Seasonal patterns of terpene content and emission from seven Mediterranean woody species in field conditions

Floral Aroma and Pollinator Relationships in Two Sympatric Late-Summer-Flowering Mediterranean Asparagus Species

This research delves into plant-pollinator relationships within the Mediterranean region, focusing on two synchronous and sympatric asparagus species: A. acutifolius and A. albus. For the first time, the floral scents of the genus Asparagus are reported. We investigate the volatile organic compounds (VOCs) present in their floral scents and their impact on pollinator attraction. Captured flower-emitted VOCs underwent solid-phase microextraction of headspace (SPME-HS) and gas chromatography and mass spectrometry (GC-MS) analysis. The investigation confirms distinctive aroma profiles for each species. A. albus predominantly emits benzene derivatives and sesquiterpenes, while A. acutifolius is characterized by carotenoid derivatives, monoterpenes, and sesquiterpenes. The only shared compounds between the two species are the sesquiterpenes (Z,E)-α-farnesene and (E,E)-α-farnesene. A positive correlation links peak floral aroma intensity (benzenoids in A. albus and ionones in A. acutifolius) with a higher pollinator visit frequency, emphasizing the critical role of intense floral scents in pollinator attraction. The study of reproductive aspects reveals almost complete gynodioecy in A. acutifolius, influencing unique dynamics for the two species. These adaptations hold significant importance within the Mediterranean ecosystem, particularly during the late dry summer period, when a limited number of plant species vie for a shared primary pollinator.

Environmental Factors Affecting Monoterpene Emissions from Terrestrial Vegetation

Monoterpenes are volatile organic compounds that play important roles in atmospheric chemistry, plant physiology, communication, and defense. This review compiles the monoterpene emission flux data reported for different regions and plant species and highlights the role of abiotic environmental factors in controlling the emissions of biogenic monoterpenes and their emission fluxes for terrestrial plant species (including seasonal variations). Previous studies have demonstrated the role and importance of ambient air temperature and light in controlling monoterpene emissions, likely contributing to higher monoterpene emissions during the summer season in temperate regions. In addition to light and temperature dependence, other important environmental variables such as carbon dioxide (CO2), ozone (O3), soil moisture, and nutrient availability are also known to influence monoterpene emissions rates, but the information available is still limited. Throughout the paper, we identify knowledge gaps and provide recommendations for future studies.

Contrasting terpene emissions from canopy and understory vegetation in response to increases in nitrogen deposition and seasonal changes in precipitation

Given global change and shifts in climate are expected to increase BVOC emissions, the quantification of links between environmental conditions, plant physiology, and terpene emission dynamics is required to improve model predictions of ecosystem responses to increasing nitrogen deposition and changes in precipitation regimes. Here, we conducted a two-factor field experiment in sub-tropical forest plots to determine effects of N addition (N), precipitation change (PC), and NP (N and PC combined treatment) on wet and dry season terpene emissions and leaf photosynthetic parameters from canopy and understory species. Changes of β-ocimene and sabinene under PC and NP in the wet season (0.4-5.6-fold change) were the largest contributor to changes in total terpene emissions. In the dry season, the standardized total terpene emission rate was enhanced by 144.9% under N addition and 185.7% under PC for the understory species, while the total terpene emission rate was lower under NP than N addition and PC, indicating that N addition tended to moderate increases in PC-induced understory total terpene emissions. In the wet season, the total terpene emission rate under N and PC was close to ambient conditions for the canopy species, while the total terpene emission rate was enhanced by 54.6% under NP, indicating that N and PC combined treatment had an additive effect on canopy total terpene emissions. Total terpene emission rates increased with rates of net leaf photosynthesis (P_n) and transpiration (Tr) and there was a decoupling between terpene emission rates and P_n under NP, indicating that complex effects between PC and N decreased the regularity of single-factor effects. We recommend that N and PC interaction effects are included in models for the prediction of terpene emissions, particularly from canopy vegetation during the wet season as a major source of forest ecosystem terpene emissions.

Characterization of the Autoxidation of Terpenes at Elevated Temperature Using High-Resolution Mass Spectrometry: Formation of Ketohydroperoxides and Highly Oxidized Products from Limonene

Low-temperature experiments on the oxidation of limonene-O₂-N₂ mixtures were conducted in a jet-stirred reactor (JSR) over a range of temperatures (520-800 K) under fuel-lean conditions (equivalence ratio φ = 0.5) with a short residence time (1.5 s) and a pressure of 1 bar. Collected samples of the reaction mixtures were analyzed by (i) online Fourier transform infrared spectroscopy (FTIR) and (ii) Orbitrap Q-Exactive high-resolution mass spectrometry after direct injection or chromatographic separation using reversed-phase ultra-high-performance liquid chromatography (RP-UHPLC) and soft ionization (with positive or negative heated electrospray ionization and atmospheric-pressure chemical ionization). H/D exchange using deuterated water (D₂O) and a reaction with 2,4-dinitrophenylhydrazine (2,4-DNPH) were performed to probe the presence of OH, OOH, and C═O groups in the oxidized products. A broad range of oxidation products ranging from water to highly oxygenated products containing five and more O atoms were detected (C₇H₁₀O_4,5, C₈H₁₂O_2,4, C₈H₁₄O_2,4, C₉H₁₂O, C₉H₁₄O_1,3-5, C₁₀H₁₂O₂, C₁₀H₁₄O_1-9, C₁₀H₁₆O_2-5, and C₁₀H₁₈O₆). Mass spectrometry analyses were only qualitative, and quantification was performed with FTIR. The results are discussed in terms of reaction routes involving the initial formation of peroxy radicals, H atom transfer, and O₂ addition sequences producing a large set of chemical products, including ketohydroperoxides and more oxygenated products. Carbonyl compounds derived from the Waddington oxidation mechanism on exo- and endo-double bonds (C═C) were observed in addition to their products of further oxidation. Products of the Korcek mechanism (carboxylic acids and carbonyls) were also detected.

Chemical Composition of Atmospheric Air in Nemoral Scots Pine Forests and Submountainous Beech Forests: The Potential Region for the Introduction of Forest Therapy

Studies show that forests are one of the main recreational destinations. This can be explained by their beneficial effects on the health of their visitors, which can be attributed to compounds from the terpene group. The aim of this research was to determine the chemical composition of air in the interiors of Nemoral Scots pine forests and submountainous beech forests, with the determination of compounds of the terpene group. Samples of organic compounds present in the air were collected with the use of Tenax TA sorbent tubes. The process of separation, identification, and determination of the extracted organic compounds was carried out with the use of the gas chromatography technique integrated with a flame ionization detector. Additional identification of the extracted compounds was carried out with the use of GC coupled with mass spectrometry. The most abundant group of compounds was the aliphatic hydrocarbons, both saturated (linear and branched) and unsaturated (terpenes). Carbonyl compounds were also found in the collected samples, but they constituted no more than 10% of all compounds present on the chromatograms. The concentrations of terpenes and terpenoids in the forest atmosphere varied from 10 to 74 µg·m^-3, representing on average 33% of the total volatile organic compounds.

