Abundant Monoterpenes Research Articles

Effects of seasonal changes in feeding management under part-time grazing on terpene concentrations of ewes' milk

Terpene composition of ewes' raw milk from nine commercial flocks was analysed from February to July. Ewes' diet consisted of concentrate and conserved forage in winter (indoor feeding) and part-time grazing from spring (transition and outdoor feeding). Regardless of the feeding, limonene and β-phellandrene were the most abundant monoterpenes and β-caryophyllene showed the highest concentrations among sesquiterpenes. Terpene content increased in the milks of commercial flocks when animals were reared under grazing management. Monoterpenes were detected in the milks of all the commercial flocks throughout the season, whereas sesquiterpenes were only detected in the milks from flocks grazing on non-cultivated community-owned grasslands in which a higher biodiversity of plant species grew. These preliminary results indicated that β-caryophyllene could be a potential pasture-diet marker in the case of milks from animals grazing a higher biodiversity of plant species but in-depth studies including information on terpene composition of plants ingested by the animals are necessary to evaluate the suitability of β-caryophyllene or another terpenoid compound as pasture biomarker.

COMPOSITION AND BIOLOGICAL ACTIVITY OF THE ESSENTIAL OIL OF PERUVIAN LANTANA CAMARA

The composition of the essential oil from Lantana camara L. (Verbenaceae) obtained by hydrodistillation of the aerial parts was examined by GC, GC/ MS, and 13C-NMR. The GC analysis showed that carvone is the most abundant monoterpene 75.9%, together with limonene 16.9%, accounting for 92.8% of the oil. The major components were also tested by 13C-NMR analysis of the essential oil. The L. camara oil was assayed against several microorganisms, showing moderate antibacterial activity against the human pathogen Staphylococcus aureus (MIC 200 µg/ml). High antioxidant activity evaluated by the Trolox equivalent antioxidant capacity assay (TEAC) was found (29.0 mmol Trolox/kg) and relative low anti-inflammatory activity due to its weak ability for inhibiting lipoxygenase (IC 50 = 81.5 µg/ml).

Terpenoid emissions from Quercus robur. A case study of Galicia (NW Spain)

Isoprene and monoterpenes emission fluxes emitted by Quercus robur seedlings were measured at a leaf scale in the field. Isoprene emissions were always predominant over the monoterpene ones, alpha-pinene, beta-pinene and camphene being the most abundant emitted monoterpenes. Emission fluxes were normalised at standard conditions of temperature and photosynthetically active radiation, PAR, (30 degrees C and 1000 micromol m(-2) s(-1) respectively) using temperature and light dependent algorithms. The standardised emission fluxes ranged from 43 to 73 microg g(DM)(-1) h(-1) for isoprene and from 0.04 to 2.95 microg g(DM)(-1) h(-1) for the monoterpenes. The values reported in the literature are within our experimental intervals. These standardised fluxes were used to estimate the Quercus robur emissions in Galicia (NW Spain). This region is characterised by its abundant forest extensions where Quercus robur occupies the second place in species abundance with a total of 195029 ha of Quercus robur pure stands. To estimate the region emission fluxes, both the extension and distribution of the forest areas and the regional climatic conditions over five years (2002-2006) were taken into account. The averaged annual fluxes regarding the forest extension were 0.04 t ha(-1) yr(-1) for isoprene and 0.52 kg ha(-1) yr(-1) for monoterpenes. This means averaged annual fluxes of 9730 t yr(-1) and 114 t yr(-1) for isoprene and monoterpenes, respectively. These values place Galicia as an important isoprene emitter power in Spain as a consequence of the extension of its forests more than of the climatic conditions.

