Olfactory pollution in the anthropocene: The impact of atmospheric NOx and ozone pollution on plant-pollinator interactions

Abstract

Olfaction is the oldest sense, and olfactory navigation is important for many animals. Air pollution from human activity has been shown to disrupt olfactory navigation, though we have only recently started investigating these impacts, and the mechanisms and scope of these disruptions remain largely unknown. We focused on the impacts of atmospheric ozone and nitrate radicals (hereafter ‘oxidants’) from air pollution on floral scent transmission, and how it affects pollinator behavior in the field. To study the impact of the oxidants on floral scent signals, we first developed an electrospray ionization source for a high-resolution time-of-flight mass spectrometer (HR-TOFMS). This ionization source is able to measure chemicals in the atmosphere with high sensitivity and time resolution by generating a variety of reagent ion species. We used the Oenothera pallida – Hyles lineata / Manduca sexta plant-pollinator system to study how oxidants affect O. pallida hawkmoth visitation by impacting floral scent transmission. We performed pollinator observations and pollinator exclusion treatments to determine that hawkmoths are important pollinators of O. pallida. Then we collected and analyzed floral scent samples from O. pallida flowers and measured the antennographic responses of the hawkmoths Hyles lineata and Manduca sexta to the floral scent. We then produced an odor blend of antennographically active chemicals representing the most salient scent signals from the flowers to the hawkmoths. Then, we determined how oxidants from nocturnal air pollution degrade these floral scent signals, and what the behavioral impacts of this scent degradation on hawkmoth pollinator visitation behavior was in the field. Finally, we modeled the global impacts of such scent degradation on pollinator scent navigation using the reaction rates and global oxidant distributions from the GEOS-Chem global chemical model under simulated present day and pre-industrial conditions. We found that atmospheric oxidants impact hawkmoth visitation rates to floral odor sources by degrading the monoterpene component of the odor. The model results show that under current global concentrations of oxidants, nitrate radicals degrade most floral volatiles significantly more than ozone does, and that many major cities have had scent recognition distances reduced by more than 70% compared to pre-industrial times.