induced concentration-dependent effect on oxygen uptake rate relative to the controls. The organisms were members of the genera Lactobacillus, Pseudomonas, Bacillus, Rhizobium, Xanthobacter, Enterobacter, Citrobacter, Nitrosomonas and Agromyces. ZnO nanoparticle exerted concentration-dependent stimulatory and inhibitory effects on the plant growth response, oxygen uptake rate and induced temporal shifts in soil microbial abundance. It is challenging to generalize a consistent response of the plant or microorganisms because ZnO nanoparticles interacted with A. hypogaea and soil bacterial community in ways that differ in the ultisol and loam soil.