Monoterpene emission of a boreal Scots pine ( Pinus sylvestris L.) forest

Large quantities of biogenic volatile organic compounds (biogenic VOCs) are emitted into the atmosphere by terrestrial vegetation. Once released into the atmosphere biogenic VOCs have a significant role in the chemistry of the lower troposphere. The biogenic emissions of VOCs from the Finnish forests are dominated by monoterpenes. In this study, the monoterpene flux of a typical Scots pine forest stand in Eastern Finland was measured within one growing period using a micrometeorological-gradient method. Additionally, branch-level emission measurements were performed to estimate the canopy scale monoterpene emission and its contribution to the total monoterpene flux of the forest. Needle monoterpene storage of the emitting tree canopy was determined as it was presumed to be the main source of monoterpene emission of the forest. The emissions measured with the two methods were used to obtain emission potential values for the canopy and whole ecosystem utilizing a commonly used temperature-based emission model. The aim was also to compare the monoterpene emission measured with the two separate methods in order to evaluate the possible differences between the emission estimates derived from both branch- and ecosystem-level measurements. Furthermore, using these values the monoterpene emission was calculated over the whole growing period. The most abundant monoterpenes measured above the forest and from the canopy were α-pinene and Δ-3-carene. Highest ecosystem scale monoterpene fluxes were observed in early July simultaneously with a pine sawfly occurrence at the site. Based on the emission potential value at 30 °C, total monoterpene flux during a period of June–September was calculated to be 502 mg m −2. Respectively, in the same time period the canopy scale emission was estimated to be 374 mg m −2. The difference between canopy emission and ecosystem flux could partly be explained by emissions from forest floor, although large uncertainty included in the ecosystem flux potential calculations reduced the reliability of these estimations. Impact of needle herbivory on the monoterpene flux of the forest is discussed.

Inhibition of atmospheric methane oxidation by monoterpenes in Norway spruce and European beech soils

Biological oxidation of atmospheric methane (CH 4) in forest soils of the northern hemisphere is an important sink in the global CH 4 cycle. The effect of tree species on atmospheric CH 4 oxidation is not well understood. Previous studies suggest that soils under European beech ( Fagus sylvatica) consume more atmospheric CH 4 than soils under Norway spruce ( Picea abies). A major difference in the chemical constituents of these tree species is the production of monoterpenes. The objectives of the present study were (i) to quantify monoterpenes in leaves, needles, organic horizons (Oi, Oe, Oa), and mineral soil of a Norway spruce site and an adjacent European beech site of a temperate forest (Steigerwald, Germany) and (ii) to evaluate the potential of abundant monoterpenes to inhibit atmospheric CH 4 oxidation. Major compounds were α- and β-pinene, limonene, and camphene. Highest concentrations were measured in Norway spruce samples (up to 63.9 μmol g dw − 1 ). In European beech samples, monoterpene concentrations were close to or below the detection limit (≤0.00015 μmol g dw − 1 ). For limonene, α- and β-pinene, the dose-dependent inhibition on atmospheric CH 4 oxidation was determined. β-Pinene had the highest inhibition efficiency, followed by limonene and α-pinene. Norway spruce roots and mineral soil samples displayed similar monoterpene profiles, suggesting that roots can be considered as a source for inhibitory monoterpenes in Norway spruce soils. Monoterpene addition was always coupled to an increased carbon dioxide production. This indicates that monoterpenes may be microbially mineralized in these soils. In summary, the study revealed that the release of monoterpenes by both roots and litter may be sources in soil and that in situ monoterpene concentrations in spruce soil are high enough to explain reduced atmospheric CH 4 uptake.

Monoterpene Emissions from Lodgepole and Jack Pine Bark Inoculated with Mountain Pine Beetle‐Associated Fungi

Relative monoterpene levels were analyzed from bark samples of lodgepole pine, jack pine, and their hybrids inoculated with mountain pine beetle (MPB)–associated fungi (Leptographium longiclavatum, Grosmannia clavigera, and Ophiostoma montium). Lodgepole pine showed the largest changes in relative emissions as a result of fungal inoculation. The relative emission of β‐phellandrene increased with fungal inoculation, making it the most abundant monoterpene for inoculated samples. Relative emissions of limonene and α‐pinene decreased in inoculated lodgepole pine. Lodgepole (5.6) and jack (146) pine differed in the ratio of α‐pinene to myrcene; two monoterpenes involved in pheromone synthesis by the MPB. These differences may contribute to the attractiveness of the two species as hosts for MPB; with jack pine potentially less attractive than lodgepole pine. Fungal inoculation reduced α‐pinene:myrcene ratios in lodgepole pine, which suggests one possible mechanism by which the fungi benefit the beetle.

