Tropospheric Ozone Alters the Chemical Signal Emitted by an Emblematic Plant of the Mediterranean Region: The True Lavender (Lavandula angustifolia Mill.)

Candice Dubuisson,Martine Hossaert-Mckey,Magali Proffit,Florence Nicolè,Bruno Buatois

doi:10.3389/fevo.2022.795588

Abstract

Among air pollutants, tropospheric ozone (O3) is one of the most stressful for organisms due to its strong oxidative potential. For instance, high ozone concentration ([O3]) has the potential to affect (i) the emission of volatile organic compounds (VOCs) by plants and (ii) the lifetime of these VOCs in the atmosphere, and consequently disturb crucial signals in the interactions between plants and other organisms. However, despite the determinant role of VOCs emitted by flowers for pollinator attraction, a very limited number of studies have investigated the impact of O3 on floral VOCs. In this study, we investigated the effect of high [O3] episodes on the VOCs emitted by a flowering Mediterranean plant: the true lavender (Lavandula angustifolia Mill., Lamiaceae). To do so, in controlled conditions, we exposed (i) the entire plant to high but realistic [O3] (200 ppb for 5 h) and (ii) only the VOCs emitted by lavender to increasing [O3] (0, 40, 80, 120, and 200 ppb). We sampled VOCs of lavender in both conditions and analyzed them by Gas Chromatography-Mass Spectrometry in order to qualify and quantify the flowering lavender’s emissions and the reaction of VOCs with O3 in the atmosphere. Our results showed that exposure to high [O3] during a short period (5 h) did not affect the emission of VOCs by flowering lavender. Incidentally, we also showed that the chemical signal varied in quantities and proportions over the day. Moreover, we showed that after their emission by the plant, composition of the VOCs changed quantitatively and qualitatively in an atmosphere containing [O3] naturally observed nowadays. Quantities of several of the major terpenes emitted by lavender decreased drastically during O3 exposure, whereas concentrations of some VOCs increased, such as carbonyls and carboxylic acids, which are probably reaction products of terpenes with O3. Exposure to high [O3] thus directly affected the proportions of VOCs in the atmosphere. Because pollinators generally use a blend of VOCs in particular proportions as a signal to localize flowers, the numerous pollinators of lavender may experience difficulty in recognizing specific floral odors during frequent and moderate [O3] episodes in the Mediterranean region.

Highlights

Since the beginning of the industrial era, anthropic activities have impacted ecosystems and their functioning (Barnosky et al, 2012)
In the volatile emission of flowering lavender, we detected a total of 34 volatile organic compounds (VOCs), seven of which were present only as traces
“Diva” (Héral et al, 2021), except that we found a smaller number of compounds. This might be explained by the fact that in all these studies headspace collection of flowering lavender VOCs was performed immediately, or at least shortly after enclosure of the inflorescences, or VOCs were sampled in liquid extractions, thereby including some other compounds stored in the plant but not emitted by flowers (Ormeño et al, 2011)

Summary

Introduction

Since the beginning of the industrial era, anthropic activities have impacted ecosystems and their functioning (Barnosky et al, 2012). Atmospheric pollution consists in increased concentrations of primary pollutants, such as carbon dioxide or nitrogen oxides (NOx), released mainly by industry and agriculture These pollutants are involved in complex chemical reactions in the troposphere that lead to the formation of secondary pollutants (Jenkin and Clemitshaw, 2000). The target value is set to 18,000 μg m−3 h−1 (900 ppb) of AOT40 (Accumulated Ozone over a Threshold of 40 ppb between 8:00 and 20:00 from April to August) in order to prevent physical and physiological injuries These thresholds do not take into account the effect of O3 on other characteristics of plants, such as the emission of volatile organic compounds (VOCs). Compared to plant-herbivore interactions, studies of the effect of O3 on signal recognition in plant-pollinator interactions are limited

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