natural fragrances

The scents of nature threatened by human activity and climate change

Human activity poses risks that have not yet been properly assessed to these complex communication networks that are the odours of nature. Agricultural processing industries, agricultural activities and livestock breeding produce large quantities of volatile organic compounds that mix with natural sources. To make matters worse, global climate change itself affects the metabolisms of plants, which react by qualitatively and quantitatively modifying their emissions. We can expect the olfactory landscapes to change profoundly in the coming decades.
Uny walk in the wilderness is often accompanied by an olfactory experience. The earthy smell of humus in a deciduous forest, the rich scents of the garrigue exacerbated by the sun, the scent of a coniferous hedge, are all fragrant landscapes that we can easily identify. A walk in the open air allows us to "breathe", that is to say, to take a breath of that vital oxygen that we cannot smell, and to feel a sense of relief by perceiving plant smells that evoke pleasant memories. In short, it offers us the opportunity to "breathe" away from the hustle and bustle of the cities.

Many of the volatile organic compounds that are the source of this sensory experience are emitted by terrestrial plants. Flowers or vegetative organs of the plants around us release molecules of a very wide chemical diversity into the air we breathe in. But why does terrestrial vegetation produce this rich variety of small molecules?

Plants know how to defend themselves

First of all, they are defence mechanisms that enable the plant to resist the many stresses or aggressions it faces, especially when it is short of water or sick. The plant can produce these volatile compounds in a constitutive way, and they are then stored in structures such as the trichomesThese glandular hairs will be easily released to repel herbivores or even intoxicate them.

In April, the flowering of tree heather dominates the olfactory landscape of the Héric gorges in the Hérault. Michel Renou, Author provided

Their biosynthesis can also be triggered by an injury such as an insect bite. They induce other parts of the plant to produce defensive substances such as phytoalexinsIt is made up of a number of different molecules, such as antimicrobial or anti-fungal molecules, which enable it to resist attack by a pathogenic organism or herbivore. Emitted into the atmosphere, these signals are perceived by other plants, which in turn produce defence molecules.

When plants communicate

These communication functions are also important in the positive interactions between the plant and its pollinating insects. Floral aromas attract a cohort of insects, bees, bumblebees, flies, beetles, or even mosquitoes that associate the smell with the presence of nectar. The ripe fruit releases compounds that are attractive to animals, which after eating the fruit will disperse their seeds.

Exchanges of chemical signals are therefore of great importance in the functioning of ecosystems. The result of a very long co-evolution, particularly between higher plants and insects, they modulate essential plant functions such as pollination. They also help to limit herbivore populations by attracting their predators and parasites. Complex communication networks are established between the different trophic levels.

Why not enjoy unlimited reading of UP'? Subscribe from €1.90 per week.

The attack of a caterpillar induces the emission of volatile molecules that affect the butterfly's egg-laying behaviour but attract parasites that lay eggs in the caterpillar. These signals are often mixtures of volatile compounds whose proportions ensure the specificity of this communication. An insect parasite can thus recognize which species of butterfly has attacked the plant. Insect responses are often dependent on the scent context in which they perceive the signal. An orchid flower can mimic the sexual signal of a pollinator to ensure the specificity of its pollination.

Human activity creates interference

Human activity is putting these complex communication networks at risk, but the risks are still poorly assessed. Agricultural processing industries, agricultural activities and livestock breeding produce large quantities of volatile organic compounds that mix with natural sources. The sensory impact of these emissions has long been known to us when they are the source of odour nuisances such as manure spreading or local composting. However, the study of the impact on the functioning of ecosystems has only just begun.

Smell, an essential sense of communication for insects (Asian hornet's head). Michel Renou, Author provided

Volatile organic compounds are naturally degraded in the atmosphere by UV radiation. However, the increase in concentrations of ozone or other reactive groups such as nitrogen monoxide caused by industrial activities or transport significantly reduces their lifetime in the atmosphere. reduces at the same time the distances at which foraging insects can detect floral aromas. But it also modifies the composition of the flowers because all their constituents are not degraded at the same speed, their proportions are no longer the same and the odorous mixture changes in nature, as shown by the bee tests.

Direct effects of pollutants on insect olfaction are also likely because olfactory communication appears particularly sensitive to the interactions between volatile molecules present in the air. in the smelly background.

Towards a modification of olfactory landscapes?

