Total Monoterpene Content Research Articles

Does green mean clean? Volatile organic emissions from regular versus green cleaning products.

Cleaning products emit a range of volatile organic compounds (VOCs), including some which are hazardous or can undergo chemical transformations to generate harmful secondary pollutants. In recent years, "green" cleaners have become increasingly popular, with an implicit assumption that these are better for our health and/or the environment. However, there is no strong evidence to suggest that they are better for indoor air quality compared to regular products. In this study, the VOC composition of 10 regular and 13 green cleaners was examined by headspace analysis. Monoterpenes were the most prevalent VOCs, with average total monoterpene concentrations of 8.6 and 25.0 mg L-1 for regular and green cleaners, respectively. Speciated monoterpene emissions were applied to a detailed chemical model to investigate the indoor air chemistry following a typical cleaning event. Green cleaners generally emitted more monoterpenes than regular cleaners, resulting in larger increases in harmful secondary pollutant concentrations following use, such as formaldehyde (up to 7%) and PAN species (up to 6%). However, emissions of the most reactive monoterpenes (α-terpinene, terpinolene and α-phellandrene), were observed more frequently from regular cleaners, resulting in a disproportionately large impact on the concentrations of radical species and secondary pollutants that were formed after cleaning occurred.

Effects of Trellis Systems on the Vegetative Growth and Fruit Quality of Muscat-Flavored Table Grapes

The selection of appropriate grapevine trellis systems is of great importance for regulating vine vigor, forming grape yield, improving fruit quality, and labor-saving field management in the North China Plain. The effects of two trellis systems on the viticultural characteristics and fruit quality of three table grape cultivars: RuiduHongyu (RDHY), RuiduXiangyu (RDXY), and Red Globe (RG) were investigated. The two trellis systems were: (i) T trellis, with shoots positioned horizontally and downwards; and (ii) V trellis, with shoots positioned upright with an inclined angle. Headspace-solid-phase micro-extraction combined with gas chromatography mass spectrometry (HS-SPME-GC-MS) was used to determine the compositions and contents of the monoterpenes in the fruit. The results showed that for RDHY and RG, the T trellis showed better shoot growth consistency. The sugar–acid ratios of RDHY in 2019 and RDXY in 2021 under the T trellis were significantly higher than those under the V trellis. In 2020 and 2021, RDHY showed significantly higher total anthocyanin, flavonoid, and proanthocyanidin concentrations under the T trellis. The total monoterpene content in RDHY berries was significantly higher under the T trellis. The aromatic profiles of RDHY and RDXY grapes were similar and were mainly composed of citrus, other floral, other fruit, and rose aromatic characteristics. Among them, the main aromatic characteristics varied greatly among the different treatments. In conclusion, the Eurasian table grape cultivars with muscat flavor showed a more moderate and controllable vine vigor, consistent shoot growth, better fruit quality and taste, and greater accumulation of polyphenolic compounds and monoterpenes under the T trellis system.

Transcriptomics Integrated with Metabolomics Reveals the Effect of Cluster Thinning on Monoterpene Biosynthesis in 'Muscat Hamburg' Grape.

Monoterpenes are crucial to floral and fruit aromas in grapes and wines. Cluster thinning is a common practice for improving grape quality. Using Vitis vinifera cv. Muscat Hamburg, the effects of three cluster-thinning regimes on the biosynthesis and accumulation of monoterpenes from véraison to harvest were investigated at the transcriptomics and targeted metabolomics levels. It was observed that more intense thinning produced higher concentrations of total monoterpenes, particularly in their bound forms. The numbers of differentially expressed genes among the three treatments were 193, 200, and 238 at the three developmental stages. In total, 10 modules were identified from a weighted gene correlation network analysis, and one module including 492 unigenes was associated with monoterpene metabolism. These findings provide new insights into the molecular basis of the relationship between cluster thinning and monoterpene biosynthesis in Muscat Hamburg grape. Cluster thinning could be carefully considered for its application in production.

Hotter droughts alter resource allocation to chemical defenses in pi\xf1on 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.

Human Breathable Air in a Mediterranean Forest: Characterization of Monoterpene Concentrations under the Canopy.