Effects of elevated ozone and warming on terpenoid emissions and concentrations of Norway spruce depend on needle phenology and age

Norway spruce (Picea abies (L.) Karst) trees are affected by ongoing climate change, including warming and exposure to phytotoxic levels of ozone. Non-volatile terpenoids and volatile terpenoids (biogenic organic volatile compounds, BVOCs) protect spruce against biotic and abiotic stresses. BVOCs also affect the atmosphere's oxidative capacity. Four-year-old Norway spruce were exposed to elevated ozone (EO) (1.4 × ambient) and warming (1.1 °C + ambient air) alone and in combination on an open-field exposure site in Central Finland. Net photosynthesis, needle terpenoid concentrations and BVOC emissions were measured four times during the experiment's second growing season: after bud opening in May, during the mid-growing season in June, and after needle maturation in August and September. Warming increased terpene concentrations in May due to advanced phenology and decreased them at the end of the growing season in matured current-year needles. Ozone enhanced these effects of warming on several compounds. Warming decreased concentrations of oxygenated sesquiterpenes in previous-year needles. Decreased emissions of oxygenated monoterpenes by warming and ozone alone in May were less prominent when ozone and warming were combined. A similar interactive treatment response in isoprene, camphene, tricyclene and α-pinene was observed in August when the temperature and ozone concentration was high. The results suggest long-term warming may reduce the terpenoid-based defence capacity of young spruce, but the defence capacity can be increased during the most sensitive growth phase (after bud break), and when high temperatures or ozone concentrations co-occur. Reduced BVOC emissions from young spruce may decrease the atmosphere's oxidative capacity in the warmer future, but the effect of EO may be marginal because less reactive minor compounds are affected.

Seasonal variability in essential oil composition and biological activity of Rosmarinus officinalis L. accessions in the western Himalaya

Rosmarinus officinalis L. is an imperative herb used in pharmaceutical yet knowledge on chemical and activity profile of essential oil (EO) to harvest seasons and accessions from the Himalayan region is limited. Thus, accessions were evaluated to determine the EO content, compositional, antimicrobial, and cytotoxic potential of rosemary in different harvest seasons during 2018‒2019. EO content was 30.5% higher in IHBT/RMAc-1 compared with IHBT/RMAc-2 accession while 27.9% and 41.6% higher in the autumn as compared with summer and rainy season, respectively. Major EO compound was 1,8-cineole; ranged from 32.50‒51.79% during harvest seasons and 38.70‒42.20% in accessions. EO was active against both the tested Gram-positive bacteria (Micrococcus luteus MTCC 2470 and Staphylococcus aureus MTCC 96). EOs showed inhibition of Gram-negative bacteria (Salmonella typhi MTCC 733), while Klebsiella pneumoniae MTCC 109 was found to be resistant. The rosemary EO of T1 (Rainy season IHBT/RMAc-1) was most effective against S. aureus MTCC 96 with the minimum inhibitory concentration (MIC) of 4% (v/v). In vitro cytotoxicity evaluation showed no potential anti-proliferative activity of EO. The rosemary EO profile in the western Himalayan region was influenced by harvesting seasons and genetic variability within the accessions; furthermore, a promising antibacterial agent in pharmaceutical and flavour industries.

Hotter droughts alter resource allocation to chemical defenses in piñon pine

Heat and drought affect plant chemical defenses and thereby plant susceptibility to pests and pathogens. Monoterpenes are of particular importance for conifers as they play critical roles in defense against bark beetles. To date, work seeking to understand the impacts of heat and drought on monoterpenes has primarily focused on young potted seedlings, leaving it unclear how older age classes that are more vulnerable to bark beetles might respond to stress. Furthermore, we lack a clear picture of what carbon resources might be prioritized to support monoterpene synthesis under drought stress. To address this, we measured needle and woody tissue monoterpene concentrations and physiological variables simultaneously from mature piñon pines (Pinus edulis) from a unique temperature and drought manipulation field experiment. While heat had no effect on total monoterpene concentrations, trees under combined heat and drought stress exhibited ~ 85% and 35% increases in needle and woody tissue, respectively, over multiple years. Plant physiological variables like maximum photosynthesis each explained less than 10% of the variation in total monoterpenes for both tissue types while starch and glucose + fructose measured 1-month prior explained ~ 45% and 60% of the variation in woody tissue total monoterpene concentrations. Although total monoterpenes increased under combined stress, some key monoterpenes with known roles in bark beetle ecology decreased. These shifts may make trees more favorable for bark beetle attack rather than well defended, which one might conclude if only considering total monoterpene concentrations. Our results point to cumulative and synergistic effects of heat and drought that may reprioritize carbon allocation of specific non-structural carbohydrates toward defense.

An Improvement of SPME-Based Sampling Technique to Collect Volatile Organic Compounds from Quercus ilex at the Environmental Level

Biogenic Volatile Organic Compounds (BVOCs) include many chemical compounds emitted by plants into the atmosphere. These compounds have a great effect on biosphere-atmosphere interactions and may affect the concentration of atmospheric pollutants, with further consequences on human health and forest ecosystems. Novel methods to measure and determine BVOCs in the atmosphere are of compelling importance considering the ongoing climate changes. In this study, we developed a fast and easy-to-handle analytical methodology to sample these compounds in field experiments using solid-phase microextraction (SPME) fibers at the atmospheric level. An improvement of BVOCs adsorption from SPME fibers was obtained by coupling the fibers with fans to create a dynamic sampling system. This innovative technique was tested sampling Q. ilex BVOCs in field conditions in comparison with the conventional static SPME sampling technique. The results showed a great potential of this dynamic sampling system to collect BVOCs at the atmosphere level, improving the efficiency and sensitivity of SPME fibers. Indeed, our novel device was able to reduce the sampling time, increase the amount of BVOCs collected through the fibers and add information regarding the emissions of these compounds at the environmental level.

Volatilome of Aleppo Pine litter over decomposition process

Biogenic Volatile Organic Compounds (BVOC) are largely accepted to contribute to both atmospheric chemistry and ecosystem functioning. While the forest canopy is recognized as a major source of BVOC, emissions from plant litter have scarcely been explored with just a couple of studies being focused on emission patterns over litter decomposition process. The aim of this study was to quantitatively and qualitatively characterize BVOC emissions (C1-C15) from Pinus halepensis litter, one of the major Mediterranean conifer species, over a 15-month litter decomposition experiment. Senescent needles of P. halepensis were collected and placed in 42 litterbags where they underwent in situ decomposition. Litterbags were collected every 3 months and litter BVOC emissions were studied in vitro using both online (PTR-ToF-MS) and offline analyses (GC-MS). Results showed a large diversity of BVOC (58 compounds detected), with a strong variation over time. Maximum total BVOC emissions were observed after 3 months of decomposition with 9.18 µg gDM -1 hr-1 mainly composed by terpene emissions (e.g., α-pinene, terpinolene, β-caryophyllene). At this stage, methanol, acetone, and acetic acid were the most important nonterpenic volatiles representing, respectively, up to 26%, 10%, and 26% of total emissions. This study gives an overview of the evolution of BVOC emissions from litter along with decomposition process and will thus contribute to better understand the dynamics and sources of BVOC emission in Mediterranean pine forests.

