Floral scents are formed by a complex mixture of Volatile Organic Compounds (VOCs) which play major roles in mediating encounter with partners in plant-pollinator interactions. Hence, VOC temporal patterns may be regulated to respond to both pollinator’s activity and pollination status. In the nursery pollination mutualism between the dioecious fig tree, Ficus carica, and its exclusive pollinator the fig wasp, Blastophaga psenes, it has been reported that VOCs emitted by receptive figs mediate species-specific interaction and that a combination of four VOCs - benzyl alcohol, (S)-linalool, (Z)-linalool oxide (furanoid) and (E)-linalool oxide (furanoid) - are responsible for pollinator attraction. However, the temporal pattern of their emissions during the day has never been studied. Previous studies on floral scents have mostly relied on offline collection methods that provide only discrete snapshots of emission rates. To bridge this gap and capture the continuous ‘pulse’ of floral signaling, we employed real-time Proton-Transfer-Reaction Time-of-Flight Mass Spectrometry (PTR-TOF-MS). This high-resolution approach allows us to characterize, for the first time, the fine-scale diurnal kinetics of VOC emissions in the F. carica nursery pollination system and to assess how these signals withstand natural environmental fluctuations. In addition, we estimated the influence of light intensity and temperature on these emissions under semi-natural conditions, based on simultaneous measurements and statistical modeling. Emissions of VOCs from flowering trees followed a diurnal pattern with a peak at midday, corresponding to the period when the pollinator is most active, with very conserved proportions of VOCs attractive to pollinators around this peak. Our results indicate that VOC emissions exhibited a diurnal rhythm closely associated with the natural fluctuation of temperature and light. While the conditions used in our studies did not allow us to disentangle the effects of these two factors, our analyses suggest nonlinear relationships between these factors and the emissions of compounds attractive to pollinators. Further experimental studies are needed on F. carica, as well as on other species, to better assess how light intensity and temperature drive floral VOC emissions.

Biogenic volatile organic compounds (BVOCs) play numerous ecological functions as they account for organism defenses and are drivers of organic matter decomposition, organism development and trophic interactions. BVOCs also act as precursors of secondary organic pollutants. Thus, studying their variability according to climate change is of crucial importance. This research aimed to assess the variability of BVOC emissions from natural forest soil under both natural drought (ND) and amplified drought (AD, 30

Biogenic volatile organic compounds (BVOCs) are produced by marine organisms but remain largely understudied in seagrasses. To address this gap, this study investigates BVOC profiles from Cymodocea nodosa across seasons and between two ecosystem types: open-sea sites (Antibes, Saint Tropez, Porto Vecchio) and coastal lagoons (Thau, Urbino, Carteau). BVOCs were collected using headspace solid-phase microextraction (HS-SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 171 compounds were identified (145 in summer, 117 in spring, 115 in winter, and 103 in autumn). Volatilome composition varied significantly with season, explaining 26.1% of the explained variance, followed by site differences (14.1%), while ecosystem type had minor effects (< 5%). Functional diversity indices supported these patterns, indicating higher richness and abundance in summer, including 31 volatile compounds solely detected in summer. Cymodocea nodosa exhibited stress-related profiles, with geranyl acetone, β-cyclocitral, β-ionone, dimethylsulfide (DMS), and dihydroactinidiolide positively correlating with light, temperature, and salinity. Molecular networking showed the highest metabolite diversity and abundance in Urbino, including additional terpenoids and chlorinated and nitrogen-containing compounds. These findings highlight a haline- and heat-responsive phenotype and demonstrate strong seasonal and spatial variability in C. nodosa BVOC profiles, suggesting the presence of distinct Mediterranean site-specific chemical signature requiring further integrative metabolomic and genetic investigation.