Monoterpenes have been identified as potential determinants of the human health effects induced by forest exposure. The present study characterizes the total monoterpene concentrations at nose height in a Mediterranean Holm oak forest located in North-East Iberian Peninsula during the annual emission peak (summer and autumn: June to November) using a Proton Transfer Reaction–Mass Spectrometry (PTR-MS). Results show a strong variability of the total monoterpene concentrations in season and daytime. The concentration peak appears during July and August. These two months displayed two average maxima in their diel cycles: One during early morning (from 6:00 to 8:00, 0.30 ppbv for July and 0.41 ppbv for August) and another one at early afternoon (from 13:00 to 15:00, 0.27 ppbv during July and 0.32 ppbv during August). Monoterpene concentrations were strongly related with the temperature (exponentially) and solar radiation (rectangular hyperbolic relationship). The concentrations registered here are similar or higher than in previous ex situ studies showcasing the effects of forests on human health. These findings provide relevant data for the scientific and healthcare community by improving the understanding of monoterpene dynamics at nose height and suggesting further research on the effects of forests on human health, particularly in the Mediterranean region.

Effect of cluster zone leaf removal on monoterpene profiles of Sauvignon Blanc grapes and wines

Monoterpenes contribute to the varietal aromas of grapes and wines. We determined the effects of cluster zone leaf removal on the monoterpene profiles of Sauvignon Blanc grape berries and wines, and on the expression of key genes in the terpenoid pathway. Leaf removal at two intensities (half basic, 50%; full basic, 100%) was conducted at two weeks before veraison, veraison, and two weeks after veraison. Half basic leaf removal increased the pH and decreased the tartaric acid content in grapes and wines. The concentrations of most free- and bound-form monoterpenes in grapes were increased by early leaf removal. The total monoterpene contents were increased in wines in the defoliation treatments, but were significantly lower in wines from the full basic leaf removal treatments than in wines from the half basic leaf removal treatments. The defoliation treatments resulted in increased transcript levels of some key genes in terpene biosynthesis (VvPNLinNer1, VvPNLinNer2, VvPNLNGl1, VvPNLNGl2, and VvUGT88A1L1).

Temporal and Spatial Variation in Scots Pine Resin Pressure and Composition

Resin is a first-line defense in pine trees, but important questions regarding its temporal and spatial variation remain unsolved. Resin pressure varies according to water potential in dry conditions, but in moist conditions, it follows temperature dynamics for a yet unknown reason. Relations between resin composition, resin pressure, and shoot monoterpene emissions are also unquantified. To gain mechanistic understanding on the resin dynamics in a boreal forest, we measured temperature and water potential dependency of Scots pine resin pressure. We attempted to quantify the temperature dependency of resin pressure in terms of three contributions: 1) saturation vapor pressure, 2) thermal expansion, and 3) N2, O2, and CO2 solubility. We also analyzed monoterpene composition in the resin and the shoot emissions of 16 pines with gas chromatography mass spectrometry to study their interrelations. We show that in moist conditions, resin pressure is driven by temperature at a diurnal scale, but also affected by soil water potential at a day-to-day scale. Diurnal temperature dependency was explained by thermal expansion of resin and changes in bubble volume due to changes in gas solubility in resin with temperature. Resin pressures correlated also with total monoterpene and α-pinene content in resin and with total monoterpene and ∆3-carene and terpinolene emissions from shoots.

Phenolic acids and terpenoids in the soils of different weed-suppressive circles of allelopathic rice

ABSTRACTAllelopathic rice ‘PI312777’ (PI) and non-allelopathic rice ‘Lemont’ (Le) were used to assess phenolic acids and terpenoids in the soils of different circles using inhibitory-circle method. The rhizosphere soils of rice (inner circle) and barnyard grass at a 12 cm distance from rice (outer circle) were collected for analyses. The results showed total content of phenolic acids in outer circle of PI was significantly higher than that of Le, while the outer soil of PI contained a higher total content of benzoic acid derivatives and a lower total content of cinnamic acid derivatives than the inner soil. Total terpenoid and monoterpene contents in inner and outer circle soils of PI were significantly higher than that of Le, and the ratio of oxygenated monoterpenes in outer soil of PI was higher than that of Le. Furthermore, phenolic acid mixtures showed a more obvious inhibitory effect on root length than on shoot length of the receptor, while oxygenated monoterpenes were opposite, and a low concentration of oxygenated monoterpenes enhanced inhibitory effect of phenolic acids mixtures on shoot length of the receptor. All results suggested oxygenated monoterpenes participated in the weed-suppressive effect together with phenolic acids of allelopathic rice.