Engineered Orange Ectopically Expressing the Arabidopsis β-Caryophyllene Synthase Is Not Attractive to Diaphorina citri, the Vector of the Bacterial Pathogen Associated to Huanglongbing

Huanglongbing (HLB) is a destructive disease, associated with psyllid-transmitted phloem-restricted pathogenic bacteria, which is seriously endangering citriculture worldwide. It affects all citrus species and cultivars regardless of the rootstock used, and despite intensive research in the last decades, there is no effective cure to control either the bacterial species (Candidatus Liberibacter spp.) or their insect vectors (Diaphorina citri and Trioza erytreae). Currently, the best attempts to manage HLB are based on three approaches: (i) reducing the psyllid population by intensive insecticide treatments; (ii) reducing inoculum sources by removing infected trees, and (iii) using nursery-certified healthy plants for replanting. The economic losses caused by HLB (decreased fruit quality, reduced yield, and tree destruction) and the huge environmental costs of disease management seriously threaten the sustainability of the citrus industry in affected regions. Here, we have generated genetically modified sweet orange lines to constitutively emit (E)-β-caryophyllene, a sesquiterpene repellent to D. citri, the main HLB psyllid vector. We demonstrate that this alteration in volatile emission affects behavioral responses of the psyllid in olfactometric and no-choice assays, making them repellent/less attractant to the HLB vector, opening a new alternative for possible HLB control in the field.

Bumblebee Behavior on Flowers, but Not Initial Attraction, Is Altered by Short-Term Drought Stress

Climate change is leading to increasing drought and higher temperatures, both of which reduce soil water levels and consequently water availability for plants. This reduction often induces physiological stress in plants, which in turn can affect floral development and production inducing phenotypic alterations in flowers. Because flower visitors notice and respond to small differences in floral phenotypes, changes in trait expression can alter trait-mediated flower visitor behavior. Temperature is also known to affect floral scent emission and foraging behavior and, therefore, might modulate trait-mediated flower visitor behavior. However, the link between changes in flower visitor behavior and floral traits in the context of increasing drought and temperature is still not fully understood. In a wind-tunnel experiment, we tested the behavior of 66 Bombus terrestris individuals in response to watered and drought-stressed Sinapis arvensis plants and determined whether these responses were modulated by air temperature. Further, we explored whether floral traits and drought treatment were correlated with bumblebee behavior. The initial attractiveness of drought and watered plants did not differ, as the time to first visit was similar. However, bumblebees visited watered plants more often, their visitation rate to flowers was higher on watered plants, and bumblebees stayed for longer, indicating that watered plants were more attractive for foraging. Bumblebee behavior differed between floral trait expressions, mostly independently of treatment, with larger inflorescences and flowers leading to a decrease in the time until the first flower visit and an increase in the number of visits and the flower visitation rate. Temperature modulated bumblebee activity, which was highest at 25°C; the interaction of drought/water treatment and temperature led to higher visitation rate on watered plants at 20°C, possibly as a result of higher nectar production. Thus, bumblebee behavior is influenced by the watered status of plants, and bumblebees can recognize differences in intraspecific phenotypes involving morphological traits and scent emission, despite overall morphological traits and scent emission not being clearly separated between treatments. Our results indicate that plants are able to buffer floral trait expressions against short-term drought events, potentially to maintain pollinator attraction.

Amazonian biogenic volatile organic compounds under global change

Biogenic volatile organic compounds (BVOCs) play important roles at cellular, foliar, ecosystem and atmospheric levels. The Amazonian rainforest represents one of the major global sources of BVOCs, so its study is essential for understanding BVOC dynamics. It also provides insights into the role of such large and biodiverse forest ecosystem in regional and global atmospheric chemistry and climate. We review the current information on Amazonian BVOCs and identify future research priorities exploring biogenic emissions and drivers, ecological interactions, atmospheric impacts, depositional processes and modifications to BVOC dynamics due to changes in climate and land cover. A feedback loop between Amazonian BVOCs and the trends of climate and land-use changes in Amazonia is then constructed. Satellite observations and model simulation time series demonstrate the validity of the proposed loop showing a combined effect of climate change and deforestation on BVOC emission in Amazonia. A decreasing trend of isoprene during the wet season, most likely due to forest biomass loss, and an increasing trend of the sesquiterpene to isoprene ratio during the dry season suggest increasing temperature stress-induced emissions due to climate change.

Rhizobium response to sole and combined exposure to cadmium and the phytocompounds alpha-pinene and quercetin

Soils can be contaminated with substances arising from anthropogenic sources, but also with natural bioactive compounds produced by plants, such as terpenes and flavonoids. While terpenes and flavonoids have received much less attention from research studies than metals, the effects that phytocompounds can have on soil organisms such as beneficial microorganisms should not be neglected. Herein we report the sole and combined exposure of Rhizobium to cadmium, to the monoterpene alpha-pinene and to the flavanol quercetin. A range of environmentally relevant concentrations of the phytocompounds was tested. Physiological (growth, protein content and intracellular Cd concentration), oxidative damage (lipid peroxidation, protein carbonylation) and antioxidant mechanisms (superoxide dismutase, catalase, glutathione, glutathione-S-transferases, protein electrophoretic profiles) were assessed. Results suggest that exposure to both phytocompounds do not influence Rhizobium growth, but for combined exposure to phytocompounds and Cd, different responses are observed. At low concentrations, phytocompounds seem to relieve the stress imposed by Cd by increasing antioxidant responses, but at high concentrations this advantage is lost and membrane damage may even be exacerbated. Thus, the presence of bioactive phytocompounds in soil may influence the tolerance of microorganisms to persistent toxicants, and may change their impact on the environment.

Metabolomic study of volatile compounds emitted by lavender grown under open-field conditions: a potential approach to investigate the yellow decline disease

INTRODUCTION

Fine lavender and lavandin are perfume and medicinal plants originate from the South of France and are widely cultivated for their essential oils. Recently, cultivated plants suffered from a severe decline in France, due to the propagation of the yellow decline disease. This disease is caused by the stolbur phytoplasma, a bacterium transmitted by a sap-sucking insect, the planthopper.

OBJECTIVES

In order to understand the complex relationships between host plant, pest, pathogen and environment responsible for the yellow decline of lavender, we use a metabolomic approach to highlight changes in chemical emissions from asymptomatic ("healthy") and symptomatic ("infected") plants.