Biogenic volatile organic compounds (BVOCs) are crucial for ecosystem functioning, atmospheric chemistry and climate. While modulation of BVOC emissions from living vegetation with biotic and abiotic factors is well documented, how these factors drive soil BVOC emissions remain less understood, particularly in Mediterranean forests. To fill this gap, this pioneer study investigates whether BVOC fluxes from natural soil covered by litter (referred to as forest soil) vary under natural and amplified long-term water stress (35% annual rain exclusion over the past 10 years) in a deciduous oak Mediterranean forest ( Quercus pubescens Willd.) compared to natural climate conditions. This aim has only been tackled in a single evergreen Mediterranean forest so far. Using proton transfer reaction time of flight mass spectrometer (PTR-ToF-MS) we also provide, for the first time, a detailed diurnal cycle of soil BVOCs in relation to air temperature, air humidity, and biotic factors including soil respiration and litter content in lignin, cellulose and hemicellulose. The main results revealed that forest soil represents a source of most BVOCs (e.g., acetaldehyde, acetone, acrolein, hexanol, monoterpenes) with maximum values at mid-day (42 mu gC.m- 2 . h- 1 ) in response to higher temperatures while it acts as a clear sink of isoprene. Total soil BVOC emission rates, together with soil respiration, decreased by 43% after a decade of partial rain restriction. These results will contribute to enhance further modeling of soil BVOC emissions under various climate scenarios both at regional and global scales.

Background - aims It is widely assumed that plant flammability in the Mediterranean region peaks during the summer fire season. We currently lack data that could evaluate these assumptions and have not assessed the mechanisms, e.g. fuel moisture content (FMC) or terpenes, that might drive these patterns.Methods To determine the mechanistic drivers of species flammability, we used leaf burning experiments coupled with foliar chemical analyses focusing on Aleppo pine (Pinus halepensis) and three introduced cypresses commonly found at the wildland-urban interface (WUI) in southeastern France.Key results Terpenes, FMC and flammability varied over time and across the species studied, with contrasting patterns for each. Rare correlations between FMC and flammability occurred, in only one season and differing among species, while correlations between flammability and terpene compounds were diverse. The best flammability drivers were terpenes (mainly diterpenes), often changing among and within seasons, and their effect on flammability also differed. Overall, FMC was not a significant explanatory parameter of leaf flammability.Conclusions - implications Highlighting the temporal variation between flammability and its drivers revealed that species flammability could also be enhanced by terpenes outside the fire season; this should be accounted for in fire prevention, especially at the WUI.

Abstract. Soil biogenic volatile organic compound (BVOC) emissions have been studied in different biomes, showing that their emissions are not negligible. However, previous studies have so far neglected the role of litter accumulation on soil BVOC fluxes, and most of them refer to coniferous and evergreen forests, while litter emissions from Mediterranean deciduous forests remain poorly explored. To fill these gaps, the present work aimed to study BVOC fluxes in a Mediterranean deciduous forest, with a particular attention to the relationship between soil BVOC fluxes and litter biomass accumulation on soils. Measurements were performed in southern France, in the downy oak (Quercus pubescens Willd.) forest of the Observatoire de Haute Provence (O3HP), during the late spring of 2023, using dynamic chambers coupled to an on-line PTR-ToF-MS. We investigated in-situ daily BVOC fluxes from soil alone and different litter biomasses mimicking low, current, high, and very high litter production, respectively, as both decreases and increases of litter accumulation are expected in the Mediterranean region under the current context of climate change and greening management policies. The results showed a high BVOC diversity with more than 135 emitted compounds. For a large majority of the measured compounds, the BVOC fluxes were negative, suggesting that soil (bare soil covered by litter) uptakes compounds through biochemical and/or physical processes. Some compounds, such as acetone, methanol or sesquiterpenes, increased with increasing litter biomass, suggesting the importance of considering litter accumulation when assessing soil BVOC emissions from Mediterranean deciduous forests. Microbial abundance was highlighted as a potential driver of this relation between litter biomass and VOC fluxes.

Biogenic Volatile Organic Compounds (BVOCs) play crucial roles in terrestrial environments, acting as defense compounds against environmental stresses and as chemical cues in species interactions. These roles were mainly highlighted on terrestrial plants whereas marine BVOCs are still understudied except dimethyl sufide (DMS) or isoprene. However, recent research highlights that marine organisms, particularly phytoplankton, and to a lesser extent benthic organisms such as macroalgae, seagrasses, and corals, also produce and emit a larger panel of BVOCs. In this review, we compiled and analyzed articles focusing on BVOCs production and emission by benthic photosynthetic organisms. Our review synthesizes current knowledge on the BVOCs produced or emitted by these species, categorized by compounds classes, geographic location and sampling methods. This synthesis provides a preliminary overview of the chemical diversity among benthic organisms, indicating rich and varied BVOCs profiles that warrants further investigation. Furthermore, we explore the potential physiological and ecological roles of BVOCs in benthic ecosystems, discussing their implications for environmental stress responses and interspecies communication. This review underscores the need for more comprehensive studies to fully understand the ecological significance and chemical complexity of BVOCs in benthic environments.

