Total Monoterpene Research Articles

Secondary Metabolite Concentrations and Terpene Emissions of Scots Pine Xylem after Long‐Term Forest Fertilization

Secondary compounds are known to be associated with the resistance of conifer xylem against insects and fungi. The effects of long-term forest fertilization with nitrogen (N) or with N, calcium (Ca), and phosphorus (P) on secondary compounds in the xylem of 50-yr-old Scots pine (Pinus sylvestris L.) trees were examined. Xylem samples were collected from trees growing in three locations in southern Finland: Vilppula, Padasjoki, and Punkaharju. Forests were fertilized every fifth (Vilppula and Padasjoki) or tenth (Punkaharju) year since the 1950s. We compared concentrations of individual and total monoterpenes and resin acids in the heartwood and sapwood of Scots pine. Terpene emissions were analyzed from the sapwood and total phenolics from the heartwood. Fertilization did not have any significant effect on the concentrations and emissions of xylem monoterpenes. Concentrations of several individual terpenes in sapwood were positively correlated with the corresponding terpene emission. The concentrations of individual resin acids (i.e., abietic and dehydroabietic) decreased significantly in Punkaharju, but increased in the sapwood of N-fertilized trees compared with control ones at Padasjoki and Vilppula. The concentrations of resin acids in the heartwood were not significantly affected by fertilization. Both fertilization treatments decreased the total phenolic concentrations in the heartwood of trees growing in Padasjoki. There was a significant positive correlation between the total phenolics and total resin acid concentration. Overall, resin acids and phenolics seemed be more responsive than monoterpenes to N treatment. These results suggest that forest fertilization might cause slight changes in secondary compound concentrations of xylem, and thus might have significance in the decay resistance of wood.

Linking deer browsing and terpene production among genetic identities in Chamaecyparis nootkatensis and Thuja plicata (Cupressaceae).

To investigate whether differential herbivore browsing reflects genetic variation in plant defense expression, variation in needle terpenes and damage caused by black-tailed deer (Odocoileus hemionus) was analyzed on yellow-cedar (Chamaecyparis nootkatensis) and western redcedar (Thuja plicata). In a 100-genet yellow-cedar population, three genets that were heavily browsed and had extremely low levels of monoterpenes (0-0.36% dry matter), sesquiterpenes, and diterpenes were compared to unbrowsed genets (0.85-3.83% monoterpenes in dry matter). These differences were maintained in individuals protected from browsing, suggesting genetically based variation in constitutive terpene production. In western redcedar, heavily browsed trees had significantly lower total monoterpene concentrations (1.69% dry matter) than lightly browsed trees (3.32% dry matter). One heavily browsed tree expressed no monoterpenes. No differences were found for diterpenes. In both species, the genotypes with extremely low monoterpene concentrations came from the same open-pollinated families.

Monoterpene fluxes measured above a Japanese red pine forest at Oshiba plateau, Japan

Monoterpene fluxes above a Japanese red pine ( Pinus densiflora) forest in Japan were measured with a heat balance method from May to November 2000. The most abundant monoterpenes were α-pinene and limonene+ β-phellandrene. Degradation losses of the major monoterpenes by the reactions with ozone and OH during transfer between the two sampling heights were estimated to be negligibly small. The highest values of average fluxes were observed in June measurement period, with values for α-pinene and limonene+ β-phellandrene of 0.6 and 0.5 nmol m −2 s −1. Their average fluxes in September, October and November measurement periods were almost the same and lowest. Vertical profiles of monoterpene concentrations inside the forest suggest that large amounts of monoterpenes are accumulated in the aerial space in the forest and transferred to the atmosphere above. The difference between logarithms of measured and calculated total monoterpene fluxes, ln F mea –ln F cal , had positive values in many morning measurements and negative values in most late afternoon measurements, indicating that monoterpenes accumulated during the night were transported to the upper atmosphere the next morning and they began to accumulate again in the late afternoon, following a decrease of turbulent mixing. Leaf wetness effect was also considered and, finally, a simple model was proposed to explain controlling parameters for monoterpene flux above the forest.

