Carbendazim Modulates the Metabolically Active Bacterial Populations in Soil and Rhizosphere

The impact of fungicide residues on non-target soil bacterial communities is relatively unexplained. We hypothesize that the persistence of fungicide residues in the soil will affect the soil bacterial populations. Persistence depends on biotic and abiotic factors, primarily determined by agricultural activities. Activities such as fallow soil (F), farmyard manure (FYM) amendment, rice straw (RS) mulching, and cultivation of maize (Zea mays) and clover (Trifolium alexandrinum) were used as treatments. The soil CO₂ efflux showed no effect of Carbendazim on dormant bacteria (unwatered condition). However, in irrigated condition, Carbendazim enhanced the CO₂ efflux by 8, 164, 131, 249, and 182% in fallow, FYM, RS, maize, and Trifolium treatments, respectively. However, 16S rRNA metagenome study after 30 days of carbendazim treatment showed that maize rhizosphere microflora was most susceptible, decreasing the Shannon diversity index from 0.321 to 0.165. Diversity indices generally increased in maize and RS treatments, and Proteobacteria was the most prominent bacterial phyla in the maize rhizosphere. The microbial communities separated into distinct groups on the Principal Co-ordinate analysis (PCoA) plot. The separation on scale 1 (35%) and scale 2 (13%) was based, respectively, on microbial activity and carbendazim treatments. Functionally Maize+Carbendazim treatment showed the highest enzyme activities dehydrogenase (82.25%), acid phosphatase (78.10%), alkaline phosphatase (48.26%), β-glucosidase (59.99%), protease (126.65%), and urease (50.66%) compared to fallow soil. Overall, Carbendazim enhanced non-target bacterial activity in metabolically active niches, while it did not affect the dormant microflora. Thus, organic amendments and cultivation of fungicide-contaminated soil may help render the contaminant through bacterial activity.