METHODS

Volatile compounds produced by fine lavender and lavandin were collected in the field using a dynamic headspace extraction approach. Afterwards, compounds trapped on Tenax adsorbent were thermodesorbed and analysed using an automated thermal desorption-gas chromatography-mass spectrometry (ATD-GC-MS). Multivariate statistical analyses was performed using principal component analysis and partial least square discriminant analyses.

RESULTS

The untargeted screening of volatiles allowed the separation of asymptomatic and symptomatic plants according to their emissions. The approach was sufficiently accurate so as to separate the emissions according to the different stages of infection. Twelve compounds were found to be deregulated metabolites of yellow disease infection, common to fine lavender (variety 7713) and lavandin (variety abrial).

CONCLUSION

The metabolomic approach allowed for the effective identification of chemical variations between infected and healthy plants in a complex field environment.

How does drought impact burned area in Mediterranean vegetation communities?

Drought and water stress are widely known to influence fuel moisture content and flammability, although differences do exist according to the response mechanisms and adaptive traits displayed by plant communities. In the Mediterranean basin, as a result of climate change, extreme drought events are expected to become more frequent and severe, envisaging episodes of increased fire risk. In this paper, we expand the scale of analysis on how does drought influence wildfire incidence exploring the joint influence on burned area of drought duration, magnitude and temporal distribution, and the affected vegetation communities (VCs). We leveraged the weekly adaptation of the Standardized Precipitation Evapotranspiration Index (SPEI) and historical fire perimeters to model complex interactions between drought and burned area mediated by VC composition and structure. We applied multivariate factor analysis (multi-group Principal Component Analysis) and non-parametric mixed regression models (GAMM) to a set of 1-to-48 weeks SPEI and 10 dominant VCs. We detected a significant influence of drought events (negative SPEI) on burned area, although differences in terms of seasonal distribution and VC were observed. Drought played a major role in explaining burned area in late spring and autumn by altering the usual positive rainfall-evapotranspiration balance, suggesting a potential lengthening of the fire season given the projected drought trends in the next decades.

Seasonal variations in emission rates and composition of terpenoids emitted from Chamaecyparis formosensis (Cupressaceae) of different ages

Chamaecyparis formosensis (Cupressaceae) is among the most precious endemic conifers in Taiwan. Field study was conducted on seasonal variations in emission rates and compositions of terpenoids from this tree species of two different ages. A total of 21 terpenoids were detected, of which there were 13 monoterpenoids (MTs), 4 sesquiterpenoids (STs), and 4 diterpenoids (DTs). MTs dominated the emissions in both saplings and adult trees and produced more than 80% of terpene emissions. Contrasting seasonal pattern between saplings and adult trees was found. Total actual emissions from saplings were higher in cold seasons (range, 64.40 ± 13.18 to 140.74 ± 18.90 ng g^-1 h^-1) than in warm seasons (range, 55.63 ± 15.84 to 63.48 ± 11.85 ng g^-1 h^-1). Photosynthetically active radiation (PAR) was found to be the most important factor affecting terpene emissions from saplings. On the contrary, higher emissions were found in warm seasons for adult trees (range, 101.49 ± 12.29 to 181.35 ± 80.15 ng g^-1 h^-1), and the emissions were mainly in response to temperature. Some compounds in C. formosensis of both ages (e.g., β-myrcene, α-terpinene, trans-β-ocimene, terpinen-4-ol, α-cedrene and trans-β-farnesene) showed comparably higher contents in cold seasons. Results presented here provide important fundamental information for better understanding of forest bathing and estimating air quality in Taiwan.

Mistletoe Versus Host Pine: Does Increased Parasite Load Alter the Host Chemical Profile?

Stress caused by parasitic plants, e.g. mistletoes, alters certain host-plant traits as a response. While several physical implications of the parasite-host relation have been well studied, shifts in the host chemical profile remain poorly understood. Here we compare the chemical profiles of mistletoe (Viscum album subsp. austriacum) leaves and host pine (Pinus nigra subsp. salzmannii) needles and we investigate chemical changes in host needles of trees with different parasite loads (control, low, medium, and high). Our results reveal that despite the intimate contact between mistletoe and host pine, their chemical profiles differed significantly, revealing extremely low concentrations of defense compounds (including a complete lack of terpenes) and high levels of N concentrations in mistletoe leaves. On the other hand, parasitized pines showed unique chemical responses depending on parasite loads. Overall, the content in monoterpenes increased with parasitism. Higher parasitized pines produced higher amounts of defense compounds (phenols and condensed tannins) than less parasitized trees, but amounts in samples of the same year did not significantly differ between parasitized and unparasitized pines. Highly parasitized pines accumulated less N than pines with other parasite loads. The strongest response was found in sesqui- and diterpenes, which were at lower levels in pines under medium and high parasitism. Chemical responses of pines to mistletoe parasitism resembled reactions to other kinds of stress. Low levels induced reactions resembling those against drought stress, while medium and high parasitism elicited responses comparable to those against burning and defoliation.

Manganese-induced changes in glandular trichomes density and essential oils production of Mentha aquatica L. at different growth stages

Production and accumulation of essential oils in plants are influenced by intrinsic and environmental factors. Here, we attempted to elucidate the effect of manganese (Mn) supply on the density of glandular trichomes and the production of essential oils in Mentha aquatica (water mint; syn. Mentha hirsuta Huds.) at the different growth stages. To this aim, plants were treated with 100 μM of Mn (supplied as MnSO₄·H₂O) at early and late vegetative stages of growth. Then, the control and treated plants were harvested, and biochemical, morphological and molecular analyses indicated that Mn supply has affected M. aquatica at the different growth stages. The biomass, Mn accumulation, glandular trichomes density, essential oils yield and expression levels of the genes encoding enzymes involved in terpenoid biosynthesis pathway (1-Deoxy d-xylulose-5-phosphate synthase (Dxs), geranyl diphosphate synthase (Gpps), isopentenyl diphosphate isomerase (Ippi), β-caryophyllene synthase (Cps), limonene synthase (Ls) and menthofuran synthase (Mfs)) were increased by Mn supply at both growth stages. However, the increased rates of the assayed parameters were varied between the early and late vegetative stages. Moreover, the content and chemical composition of terpenoid components were affected by Mn supply and plant growth stage. There were positive and weak correlations among the study variables under the Mn supply at the different growth stages. Given these findings, we propose that the application of Mn supply at both early and late vegetative stages elevates the growth, density of glandular trichomes and production of essential oils in M. aquatica.