Time-integrated thermal desorption for quantitative SIFT-MS analyses of atmospheric monoterpenes.

A new time-integrated thermal desorption technique has been developed that can be used with selected ion flow tube mass spectrometry, TI-TD/SIFT-MS, for off-line quantitative analyses of VOCs accumulated onto sorbents. Using a slow desorption temperature ramp, the absolute amounts of desorbed compounds can be quantified in real time by SIFT-MS and constitutional isomers can be separated. To facilitate application of this technique to environmental atmospheric monitoring, method parameters were optimised for quantification of the three common atmospheric monoterpenes: β-pinene, R-limonene and 3-carene. Three sorbent types, Tenax TA, Tenax GR and Porapak Q, were tested under 26 different desorption conditions determined by the "design of experiment", DOE, systematic approach. The optimal combination of type of sorbent, bed length, sampling flow rate, sample volume and the initial desorption temperature was determined from the experimental results by ANOVA. It was found that Porapak Q exhibited better efficiency of sample collection and further extraction for total monoterpene concentration measurements. On the other hand, Tenax GR or TA enabled separation of all three monoterpenes. The results of this laboratory study were tested with the sample accumulated from a branch of a Pinus nigra tree. Graphical abstract.

Spatiotemporal variations of below-ground monoterpene concentrations in an upland black spruce stand in interior Alaska

Monoterpenes play important roles in atmospheric chemistry and g lobal warming, and their sources and sinks have been investigated. However, there is no information about monoterpene concentrations in black spruce (Picea mariana) forest soil. Here, we investigated seasonal and spatial variations of monoterpene concentrations in soil of an upland black spruce stand in interior Alaska. The site comprised three plots with different tree biomasses, organic layer depths, and vegetation types (mosses and lichens). At each plot, monoterpene concentrations in air in the atmosphere, the soil, and the organic layer under various vegetation types (including leaf litter) were determined. Nine monoterpenes were identified: α-pinene, camphene, β-pinene, 3-carene, sabinene, myrcene, p-cymene, limonene, and β-phellandrene. The total monoterpene concentration in the atmosphere was <0.01 mg m−3, whereas the total concentration in the organic layer sometimes exceeded 1.0 mg m−3. The total monoterpene concentration in the organic layer was lower in the fall than in the spring and summer, and the concentrations differed among the plots, perhaps because of differences in tree biomass and vegetation. The most abundant monoterpene in the organic layer was α-pinene, accounting for ∼50% of the total monoterpenes; and camphene emission may a unique feature of black spruce forest soils.

Monoterpene responses to interacting effects of drought stress and infection by the fungus Heterobasidion parviporum in two clones of Norway spruce (Picea abies)

To study simultaneous biotic and abiotic stress effects on monoterpene mediated defence response, four-year-old seedlings of two clones of Picea abies (c386: “relatively resistant” c386; c171: “relatively susceptible” clone 171) were inoculated with an isolate of rot fungus Heterobasidion parviporum and simultaneously subjected to a drought stress recovery cycle. Fungal growth into the wood was generally higher in well-watered (W) than in drought-stressed (D) plants. As predawn water potential decreased, gas exchange and maximal photochemical efficiency of PSII also declined. Water potential and chlorophyll fluorescence showed differences between clones in D plants, c386 being more tolerant than c171, while stomatal conductance and net photosynthesis differed between clones in W plants; c171 showing higher values than c386. A recovery of physiological functions was observed after re-watering. The clones showed different constitutive monoterpene profiles. The infection generally caused some extensive compositional changes in the relative contents of several monoterpenes and their enantiomers; also, sterile infection (wounded only samples) affected the relative proportions of monoterpenes, although to a lesser extent than reactions elicited by the fungus. The trend in monoterpene response to disease treatments was the same in D and W plants of both clones. In particular, higher proportion of δ-3-carene was found constitutively in c386 in comparison with c171; besides, infection with H. parviporum increased the relative contents of δ-3-carene in all the samples, even if proportions of this monoterpene in wounded plus inoculated tissues of c386 were significantly higher than cortical tissues from non-inoculated branches only in W seedlings 44 days after treatment.Although drought stress decreased the total absolute contents of monoterpenes, total monoterpene concentrations significantly increased in response to infection by H. parviporum.