Biological invasions are one of the major threats to ecosystem services and biodiversity. Thus, it is crucial to understand the mechanisms involved in the invasion success of alien species. In addition to generalist traits and high tolerance that enable persistence in novel environments, invasive species can use volatile chemical compounds from specialized metabolism [biogenic volatile organic compounds (BVOCs)] to compete with native species, a process known as allelopathy. These compounds could contribute to invasions in marine environments, and the associated mechanisms need to be deciphered. The aim of this study was to characterize the volatilome (i.e., all BVOCs produced by a species) of two Caribbean native seagrass species (Syringodium filiforme and Thalassia testudinum) and one invasive (Halophila stipulacea). For that purpose, leaf samples were collected, and BVOCs were trapped through headspace solid-phase microextraction followed by analyses in GC-MS. H. stipulacea’s volatilome was significantly different from the two native species, with the presence of compounds showing, in literature, allelochemical properties (e.g., geranyl acetone, 6-methyl, 5-hepten-2-one, and cyclohexane isothiocyanate). We hypothesized that these compounds could be “novel weapons” to enhance the invasion success of H. stipulacea, but it needs further investigations in the laboratory (e.g., mesocosms) as well as in situ.

Biogenic Volatile Organic Compounds (BVOCs) are important precursors of tropospheric atmospheric pollutants such as ozone and secondary organic aerosols. Thus, it is crucial to characterize BVOCs sources at regional and global scales. Marine environments, especially benthic ecosystems, are still overlooked although they can produce a wide range of BVOCs. In this study, BVOCs emissions from Posidonia oceanica, the main seagrass species in the Mediterranean Sea, were characterised over several days using dynamic enclosure systems. A total of 105 different compounds were detected through PTR-ToF-MS and GC-MS analyses (after checking compounds correspondence between both analyses) and included terpenoids (isoprene), sulfur- (dimethyl sulfide (DMS)), halogenenated- (chloromethane), and oxygenated compounds (methanol, acetone). High BVOCs emissions were measured (up to 10 and 4 μg.gDW-1.h-1 for DMS and acetone, respectively), in the same ranges reported for terrestrial plant species. Most BVOCs followed diurnal cycles with higher emissions during the day compared to night, although nocturnal emissions were also detected. Surprisingly, DMS emissions showed an opposite pattern with higher emissions at night. Uptakes were recorded for formic acid all through the day, at night for acetonitrile and only punctually for most other BVOCs. Our results strongly suggest that P. oceanica meadows are important contributors to the regional BVOCs budget in the Mediterranean basin.

Background/Objectives: Biogenic volatile organic compounds (BVOCs), extensively studied in terrestrial plants with global emissions around 1 PgC yr-1, are also produced by marine organisms. However, benthic species, especially seagrasses, are understudied despite their global distribution (177,000-600,000 km2). This study aims to examine BVOC emissions from key Mediterranean seagrass species (Cymodocea nodosa, Posidonia oceanica, Zostera noltei, and Zostera marina) in marine and coastal lagoon environments. Methods: BVOCs were collected using headspace solid-phase microextraction (HS-SPME) using divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fibers and analyzed by gas chromatography-mass spectrometry (GC-MS). Results: An important chemical diversity was found with a total of 92 volatile compounds (61 for Z. noltei, 59 for C. nodosa, 55 for P. oceanica, and 51 for Z. marina), from different biosynthetic pathways (e.g., terpenoids, benzenoids, and fatty acid derivatives) and with several types of chemical functions (e.g., alkanes, esters, aldehydes, and ketones) or heteroatoms (e.g., sulfur). No differences in chemical richness or diversity of compounds were observed between species. The four species shared 29 compounds enabling us to establish a specific chemical footprint for Mediterranean marine plants, including compounds like benzaldehyde, benzeneacetaldehyde, 8-heptadecene, heneicosane, heptadecane, nonadecane, octadecane, pentadecane, tetradecane, and tridecanal. PLS-DA and Heatmap show that the four species presented significantly different chemical profiles. The major compounds per species in relative abundance were isopropyl myristate for C. nodosa (25.6%), DMS for P. oceanica (39.3%), pentadecane for Z. marina (42.9%), and heptadecane for Z. noltei (46%). Conclusions: These results highlight the potential of BVOCs' emission from seagrass ecosystems and reveal species-specific chemical markers.