In addition to these pollutants, global climate change, including increases in CO2 and temperature rises, itself affects the metabolisms of the reacting plants by qualitatively and quantitatively modifying their emissions. We can expect the olfactory landscape to change profoundly in the coming decades. While the development of chemical ecology has enabled us to unlock the secrets of olfactory communication, we are still far from being able to assess the overall importance of these olfactory landscapes on biodiversity and the consequences of their alteration. Through a leverage effect, any change in signals essential to the location of a vital resource, or to the synchronization of the cycles of two species, can have significant repercussions on animal populations or plant communities.

The impacts will be all the more important on specialist species that use very specific signals to locate their host. We should therefore question the need to take into account the sensory dimension in biodiversity management programmes. Our data in this area are very recent, with analyses dating back only a few decades. It would therefore be urgent to take stock of the state of fragrant landscapes, monitor their evolution, assess the risks represented by each type of disturbance, and then look for methods to preserve their important components.

We're already trying to remedy the nuisance emissions from composting platforms or livestock buildings by emitting masking odours or by surrounding hedgerow sites that create turbulence that dilutes the emissions and directs them higher into the atmosphere.

In addition to the sensory loss that we would feel during a walk in the forest that has become odourless, the impact could be significant for insect populations already weakened by multiple stresses and plant communities deprived of their means of communication.

To fight against disinformation and to favour analyses that decipher the news, join the circle of UP' subscribers.

Michel RenouDirector of Research in Insect Biology, Inra

This article is republished from The ConversationUP' Magazine's editorial partner. Read theoriginal paper

Anything to add? Say it as a comment.The Conversation


Nous avons un message pour vous…

Dès sa création, il y a plus de dix ans,  nous avons pris l’engagement que UP’ Magazine accordera au dérèglement climatique, à l’extinction des espèces sauvages, à la pollution, à la qualité de notre alimentation et à la transition écologique l’attention et l’importance urgentes que ces défis exigent. Cet engagement s’est traduit, en 2020, par le partenariat de UP’ Magazine avec Covering Climate Now, une collaboration mondiale de 300 médias sélectionnés pour renforcer la couverture journalistique des enjeux climatiques. En septembre 2022, UP’ Magazine a adhéré à la Charte pour un journalisme à la hauteur de l’urgence écologique.

Nous promettons de vous tenir informés des mesures que nous prenons pour nous responsabiliser à ce moment décisif de notre vie. La désinformation sur le climat étant monnaie courante, et jamais plus dangereuse qu’aujourd’hui, il est essentiel que UP’ Magazine publie des rapports précis et relaye des informations faisant autorité – et nous ne resterons pas silencieux.

Notre indépendance éditoriale signifie que nous sommes libres d’enquêter et de contester l’inaction de ceux qui sont au pouvoir. Nous informerons nos lecteurs des menaces qui pèsent sur l’environnement en nous fondant sur des faits scientifiques et non sur des intérêts commerciaux ou politiques. Et nous avons apporté plusieurs modifications importantes à notre expression éditoriale pour que le langage que nous utilisons reflète fidèlement, mais sans catastrophisme, l’urgence écologique.

UP’ Magazine estime que les problèmes auxquels nous sommes confrontés dans le cadre de la crise climatique sont systémiques et qu’un changement sociétal fondamental est nécessaire. Nous continuerons à rendre compte des efforts des individus et des communautés du monde entier qui prennent courageusement position pour les générations futures et la préservation de la vie humaine sur terre. Nous voulons que leurs histoires inspirent l’espoir.

Nous espérons que vous envisagerez de nous soutenir aujourd’hui. Nous avons besoin de votre soutien pour continuer à offrir un journalisme de qualité, ouvert et indépendant. Chaque abonnement des lecteurs, quelle que soit sa taille, est précieux. Soutenez UP’ Magazine à partir d’1.90 € par semaine seulement – et cela ne prend qu’une minute. Merci de votre soutien.

Je m’abonne →

Inline Feedbacks
View all comments
coal-fired power plants
Previous article

All is not well: carbon emissions are breaking world records

nuclear waste
Next article

Nuclear waste: what legacy for future generations?

Latest articles from Biodiversity



Already registered? I'm connecting

Inscrivez-vous et lisez three articles for free. Recevez aussi notre newsletter pour être informé des dernières infos publiées.

→ Register for free to continue reading.



You have received 3 free articles to discover UP'.

Enjoy unlimited access to our content!

From $1.99 per week only.