Successful Colonization of Lodgepole Pine Trees by Mountain Pine Beetle Increased Monoterpene Production and Exhausted Carbohydrate Reserves.

Lodgepole pine (Pinus contorta) forests have experienced severe mortality from mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins) in western North America for the last several years. Although the mechanisms by which beetles kill host trees are unclear, they are likely linked to pine defense monoterpenes that are synthesized from carbohydrate reserves. However, how carbohydrates and monoterpenes interact in response to MPB colonization is unknown. Understanding this relationship could help to elucidate how pines succumb to bark beetle attack. We compared concentrations of individual and total monoterpenes and carbohydrates in the phloem of healthy pine trees with those naturally colonized by MPB. Trees attacked by MPB had nearly 300% more monoterpenes and 40% less carbohydrates. Total monoterpene concentrations were most strongly associated with the concentration of sugars in the phloem. These results suggest that bark beetle colonization likely depletes carbohydrate reserves by increasing the production of carbon-rich monoterpenes, and other carbon-based secondary compounds. Bark beetle attacks also reduce water transport causing the disruption of carbon transport between tree foliage and roots, which restricts carbon assimilation. Reduction in carbohydrate reserves likely contributes to tree mortality.

Resin monoterpene defenses decline within three widespread species of pine (Pinus) along a 1530‐m elevational gradient

AbstractThe elevational gradient in plant defense (EGPD) hypothesis posits that natural enemy pressures increase alongside temperature across elevational climatic gradients, thereby selecting for enhanced defenses at lower elevations while leaving plants less defended at higher elevations. Phylogenetically constrained tests of this hypothesis are uncommon, with tests focused on defenses of mature trees in natural settings being exceedingly rare. In the absence of this information, predicting the spatiotemporal dynamics of forest pests that preferentially attack mature trees is rendered more difficult. Tree properties such as age, growth rate, and size have all been correlated with levels of tree defenses against insect pests. Thus, we sought to disentangle the interacting influences of these properties from possible elevational climatic effects on monoterpene concentrations, diversity, and intraspecific dissimilarity of constitutive resin within three widespread pines (Pinus contorta, Pinus ponderosa, and Pinus flexilis) across a 1530‐m elevational transect in the Rocky Mountains, Colorado, USA. Overall, we found some support for the EGPD hypothesis within all three of the pine species studied. However, while elevation and tree properties were strong predictors of the variation in monoterpene concentration and moderate predictors of variation in diversity and dissimilarity in P. contorta, they were a relatively weak set of predictors in P. ponderosa and P. flexilis. Significant, (negative) elevational effects were found for total monoterpene concentration in P. contorta and monoterpene diversity in P. ponderosa, while elevation had a significant negative effect on monoterpene concentration and diversity, and a positive effect on dissimilarity in P. flexilis. Nevertheless, tree age, size, and/or growth measures had significant influences on one or more monoterpene measures in all three of the pine species indicating a need to parse effects of these factors within studies of tree defenses across environmental gradients. Our results offer some support for the EGPD hypothesis while suggesting the presence of a variable hierarchy of drivers of pine defense and resistance across congeners in shared environments—a situation that presents challenges for predicting spatiotemporal patterns in secondary chemistry across species from a common set of potential drivers.

Estimation of terpene content in loblolly pine biomass using a hybrid fast-GC and pyrolysis-molecular beam mass spectrometry method

Terpenes can be used as renewable fuels and chemicals and quantifying their presence in biomass is becoming increasingly important. A novel method was developed to rapidly quantify total diterpenoid resin acids using pyrolysis-molecular beam mass spectrometry (py-MBMS). Pine sapling monoterpenes and diterpenoids were extracted from wood using a 1:1 (v/v) mixture of hexane and acetone and analyses were performed before and after extraction to determine the extraction efficiency of the solvent system. The resulting extract was analyzed for total diterpenoid content using py-MBMS and was combined with total monoterpene content that was determined using a low thermal mass modular accelerated column heater (LTM MACH) fast-GC/FID to measure the terpene content present in pine saplings. Oleoresin extruded from larger pine trees was used to validate mass balance closure of the terpene content in the extract solvent.

Conifer Monoterpene Chemistry during an Outbreak Enhances Consumption and Immune Response of an Eruptive Folivore.