Nutrient-rich plants emit a less intense blend of volatile isoprenoids

The emission of isoprenoids (e.g. isoprene and monoterpenes) by plants plays an important defensive role against biotic and abiotic stresses. Little is known, however, about the functional traits linked to species-specific variability in the types and rates of isoprenoids emitted and about possible co-evolution of functional traits with isoprenoid emission type (isoprene emitter, monoterpene emitter or both). We combined data for isoprene and monoterpene emission rates per unit dry mass with key functional traits (foliar nitrogen (N) and phosphorus (P) concentrations, and leaf mass per area) and climate for 113 plant species, covering the boreal, wet temperate, Mediterranean and tropical biomes. Foliar N was positively correlated with isoprene emission, and foliar P was negatively correlated with both isoprene and monoterpene emission rate. Nonemitting plants generally had the highest nutrient concentrations, and those storing monoterpenes had the lowest concentrations. Our phylogenetic analyses found that the type of isoprenoid emission followed an adaptive, rather than a random model of evolution. Evolution of isoprenoids may be linked to nutrient availability. Foliar N and P are good predictors of the type of isoprenoid emission and the rate at which monoterpenes, and to a lesser extent isoprene, are emitted.

Terpenoid Emissions of Two Mediterranean Woody Species in Response to Drought Stress

Drought is a major environmental constrain affecting plant performance and survival, particularly in Mediterranean ecosystems. Terpenoids may play a protective role under these conditions, however, observations of drought effects on plant terpenoid emissions are controversial ranging from decreased emissions to unaffected or increased release of terpenoids. In the present study we investigated terpenoid emissions of cork oak (Quercus suber) and gum rockrose (Cistus ladanifer) in response to summer drought stress in 2017. Pre-dawn leaf water potential (ΨPD) decreased from -0.64 to -1.72 MPa in Q. suber and from -1.69 to -4.05 MPa in C. ladanifer, indicating a transition from mild to severe drought along summer. Total terpenoid emissions decreased with drought, but differed significantly between species (p < 0.001) and in response to ΨPD, air temperature and assimilation rates. C. ladanifer emitted a large variety of >75 compounds comprising monoterpenes, sesquiterpenes and even diterpenes, which strongly decreased from 1.37 ± 0.23 μg g-1h-1 to 0.40 ± 0.08 μg g-1h-1 (p < 0.001) in response to drought. Total emission rates were positively correlated to air temperature (p < 0.001). C. ladanifer behavior points toward terpenoid leaf storage depletion and reduced substrate availability for terpenoid synthesis with increasing drought, most likely accelerated by high air temperatures. Q. suber emitted mainly monoterpenes and emissions declined significantly from June (0.50 ± 0.08 μg g-1h-1) to August (0.29 ± 0.02 μg g-1h-1) (p < 0.01). Emission rates were weakly correlated with net assimilation rates (R2 = 0.19, p < 0.001), but did not respond strongly to ΨPD and air temperature. Early onset of drought in 2017 most likely reduced plant metabolism in Q. suber, resulting in diminished, but stable terpenoid fluxes. Calculation of standard emission factors (at 30°C) revealed contrasting emission patterns of decreasing, unaffected, or increasing fluxes of single terpenoid compounds. Unaffected or drought-enhanced emissions of compounds such as α-pinene, camphene or manoyl oxide may point toward a specific role of these terpenoids in abiotic stress adaptation. In conclusion, these results suggest a strong negative, but species- and compound-specific effect of severe drought on terpenoid fluxes in Mediterranean ecosystems.

Identification, Functional Characterization, and Seasonal Expression Patterns of Five Sesquiterpene Synthases in Liquidambar formosana

Terpenoids are a large group of important secondary metabolites that are involved in a variety of physiological mechanisms, and many are used commercially in the cosmetics and pharmaceutical industries. During the past decade, the topic of seasonal variation in terpenoid biosynthesis has garnered increasing attention. Formosan sweet gum ( Liquidambar formosana Hance) is a deciduous tree species. The expression of terpene synthase and accumulation of terpenoids in leaves may vary in different seasons. Here, four sesquiterpene synthases (i.e., LfTPS01, LfTPS02, LfTPS03, and LfTPS04) and a bifunctional mono/sesquiterpene synthase ( LfTPS05) were identified from Formosan sweet gum. The gene expression of LfTPS01, LfTPS02, and LfTPS03 showed seasonal diversification, and, in addition, expression of LfTPS04 and LfTPS05 was induced by methyl jasmonate treatment. The major products LfTPS01, LfTPS02, LfTPS04, and LfTPS05 are hedycaryol, α-selinene, trans-β-caryophyllene, α-copaene/δ-cadinene, and nerolidol/linalool, respectively. The data indicated that the sesquiterpenoid content in the essential oil of Formosan sweet gum leaves shows seasonal differences that were correlated to the sesquiterpene synthase gene expression.

Changes in primary and secondary metabolites of Mentha aquatica L. exposed to different concentrations of manganese

This experiment was conducted in order to determine the effects of different concentrations of manganese (Mn) on the levels and correlations of multiple primary and secondary metabolites in Mentha aquatica. With this aim, four levels of Mn concentrations were used as follows: basic Hoagland's solution (control), 40, 80, and 160 μM of Mn supplied as MnSO₄.H₂O. The results indicated that the biomass and the contents of photosynthetic pigments and soluble carbohydrates were higher in the plants that were treated with the moderate concentrations of Mn (40 and 80 μM) than the control and 160 μM-treated plants. On the other hand, the contents of flavonoids, anthocyanins, malonaldehyde (MDA), hydrogen peroxide (H₂O₂), and the activities of antioxidant enzymes (total superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX)) were progressively increased with the enhancement of Mn concentration in the nutrient solution. In addition, there were clear differences in the content and chemical composition of essential oils among the control and treatment groups. In this study, 1,8-cineole, menthofuran, and β-caryophyllene were the most abundant constituents of essential oils in both the control and Mn-treated plants. The correlation analysis between pairs of the primary and secondary metabolites showed that there were positive and negative correlations among the variables when the Mn concentration was increased in the nutrient solution. These findings clearly display a positive effect of Mn up to 80 μM in the nutrient solution on the growth of M. aquatica.

Manganese modulates the physiological and biochemical responses of Mentha aquatica L. to ultraviolet radiation

Ultraviolet (UV) radiation as an environmental factor alters the physiological and metabolic processes in plants. Manganese (Mn) is an essential element that is required for plant growth and development. This experiment was conducted in order to determine the effects of Mn supply and UV radiation on the physiological and metabolic responses in Mentha aquatica. With this aim, three levels of Mn and UV treatments were used as follows: basic Hoagland's nutrient solution without UV radiation (control), Mn supply (100μM), UV radiation (2h daily), and UV+100μM Mn. After three weeks of treatments, the root and shoot dry weights and the contents of photosynthetic pigments were decreased under UV radiation condition. However, the contents of flavonoids, soluble carbohydrate, anthocyanins, malonaldehyde (MDA), hydrogen peroxide (H₂O₂), and the activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase) were increased. Interestingly, Mn at 100μM concentration decreased the harmful effects of UV radiation on M. aquatica. In addition, the clear differences were observed in the terpene constituents of M. aquatica after the Mn and UV treatments. In this study, 1, 8-cineole, menthofuran and β-caryophyllene were the most abundant constituents of essential oils in both the control and treated plants. The correlation analysis between pairs of the primary and secondary metabolites showed that there were positive and negative correlations among the variables under the Mn supply and UV radiation conditions. These findings clearly display a positive effect of external Mn up to 100μM in the nutrient solution on the resistant of M. aquatica to UV radiation.

