Unveiling the potential impacts of oxygen and nitrogen nanobubbles in water on plant rhizosphere microbiome

Nanobubbles (NBs) in water have shown promise in promoting plant growth and seed germination, potentially reducing the need for water and fertilizer inputs. To elucidate the mechanisms underlying these benefits, this study investigated the effects of oxygen nanobubbles (ONBs) and nitrogen nanobubbles (NNBs) on the tomato rhizosphere microbiome over a 34-day irrigation period. Treatments included varying NB types, dissolved oxygen (DO) levels (9.30 and 26.73 mg L⁻¹ for ONBs; 2.69 and 8.84 mg L⁻¹ for NNBs), and irrigation frequencies. Multivariate analysis of 16S rRNA gene sequencing revealed that both ONBs and NNBs significantly altered rhizosphere microbial community composition compared to controls. NB concentration and irrigation frequency further influenced microbiome structure. High-concentration NB treatments increased the relative abundance of multiple beneficial rhizobacteria involved in nutrient cycling, including Bacteroidota, Chitinophagales, Gemmatimonadota, and Ureibacillus, while low-concentration treatments had lower impacts on plant growth-promoting rhizobacteria. Network analysis indicated enhanced microbial connectivity and reduced niche specialization in NB-treated rhizosphere soils. Moreover, significant positive correlations were observed between tomato agronomic traits and several rhizobacteria, including known plant growth-promoting taxa like Comamonadaceae and other potentially beneficial microbes. These findings demonstrate that NB type, concentration, and irrigation regime can modulate rhizosphere microbial dynamics, offering insights for optimizing nanobubble applications in sustainable precision agriculture.