Changes in the chemical composition of plant defense compounds during herbivory can impact herbivore resource allocation patterns and thereby herbivore survival, growth, and immune response against endoparasitoid infection. Few studies have investigated folivore responses to changes in plant chemistry that occur under outbreak conditions in mature conifer systems. Using data from an earlier observational field study, we carried out laboratory bioassays to test how variation in monoterpenes in piñon pine trees (Pinus edulis, Pinaceae) during an outbreak affects growth, consumption, and immune response of a specialist herbivore, the Southwestern tiger moth (Lophocampa ingens, Arctiidae). Larvae were fed on artificial diets containing four monoterpenes at concentrations that mimicked those observed in undamaged and herbivore-damaged trees in situ during an outbreak. Damaged trees contained 30% lower total monoterpene concentrations, likely reflecting volatile losses as observed in a previous field study Trowbridge et al. (Ecology 95:1591-1603, Trowbridge et al. 2014). Herbivores reared on diets mimicking terpene concentrations in the needles of damaged trees exhibited an approximately 60% increase in consumption relative to larvae reared on diets characteristic of trees without herbivore damage. Higher consumption was accompanied by a 40% increase in immune response with no change in growth rate. These observations suggest preferential resource allocation towards immunity and/or a strong genetic component that determines growth under these conditions. These outcomes, which favor the herbivore, point to: (i) a potential positive feedback mechanism that may increase L. ingens's chance of escaping parasitism during the early phases of an outbreak; and (ii) the important role of monoterpenes in mediating conifer-folivore interactions specifically for P. edulis, which has suffered large-scale drought-induced mortality events exacerbated by the presence of insects.

De novo production of six key grape aroma monoterpenes by a geraniol synthase-engineered S. cerevisiae wine strain.

BackgroundMonoterpenes are important contributors to grape and wine aroma. Moreover, certain monoterpenes have been shown to display health benefits with antimicrobial, anti-inflammatory, anticancer or hypotensive properties amongst others. The aim of this study was to construct self-aromatizing wine yeasts to overproduce de novo these plant metabolites in wines.ResultsExpression of the Ocimum basilicum (sweet basil) geraniol synthase (GES) gene in a Saccharomyces cerevisiae wine strain substantially changed the terpene profile of wine produced from a non-aromatic grape variety. Under microvinification conditions, and without compromising other fermentative traits, the recombinant yeast excreted geraniol de novo at an amount (~750 μg/L) well exceeding (>10-fold) its threshold for olfactory perception and also exceeding the quantities present in wines obtained from highly aromatic Muscat grapes. Interestingly, geraniol was further metabolized by yeast enzymes to additional monoterpenes and esters: citronellol, linalool, nerol, citronellyl acetate and geranyl acetate, resulting in a total monoterpene concentration (~1,558 μg/L) 230-fold greater than that of the control. We also found that monoterpene profiles of wines derived from mixed fermentations were found to be determined by the composition of the initial yeast inocula suggesting the feasibility of producing ‘à la carte’ wines having predetermined monoterpene contents.ConclusionsGeraniol synthase-engineered yeasts demonstrate potential in the development of monoterpene enhanced wines.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-015-0306-5) contains supplementary material, which is available to authorized users.

The Differential Effects of the Blue-Stain Fungus Leptographium qinlingensis on Monoterpenes and Sesquiterpenes in the Stem of Chinese White Pine (Pinus armandi) Saplings

When conifers such as Chinese white pine (Pinus armandi Fr.) are attacked by insects or pathogens, they respond by increasing their content of monoterpenes and sesquiterpenes. In this study, we determined the effects of the blue-stain fungus Leptographium qinlingensis Tang and Chen on monoterpenes and sesquiterpenes in the phloem and xylem of the stem of P. armandi saplings. We found that the total monoterpene concentrations in the phloem and xylem of the stem and the total sesquiterpene concentrations in the xylem of the stem were significantly higher in L. qinlingensis-inoculated saplings than in control (mechanically wounded) saplings or untreated saplings. Additionally, the proportions of β-pinene in the xylem of the stem and limonene + β-phellandrene in the phloem and xylem of the stem were significantly higher in L. qinlingensis-inoculated saplings than in both control and untreated saplings. The proportions of individual sesquiterpenes in the phloem and xylem of the stem were significantly greater in L. qinlingensis-inoculated saplings than in untreated saplings. Based on the results of this study, we suggest that increases in total monoterpene and sesquiterpene concentrations, as well as increases in the concentrations of β-pinene and limonene + β-phellandrene, may play an important defensive role against blue-stain fungus L. qinlingensis inoculation.