Physiological, biochemical and molecular responses of Mentha aquatica L. to manganese

Mentha aquatica is an aromatic herb which possesses valuable terpenoids constituents. Here, we intended to evaluate the effects of the different manganese (Mn) concentrations on the physiological, biochemical and molecular responses in M. aquatica. Basic Hoagland's solution (control), 40, 80, and 160 μM of Mn supplied as MnSO₄·H₂O were applied to the nutrient solution. The results indicated that the different concentrations of Mn differently affected the physiological, biochemical and molecular responses in M. aquatica. The growth parameters (biomass and photosynthetic pigments) and expression levels of β-caryophyllene synthase (CPS), limonene synthase (Ls), geranyl diphosphate synthase (Gpps), and menthofuran synthase (Mfs) genes were increased at the moderate Mn concentrations (40 and 80 μM) and began to decrease at the higher levels. However, the contents of anthocyanins, flavonoids, malonaldehyde (MDA) and hydrogen peroxide (H₂O₂), Mn accumulation, activities of antioxidant enzymes, yield of essential oils and the expression levels of 1-Deoxy d-xylulose-5-phosphate synthase (Dxs) and isopentenyl diphosphate isomerase (Ippi) genes were gradually increased with increasing concentration of Mn in the nutrient solution. Also, the content and chemical composition of terpenoid constituents were altered in the Mn-treated plants. Here, we suggest that the application of external Mn in nutrient solution elevates the growth and expression levels of the genes that are involved in the terpenoid biosynthesis pathway in M. aquatica. Nevertheless, the extent and stability of these growth and gene expression elevation are varied among the different Mn treatments.

Potential protective effects of alpha-pinene against cytotoxicity caused by aspirin in the IEC-6 cells

Alpha-pinene is a key compound of the essential oils extracted from many species of coniferous trees. It is known for its biological activities. The aim of the present study was to determine the preventive effect of alpha-pinene on aspirin-induced toxicity in vitro, using IEC-6 cells, and to investigate its antioxidant activities. The antioxidant activities were determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP). The cytotoxicity and oxidative stress were detected by cell viability, antioxidant enzyme activity, malondialdehyde (MDA) and GSH production, and the activation of MAPK pathways. The results indicated that alpha-pinene revealed an important antioxidant activity. It was evaluated by DPPH test (EC₅₀=310±10μg/mL) and FRAP test (EC₅₀=238±18.92μg/mL). The co-exposure of alpha-pinene with aspirin on cells significantly increased the survival of cells and the level of GSH, and decreased the levels of MDA and total SOD and the activity of Mn-SOD. In addition, the activation of p38 and JNK was blocked by alpha-pinene. Therefore, these findings suggest that alpha-pinene can protect IEC-6 cells against aspirin-induced oxidative stress.

Vibrational and Thermal Studies of Essential Oils Derived from Cistus ladanifer and Erica arborea Shrubs

Essential oils from the two most representative shrub species from the Iberian Peninsula (namely Cistus ladanifer L. and Erica arborea L.) have been characterized by Fourier transform infrared spectroscopy (FTIR) and thermoanalytical techniques (TG/DTG and DSC). Vibrational spectra have been compared with those of components of the plants, and with those of oils, gums and resins from other species. The different content in terpenoids of C. ladanifer oil (mainly mono- and sesquiterpenoids) and E. arborea oil (mainly triterpenoids) is reflected in the ATR-FTIR by the position of the bands at around 2873 cm−1, 1730 cm−1 and 1678 cm−1. As regards their thermal behavior, C. ladanifer-derived oil evinced higher thermal stability than that of obtained from E. arborea: the pyrolysis of the former was sensitized at 210°C, whereas for the later it occurred at 143°C. These temperatures are high enough to state that thermolabile constituents such as terpenoids are conserved in the hydrodistillation and that this extraction process ensures the recovery of the main constituents of both essential oils.

Genomic Analysis of Terpene Synthase Family and Functional Characterization of Seven Sesquiterpene Synthases from Citrus sinensis

Citrus aroma and flavor, chief traits of fruit quality, are derived from their high content in essential oils of most plant tissues, including leaves, stems, flowers, and fruits. Accumulated in secretory cavities, most components of these oils are volatile terpenes. They contribute to defense against herbivores and pathogens, and perhaps also protect tissues against abiotic stress. In spite of their importance, our understanding of the physiological, biochemical, and genetic regulation of citrus terpene volatiles is still limited. The availability of the sweet orange (Citrus sinensis L. Osbeck) genome sequence allowed us to characterize for the first time the terpene synthase (TPS) family in a citrus type. CsTPS is one of the largest angiosperm TPS families characterized so far, formed by 95 loci from which just 55 encode for putative functional TPSs. All TPS angiosperm families, TPS-a, TPS-b, TPS-c, TPS-e/f, and TPS-g were represented in the sweet orange genome, with 28, 18, 2, 2, and 5 putative full length genes each. Additionally, sweet orange β-farnesene synthase, (Z)-β-cubebene/α-copaene synthase, two β-caryophyllene synthases, and three multiproduct enzymes yielding β-cadinene/α-copaene, β-elemene, and β-cadinene/ledene/allo-aromandendrene as major products were identified, and functionally characterized via in vivo recombinant Escherichia coli assays.

Impact of summer drought on isoprenoid emissions and carbon sink of three Scots pine provenances

Scots pine (Pinus sylvestris L.) provenances cover broad ecological amplitudes. In a greenhouse study, we investigated the impact of drought stress and rewetting on gas exchange for three provenances (Italy: Emilia Romagna; Spain: Alto Ebro; Germany: East-German lowlands) of 2-year old Scots pine seedlings. CO₂, water vapour and isoprenoid exchange of stressed and control trees were quantified with a four-chamber dynamic-enclosure system in the controlled environment of a climate chamber. The three provenances showed distinct isoprenoid emission patterns and were classified into a non-Δ³-carene, with either high α-/β-pinene or β-myrcene fraction, and a Δ³-carene dominated type. Isoprenoid emission rates, net-photosynthesis and transpiration were reduced during summer drought stress and significantly recovered after rewetting. A seasonal increase of isoprenoid emission rates towards autumn was observed for all control groups. Compared with the German provenance, the Spanish and Italian provenances revealed higher isoprenoid emission rates and more plastic responses to drought stress and seasonal development, which points to a local adaptation to climate. As a result of drought, net carbon uptake and transpiration of trees was reduced, but recovered after rewetting. We conclude from our study that Scots pine isoprenoid emission is more variable than expected and sensitive to drought periods, likely impacting regional air chemistry. Thus, a provenance-specific emission assessment accounting for reduced emission during prolonged (summer) drought is recommend for setting up biogenic volatile organic compound emission inventories used in air quality models.