A model coupling foliar monoterpene emissions to leaf photosynthetic characteristics in Mediterranean evergreen Quercus species

Summary A model was developed and parameterized to simulate monoterpene emission rates per unit leaf area (E) dependent on foliar photosynthetic potentials and activity of monoterpene synthases in the evergreen sclerophylls Quercus coccifera L. and Q. ilex L. Assuming that total activity of monoterpene synthases controls the pathway flux, the product of leaf dry mass per unit area E was culculated as the fraction of total electron flow used for monoterpene synthesis (ɛ), the rate of photosynthetic electron transport (J) per unit leaf dry mass and the reciprocal of the electron cost of monoterpene synthesis. In the model, light effects on E result from light responses of J, and the temperature relationship of E combines temperature dependencies of J and the specific activity of monoterpene synthase (SS). Having determined J from leaf photosynthesis data and deriving an estimate of SS from in vitro laboratory measurements, good fits to diurnal time‐courses of monoterpenoid emission rates were obtained using a single leaf‐dependent coefficient, the total monoterpene synthase activity in the leaves. Our analysis demonstrates that using J as a surrogate of E leads to a realistic description of E, especially under stress conditions where the previous models fail. However, analysis of daily time courses of E indicated that storage of monoterpenoids in nonspecific leaf compartments might alter the correspondence between monoterpenoid synthesis and emission rates, especially after rapid environmental change.

Testing the ecophysiological basis for the control of monoterpene concentrations in thinned and unthinned balsam fir stands across different drainage classes.

Stand thinning across different soil drainage types was used to test the ecophysiological basis for the control of foliar monoterpenes in current-year foliage of balsam trees [Abies balsamea (L.) P. Mill.] the year following treatment. Photosynthetic capacity (A max) was greater on mesic sites than on sub-hygric and hydric sites (1.81, 1.33 and 0.88 µmol m-2 s-1, respectively) and greater in mid-July than at the end of June (1.86 vs 0.77 µmol m-2 s-1). Foliar N was greater on thinned plots than control plots (2.6 vs 2.2g m-2); starch was greater on mesic control plots than mesic thinned plots (16.3 vs 10.9g m-2); and total soluble sugars (TSS) were higher in mid-July than at the end of June (16.5 vs 12.8g m-2). Total monoterpenes, as well as five individual monoterpenes, showed a complex interaction between site drainage class, thinning treatment and time of sampling (P<0.05). For all sites and dates combined, total monoterpenes were negatively correlated with specific leaf area (r 2=0.46), and positively but weakly correlated with A max (r 2=0.35), foliar N (r 2=0.29) and TSS (r 2=0.24). Total monoterpenes were not correlated with the different measures of carbon to nitrogen ratio as predicted by the carbon-nutrient balance hypothesis. Our results offer partial support to the different hypotheses proposing that foliage having greater resource availability, enzymatic machinery and potential for building storage structures will have greater monoterpene content. However, the strength of the relationships with monoterpenes often varied with sampling date, suggesting that phenological development may play a strong role in determining which factors control monoterpenes at a given time.

The role of monoterpenes in resistance of Douglas fir to western spruce budworm defoliation.

We conducted defoliation experiments with 7- to 8-year-old clones of Douglas fir [Pseudotsuga menziesii (Mirb.) Franco var. glauca] to assess the role of monoterpenes as a resistance mechanism to western spruce budworm (Choristoneura occidentalis Freeman) defoliation. The grafted clones were derived from mature trees that showed resistance or susceptibility to budworm defoliation in the forest. All clones were exposed to either budworm defoliation or nondefoliation treatments in 1998 and 1999 under greenhouse conditions. We found that the total concentration of monoterpenes in current-year foliage varied greatly between two consecutive years in clones in the greenhouse and in their corresponding mature trees in the forest. Fractional composition of different monoterpenes was similar between different years and between clones and mature trees, indicating genetic control of this trait. Two different defoliation experiments were conducted to assess the importance of budburst phenology as a factor determining host plant resistance. In the 1998 experiment, budworm feeding was matched to the budburst of each individual plant. Monoterpene concentration was high in 1998, and budworm potential fitness was greater on clones from the resistant mature trees that had lower concentrations of total monoterpenes. In the 1999 experiment, budworm feeding was matched to budburst of the whole population of plants in order to mimic conditions similar to insects feeding on trees in the field. The concentration of monoterpenes was low in 1999, and budworm fitness was not related to monoterpenes. Total monoterpene concentration was negatively related to foliar nitrogen concentration, suggesting that C/N balance may affect monoterpene synthesis in needles. However, tree growth was not related to total monoterpene concentration. We concluded that expression of differences in budworm resistance among Douglas fir genotypes might be caused by interactions among multiple resistance mechanisms such as needle monoterpenes and tree budburst phenology.