Differential response of ectomycorrhizal and saprotrophic fungal mycelium from coniferous forest soils to selected monoterpenes

The mycelia of saprotrophic (SP) and ectomycorrhizal (ECM) fungi occur throughout the upper soil horizons in coniferous forests and could therefore be exposed to high concentrations of monoterpenes occurring in the needle litter of some tree species. Monoterpenes are mycotoxic and could potentially affect fungi that are exposed to them in the litter layers. In order to investigate whether monoterpenes typical of coniferous litters could influence fungal communities, we analysed the monoterpene content of freshly fallen needles of Pinus sylvestris, Picea abies and Picea sitchensis. The most abundant monoterpenes were found to be α-pinene, β-pinene and 3-carene. We evaluated the effects of these three monoterpene vapours on the biomass production of 23 SP isolates and 16 ECM isolates. Overall, 75% of ECM isolates and 26% of SP isolates were significantly inhibited by at least one of the monoterpene treatments and both intra- and inter-specific variations in response were observed. Monoterpene concentrations are highest in surface litters. The differential effects on fungal taxa may influence the spatial and temporal distribution of fungal community composition, indirectly affecting decomposition and nutrient cycling, the fundamental ecosystem processes in which fungi have a key role in coniferous forest soils.

Thymol and carvacrol production from leaves of wild Palestinian Majorana syriaca

Majorana syriaca (Zaatar in Arabic), belonging to the mint family, Labiates, is cultivated widely and grows wild in the mountains of Palestine between the months April to August. In order to determine the secondary metabolites from wild leaves of Palestinian M. syriaca, comparative analysis by static headspace (HS) and steam distillation (SD) GC–MS was used. Among the samples examined, the major constituents identified varied greatly throughout the different harvesting periods. Headspace revealed major volatiles and semi-volatiles of α-pinene, β-myrecene, o-cymene, p-cymene, γ-terpinene, thymol, and carvacrol. We found that the most abundant monoterpenes, i.e. γ-terpinene and p-cymene were decreased in the month of May since they are the biogenetic precursors (via enzymic hydroxylation) of the phenolic terpenes, thymol and carvacrol. The harvesting time, location and the thyme type (i.e., wild) affects the yield of essential oils as reflected by normal steam distillation.

Volatiles in the Dorsal Abdominal Glands and Exuviae of <I>Leptocoris abdominalis</I> and <I>Leptocoris augur</I> (Heteroptera: Rhopalidae)

Compounds in the dorsal abdominal glands (DAGs) of adults and nymphs, and exuviae of two scentless plant bugs Leptocoris abdominalis (F.) and Leptocoris augur (F.) (Heteroptera: Rhopalidae), were studied by gas chromatography-mass spectrometry. For both species, two dorsal abdominal glands (median and posterior glands) are found in the nymphs, whereas in adults only the posterior gland is functional and the median gland is reduced. Monoterpenes are the major compounds in posterior glands for both species. For L. abdominalis β-pinene is most abundant monoterpene and for L. augur, limonene is most abundant monoterpene. Alkenals and alkenoic acids were found in median glands of both species. There was no sexual dimorphism in the morphology and the contents of the DAGs of adults. Analysis of the compounds found in the exuvia indicated that components in the median gland were shed with the exuvia. Quantitative analysis of the major monoterpenes and alkenals in the DAGs of different ages of L. abdominalis supported the observation that components in the posterior gland were retained in the insect after each molting. Possible functions of the components in the DAGs are discussed.

Leaf Essential Oils of the Queensland Species of Phebalium (Rutaceae: Boronieae)

The leaf oils of the eight Queensland specific and subspecific taxa of Phebalium have been examined. Phebalium distans produced a variable oil, with α-pinene (0.8–42%) being the most abundant prominent monoterpene and bicyclogermacrene (12–22%) as the most significant sesquiterpene. In P. glandulosum subsp. glandulosum by far the major component is dihydrotagetone (75–95%). β-Caryophyllene (9–20%) and bicyclogermacrene (7–23%) were the major components of P. longifolium. In P. nottii the principal monoterpene detected was α-pinene (25–42%), while the principal sesquiterpenes detected were guaiol (t-28%) and bulnesol (nil to 34%). The two monoterpene hydrocarbons, α-phellandrene (12–25%) and β-phellandrene (14–15%), together with bicyclogermacrene (2–12%), elemol/hedycaryol (12–36%) were major components in the leaf oil of P. squamulosum subsp. squamulosum, while in P. squamulosum subsp. gracile, geijerene (4–8%) was present together with α-pinene (44–50%) and guaiol (9–11%). The leaf oil of P. whitei contained α-pinene (22–42%), limonene (1–12%) and bicyclogermacrene (11–20%) as major components. In P. woombye the main components were α-pinene (10–21%), β-phellandrene (12–20%), bicyclogermacrene (11–20%) and germacrene D (5–10%).