Isoprenoids emission in Stipa tenacissima L.: Photosynthetic control and the effect of UV light

Fluxes of CO2 and isoprenoids were measured for the first time in Stipa tenacissima L (alfa grass), a perennial tussock grass dominant in the driest areas of Europe. In addition, we studied how those fluxes were influenced by environmental conditions, leaf ontogeny and UV radiation and compared emission rates in two contrasting seasons: summer when plants are mostly inactive and autumn, the growing season in this region. Leaf ontogeny significantly affected both photosynthesis and isoprenoids emission. Isoprene emission was positively correlated with photosynthesis, although a low isoprene emission was detected in brown leaves with a net carbon loss. Moreover, leaves with a significant lower photosynthesis emitted only monoterpenes, while at higher photosynthetic rates also isoprene was produced. Ambient UV radiation uncoupled photosynthesis and isoprene emission. It is speculated that alfa grass represent an exception from the general rules governing plant isoprenoid emitters.

Drought and soil amendment effects on monoterpene emission in rosemary plants

The aim of this work was to study the changes during 15days in the monoterpene emission rates of the Mediterranean shrub rosemary (Rosmarinus officinalis L.), in response to increasing drought stress and fertilisation using two different composts derived from livestock anaerobic digestates (cattle and pig slurry). Drought stress considerably reduced photosynthetic rates, stomatal conductance and isoprenoid emissions and also induced a change in blend composition. In the drought stressed rosemary plants, a positive relationship of non-oxygenated monoterpene emissions and a negative relationship of oxygenated monoterpene with photosynthesis were observed, indicating a different control mechanism over the emissions of the two types of isoprenoids. The emission of non-oxygenated monoterpenes seemed to depend more on photosynthesis and "de novo" synthesis, whereas emission of oxygenate monoterpenes was more dependent on volatilisation from storage, mainly driven by cumulative temperatures. In the short term, the addition of composted organic materials to the soil did not induce a significant effect on isoprenoid emission rates in the rosemary plants. However, the effect of the interaction between fertilisation and seasonality on isoprenoid emission rates was influenced by the amendment origin. Also, we emphasized changes in potential isoprenoid emission factors throughout the experiment, probably indicating changes in the leaf developmental stage.

Secondary compounds enhance flammability in a Mediterranean plant

Some plant secondary compounds, such as terpenes, are very flammable; however, their role in enhancing plant flammability is poorly understood and often neglected in reviews on plant chemical ecology. This is relevant as there is growing evidence that flammability-enhancing traits are adaptive in fire-prone ecosystems. We analyzed the content of monoterpenes and sesquiterpenes, performed flammability tests and genotyped microsatellite markers, all in the same individuals of Rosmarinus officinalis, to evaluate the link between the content of terpenes, flammability and the genetic similarity among individuals. The results suggest that terpenes enhance flammability in R. officinalis, and that variability in flammability among individuals is likely to have a genetic basis. Overall our results suggest that the capacity to produce and store terpenes can be considered a flammability-enhancing trait and could have an adaptive value in fire-prone ecosystems.

Changes in floral bouquets from compound-specific responses to increasing temperatures

We addressed the potential effects of changes in ambient temperature on the profiles of volatile emissions from flowers and tested whether warming could induce significant quantitative and qualitative changes in floral emissions, which would potentially interfere with plant-pollinator chemical communication. We measured the temperature responses of floral emissions of various common species of Mediterranean plants using dynamic headspace sampling and used GC-MS to identify and quantify the emitted terpenes. Floral emissions increased with temperature to an optimum and thereafter decreased. The responses to temperature modeled here predicted increases in the rates of floral terpene emission of 0.03-1.4-fold, depending on the species, in response to an increase of 1 °C in the mean global ambient temperature. Under the warmest projections that predict a maximum increase of 5 °C in the mean temperature of Mediterranean climates in the Northern Hemisphere by the end of the century, our models predicted increases in the rates of floral terpene emissions of 0.34-9.1-fold, depending on the species. The species with the lowest emission rates had the highest relative increases in floral terpene emissions with temperature increases of 1-5 °C. The response of floral emissions to temperature differed among species and among different compounds within the species. Warming not only increased the rates of total emissions, but also changed the ratios among compounds that constituted the floral scents, i.e. increased the signal for pollinators, but also importantly altered the signal fidelity and probability of identification by pollinators, especially for specialists with a strong reliance on species-specific floral blends.

Biogenic volatile organic compound (BVOC) emissions from forested areas in Turkey: determination of specific emission rates for thirty-one tree species

Normalized biogenic volatile organic compound (BVOC) emission rates for thirty one tree species that cover the 98% of national forested areas in Turkey were determined. Field samplings were performed at fourteen different forested areas in Turkey using a specific dynamic enclosure system. The selected branches of tree species were enclosed in a chamber consisted of a transparent Nalofan bag. The air-flows were sampled from both inlet and outlet of the chamber by Tenax-filled sorbent tubes during photosynthesis of trees under the presence of sunlight. Several environmental parameters (temperature, humidity, photosynthetically active radiation-PAR, and CO2) were continuously monitored inside and outside the enclosure chamber during the samplings. Collected samples were analyzed using a gas chromatography mass spectrometry (GC/MS) system equipped with a thermal desorber (TD). Sixty five BVOCs classified in five major groups (isoprene, monoterpenes, sesquiterpenes, oxygenated sesquiterpenes, and other oxygenated compounds) were analyzed. Emission rates were determined by normalization to standard conditions (1000 μmol/m(2)s PAR and 30 °C temperature for isoprene and 30 °C temperature for the remaining compounds). In agreement with the literature, isoprene was mostly emitted by broad-leaved trees while coniferous species mainly emitted monoterpenes. Several tree species such as Sweet Chestnut, Silver Lime, and European Alder had higher monoterpene emissions although they are broad-leaved species. High isoprene emissions were also observed for a few coniferous species such as Nordmann Fir and Oriental Spruce. The highest normalized total BVOC emission rate of 27.1 μg/gh was observed for Oriental Plane while South European Flowering Ash was the weakest BVOC emitter with a total normalized emission rate of 0.031 μg/gh. Monoterpene emissions of broad-leaved species mainly consisted of sabinene, limonene and trans-beta-ocimene, while alpha-pinene, beta-pinene and beta-myrcene were generally emitted by coniferous species. Oxygenated compounds were the third most prominent BVOC group and sesquiterpenes had slightly lower contributions.

