Volatile organic compounds emitted by vegetation, also called biogenic volatile organic compounds (BVOC), are a diverse set of chemical molecules with a wide range of functions from plant ecology to being key constraints of the physical and chemical properties of the atmosphere and climate. An estimated amount of 500 to 1000 Tg C is emitted annually from terrestrial vegetation, dominated by isoprenoids and methanol. The emission by oceans and aquatic vegetation is much less defined, but very low according to current estimates.
From an ecological point of view, BVOC mediate vital organism functions and interactions. They are emerging as one of the most important traits of plant communication with other organisms, and as a fundamental defence of plants against abiotic and biotic stress. Pioneering research has shown that tiny emissions of BVOC at the leaf level are able to attract or deter herbivorous arthropods and their parasitoids or predators. Using such emissions, plants attacked by herbivorous insects “call for help” attracting carnivorous insects to control herbivorous species. From an evolutionary point of view, insect parasitoids and arthropod predators have been progressively selected to learn how to respond to signalling cues released by their herbivorous preys and host plants.
Generally, constitutive expression of resistant traits in plants is accompanied by fitness costs when insect pests are absent. Therefore, plants can also start to express defences when being attacked by herbivores. However, costs of such attack-induced responses may be influenced by environmental conditions, and by the presence of competitors and/or natural enemies of herbivorous arthropods.
Some BVOC also are powerful antioxidants and protect plants from abiotic stress. BVOC are able to strengthen cellular membranes and scavenge substantial amounts of reactive oxygen compounds, thereby reducing oxidative damage to sensitive plant organelles and structures. Moreover, BVOC may play a signalling role in activating plant biochemical pathways. As an example, the isoprene-induced biosynthesis of other molecules signalling programmed plant cell death has been recently demonstrated.
In addition to local ecological effects of BVOC emissions on plants and ecological interactions in the ecosystem, once emitted in the atmosphere, BVOC also significantly influence the atmospheric chemistry and the climate. BVOC are chief precursors of the photochemical O3 production in the troposphere, where O3 acts as a potent greenhouse gas. At current concentrations, the O3 radiative forcing potential is of near-equal magnitude to that of methane, making it the third largest contributor to anthropogenic warming. O3 is also a toxic pollutant that not only significantly reduces crop and forestry yield worldwide, but also reduces the carbon sink strength of the terrestrial atmosphere. Low-volatility atmospheric oxidation products of BVOC contribute to the growth of secondary organic aerosol (SOA) particles that are climatically important through scattering and absorbing solar and thermal radiation, and by acting as cloud condensation nuclei (CCN), thereby affecting cloud properties and precipitation. Finally, BVOC emissions have been proposed to play a central role in trends of glacial-interglacial atmospheric methane concentrations and thus to contribute to climate changes over the Holocene.
The overall objective of EUROVOL will be to understand the roles of biogenic volatiles in the food-web and in plant interactions with the environment under current and future climate, and changes of land cover. In particular, the following specific goals are to be achieved:
(i) to elucidate internal (molecular, genetic, biochemical, phenological) control of (constitutive and induced) BVOC synthesis and emission;
(ii) to provide detailed knowledge on the abiotic and biotic (external) controls of BVOC emission;
(iii) to enhance mechanistic understanding of BVOC functional roles (e.g. priming, signalling) in plants coping with stresses;
(iv) to characterize the cross-talk of BVOC formation with other key biochemical pathways of synthesis of non-volatile compounds involved in stress response/defence (costs / benefits);
(v) to understand the impact of climate change on BVOC-mediated interactions of plants with biotic and abiotic stresses, and the associated consequences on plant defence mechanisms;
(vi) to understand how plants communicate within the trophic web (induced emissions), also, consequentially,
(vii) to unravel evolutionary mechanisms that shape the ecological and behavioural features of natural enemies of plants and herbivores and the overall community structure;
(viii) to control target pest species that damage plants (task also including other applications; e.g. BVOCs as stress indicators); and
(ix) to estimate regional and global BVOC emission patterns in past, present and
projected future climates, also assessing consequences of vegetation distribution (land use change) on BVOC spectrum/load, and feedbacks on ecosystem functions and services.