Behavior of Chiral Paclobutrazol in Soils: Enantioselective Degradation, Transformation Products, and Effects on Soil Microorganisms and Their Metabolic Functions

Paclobutrazol, a triazole chiral plant growth regulator, has been widely applied as a racemic mixture in crop and fruit tree production. However, the enantioselective fate and effects of chiral paclobutrazol in the soil ecosystem are still unclear. In this study, systemic assessments of dissipation dynamics, transformation products (TPs) and pathways, and interactions between soil microorganisms and related metabolites are first carried out using suspect and nontarget screening, high-throughput sequencing, and soil metabolomics. The dissipation half-lives of R- and S-paclobutrazol were 30.7 and 40.7 d, and interconversion between the two enantiomers occurred in soils. Nine previously unreported TPs were identified, and one was synthesized and confirmed with an authentic standard. Aerobic degradation pathways of R- and S-enantiomers were proposed, showing enantioselective degradation. 16S rRNA and ITS sequencing results showed that both R- and S-enantiomers increased bacterial diversity but decreased fungal diversity and disrupted microbial symbiosis networks’ complexity. Chiral paclobutrazol enantioselectively and significantly changed the soil metabolite spectrum. Integrated analyses revealed a strong association between microorganisms and certain metabolite expressions. These findings indicate the importance of TP analysis, provide new insights into how soil microbes and metabolite profiles are affected by paclobutrazol enantiomers, and lay the foundation for conducting all-sided impact assessments.