Effects of herbicides on soil microbial community characteristics in tobacco fields

This study systematically analyzed the dynamic effects of four herbicides (tribenuron-methyl, nicosulfuron, quinclorac, and fomesafen) on the community, diversity, and metabolic function of the microbial community in the rhizosphere soil of flue-cured tobacco through high-throughput sequencing technology. The results showed that: Herbicide treatment significantly changed the alpha diversity of fungal communities, with a trend of first increasing and then decreasing, while bacterial alpha diversity remained relatively stable. Non-metric multidimensional scaling analysis showed significant differences (P < 0.01) in microbial beta diversity among different treatments and sampling times (30 d vs 60 d), and fungal communities were significantly separated from the control group. The dominant bacterial groups evolved from Acidobacteria to Actinobacteria. Among them, sulfonamide had the strongest inhibition on beneficial Bacillus (a decrease of 48.29%), while chloroquine had the weakest inhibition (11.83%). The fungal community generally exhibits a pattern of "proliferation of pathogenic bacteria (Penicillium) and decline of beneficial bacteria (Aspergillus)". All the herbicide treatments resulted in a decrease in rare and conditionally rare bacterial communities. Functional predictions show that herbicide treatment generally enhances bacterial nitrogen fixation but inhibits nitrate respiration and promotes the evolution of fungal communities towards a saprophytic pathogen complex. Co-occurring network analysis further revealed that different herbicides drive specific microbial adaptation strategies: nicotinuron enriches acid-resistant and nitrogen-fixing bacterial communities; sulfonamide selects for stress-resistant structural groups and activates efficient degradation networks; and chloroquine shapes complex communities tolerant to multiple stresses. In summary, the four herbicides significantly alter the structure and function of soil microorganisms, increasing the potential risk of beneficial bacteria decay and pathogen enrichment.