Biotransformation of Limonene by Marine Bacteria

The biotransformation of d-limonene by marine bacteria, Vibrio cholerae, Listonella damsela, Vibrio alginolyticus, and the products were investigated. Each bacterial strain was fermented in the liquid medium 2216 E and was divided into the biotransformation group and the control group. In the biotransformation group, 200 mg l −1 d-limonene was distributed among the culture flasks. All flasks were incubated at 28°C on a rotary shaker at a speed of 120 rpm for 6 days. On completion of incubation, the culture broth was successively extracted with ethyl acetate. The extracts were quantitatively measured by gas chromatography mass spectrometry analysis. The results show that these bacterial strains possess distinctive biocatalytic capacities toward d-limonene. The biocatalytic reactions encompassed oxidation, including hydroxylation and ketonization, which occurred at different positions on d-limonene, as well as hydrogenation, hydrolyzation, esterification, and cyclic cleavage. In the biotransformation group, besides oxygenated monoterpenoids, a series of sesqui-, di-, triterpe noids were also detected, which were not found in the control group. A tentative explanation is that d-limonene influences the microbial metabolites and that the biosynthetic pathways of terpenoids were triggered during the biotransformation of d-limonene. Microbial biotransformation has the following advantages: it is simple to manipulate, it can work under mild reaction conditions, it has high efficiency, it is reaction-, regio- and stereoselective, and it is environment friendly; therefore, microbial biotransformation definitely represents a new attractive approach to the utilization of the abundant natural monoterpenes and provides endless opportunities to obtain some significant compounds that can be used in the fields of medicine, organic synthesis, and fine chemistry.

Changes in Terpene Content in Milk from Pasture-Fed Cows

Changes of terpene content in milk from cows grazing natural diversified upland pasture were examined in this observational trial. A homogeneous plot divided into 2 subplots was used from May 31 to July 1, 2003 (first growth) and again from October 1 to October 7, 2003 (vegetative regrowth). Each subplot was grazed by 6 dairy cows in 2 ways: strip grazing (SG), with new allocations of pasture strips at 2-d intervals, and paddock grazing (PG). The PG subplot was divided into 3 paddocks and the cows were moved to a new paddock on June 13 and June 24, 2003. Milk from the 6 cows was collected twice a week, pooled, and used for terpene analyses by dynamic headspace gas chromatography-mass spectrometry system. Twenty mono- and 23 sesquiterpenes desorbing from the milk fat were separated. The most abundant monoterpenes were β-pinene, α-pinene, γ-terpinene, limonene, α-tujene, terpinolene, and α-phellandrene. The most abundant sesquiterpenes were β-caryophyllene, α-copaene, β-cedrene, transmuurola-4-(14)-5-diene, β-bisabolene, and δ-cadinene. Both mono- and sesquiterpenes in SG milk increased across time with an 8-fold increase in total terpenes in milk from the beginning to the end of June. In parallel, dicotyledons, including the main terpene-rich plants, increased from 17 to 31% of total biomass of the vegetation and the development of Dactylis glomerata progressed from boot to ripening stage. The terpenes in PG milk were equivalent to those in SG milk for the first paddock at the beginning of June and remained constant or doubled for the sum of mono- and sesquiterpenes, respectively. The lower variability of the PG milk terpene content could be related to the opportunity that PG cows had to choose ingested herbage, whereas the SG cows had limited choice within the smaller allocated pasture strips. Milk from cows grazing regrowth pastures in October contained low levels of terpenes, and values were similar for PG and SG milks. Change in the sum of monoterpenes is representative of changes for most monoterpenes (except for limonene) and, conversely, the change in the sum of sesquiterpenes mainly reflected changes in β-caryophyllene and α-copaene. In addition to effects of botanical composition of pasture, it appears that terpene content in milk may vary according to factors linked to grazing management that need more intensive study. Nevertheless, current results raise questions about the precision of terpenes as feed tracers.

