Ecotoxicological Impact of the Bioherbicide Leptospermone on the Microbial Community of Two Arable Soils

The ecotoxicological impact of leptospermone, a beta-triketone bioherbicide, on the bacterial community of two arable soils was investigated. Soil microcosms were exposed to 0 x (control), 1 x or 10 x recommended dose of leptospermone. The beta-triketone was moderately adsorbed to both soils (i.e.,: K-fa similar to 1.2 and K-oc similar to 140 mLg(-1)). Its dissipation was lower in sterilized than in unsterilized soils suggesting that it was mainly influenced by biotic factors. Within 45 days, leptospermone disappeared almost entirely from one of the two soils (i.e., DT50 < 10 days), while 25% remained in the other. The composition of the microbial community assessed by qPCR targeting 11 microbial groups was found to be significantly modified in soil microcosms exposed to leptospermone. Pyrosequencing of 16S rRNA gene amplicons showed a shift in the bacterial community structure and a significant impact of leptospermone on the diversity of the soil bacterial community. Changes in the composition, and in the alpha- and beta-diversity of microbial community were transient in the soil able to fully dissipate the leptospermone, but were persistent in the soil where beta-triketone remained. To conclude the bacterial community of the two soils was sensitive to leptospermone and its resilience was observed only when leptospermone was fully dissipated.