Reapplication of glyphosate mitigate fitness costs for soil bacterial communities

Glyphosate (GLP) is a globally ubiquitous herbicide that poses a threat to living organisms due to its widespread presence in soil ecosystems. However, the results of current research regarding the effects of glyphosate on soil microorganisms and its ecological risks are vague and inconsistent. In this study, we investigated the impact of single (low/high-dose) and reapplication (high-dose) of glyphosate applications on soil microbes through indoor incubation experiments using 16S rRNA gene high-throughput sequencing technology. Our findings indicate that in the short term, whether it's single or reapplication glyphosate applications, changes in diversities of soil bacterial community were less than those in community composition. Glyphosate exerts selective pressure on soil microbial communities, resulting in a predominant process of species replacement after glyphosate application, and quantitative analysis revealed a higher turnover rate of microbial communities under glyphosate reapplication. Factors related to nitrogen cycling, especially NH₄⁺-N and NO₃^--N, were identified as the main drivers responsible for the changes in soil microbial community composition following glyphosate addition. Changes in the functionality of soil microbial communities are observed after glyphosate application, with the adaptability of microbial communities resulting in smaller changes with reapplication addition compared to a single application. Furthermore, We observed that glyphosate application leads to a phenomenon resembling the "fitness cost" found in resistant bacteria. When glyphosate as a single application, it has a significant impact on bacterial communities, leading to decreased community diversity, stability, and function, alongside alterations in community structure, however, the effect can be mitigated by reapplying glyphosate.