Tropospheric ozone (O3) is likely to affect the chemical signal emitted by flowers to attract their pollinators through its effects on the emission of volatile organic compounds (VOCs) and its high reactivity with these compounds in the atmosphere. We investigated these possible effects using a plant -pollinator interaction where the VOCs responsible for pollinator attraction are known and which is commonly exposed to high O3 concentration episodes: the Mediterranean fig tree (Ficus carica) and its unique pollinator, the fig wasp (Blastophaga psenes). In controlled conditions, we exposed fig trees bearing receptive figs to a high -O3 episode (5 h) of 200 ppb and analyzed VOC emission. In addition, we investigated the chemical reactions occurring in the atmosphere between O3 and pollinator -attractive VOCs using real-time monitoring. Finally, we tested the response of fig wasps to the chemical signal when exposed to increasing O3 mixing ratios (0, 40, 80, 120 and 200 ppb). The exposure of the fig tree to high O3 levels induced a significant decrease in leaf stomatal conductance, a limited change in the emission by receptive figs of VOCs not involved in pollinator attraction, but a major change in the relative abundances of the compounds among pollinator -attractive VOCs in O3 -enriched atmosphere. Fig VOCs reacted with O3 in the atmosphere even at the lowest level tested (40 ppb) and the resulting changes in VOC composition significantly disrupted the attraction of the specific pollinator. These results strongly suggest that current O3 episodes are probably already affecting the interaction between the fig tree and its specific pollinator.

In the Mediterranean region, a reduction of annual precipitation and a longer and drier summer season are expected with climate change by the end of the century, eventually endangering forest survival. To cope with such rapid changes, trees may modulate their morpho-anatomical and physiological traits. In the present study, we focused on the variation in leaf gas exchange and different leaf morpho-anatomical functional traits of Quercus pubescens Willd. in summer using a long-term drought experiment in natura consisting of a dynamic rainfall exclusion system where trees have been submitted to amplified drought (AD) (~-30% of annual precipitation) since April 2012 and compared them with trees under natural drought (ND) in a Mediterranean forest. During the study, we analyzed net CO2 assimilation (An), stomatal conductance (gs), transpiration (E), water-use efficiency (WUE), stomatal size and density, density of glandular trichomes and non-glandular trichomes, thickness of the different leaf tissues, specific leaf area and leaf surface. Under AD, tree functioning was slightly impacted, since only An exhibited a 49% drop, while gs, E and WUE remained stable. The decrease in An under AD was regulated by concomitant lower stomatal density and reduced leaf thickness. Trees under AD also featured leaves with a higher non-glandular trichome density and a lower glandular trichome density compared with ND, which simultaneously limits transpiration and production costs. This study points out that Q. pubescens exhibits adjustments of leaf morpho-anatomical traits which can help trees to acclimate to AD scenarios as those expected in the future in the Mediterranean region.

Hydraulic failure due to xylem embolism has been identified as one of the main mechanisms involved in drought-induced forest decline. Trees vulnerability to hydraulic failure depends on their hydraulic safety margin (HSM). While it has been shown that HSM globally converges between tree species and biomes, there is still limited knowledge regarding how HSM can adjust locally to varying drought conditions within species. In this study, we relied on three long-term partial rainfall exclusion experiments to investigate the plasticity of hydraulic traits and HSM for three Mediterranean tree species (Quercus ilex L., Quercus pubescens Willd., and Pinus halepensis Mill.). For all species, a homeostasis of HSM in response to rainfall reduction was found, achieved through different mechanisms. For Q. ilex, the convergence in HSM is attributed to the adjustment of both the turgor loss point (Ψtlp) and the water potential at which 50% of xylem conductivity is lost due to embolism (P50). In contrast, the maintenance of HSM for P. halepensis and Q. pubescens is related to its isohydric behavior for the first and leaf area adjustment for the latter. It remains to be seen whether this HSM homeostasis can be generalized and if it will be sufficient to withstand extreme droughts expected in the Mediterranean region.

