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

**Background:** Many crops depend on insect pollination, and floral scents are critical for attracting bee pollinators. Global warming is predicted to increase mean surface temperatures by up to 5°C this century (SSP-8.5 scenario), but little is known about how this will affect floral scent emissions and pollinator attraction in crop species. This study investigated the impact of increased temperatures on floral scent in two economically important crops—buckwheat (Fagopyrum esculentum) and oilseed rape (Brassica napus)—and whether temperature-induced changes affect olfactory detection by honeybees (Apis mellifera) and bumblebees (Bombus terrestris).

**Methods:** Plants were cultivated in growth chambers under two temperature regimes: optimal (buckwheat: mean 22°C, 26°C day/16°C night; oilseed rape: mean 20°C, 23°C day/13°C night) and warmer (+5°C; buckwheat: mean 27°C, 31°C day/21°C night; oilseed rape: mean 25°C, 28°C day/18°C night). Floral scents were collected via dynamic headspace sampling from inflorescences at first-day anthesis and analyzed by GC/MS. For buckwheat, 11 individuals were sampled in the optimum scenario and 7 in the warmer scenario; for oilseed rape, 7 and 6 individuals, respectively. Total scent amount per flower was compared using Mann-Whitney U tests, and scent composition using PERMANOVA and NMDS. A synthetic mixture of 12 buckwheat compounds (covering 94% and 100% of total scent in optimum and warmer scenarios, respectively) was tested on antennae of A. mellifera (N=5) and B. terrestris (N=12) using GC/EAD to identify physiologically active compounds.

**Key Results:** Buckwheat emitted 2.38 ± 0.39 ng/flower/hour at optimal temperatures but only 0.71 ± 0.28 ng/flower/hour at warmer temperatures—a threefold reduction (Z = −2.89, N = 18, p = 0.004). Scent composition also differed significantly (Pseudo-F₁,₁₇ = 7.19, p = 0.0001). At optimal temperatures, buckwheat scent was dominated by 2- and 3-methylbutanoic acid (46% combined) and linalool (10%). At warmer temperatures, 2- and 3-methylbutanoic acid increased to 73% of total scent, while linalool and several other compounds (indole, terpinene-4-ol, phenylacetonitrile, pentanoic acid, among others) were absent. Overall, 23 VOCs were detected in buckwheat at optimal temperatures versus only 11 at warmer temperatures. In contrast, oilseed rape showed no significant differences between temperature scenarios in total scent amount (optimum: 0.29 ± 0.11 ng/flower/hour; warmer: 0.57 ± 0.28 ng/flower/hour; Z = −0.93, N = 13, p = 0.353) or scent composition (Pseudo-F₁,₁₂ = 0.62, p = 0.729). Oilseed rape scent was consistently dominated by p-anisaldehyde and linalool at both temperatures. Of the 12 buckwheat compounds tested via GC/EAD, 11 elicited antennal responses in both bee species, including linalool, indole, 2- and 3-methylbutanoic acid, and butanoic acid. Only sabinene did not elicit a response. Notably, bees could detect compounds that disappeared or were reduced at warmer temperatures.

**Clinical Implications:** This study demonstrates that crop species differ markedly in their thermal resilience regarding floral chemical signaling. Buckwheat is vulnerable to warming-induced disruption of olfactory cues, with reduced scent emission and loss of key attractant compounds that bees can detect. This could reduce pollinator attraction and negatively impact yield, as buckwheat pollination is highly insect-dependent. Oilseed rape appears more resilient, with stable scent emissions under warming, though it may be more sensitive to other stressors like drought and ozone. These findings have implications for agricultural planning under climate change, suggesting that heat-tolerant crop varieties or supplemental pollination strategies may be needed for vulnerable species like buckwheat. Future studies should test whether the observed electrophysiological differences translate into behavioral changes and reduced pollinator visitation in the field.