Drought stress alters floral volatiles and reduces floral rewards, pollinator activity, and seed set in a global plant

Authors: Rering, Caitlin; Franco, Jose; Yeater, Kathleen; MALLINGER, RACHEL - University Of Florida

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2020
Publication Date: 9/21/2020
Publication URL: https://handle.nal.usda.gov/10113/7122460
Citation: Rering, C.C.; Franco Jr, J.G.; Yeater, K.M.; Mallinger, R.E. 2020. Drought stress alters floral volatiles and reduces floral rewards, pollinator activity, and seed set in a global plant. Ecosphere. 11:e03254. https://doi.org/10.1002/ecs2.3254.
DOI: https://doi.org/10.1002/ecs2.3254

Interpretive Summary: Droughts are expected to occur with greater frequency and severity in the future. Drought stress can have significant negative impacts on plant health, but its effects on flowers and pollinators is not well understood. Buckwheat, a flowering plant used as a crop, ground cover, and as forage for bees or cattle, was selected for study. ARS scientists at the Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, FL, in collaboration with University of Florida scientists and ARS scientists in North Dakota and the Plains Area tested whether floral traits like nectar volume, nectar sugar content, pollen quantity, and floral aroma were impacted by drought stress. We also evaluated whether pollinators (including honey bees, bumble bees and other floral visitors) discriminated between drought-stressed and well-watered plants and whether drought stress affected buckwheat yield. We found all floral traits we tested were changed by drought stress, except pollen quantity. Under drought stress, flowers had less nectar and the nectar contained a different concentration of sugars. Floral aroma was also changed under drought. Honey bees preferred to forage from well-watered plants relative to drought-stressed plants and drought-stressed plants produced fewer seeds. These results contribute to our understanding of the dramatic impacts droughts can have on pollinators and agricultural productivity.

Technical Abstract: • Climate change can disrupt plant-pollinator interactions through multiple mechanisms, including through changes to floral rewards and associated floral cues. These changes can affect pollinator attraction, plant pollination success, and pollinator fitness. • We examined the effects of drought on buckwheat (Fagopyrum esculentum Moensch), a widespread plant that is prone to drought stress, dependent on insect pollination, and increasingly utilized for pollinator conservation. We assessed effects of drought on nectar quantity and chemical composition, pollen quantity, relative abundance and chemical composition of floral volatile emissions, visitation rates by pollinators, and plant reproductive success. • Flowers on drought-stressed plants produced significantly less nectar with lower ratios of sucrose to hexose sugars, though pollen quantity was unaffected. Drought-stressed plants received significantly fewer visits by honey bees and flies though bumble bee visitation rates did not differ. While there was no significant difference in the quantity of total floral volatile emissions, volatile compositions differed, with drought-stressed plants having higher emissions of cis-3-hexenol and three aldehydes. Finally, drought stress reduced seed set both directly and indirectly via reduced pollinator visitation. • We show that drought can disrupt plant-pollinator interactions both by reducing floral rewards and altering floral volatile cues, with consequences for plant reproduction and floral resource availability.