Increasing aridity in the Mediterranean region will result in longer and recurrent drought. These changes could strongly modify plant defenses, endangering tree survival. We investigate the response of chemical defenses from central and specialized metabolism in Quercus pubescens Willd. to future Mediterranean drought using a long-term drought experiment in natura where trees have been submitted to amplified drought (similar to -30% annual precipitation) since April 2012. We focused on leaf metabolites including chlorophylls and carotenoids (central metabolism) and flavonols (specialized metabolism). Measurements were performed in summer from 2016 to 2022. Amplified drought led to higher concentrations of total photosynthetic pigments over the 2016-2022 period. However, it also led to lower AZ/VAZ and flavonol concentrations. Additionally, chemical defenses of Q. pubescens responded to previous precipitation where low precipitation 1 year and/or 2 years preceding sampling was associated to low concentrations of VAZ, flavonol and high neoxanthin concentrations. Our study indicates that the decline of flavonol concentration under long-term drought is counterbalanced by a higher production of several central metabolites. Such results are potentially due to an adjustment in tree metabolism, highlighting the importance of performing long-term experimental studies in natura for assessing drought legacy effects and thus forest adaptation to climate change.

Organic aerosol (OA) still remains one of the most difficult components of the atmospheric aerosols to simulate, given the multitude of its precursors, the uncertainty in its formation pathways, and the lack of measurements of its detailed composition. The LANDEX (LANDes Experiment) project, during its intensive field campaign in summer 2017, gives us the opportunity to compare biogenic secondary OA (BSOA) and its precursors and oxidants obtained within and above the Landes forest canopy to simulations performed with CHIMERE, a state-of-the-art regional chemistry transport model. The Landes forest is situated in the southwestern part of France and is one of the largest anthropized forests in Europe (1×106 ha). The majority of the forest is comprised of maritime pine trees, which are strong terpenoid emitters, providing a large potential for BSOA formation. In order to simulate OA buildup in this area, a specific model configuration setup adapted to the local peculiarities was necessary. As the forest is nonhomogeneous, with interstitial agricultural fields, high-resolution 1 km simulations over the forest area were performed. Biogenic volatile organic compound (BVOC) emissions were predicted by MEGAN, but specific land cover information needed to be used and was thus chosen from the comparison of several high-resolution land cover databases. Moreover, the tree species distribution needed to be updated for the specific conditions of the Landes forest. In order to understand the canopy effect in the forest, canopy effects on vertical diffusivity, winds, and radiation were implemented in the model in a simplified way. The refined simulations show a redistribution of BVOCs with a decrease in isoprene and an increase in terpenoid emissions with respect to the standard case, both of which are in line with observations. Corresponding changes to simulated BSOA sources are tracked. Very low nighttime ozone, sometimes near zero, remains overestimated in all simulations. This has implications for the nighttime oxidant budget, including NO3. Despite careful treatment of physical conditions, simulated BSOA is overestimated in the most refined simulation. Simulations are also compared to air quality sites surrounding the Landes forest, reporting a more realistic simulation in these stations in the most refined test case. Finally, the importance of the sea breeze system, which also impacts species concentrations inside the forest, is made evident.

Sesquiterpene cyclases (STC) catalyse the cyclization of the C15 molecule farnesyl diphosphate into a vast variety of mono- or polycyclic hydrocarbons and, for a few enzymes, oxygenated structures, with diverse stereogenic centres. The huge diversity in sesquiterpene skeleton structures in nature is primarily the result of the type of cyclization driven by the STC. Despite the phenomenal impact of fungal sesquiterpenes on the ecology of fungi and their potentials for applications, the fungal sesquiterpenome is largely untapped. The identification of fungal STC is generally based on protein sequence similarity with characterized enzymes. This approach has improved our knowledge on STC in a few fungal species, but it has limited success for the discovery of distant sequences. Besides, the tools based on secondary metabolite biosynthesis gene clusters have shown poor performance for terpene cyclases. Here, we used four sets of sequences of fungal STC that catalyse four types of cyclization, and specific amino acid motives to identify phylogenetically related sequences in the genomes of basidiomycetes fungi from the order Polyporales. We validated that four STC genes newly identified from the genome sequence of Leiotrametes menziesii, each classified in a different phylogenetic clade, catalysed a predicted cyclization of farnesyl diphosphate. We built HMM models and searched STC genes in 656 fungal genomes genomes. We identified 5605 STC genes, which were classified in one of the four clades and had a predicted cyclization mechanism. We noticed that the HMM models were more accurate for the prediction of the type of cyclization catalysed by basidiomycete STC than for ascomycete STC.

