Effects of a bioherbicide and a chemical herbicide on soil microbial community structure, diversity, and nitrogen cycling functions

The fermentation broth of the bioherbicidal fungus Aspergillus versicolor D5 shows efficacy against dicotyledonous weeds in tobacco fields. However, little is known about its impact on the soil ecological environment of tobacco fields, particularly in comparison with chemical herbicides. This study compares the effects of a bioherbicide (BIO) and rimsulfuron (CHE) on tobacco field soil ecology. Both show comparable weed control efficacy and increase urease and dehydrogenase activities, although BIO causes a smaller urease increase. Unlike CHE, BIO does not inhibit nitrite reductase. Metagenomics shows that BIO slightly alters community structure without reducing diversity, whereas CHE decreases it. BIO increases the abundance of Luteitalea (involved in decomposing complex organic carbon and nitrogen cycling) and Chloracidobacterium (light-assisted carbon metabolism) within the phylum Acidobacteria, whereas CHE significantly reduces the abundance of these bacteria. BIO decreases the abundance of arbuscular mycorrhizal fungi Rhizophagus and Funneliformis, while CHE increases them. Nitrogen cycling analysis shows that BIO only significantly reduces the anammox pathway, causing little overall disturbance, whereas CHE strongly promotes dissimilatory/assimilatory nitrate reduction and nitrate/nitrite uptake pathways. These findings indicate that the fermentation extract of A. versicolor D5 affects soil ecology less than rimsulfuron, causing less disturbance to soil microbial diversity in this study.