Patterns in consumption of woody plants by snowshoe hares in the northwestern United States

Herbivores manifesting spatially variable population densities may elicit geographical differences in the characteristics of the plants upon which they feed. Northern snowshoe hare (Lepus americanus) populations undergo dramatic numerical cycles; during periods of hare abundance, browsing by these populations can result in both absolute food shortage and the production of chemical defenses among browsed plants. Southern hare populations never achieve the densities characteristic of their northern counterparts and, therefore, should be less likely to elicit either food biomass limitation or the production of plant chemical defenses. Thus, hares in these populations should have access to a superabundant food supply and select browse species according to their nutrient content rather than their defensive chemical composition. We measured the extent of browse use by hares in the southwestern portion of the species’ range by calculating per capita winter browse availability (total biomass of potential food divided by winter hare population estimate) on six study sites during the winter of 1999. In addition, we used feeding trials on captive hares to determine patterns of browse consumption. Per capita browse biomass estimates were adequate to support the hares residing on each study site; on average, a 10-fold numerical increase would have been required to produce absolute food shortage. Patterns in consumption of browse by hares were not related to concentrations of plant chemical defenses (total phenols and monoterpenes), but rather to crude protein content. Levels of protein and copper (and possibly selenium) in the major browse species in our area were low, implying that, despite having access to a superabundance of poorly defended food, hares in southwestern populations may be subject to a poor-quality diet. In support of this possibility, we found that free-ranging hares had reproductive rates (potential natality = 5.64 young female-1 year-1) that were qualitatively lower than any reported in the literature (n = 18 studies) and males had relatively poor overwinter condition as well as delayed testes recrudescence. Poor diet quality and, consequently, low reproductive rates may contribute to the allegedly non-cyclic and generally lower densities of southwestern hare populations.Keywords: snowshoe hare, Lepus americanus, browse availability, plant chemical defenses, browse consumption patterns, reproductive rates, protein, copper.

Isoprene and monoterpene fluxes measured above Amazonian rainforest and their dependence on light and temperature

Canopy scale emissions of isoprene and monoterpenes from Amazonian rainforest were measured by eddy covariance and eddy accumulation techniques. The peak mixing ratios at about 10 m above the canopy occurred in the afternoon and were typically about 90 ppt v of α-pinene and 4–5 ppb v of isoprene. α-pinene was the most abundant monoterpene in the air above the canopy comprising ≈50% of the total monoterpene mixing ratio. Measured isoprene fluxes were almost 10 times higher than α-pinene fluxes. Normalized conditions of 30°C and 1000 μmol m −2 s −1 were associated with an isoprene flux of 2.4 mg m −2 h −1 and a β-pinene flux of 0.26 mg m −2 h −1. Both fluxes were lower than values that have been specified for Amazon rainforests in global emission models. Isoprene flux correlated with a light- and temperature-dependent emission activity factor, and even better with measured sensible heat flux. The variation in the measured α-pinene fluxes, as well as the diurnal cycle of mixing ratio, suggest emissions that are dependent on both light and temperature. The light and temperature dependence can have a significant effect on the modeled diurnal cycle of monoterpene emission as well as on the total monoterpene emission.

Quantitative analysis of aroma compounds in carrot (Daucus carota L.) cultivars by capillary gas chromatography using large-volume injection technique.

