Tetracycline inhibits the nitrogen fixation ability of soybean (Glycine max (L.) Merr.) nodules in black soil by altering the root and rhizosphere bacterial communities

Abstract

Tetracycline is a widely used antibiotic and may thus also be an environmental contaminant with an influence on plant growth. The aim of this study was to investigate the inhibition mechanisms of tetracycline in relation to soybean growth and ecological networks in the roots and rhizosphere. To this end, we conducted a pot experiment in which soybean seedlings were grown in soil treated with 0, 10, or 25 mg/kg tetracycline. The effects of tetracycline pollution on growth, productivity, oxidative stress, and nitrogenase activity were evaluated. We further identified the changes in microbial taxa composition and structure at the genus and species levels by sequencing the 16S rRNA gene region. The results showed that tetracycline activates the antioxidant defense system in soybeans, which reduces the abundance of Bradyrhizobiaceae, inhibits the nitrogen-fixing ability, and decreases the nitrogen content in the root system. Tetracycline was also found to suppress the formation of the rhizospheric environment and decrease the complexity and stability of bacterial networks. Beta diversity analysis showed that the community structure of the root was markedly changed by the addition of tetracycline, which predominantly affected stochastic processes. These findings demonstrate that the influence of tetracycline on soybean roots could be attributed to the decreased stability of the bacterial community structure, which limits the number of rhizobium nodules and inhibits the nitrogen-fixing capacity. This exploration of the inhibitory mechanisms of tetracycline in relation to soybean root development emphasises the potential risks of tetracycline pollution to plant growth in an agricultural setting. Furthermore, this study provides a theoretical foundation from which to improve our understanding of the physiological toxicity of antibiotics in farmland.