Interactive effects of ozone and carbon dioxide on plant-pollinator interactions and yields in a legume crop

Abstract

• Increasing greenhouse gas emissions is linked to disruption of ecosystem services. • How ozone and carbon dioxide impact pollination services is not well understood. • We report on the effects of elevated ozone and carbon dioxide on field bean plants. • Elevated ozone reversed the positive effects of enhanced carbon dioxide on yield. Recent studies link increased levels of ozone and carbon dioxide to plant performance and plant-herbivore interactions, but the interactive effects on plant-pollinator interactions and ecosystem services have rarely been studied. Here we experimentally tested whether elevated levels of these two gases alter plant growth, flower visitation, and yield in field bean crop ( Vicia faba : Fabaceae or Leguminosae) using a full-factorial experimental set-up. Plants were exposed to (i) clean air (control), (ii) carbon dioxide-enriched (900 ppm), (iii) ozone-enriched (120 ppb) or (iv) carbon dioxide (900 ppm) + ozone (120 ppb) - enriched treatments. We examined how flower visitation by two widespread bee pollinators, Bombus terrestris and Osmia cornuta , and consequent yields responded to the treatments. Increased carbon dioxide levels enhanced flower visitation by B. terrestris and O. cornuta, while an increase in ozone led to a decline in visitation rates. The seed set of field beans generally increased with flower visitation rates of pollinators, revealing a pollination-mediated effect of the increased greenhouse gas concentrations on plant reproduction. In addition to the pollinator-mediated effect, we found an interactive effect of ozone and carbon dioxide on the seeds set in plants visited by B. terrestris: while increases in carbon dioxide enhanced seed set, increases in ozone generally decreased seed set - overruling the effect of increased carbon dioxide. Our results suggest that negative impacts of high ozone levels on flower visitation and fruit set counteract potential increases of legume crop yields with enhanced carbon dioxide concentrations under future climates.