Floral Scents in Bee-Pollinated Buckwheat and Oilseed Rape under a Global Warming Scenario

Simple Summary Global warming is expected to impact the communication between flowering plants and their pollinators. We aimed to test how increased temperatures affect the chemical signaling between two important crop species (buckwheat, Fagopyrum esculentum; oilseed rape, Brassica napus) and their bee pollinators (Apis mellifera, Bombus terrestris). Floral scent analyses showed that buckwheat was affected by increased temperatures, whereas in oilseed rape, both total scent emission and scent composition were independent of temperature. The floral scent of oilseed rape was dominated by p-anisaldehyde and linalool at both temperatures tested. Buckwheat emitted threefold less floral scent and a different composition at warmer temperatures. Some compounds, among them linalool and indole, were only released from buckwheat plants cultivated at optimum temperatures but not from plants cultivated at warmer temperatures; however, 2- and 3-methylbutanoic acid were the most abundant compounds at both temperature regimes. The bees detected many floral scent compounds of buckwheat in electroantennographic analyses, among them compounds that disappeared at warmer temperatures. Our study highlights that oilseed rape is more heat tolerant and resilient than buckwheat and that the temperature-induced scent changes in buckwheat affect the olfactory perception of the flowers by bees. Many wild plants and crops are pollinated by insects, which often use floral scents to locate their host plants. The production and emission of floral scents are temperature-dependent; however, little is known about how global warming affects scent emissions and the attraction of pollinators. We used a combination of chemical analytical and electrophysiological approaches to quantify the influence of a global warming scenario (+5 degrees C in this century) on the floral scent emissions of two important crop species, i.e., buckwheat (Fagopyrum esculentum) and oilseed rape (Brassica napus), and to test whether compounds that are potentially different between the treatments can be detected by their bee pollinators (Apis mellifera and Bombus terrestris). We found that only buckwheat was affected by increased temperatures. Independent of temperature, the scent of oilseed rape was dominated by p-anisaldehyde and linalool, with no differences in relative scent composition and the total amount of scent. Buckwheat emitted 2.4 ng of scent per flower and hour at optimal temperatures, dominated by 2- and 3-methylbutanoic acid (46%) and linalool (10%), and at warmer temperatures threefold less scent (0.7 ng/flower/hour), with increased contributions of 2- and 3-methylbutanoic acid (73%) to the total scent and linalool and other compounds being absent. The antennae of the pollinators responded to various buckwheat floral scent compounds, among them compounds that disappeared at increased temperatures or were affected in their (relative) amounts. Our results highlight that increased temperatures differentially affect floral scent emissions of crop plants and that, in buckwheat, the temperature-induced changes in floral scent emissions affect the olfactory perception of the flowers by bees. Future studies should test whether these differences in olfactory perception translate into different attractiveness of buckwheat flowers to bees.