Contrasting trait syndromes in angiosperms and conifers are associated with different responses of tree growth to temperature on a large scale

Recent large-scale studies of tree growth in the Iberian Peninsula reported contrasting positive and negative effects of temperature in Mediterranean angiosperms and conifers. Here we review the different hypotheses that may explain these trends and propose that the observed contrasting responses of tree growth to temperature in this region could be associated with a continuum of trait differences between angiosperms and conifers. Angiosperm and conifer trees differ in the effects of phenology in their productivity, in their growth allometry, and in their sensitivity to competition. Moreover, angiosperms and conifers significantly differ in hydraulic safety margins, sensitivity of stomatal conductance to vapor-pressure deficit (VPD), xylem recovery capacity or the rate of carbon transfer. These differences could be explained by key features of the xylem such as non-structural carbohydrate content (NSC), wood parenchymal fraction or wood capacitance. We suggest that the reviewed trait differences define two contrasting ecophysiological strategies that may determine qualitatively different growth responses to increased temperature and drought. Improved reciprocal common garden experiments along altitudinal or latitudinal gradients would be key to quantify the relative importance of the different hypotheses reviewed. Finally, we show that warming impacts in this area occur in an ecological context characterized by the advance of forest succession and increased dominance of angiosperm trees over extensive areas. In this context, we examined the empirical relationships between the responses of tree growth to temperature and hydraulic safety margins in angiosperm and coniferous trees. Our findings suggest a future scenario in Mediterranean forests characterized by contrasting demographic responses in conifer and angiosperm trees to both temperature and forest succession, with increased dominance of angiosperm trees, and particularly negative impacts in pines.

Seasonal trends of biogenic terpene emissions

Biogenic volatile organic compound (BVOC) emissions from six coniferous tree species, i.e. Pinus ponderosa (Ponderosa Pine), Picea pungens (Blue Spruce), Pseudotsuga menziesii (Rocky Mountain Douglas Fir) and Pinus longaeva (Bristlecone Pine), as well as from two deciduous species, Quercus gambelii (Gamble Oak) and Betula occidentalis (Western River Birch) were studied over a full annual growing cycle. Monoterpene (MT) and sesquiterpene (SQT) emissions rates were quantified in a total of 1236 individual branch enclosure samples. MT dominated coniferous emissions, producing greater than 95% of BVOC emissions. MT and SQT demonstrated short-term emission dependence with temperature. Two oxygenated MT, 1,8-cineol and piperitone, were both light and temperature dependent. Basal emission rates (BER, normalized to 1000μmolm(-2)s(-1) and 30°C) were generally higher in spring and summer than in winter; MT seasonal BER from the coniferous trees maximized between 1.5 and 6.0μgg(-1)h(-1), while seasonal lows were near 0.1μgg(-1)h(-1). The fractional contribution of individual MT to total emissions was found to fluctuate with season. SQT BER measured from the coniferous trees ranged from <0.01 to 0.15μgg(-1)h(-1). BER of up to 1.2μgg(-1)h(-1) of the SQT germacrene B were found from Q. gambelii, peaking in late summer. The β-factor, used to define temperature dependence in emissions modeling, was not found to exhibit discernible growth season trends. A seasonal correction factor proposed by others in previous work to account for a sinusoidal shaped emission pattern was applied to the data. Varying levels of agreement were found between the data and model results for the different plant species seasonal data sets using this correction. Consequently, the analyses on this extensive data set suggest that it is not feasible to apply a universal seasonal correction factor across different vegetation species. A modeling exercise comparing two case scenarios, (1) without and (2) with consideration of the seasonal changes in emission factors illustrated large deviations when emission factors are applied for other seasons than those in which they were experimentally determined.

Organic constituents on the surfaces of aerosol particles from Southern Finland, Amazonia, and California studied by vibrational sum frequency generation

This article summarizes and compares the analysis of the surfaces of natural aerosol particles from three different forest environments by vibrational sum frequency generation. The experiments were carried out directly on filter and impactor substrates, without the need for sample preconcentration, manipulation, or destruction. We discuss the important first steps leading to secondary organic aerosol (SOA) particle nucleation and growth from terpene oxidation by showing that, as viewed by coherent vibrational spectroscopy, the chemical composition of the surface region of aerosol particles having sizes of 1 μm and lower appears to be close to size-invariant. We also discuss the concept of molecular chirality as a chemical marker that could be useful for quantifying how chemical constituents in the SOA gas phase and the SOA particle phase are related in time. Finally, we describe how the combination of multiple disciplines, such as aerosol science, advanced vibrational spectroscopy, meteorology, and chemistry can be highly informative when studying particles collected during atmospheric chemistry field campaigns, such as those carried out during HUMPPA-COPEC-2010, AMAZE-08, or BEARPEX-2009, and when they are compared to results from synthetic model systems such as particles from the Harvard Environmental Chamber (HEC). Discussions regarding the future of SOA chemical analysis approaches are given in the context of providing a path toward detailed spectroscopic assignments of SOA particle precursors and constituents and to fast-forward, in terms of mechanistic studies, through the SOA particle formation process.

Direct and indirect impact of sewage sludge compost spreading on Quercus coccifera monoterpene emissions in a Mediterranean shrubland

Monoterpene emissions of Quercus coccifera L. were repeatedly measured during the two years following the spreading of a sewage sludge compost at rates of 50 Mg ha⁻¹ and 100 Mg ha⁻¹, in a twelve-year-old post-fire Mediterranean shrubland. We also monitored the patterns of change in soil and leaf nutrient content, plant water potential, chlorophyll fluorescence, and plant growth. Compost spreading resulted in weak changes in leaf nutrient content and plant water status, and therefore no significant effect on monoterpene emissions at leaf scale, except during one summer sampling, probably related to advanced leaf maturity with the highest compost rate. However, compost increased plant growth, particularly the leaf biomass. The results suggest that compost spreading in Mediterranean shrublands has no strong short-term effect on Q. coccifera monoterpene emissions at leaf level, but may indirectly increase volatile organic compound fluxes at the stand scale, which may contribute to regional ozone pollution.

Doubled volatile organic compound emissions from subarctic tundra under simulated climate warming

*Biogenic volatile organic compound (BVOC) emissions from arctic ecosystems are important in view of their role in global atmospheric chemistry and unknown feedbacks to global warming. These cold ecosystems are hotspots of climate warming, which will be more severe here than averaged over the globe. We assess the effects of climatic warming on non-methane BVOC emissions from a subarctic heath. *We performed ecosystem-based chamber measurements and gas chromatography-mass spectrometry (GC-MS) analyses of the BVOCs collected on adsorbent over two growing seasons at a wet subarctic tundra heath hosting a long-term warming and mountain birch (Betula pubescens ssp. czerepanovii) litter addition experiment. *The relatively low emissions of monoterpenes and sesquiterpenes were doubled in response to an air temperature increment of only 1.9-2.5 degrees C, while litter addition had a minor influence. BVOC emissions were seasonal, and warming combined with litter addition triggered emissions of specific compounds. *The unexpectedly high rate of release of BVOCs measured in this conservative warming scenario is far above the estimates produced by the current models, which underlines the importance of a focus on BVOC emissions during climate change. The observed changes have implications for ecological interactions and feedback effects on climate change via impacts on aerosol formation and indirect greenhouse effects.