Changes of monoterpenes in stem of Chinese white pine (Pinus armandi) saplings following treatment with Methyl Jasmonate

Abstract The Chinese white pine beetle (Dendroctonus armandi Tsai and Li) is the causal organism for the colossal death of the Chinese white pine (Pinus armandi Fr). We investigated the change of monoterpenes in the stem pholem and xylem in P. armandi saplings at 4 days, 8 days, and 30 days after treatment using treatment (MeJa + Tween-20 and Tween-20 as control) and untreated. GC-MS analysis found that the total monoterpene concentrations in the pholem and xylem in MeJa-treated saplings increased significantly compared with control or untreated saplings. Additionally, the proportions of β-pinene in the stem pholem, β-myrcene in the stem xylem, and limonene + β-phellandrene in both pholem and xylem of MeJa-treated saplings were increased significantly compared with control or untreated saplings. Based on our results, we suggest that by increasing the total concentration of monoterpene and the concentrations of β-myrcene, β-pinene and limonene + β-phellandrene maybe play an important defensive role against insect pests in P. armandi defense.

Bacteria Associated with a Tree-Killing Insect Reduce Concentrations of Plant Defense Compounds

Bark beetles encounter a diverse array of constitutive and rapidly induced terpenes when attempting to colonize living conifers. Concentrations of these compounds at entry sites can rapidly reach levels toxic to beetles, their brood, and fungal symbionts. Large numbers of beetles can overwhelm tree defenses via pheromone-mediated mass attacks, but the mechanisms are poorly understood. We show that bacteria associated with mountain pine beetles can metabolize monoterpenes and diterpene acids. The abilities of different symbionts to reduce concentrations of different terpenes appear complementary. Serratia reduced concentrations of all monoterpenes applied to media by 55-75 %, except for α-pinene. Beetle-associated Rahnella reduced (-)- and (+)-α-pinene by 40 % and 45 %, respectively. Serratia and Brevundimonas reduced diterpene abietic acid levels by 100 % at low concentrations. However, high concentrations exhausted this ability, suggesting that opposing rates of bacterial metabolism and plant induction of terpenes are critical. The two major fungal symbionts of mountain pine beetle, Grosmannia clavigera and Ophiostoma montium were highly susceptible to abietic acid. Grosmannia clavigera did not reduce total monoterpene concentrations in lodgepole pine turpentine. We propose the ability of bark beetles to exert landscape-scale impacts may arise partly from micro-scale processes driven by bacterial symbionts.

Seasonal variation in vertical volatile compounds air concentrations within a remote hemiboreal mixed forest

Abstract. The vertical distribution of ambient biogenic volatile organic compounds (BVOC) concentrations within a hemiboreal forest canopy was investigated over a period of one year. Variability in temporal and spatial isoprene concentrations, ranging from 0.1 to 7.5 μg m−3, can be mainly explained by biogenic emissions from deciduous trees. Monoterpene concentrations exceeded isoprene largely and ranged from 0.01 to 140 μg m−3 and during winter time anthropogenic contributions are likely. Variation in monoterpene concentrations were found to be largest right above the ground and the vertical profiles suggest a weak mixing leading to terpene accumulation in the lower canopy. Exceptionally high values were recorded during a heat wave in July 2010 with very high midday temperatures above 30 °C for several weeks. During summer months, monoterpene exceeded isoprene concentrations 6-fold and during winter 12-fold. During summer months, dominance of α-pinene in the lower and of limonene in the upper part of the canopy was observed, both accounting for up to 70% of the total monoterpene concentration. During wintertime, Δ3-carene was the dominant species, accounting for 60% of total monoterpene concentration in January. Possible biogenic monoterpene sources beside the foliage are the leaf litter, the soil and also resins exuding from stems. In comparison, the hemiboreal mixed forest canopy showed similar isoprene but higher monoterpene concentrations than the boreal forest and lower isoprene but substantially higher monoterpene concentrations than the temperate mixed forest canopies. These results have major implications for simulating air chemistry and secondary organic aerosol formation within and above hemiboreal forest canopies. Possible effects of in-cartridge oxidation reactions are discussed as our measurement technique did not include oxidant scavenging. A comparison between measurements with and without scavenging oxidants is presented.