The effect of nitrogen dioxide on particle formation during ozonolysis of two abundant monoterpenes indoors

The effect of the nitrogen dioxide (NO 2) concentration on particle formation during ozonolysis of two abundant monoterpenes indoors, α-pinene and d-limonene, was studied in dry air in 1000 l Tedlar bags at 21±2 °C and ambient pressure. Particle size distributions were measured during 1 h after the reaction was initiated. In mixtures of 50 parts per billion volume (ppbv) of monoterpene and 50 ppbv of ozone (O 3), d-limonene produced about five times as many particles (10–350 nm) as α-pinene after 60 min. The presence of NO 2 introduced an additional loss term for O 3, resulting in formation of the nitrate radical. This affected particle formation, since the nucleation potential of NO 3 is much lower than O 3. Modeling showed that the observed decrease in particle concentration from d-limonene/O 3/NO 2 mixtures was likely to be ascribed to the O 3/NO 2 reaction at NO 2 concentrations <150 ppb, above which unknown mechanisms additionally reduced the particle formation. In similar experiments with α-pinene, the particle concentration and volume were substantially reduced in the presence of NO 2, e.g. 162 ppbv NO 2 reduced the particle number concentration by a factor of 10. In addition, the detection of particle formation was delayed as the NO 2 concentration increased, but the additional loss of O 3 in the O 3/NO 2 reaction could not explain the observation. The particle mode progressively increased with the NO 2 concentration for both monoterpenes. Oxidation of d-limonene may be highly relevant for new particle formation in indoor air, whereas ozonolysis products of α-pinene seem less likely to nucleate in indoor environments.

Modeling secondary organic aerosol formation from oxidation of α-pinene, β-pinene, and d-limonene

The biogenic species α-pinene, β-pinene, and d-limonene are among the most abundant monoterpenes emitted globally. They are also important precursors to secondary organic aerosol (SOA) formation in the atmosphere. This study involves the development of proposed oxidation mechanisms for these three species. Semi- and non-volatile oxidation products with the potential to lead to SOA formation are predicted explicitly. Simulation code that describes the gas-phase oxidation mechanisms including reactions that lead to ozone (O 3) formation is coupled to an equilibrium absorptive partitioning code. The coupled model is used to simulate both gas-phase chemistry and SOA formation associated with oxidation of these three species in chamber experiments involving single as well as multiple oxidants. For the partitioning model, required molecular properties of the oxidation products are taken from the literature or estimated based on structural characteristics. The predicted O 3 and SOA concentrations are typically within ±50% of measured values for most of the experiments except for the experiments with low initial hydrocarbon concentrations and the nitrate radical experiments with α-pinene. The developed model will be used to update a gas-phase chemical mechanism and a SOA formation module used in a three-dimensional air quality model.

Sesquiterpene ozonolysis: Origin of atmospheric new particle formation from biogenic hydrocarbons

Atmospheric new aerosol particle formation observed in remote areas (e.g., in Finland, Portugal and in the U.S.). is generally attributed to low‐volatile oxidation products of monoterpenes (C10H16), which are emitted by the vegetation. In this article we show that this atmospheric new particle formation is not caused by monoterpene products, but most likely initiated by very low‐volatile substances produced during sesquiterpene (C15H24)‐ozone reactions. For this purpose, the nucleation times of the most abundant monoterpene reactions have been calculated and discussed exemplarily for the Finnish site Hyytiälä, at which nucleation events have been observed. In addition, the important negative influence of water vapor on the nucleation threshold of the β‐caryophyllene‐ozone reaction has been studied in detail at different dew points in the laboratory. Therein, the saturation vapor pressure of the nucleating compounds was estimated to be less than 1.2 · 10−10 hPa, which is recommended for atmospheric homogeneous nucleation of non‐volatile organics.

