Controls over monoterpene emissions from boreal forest conifers

Differential responses and mechanisms of monoterpene emissions from broad-leaved and coniferous species under elevated ozone scenarios

Although ozone (O3) pollution affects plant growth and monoterpene (MT) emissions, the responses of MT emission rates to elevated O3 and the related mechanisms are not entirely understood. To gain an insight into these effects and mechanisms, we evaluated physiological (leaf MT synthesis ability, including precursor availability and enzyme kinetics) and physicochemical limiting factors (e.g. leaf thickness of the lower and upper epidermis, palisade and spongy tissue, and size of resin ducts and stomatal aperture) affecting MT emissions simultaneously from two broad-leaved and two coniferous species after one growing season of field experiment. The effects of elevated O3 on MT emissions and the related mechanisms differed between plant functional types. Specifically, long-term moderate O3 exposure significantly reduced MT emissions in broad-leaved species, primarily attributed to a systematic decrease in MT synthesis ability, including reductions in all MT precursors, geranyl diphosphate content, and MT synthase protein levels. In contrast, the same O3 exposure significantly enhanced MT emissions in coniferous species. However, the change in MT emissions in coniferous species was not due to modifications in leaf MT synthesis ability but rather because of alterations in leaf anatomical structure characteristics, particularly the size of resin ducts and stomatal aperture. These findings provide an important understanding of the mechanisms driving MT emissions from different tree functional groups and can enlighten the estimation of MT emissions in the context of O3 pollution scenarios as well as the development of MT emission algorithms.

Drivers of biogenic volatile organic compound emissions in hygrophytic bryophytes

Bryophytes can both emit and take up biogenic volatile organic compounds (BVOCs) to and from the environment. Despite the scarce study of these exchanges, BVOCs have been shown to be important for a wide range of ecological roles. Bryophytes are the most ancient clade of land plants and preserve very similar traits to those first land colonisers. Therefore, the study of these plants can help understand the early processes of BVOC emissions as an adaptation to terrestrial life. Here, we determine the emission rates of BVOCs from different bryophyte species to understand what drives such emissions. We studied 26 bryophyte species from temperate regions that can be found in mountain springs located in NE Spain. Bryophyte BVOC emission presented no significant phylogenetic signal for any of the compounds analysed. Hence, we used mixed linear models to investigate the species-specific differences and eco-physiological and environmental drivers of bryophyte BVOC emission. In general, species-specific variability was the main factor explaining bryophyte BVOC emissions; but additionally, photosynthetic rates and light intensity increased BVOC emissions. Despite emission measurements reported here were conducted at 30°, and may not directly correspond to emission rates in natural conditions, most of the screened species have never been measured before for BVOC emissions and therefore this information can help understand the drivers of the emissions of BVOCs in bryophytes.

Trace gas emissions from municipal solid waste landfills: A review

Trace gas emissions from municipal solid waste (MSW) landfills have received increasing attention in recent years. This paper reviews literature published between 1983 and 2019, focusing on (i) the origin and fate of trace gas in MSW landfills, (ii) sampling and analytical techniques, (iii) quantitative emission measurement techniques, (iv) concentration and surface emission rates of common trace compounds at different landfill units and (v) the environmental and health concerns associated with trace gas emissions from MSW landfills. Trace gases can be produced from waste degradation, direct volatilisation of chemicals in waste products or from conversions/reactions between other compounds. Different chemical groups dominate the different waste decomposition stages. In general, organic sulphur compounds and oxygenated compounds are connected with fresh waste, while abundant hydrogen sulphide, aromatics and aliphatic hydrocarbons are usually found during the methane fermentation stage. Selection of different sampling, analytical and emission rate measurement techniques might generate different results when quantifying trace gas emission from landfills, and validation tests are needed to evaluate the reliability of current methods. The concentrations of trace gases and their surface emission rates vary largely from site to site, and fresh waste dumping areas and uncovered waste surfaces are the most important fugitive emission sources. The adverse effects of trace gas emission are not fully understood, and more emission data are required in future studies to assess quantitatively their environmental impacts as well as health risks.