Dynamic headspace sampling was used to collect aroma compounds from raw samples of four carrot (Daucus carota L.) cultivars (Brasilia, Duke, Fancy, and Cortez). The collected volatiles were analyzed by capillary GC-FID and GC-MS using large-volume cool on-column injection (LVI-COC). Of the 36 compounds identified, 6 had not been previously detected in carrots. Significant differences between the carrot cultivars were found for 31 of the identified volatiles as well as for total monoterpenes, sesquiterpenes, and total volatile content. Mono- and sesquiterpenes accounted for about 98% of the total volatile mass in all cultivars. LVI-COC injection was used to determine the loss of carrot volatiles during concentration of headspace samples under a stream of nitrogen. The loss among major monoterpenes in the concentrated samples varied from 16% for p-cymene to >40% for alpha-pinene as compared to nonconcentrated samples. The loss among high-boiling sesquiterpenes varied from not detectable (beta-caryophyllene, alpha-humulene, and caryophyllene oxide) to approximately 7% for (E)- and (Z)-gamma-bisabolene.

Isoprene and monoterpene emission from the coniferous species Abies Borisii-regis—implications for regional air chemistry in Greece

The emission of isoprene has been studied from a forest of Abies Borisii-regis, a Mediterranean fir species previously thought to emit only monoterpenes. Emission studies from two independent enclosure experiments indicated a standardised isoprene emission rate of (18.4±3.8) μg g dry-weight −1 h −1, similar in magnitude to species such as eucalyptus and oak which are considered to be strong isoprene emitters. Isoprene emission depended strongly on both leaf temperature (2°C–34°C) and photosynthetically active radiation (PAR) below 250 μmol m −2 s −1, becoming saturated with respect to PAR above this value. The annual isoprene emission rate was estimated to be (132±29) kT yr −1 for those trees growing within Greece, comparable to current estimates of the total isoprene budget of Greece as a whole, and contributing significantly to regional ozone and carbon monoxide budgets. Monoterpene emission exhibited exponential temperature dependence, with 1,8-cineole, α-pinene, β-pinene and limonene forming the primary emissions. A standardised total monoterpene emission rate of (2.7±1.1) μg g dry-weight −1 h −1 was calculated, corresponding to an annual monoterpene emission rate of (24±12) kT yr −1. Research was conducted as part of the AEROBIC’97 (AEROsol formation from BIogenic organic Carbon) series of field campaigns.

Ambient isoprene and monoterpene concentrations in a Greek fir ( Abies Borisii-regis) forest. Reconciliation with emissions measurements and effects on measured OH concentrations

Ambient biogenic hydrocarbons were monitored in a forested site in Northern Greece during the summer of 1997 as part of the AEROBIC campaign. Significant concentrations of isoprene were observed, consistent with enclosure measurements presented in the previous paper (Harrison et al., 2001, Atmospheric Environment 35, 4687–4698). In addition, significant concentrations of monoterpenes were observed (nighttime maximum of 2.9 ppbv for total monoterpene concentration). Isoprene and the monoterpenes exhibited pronounced, but different, diurnal cycles which are interpreted via enclosure and OH measurements. The combination of relatively high emission rates at a time when OH concentrations are significantly lower leads to peak isoprene concentrations (∼3.0 ppbv) during the late evening. The temporal behaviour of the biogenic hydrocarbons is used to interpret the radical chemistry at the site and may indicate the presence of high (∼1×10 6 cm −3) nighttime concentrations of the OH radical. Biogenic hydrocarbon measurements were supported by a range of organic and inorganic measurements which are also presented in this paper.

Altered monoterpene composition in transgenic mint following the introduction of 4 S-limonene synthase

Genetic transformation of Mentha arvensis and M. × piperita with the neomycine phosphotransferase marker gene and a 4 S-limonene synthase cDNA from M. spicata led to the regeneration of 47 transformed plants. In these plants, integration of the transgene was checked by PCR and Southern blots. Transcripts were detected by RT-PCR and monoterpene profiles were determined by gas chromatography. Quantitative and qualitative modifications in monoterpene levels were observed in both M. arvensis and M. × piperita transgenic plants. Four M. × piperita transgenic plants contained higher levels of total monoterpenes, whereas monoterpene levels were lower in two M. arvensis transgenic lines. In both M. × piperita and M. arvensis transgenic lines, altered levels of compounds formed directly from geranyl diphosphate such as cineole or ocimene and monoterpene end-products such as pulegone or piperitone were observed. These effects were consistent with either over-expression or co-suppression of the 4S-ls gene, depending on the transgenic line. These data demonstrate the feasibility of modifying essential oil content by the introduction of a cDNA encoding an enzyme involved in monoterpene metabolism.

