Damage and recovery from drift of synthetic-auxin herbicide dicamba depends on concentration and varies among floral, vegetative, and lifetime traits in rapid cycling Brassica rapa

Herbicides can drift from intended plants onto non-target species. It remains unclear how drift impacts plant functional traits that are important for fitness. To address this gap, we conducted an experiment where fast cy-cling Brassica rapa plants were exposed to one of three drift concentrations (0.5%, 1%, 10%) of synthetic-auxin di-camba. We evaluated damage to and capacity of floral and vegetative traits to recover as well as lifetime fitness by comparing treated plants to controls. Response to dicamba exposure was concentration-dependent across all traits but varied with trait type. At 0.5% dicamba, three out of five floral traits were affected, while at 1% dicamba, four floral traits and one out of two vegetative traits were negatively impacted. At 10% dicamba all floral and veg-etative traits were stunted. Overall, floral traits were more responsive to all dicamba drift concentrations than vegetative traits and displayed a wide range of variation ranging from no response (e.g., pistil length) to up to 84% reduction (ovule number). However, despite floral traits were more affected across the dicamba drift con-centrations they were also more likely to recover than the vegetative traits. There was also variation among life-time traits; the onset of flowering was delayed, and reproductive fitness was negatively affected in a concentration-dependent manner, but the final biomass and total flower production were not affected. Alto-gether, we show substantial variation across plant traits in their response to dicamba and conclude that account-ing for this variation is essential to understand the full impact of herbicide drift on plants and the ecological interactions these traits mediate . (c) 2021 Published by Elsevier B.V.

Automated summary

There is substantial variation in plant traits' response to herbicide drift, with floral traits being more responsive and more likely to recover compared to vegetative traits, which are more affected at higher drift concentrations. Lifetime traits such as flowering onset and reproductive fitness are negatively affected in a concentration-dependent manner, while biomass and total flower production remain unaffected. Understanding and accounting for this variation is essential to fully grasp the impact of herbicide drift on plants and the ecological interactions these traits mediate.