Interspecific variation in resistance and tolerance to herbicide drift reveals potential consequences for plant community co-flowering interactions and structure at the agro-eco interface

Abstract

Background and Aims When plant communities are exposed to herbicide ‘drift’, wherein particles containing the active ingredient travel off-target, interspecific variation in resistance or tolerance may scale up to affect community dynamics. In turn, these alterations could threaten the diversity and stability of agro-ecosystems. We investigated the effects of herbicide drift on the growth and reproduction of 25 wild plant species to make predictions about the consequences of drift exposure on plant-plant interactions and the broader ecological community. Methods We exposed potted plants from species that commonly occur in agricultural areas to a drift-level dose of the widely used herbicide dicamba or a control solution in the glasshouse. We evaluated species-level variation in resistance and tolerance for vegetative and floral traits. We assessed community-level impacts of drift by comparing species evenness and flowering networks of glasshouse synthetic communities comprised of drift-exposed and control plants. Key Results Species varied significantly in resistance and tolerance to dicamba drift: some were negatively impacted while others showed overcompensatory responses. Species also differed in the way they deployed flowers over time following drift exposure. While drift had negligeable effects on community evenness based on vegetative biomass, it caused salient differences in the structure of coflowering networks within communities. Drift reduced the degree and intensity of flowering overlap among species, altered the composition of groups of species that were more likely to coflower with each other than with others, and shifted species roles (e.g., from dominant to inferior floral producers and vice versa). Conclusions These results demonstrate that even low levels of herbicide exposure can significantly alter plant growth and reproduction, particularly flowering phenology. If field-grown plants respond similarly, then these changes would likely impact plant-plant competitive dynamics and potentially plant-pollinator interactions occurring within plant communities at the agro-ecological interface.

Off-target drift of the herbicide dicamba disrupts plant-pollinator interactionsvianovel pathways

“…Thus, plants that experienced significant leaf damage following dicamba exposure also exhibited later flowering, which then led to a reduction in pollinator approaches. Our results confirm past work showing herbicide-induced delays in flowering and predicted shifts in flowering community (38, 43–46), yet significantly expands our understanding of how this delay in flowering can influence pollinator pool foraging behavior.…”

“…Unfortunately, dicamba, which mimics the natural plant hormone auxin, is known for its propensity to drift to nontarget areas (31), and in 2021 alone, there were 3,461 reports of dicamba drift from farmers and landowners (30). Although dicamba drift has the potential to negatively influence natural populations of plants and insects in agricultural landscapes, current studies of this dynamic revolve almost entirely around the impact of dicamba drift on crop yield (32)(33)(34)(35), such that only a handful of projects have examined the potential that dicamba drift may alter the availability of crucial resources to pollinating insects (20,(36)(37)(38). Thus, the consequences of dicamba drift to natural plant and insect communities-in light of the recent shift in the US to the herbicide dicamba for weed control-is both an understudied and highly consequential issue in agriculture.…”

“…The copyright holder for this preprint this version posted June 24, 2024. ; https://doi.org/10.1101/2024.06. 20.599889 doi: bioRxiv preprint reduce the total number of flowers produced (20,36,38). Strikingly, previous work has largely focused on the effect of dicamba drift using a single weed species (36), or by studying multiple weeds in greenhouse conditions (38).…”

“…20.599889 doi: bioRxiv preprint reduce the total number of flowers produced (20,36,38). Strikingly, previous work has largely focused on the effect of dicamba drift using a single weed species (36), or by studying multiple weeds in greenhouse conditions (38). There are currently no examinations of the effect of dicamba drift on plant-pollinator interactions set in realistic field settings and using multiple ecologically relevant weed species.…”

“…Currently, the available but limited work assessing the effects of dicamba exposure on natural, non-target plants demonstrates that low doses of the herbicide can delay flowering, reduce flowering duration, and reduce the total number of flowers produced (20, 36, 38). Strikingly, previous work has largely focused on the effect of dicamba drift using a single weed species (36), or by studying multiple weeds in greenhouse conditions (38). There are currently no examinations of the effect of dicamba drift on plant-pollinator interactions set in realistic field settings and using multiple ecologically relevant weed species.…”