Monoterpene emissions from soil in a Sitka spruce forest

A dynamic soil enclosure was used to characterise monoterpene emissions from 3 soil depths within a Picea sitchensis (Sitka spruce) forest. In addition, a dynamic branch enclosure was used to provide comparative emissions data from foliage. In all cases, limonene and α-pinene dominated monoterpene soil emissions, whilst camphene, β-pinene and myrcene were also present in significant quantities. α-Phellandrene, 3-carene and α-terpinene were occasionally emitted in quantifiable amounts whilst cymene and cineole, although tentatively identified, were always non-quantifiable. Total daily mean monoterpene emission rates, normalised to 30°C, varied considerably between soil depths from 33.6 μg m −2 h −1 (range 28.3–38.4) for undisturbed soil, to 13.0 μg m −2 h −1 (8.97–16.4) with uppermost layer removed, to 199 μg m −2 h −1 (157–216) with partially decayed layer removed, suggesting that the surface needle litter was the most likely source of soil emissions to the atmosphere. Relative monoterpene ratios did not vary significantly between layers. Foliar monoterpenes exhibited a similar emission profile to soils with the exceptions of camphene and 3-carene whose contributions decreased and increased, respectively. Emission rates from foliage, normalised to 30°C were found to have a daily mean of 625 ng g −1 dw h −1 (299–1360). On a land area basis however, total soil emissions were demonstrated to be relatively insignificant to total emissions from the forest ecosystem.

Attraction of Scolytus unispinosus bark beetles to ethanol in water-stressed Douglas-fir branches

Three similar-sized branches on each of seven Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) trees with a southern exposure were selected randomly to receive a water-stress, defoliation, or control treatment. All water-stressed branches were attacked by Scolytus unispinosus LeConte at 12–24 days after imposing the treatments, resulting in a significantly higher mean density of gallery holes (107 m −2) than in the defoliated or control branches, which were not attacked. Needles and woody tissues from stressed branches, sampled after being attacked, contained significantly higher ethanol concentrations (ranging from 2.91 to 15.26 μmol g −1 fresh weight) than tissue from defoliated or control branches (0.005–0.12 μmol g −1 fresh weight). Ethanol concentrations did not differ between defoliated and control branches. The water content in woody tissues and needles of stressed branches was 40.9 and 28.1% of the amount in control branches, respectively, when sampled for ethanol analysis. Woody tissues in defoliated branches remained moist, with 91.3% of the water in controls. Drying needles from water-stressed branches also lost 18.3–33.7% of their total monoterpenes compared to needles on the controls. The mechanism for ethanol synthesis in water-stressed branches appears to be distinctly different from that of logs overwintering on the forest floor. Ethanol synthesis in stressed branches probably was initiated by cytoplasmic acidification as a result of damage to cellular membranes from drying and heating. The ethanol that accumulated in needles and woody tissues of stressed branches functioned as a primary host attractant for S. unispinosus at our Willamette Valley, Oregon, site.

Chemical Induced Vigour for Heterotic Effects on Yield and Quality of Essential Oil in Palmarosa (Cymbopogon martinii Wats)

ABSTRACT The efficacy of a few selected synergistic combinations of ethephon as chemical hybridizing agent for stimulatory heterotic effects on biomass and essential oil yield in palmarosa plants has been tested. Ethephon in solo treatment as well as in various synergistic combinations with the two precursor compounds of m-coumaric acid/3-hydroxycinnamic acid-spermidine and putrescine, and with four micronutrients, Fe-EDTA, CuSO4, ZnSO4, MnCl2 was “mist sprayed” during the vegetative and anthesis growth stages of palmarosa plant. Ethephon treatment along with spermidine (2%) or putrescine (2%) in conjunction with any of the four micronutrient (0.5% solution) exhibited maximum fresh herbage yield (99 kg/plot) and dry matter yield (32 kg/plot) as compared to the control values of 68 kg/plot, and 23 kg/plot, respectively. Further, the treated plants possessed maximum total essential monoterpene oil(s) (2.3%) and geraniol (69%) as compared to control values of 0.66% and 57.3%, respectively. The positive significant correlation coefficient values between geraniol content and leaf area index (r = 0.941 ≤ = 0.01), and geraniol and dry matter content (r = 0.739 ≤ p = 0.01) suggested the increased availability of photosynthates and other precursor metabolites for enhanced growth and oil content. The data suggest that ethephon in synergistic treatment(s) of m-coumaric acid results into greater accumulation of endogenous ethylene in the anther leading to male sterility condition.