Monoterpene emissions from Scots pine (Pinus sylvestris): Field studies of emission rate variabilities

Monoterpene emission rates from young and adult Scots pines (Pinus sylvestris), a typical central European conifer, were measured under ambient conditions using a dynamic enclosure chamber. We investigated diurnal and seasonal cycles of monoterpene emissions and branch‐to‐branch and plant‐to‐plant variabilities of emission rates. The four most abundant monoterpenes usually emitted from Pinus sylvestris were α‐pinene, 3‐carene, camphene, and β‐pinene. Emissions of individual monoterpenes were highly correlated to each other and increased exponentially with temperature. We obtained β coefficients for the temperature dependence of different monoterpenes between 0.08 and 0.13 K−1. The β coefficients varied with season by a factor of 2; the standard emission rates varied by more than 1 order of magnitude. Highest standard emission rates were found in April; lowest standard emission rates were found in July and October. In July and October the standard emission rates from two different branches of the same tree showed no significant differences; in September they differed by a factor of 2. Seasonal variations of a single branch and branch‐to‐branch variations in the spectrum of emitted monoterpenes were small. On the other hand, different individual Scots pines emitted a completely different spectrum of monoterpenes, indicating that the monoterpene emission spectrum is only typical for an individual plant but not for the whole plant species. The temperature normalized standard emission rates were found to be highly variable. Values for the sum of monoterpenes ranged between 0.06 and 3.7 μg g(dry weight)−1 h−1 (micrograms monoterpenes per gram dry weight (dw) of needles and hour). Temperature‐normalized monoterpene emission rates and temperature dependencies of the emissions were used to calculate monthly flux estimates of monoterpenes for the Hartheimer Wald.

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.

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.

The role of the monoterpene composition inPinus spp. needles, in host selection by the pine processionary caterpillar,Thaumetopoea pityocampa

This paper presents preliminary results on attempts to extract and characterize the volatile secondary metabolites contained in needles of differentPinus species and to ascertain the role played by these substances on the behavior ofThaumetopoea pityocampa (Denis et Schiffermuller) females, which show a marked preference, during the oviposition period, for some indigenous and exotic species of host plants existing in mixed formation. Limonene is the most abundant monoterpene extracted fromP. pinea needles, the least favored species of pine processionary caterpillar (PPC) females, although it is present in only very low amounts in otherPinus species. An increase was observed in limonene production byP. pinea at the start of the flight period of the PPC adult, and subsequently at the beginning of the females’ oviposition period. Assays carried out in two pine stands in central Italy showed that limonene, emulsified with water and sprayed on foliage of four different pine species plants,P. sylvestris, P. nigra, P. pinaster andP. radiata, during the PPC oviposition period, provided a satisfactory degree of protection. In fact, the number of egg clusters collected from treated plants was often lower than the number of egg clusters collected from control plants and was comparable to the number of egg clusters laid onP. pinea plants. In particular (R)-(+)-limonene, although not produced in nature by pines, was the most effective deterrent. However, the effect of (S)-(-)-limonene, the enantiomer biosynthesized by pines, was also adequate.

Inhibition of Nitrosomonas europaea by Monoterpenes from Coastal Redwood (Sequoia sempervirens) in Whole-Cell Studies

Inhibition by allelochemicals, including monoterpenes, has been suggested as a factor in the extremely low nitrification rates observed in coastal redwood forests. Similarities between the molecular structure of known nitrification inhibitors and some conifer monoterpenes have been suggested as one reason for the inhibition of autotrophic nitrifiers by conifer monoterpenes. The effect of monolerpenes on nitrification rate and growth of Nitrosomonas europaea was examined in whole-cell pure culture experiments using the five most abundant monoterpenes in coastal redwood needles. These are (in order of decreasing concentration in the needles) limonene, α-pinenc, sabinene, myrcene, and γ-terpinene. Four of the five compounds significantly inhibited growth of N. europaea in batch culture experiments. Short-term kinetic studies of the two most inhibitory monoterpenes, limonene and α-pinene, were performed on whole cells to evaluate the mode of interaction between these chemicals and nitrification rates. Inhibition constants (Ki) of limonene (38 μM) and α-pinene (95 μM) were determined. Lineweaver-Burk plots of nitrification in the presence of monoterpenes appear to fit a noncompetitive inhibition model; however, the mechanisms of inhibition may be more complex.