Mangroves are ecosystems interfacing terrestrial and marine environments submitted to extreme abiotic factors (e.g. anoxia, flooding, salinity) producing stress on vegetation. Due to these stresses, we hypothesized that mangroves potentially emit biogenic volatile organic compound (BVOC), particularly isoprenoids as they are defense compounds. Despite mangroves cover only about 5% of the forest areas of the world, their emissions could impact air quality at the continental-ocean interface. As a result, it is important to fill the gap in the knowledge about BVOC emissions from the canopy of the major mangrove trees. The aim of this study was thus to screen isoprenoid emissions of the mangrove species. In this study, we sampled isoprenoid emissions of 14 species foliage among the 38 core species existing in the Indo-West Pacific (IWP) and the Atlantic Est Pacific (AEP) regions. Sampling was performed using a branch-bag dynamic enclosure system and analyzed with gas chromatography coupled to mass spectrometry. Our analysis showed that mangrove tree species are very low emitters suggesting that mangrove ecosystems would not strongly influence atmospheric chemistry and air quality.

With climate change, an aggravation in summer drought is expected in the Mediterranean region. To assess the impact of such a future scenario, we compared the response of Quercus pubescens, a drought-resistant deciduous oak species, to long-term amplified drought (AD) (partial rain exclusion in natura for 10 years) and natural drought (ND). We studied leaf physiological and physico-chemical trait responses to ND and AD over the seasonal cycle, with a focus on chemical traits including major groups of central (photosynthetic pigments and plastoquinones) and specialized (tocochromanols, phenolic compounds, and cuticular waxes) metabolites. Seasonality was the main driver of all leaf traits, including cuticular triterpenoids, which were highly concentrated in summer, suggesting their importance to cope with drought and thermal stress periods. Under AD, trees not only reduced CO2 assimilation (-42%) in summer and leaf concentrations of some phenolic compounds and photosynthetic pigments (carotenoids from the xanthophyll cycle) but also enhanced the levels of other photosynthetic pigments (chlorophylls, lutein, and neoxanthin) and plastochromanol-8, an antioxidant located in chloroplasts. Overall, the metabolomic adjustments across seasons and drought conditions reinforce the idea that Q. pubescens is highly resistant to drought although significant losses of antioxidant defenses and photoprotection were identified under AD.

The intensification of summer drought expected with climate change can induce metabolism modifications in plants to face such constraints. In this experiment, we used both a targeted approach focused on flavonoids, as well as an untargeted approach, to study a broader fraction of the leaf metabolome of Quercus pubescens exposed to amplified drought. A forest site equipped with a rainfall exclusion device allowed reduction of natural rainfall by ~30% over the tree canopy. Leaves of natural drought (ND) and amplified drought (AD) plots were collected over three seasonal cycles (spring, summer, and autumn) in 2013 (the second year of rain exclusion), 2014, and 2015. As expected, Q. pubescens metabolome followed a seasonal course. In the summer of 2015, the leaf metabolome presented a shifted and early autumnal pattern because of harsher conditions during this year. Despite low metabolic modification at the global scale, our results demonstrated that 75% of Quercus metabolites were upregulated in springs when trees were exposed to AD, whereas 60 to 73% of metabolites (93% in summer 2015), such as kaempferols and quercetins, were downregulated in summers/autumns. Juglanin, a kaempferol pentoside, as well as rhododendrin derivatives, were upregulated throughout the year, suggesting an antioxidant ability of these metabolites. Those changes in terms of phenology and leaf chemistry could, in the end, affect the ecosystem functioning.