Defensive adaptations of Thuja plicata to ungulate browsing: a comparative study between mainland and island populations.

Forests on the Haida Gwaii (HG) archipelago (British Columbia, Canada) evolved for about 10,000years in the absence of large-mammal browsing. The introduction of black-tailed deer (Odocoileus hemionus sitkensis) from the mainland prior to 1901 provides an opportunity to evaluate changes in the adaptive defensive responses of plants to herbivory. We compared (1) food choice by deer and (2) chemical defence (terpene concentrations) between HG and mainland red cedars (Thuja plicata) using (1) nursery-grown seedlings never exposed to deer, (2) branches from trees that grew before the introduction of deer ("old trees") and (3) saplings exposed to deer herbivory on the mainland and on HG. We used the first two plant categories to test the hypothesis that plants that evolve under low herbivory levels have lower anti-herbivore defences. We used saplings to study the consequences of the dramatic increase in browsing on HG. During food experiments, deer preferred HG seedlings and old tree branches compared to those from the mainland. Total monoterpene concentrations were much higher than diterpene concentrations in all plant categories. Within plant categories, multivariate analysis showed that terpene profiles differed significantly between HG and mainland red cedars: HG seedlings and old trees had lower monoterpene levels. These results suggest that some monoterpenes may be determinants of deer food choice and that the defences of HG plants are less effective than those of mainland plants. The deer used branches from HG and mainland saplings indiscriminately. However, terpene profiles differed significantly between HG and mainland saplings, with multivariate analysis suggesting a higher defensive response in browsed HG saplings. Monoterpene profiles were different in lightly and heavily browsed saplings from HG, suggesting that under the current browsing regime, individuals with the greatest constitutive defences, or with greatest potential for induced defences, grow better and are selected on HG.

Seasonal variations in VOC emission rates from gorse (Ulex europaeus)

Seasonal variations of biogenic volatile organic compound (VOC) emission rates and standardised emission factors from gorse (Ulex europaeus) have been measured at two sites in the United Kingdom, from October 1994 to September 1995, within temperature and PAR conditions ranging from 3 to 34°C and 10–1300μmolm−2s−1, respectively. Isoprene was the dominant emitted compound with a relative composition fluctuating from 7% of the total VOC (winter) to 97% (late summer). The monoterpenes α-pinene, camphene, sabinene, β-pinene, myrcene, limonene, trans-ocimene and γ-terpinene were also emitted, with α-pinene being the dominant monoterpene during most the year. Trans-ocimene represented 33–66% of the total monoterpene during the hottest months from June to September. VOC emissions were found to be accurately predicted using existing algorithms. Standard (normalised) emission factors of VOCs from gorse were calculated using experimental parameters measured during the experiment and found to fluctuate with season, from 13.3±2.1 to 0.1±0.1μgC (gdwt)−1h−1 in August 1995 and January 1995, respectively, for isoprene, and from 2.5±0.2 to 0.4±0.2μgC (gdwt)−1h−1 in July and November 1995, respectively, for total monoterpenes. No simple clear relation was found to allow prediction of these seasonal variations with respect to temperature and light intensity. The effects of using inappropriate algorithms to derive VOC fluxes from gorse were assessed for isoprene and monoterpenes. Although on an annual basis the discrepancies are not significant, monthly estimation of isoprene were found to be overestimated by more than a factor of 50 during wintertime when the seasonality of emission factors is not considered.

Inter-population differences in the essential oils of Pinus caribaea needles.

