Seasonal Environmental Variation Impacts 2,4-D Fate and Metabolism in Urban Landscapes

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) is commonly applied to urban landscapes such as turfgrass lawns. Though 2,4-D’s degradative pathway has been extensively researched, the interaction of soil microbiota with 2,4-D under varying seasonal conditions remains unclear. This study aimed to assess the role of seasonal environmental conditions on the soil bacterial community and the resulting impact on the degradation of 2,4-D and the formation of its major transformation product, 2,4-dichlorophenol (2,4-DCP). Field and controlled environment studies were conducted near Madison, WI, USA in 2018 and 2019 and demonstrated that 2,4-D concentrations steadily declined in both the soil and leaves in the 10 days following application. The metabolite 2,4-DCP was only detected in the controlled environment study and was always below the limit of quantification. The impact of seasonal environmental variations on bacterial community structure, function, and composition were also assessed. Distinct bacterial communities were observed between season-simulated temperatures, soil depths, field sites, and 2,4-D treatment application timings. These findings emphasize that environmental variations shift the soil bacterial community over the course of a growing season with potentially important implications for the degradation of 2,4-D in urban landscapes.