Biochar alters microbial community structure in experimental treatment wetlands exposed to pesticides
Treatment wetlands are increasingly used to treat agricultural wastewater. While plants and substrates contribute to pollutant immobilization and removal, most of the metabolic degradation is carried out by microorganisms. This study aimed to assess the combined effects of biochar and pesticides on microbial communities inhabiting the roots and substrate of treatment wetlands. Six treatment wetland mesocosms planted with Scirpus cyperinus were sampled before and after exposure to a pesticide mixture containing atrazine, glyphosate, and chlorantraniliprole at three concentration levels. Half of the mesocosms were amended with biochar. Bacterial and fungal DNA from root and substrate samples was amplified and sequenced to analyze microbial diversity and composition. Proteobacteria (bacteria) and Ascomycota (fungi) were the dominant groups in all mesocosms, both before and after the application of pesticides. Biochar had no significant effect on microbial alpha diversity but did alter community composition, particularly by altering the abundance of several bacterial taxa involved in nitrogen cycling. In contrast, pesticide concentration significantly affected fungal community structure in roots only. Additionally, the relative abundance of eight pesticide-degrading microorganisms increased after pesticide application. Overall, this study provides valuable insight into how increasing pesticide concentrations impact microbial communities in treatment wetlands, and how biochar influences these microbial communities under pesticide stress.