Differences in volatile terpene content of Pinus caribaea needles and soil qualities between two pine plantations (Uverito and Sartenejas) in Venezuela were analyzed. Soils in the Uverito pine plantation were sandy, low in nutritional quality, and deficient in available nitrogen and phosphorus content. Pines grown on these soils presented in their needles higher concentrations of alpha-pinene, camphene, sabinene, myrcene+alpha-phellandrene mixture, beta-phellandrene, beta-caryophyllene, alpha-humulene, and a higher total monoterpene content than pines of the Sartenejas plantation, where soils were nutritionally richer and higher in nitrogen and phosphorus content. The hypothesis of the carbon/nutrient balance could explain these results. Alternatively, continuous stress on the pines of the Uverito plantation due to herbivory by the leafcutter ant Atta laevigata may induce, in part, the differences observed between these pines and those of the Sartenejas plantation.

Testing the ecophysiological basis for the control of monoterpene concentrations along canopy profiles in thinned and unthinned balsam fir stands.

To determine which ecophysiological factors appear to control monoterpene concentrations in balsam fir foliage [Abies balsamea (L.) P. Mill.], the percentage of photosynthetically active radiation (%PAR), specific leaf area (SLA), light-saturated photosynthesis (A max), and concentrations per unit leaf area of foliar nitrogen (N), total soluble sugars (TSS), starch and monoterpenes were measured on current-year needles from three canopy levels (upper, middle and lower) the year following a pre-commercial thinning. The thinning only modestly changed the light profile within the canopy. %PAR was negatively correlated with SLA (r 2=0.62 in June, r 2=0.53 in July and August) and positively correlated with foliar nitrogen concentrations (r 2=0.51) within the crown profile. The positive relationship between N and A max was quite weak (r 2=0.15), suggesting significant variations in non-photosynthetic N within the canopies. Total monoterpenes were positively correlated with both %PAR (r 2=0.29) and A max (r 2=0.27), and negatively correlated with SLA (r 2=0.30). Contrary to that predicted by the carbon-nutrient balance hypothesis, total monoterpenes were negatively and only very weakly correlated with the starch/N ratio (r 2=0.06) and were not significantly correlated with either the TSS/N or the [TSS+starch]/N ratios. Monoterpenes were positively correlated with both N and TSS, although the relationship varied with the phenological state of the foliage, i.e., monoterpenes were more highly correlated with TSS (r 2=0.67) (immature foliage) in June, and in July and August with N (r 2=0.63) (mature foliage). Thus, it appears that monoterpene concentrations may be controlled primarily by carbohydrate supply in the early growing season and later by enzymatic capacity. Data expressed on a dry weight basis showed a similar pattern.

Extrapolating branch enclosure measurements to estimates of regional scale biogenic VOC fluxes in the northwestern Mediterranean basin

Simple summation and averaging methods were used to extrapolate 870 branch‐scale measurements of volatile organic compound (VOC) emissions from 40 native Mediterranean plant species to give estimates of habitat‐scale emission factors (EH) for dunes, macchia, garrigue, forest, and riverside habitats in the northwest Mediterranean area. The summation method derived biomass‐weighted VOC EH using local vegetation cover data and component species emission factors and leaf area indices (LAIs). The averaging method generated mean and median EH and LAI from component species. Summer biomass‐weighted EH (ng m−2 s−1) for monoterpenes and isoprene, respectively, were 1700, 125 (forest, Italy); 460, 8 (macchia, Italy); 280, 40 (dunes, Italy); 160, 1600 (forest, southern France); 34, 550 (garrigue, southern France); 0, 12000 (riverside, Spain); 90, 240 (garrigue, Spain). Autumn biomass‐weighted EH (ng m−2 s−1) for monoterpenes and isoprene, respectively were 700, 31 (dunes, Italy); 2030, 1620 (forest, southern France); 64, 110 (garrigue, Spain). In general, mean and median EH underestimated biomass‐weighted monoterpene EH and overestimated isoprene EH. Habitat isoprene flux estimates followed an annual cycle with a peak in summer. An autumn peak for habitat monoterpene flux estimates may be due to drought relief following autumn rains. When extrapolated to the total area of land covered by natural habitats in the northwest Mediterranean area (71,300 km2), total monoterpene and isoprene fluxes were estimated to be 0.07 and 0.1 Tg yr−1, respectively. Within the limits of uncertainty, the VOC flux estimates presented here for the Mediterranean region agree with previously published work. However, there are indications that previous published studies may underestimate monoterpene fluxes from this area.