Effect of glyphosate formulations on low-affinity methanotrophy in agricultural soils

Methane (CH₄) accounts for approximately 20% of the global greenhouse effect, and its atmospheric concentration continues to rise. The activity of low-affinity methanotrophs (MT) in soils plays a key role in mitigating CH₄ emissions by oxidizing methane before it can escape into the atmosphere. This study presents the first dedicated analysis of the response of soil MT to the most extensively used herbicide worldwide - glyphosate. Response of MT communities of Gleysol, Leptosol and Fluvisol indicate that label doses both of pure glyphosate (GFP) and its commercial formulation (GFC) had insignificant effect on the low-affinity CH₄ oxidation rate (MT-L). In Gleysol, a significant decrease in MT-L was observed at 50 μg g^-1 GFC and 1500 μg g^-1 GFP, whereas the other soils were considerably more resistant. Notably, the decline in MT-L occurred in parallel with an increase in MT abundance, particularly under GFC treatment. This pattern can be explained by an increase in facultative methanotrophs and their preferential utilization of herbicide-derived substrates. The overall stronger effects of GFC compared to GFP on soil microbiota, the methanotrophic community, and MT-L It clearly underscores the critical role of adjuvants present in commercial glyphosate formulations in shaping the soil microbiota response to agrochemicals.