ZnO nanoparticles in combination with Zn biofertilizer improve wheat plant growth and grain Zn content without significantly changing the rhizospheric microbiome

Zinc-deficient diet and poor bioavailability are leading to Zn deficiency a major form of hidden hunger affecting millions across the globe with significant economic and health consequences. Agronomic Zn-fortification of cereals using Zn-solubilizing bacteria based biofertilizers (Zn biofertilizer) can be an effective, economic, and socially acceptable solution. This field study explores the prospect of using a combination of ZnO-nanoparticles (5 kg ha-1) with Zn-biofertilizer (20 g kg-1 of seeds) for agronomic fortification of wheat. Culture-dependent technique and Illumina sequencing were used to evaluate the shift in soil microbial community in response to these amendments. The change in vegetative growth of wheat (Triticum aestivum) plant and grain Zn-content was also monitored. The results were compared with those obtained with bulk ZnO amendment. In the presence of ZnO-NPs and biofertilizer the total length, fresh weight, dry weight, chlorophyll, and carotenoid content increased by 14.6 %, 37.5 %, 40 %, 30.9 %, and 31.7 %, respectively, compared to control indicating a significant improvement in plant growth. The grain’s protein, grain yield, and Zn content increased by 30.74 %, 8.8 %, and 66.3 %, respectively. The total aerobic bacteria, fungal count, N2-fixing bacteria, phosphate solubilizers, and Zn-solubilizing bacteria increased by 99, 34, 31, 166, and 1400 %, respectively. While the population of actinobacteria remained unchanged. The Illumina sequence analysis shows an increase in the population of bacteria belonging to the phylum Bacillota and Pseudomonadota, and genera like Bacillus, Masillia, and Rhizobium indicating a shift towards plant growth promotion. Alpha diversity indices and ordination analysis do not indicate any significant change in the microbial community. Results presented in this study indicate that the soil amendment with a combination of Zn-biofertilizer and ZnO-nanoparticles significantly promotes plant growth and improve grain Zn-content without significantly shifting microbial community structure. [Display omitted] •For controlling Zn deficiency, agronomic fortification of wheat is the best strategy.•Commercial-grade Zn-biofertilizer was prepared and its survival in soil was confirmed.•Zn biofertilizer and ZnO-NPs conferred better growth and yielded Zn-dense protein-rich grains.•Illumina sequencing shows no remarkable shift in the microbial community structure.•This approach can yield Zn-dense wheat without significantly