Forest Volatile Organic Compounds and Their Effects on Human Health: A State-of-the-Art Review

The aim of this research work is to analyze the chemistry and diversity of forest VOCs (volatile organic compounds) and to outline their evidence-based effects on health. This research work was designed as a narrative overview of the scientific literature. Inhaling forest VOCs like limonene and pinene can result in useful antioxidant and anti-inflammatory effects on the airways, and the pharmacological activity of some terpenes absorbed through inhalation may be also beneficial to promote brain functions by decreasing mental fatigue, inducing relaxation, and improving cognitive performance and mood. The tree composition can markedly influence the concentration of specific VOCs in the forest air, which also exhibits cyclic diurnal variations. Moreover, beneficial psychological and physiological effects of visiting a forest cannot be solely attributed to VOC inhalation but are due to a global and integrated stimulation of the five senses, induced by all specific characteristics of the natural environment, with the visual component probably playing a fundamental role in the overall effect. Globally, these findings can have useful implications for individual wellbeing, public health, and landscape design. Further clinical and environmental studies are advised, since the majority of the existing evidence is derived from laboratory findings.

Effect of biochemical composition on odor emission potential of biowaste during aerobic biodegradation

This study aimed to identify the individual effect of biochemical composition on odor emission potential of biowaste during aerobic biodegradation. Three kinds of typical mixed wastes, including vegetable-fruit waste, garden waste, and protein-rich waste, were tested for emission quantity of seven common odorous families within 21 days of biodegradation under aerobic conditions. The cumulative odor yields (COY) were as follows: protein-rich waste (2408 μg g^-1 DM) > vegetable-fruit waste (1169 μg g^-1 DM) > garden waste (62 μg g^-1 DM), and their cumulative odor intensity were 16,701, 1888, and 212 g^-1 DM, respectively. The odor emission of vegetable-fruit waste mainly occurred in the first 3 days, accounting for 91.7% COY, and the predominant contributor to odor intensity (PCOI) were terpenes and sulfur compounds. With regard to garden waste, the odor emission rate was the highest on day 1 (22.4 μg g^-1 DM d^-1) and then rapidly decreased, and the PCOI were aldehydes. The odor emission rate of protein-rich waste increased gradually in the initial stage and reached the peak value on day 10 (661.9 μg g^-1 DM d^-1), and its PCOI were sulfur compounds. This study revealed for the first time the relationship between the odor emission potential of biowaste and its characteristic of biochemical composition, then proposed potential application for odor pollution control during aerobic composting.

Effects of nitrogen deposition and litter layer management on soil CO2, N2O, and CH4 emissions in a subtropical pine forestland

Forestland soils play vital role in regulating global soil greenhouse gas (GHG) budgets, but the interactive effect of the litter layer management and simulated nitrogen (N) deposition on these GHG flux has not been elucidated clearly in subtropical forestland. A field trial was conducted to study these effects by using litter removal method under 0 and 40 kg N ha⁻¹ yr⁻¹ addition in a subtropical forestland in Yingtan, Jiangxi Province, China. Soil CO₂ emission was increased by N addition (18–24%) but decreased by litter removal (24–32%). Litter removal significantly (P < 0.05) decreased cumulative N₂O emission by 21% in treatments without N addition but only by 10% in treatments with 40 kg N ha⁻¹ yr⁻¹ addition. Moreover, litter-induced N₂O emission under elevated N deposition (0.094 kg N₂O-N ha⁻¹) was almost the same as without N addition (0.088 kg N₂O-N ha⁻¹). Diffusion of atmospheric CH₄ into soil was facilitated by litter removal, which increased CH₄ uptake by 55%. Given that the increasing trend of atmospheric N deposition in future, which would reduce litterfall in subtropical N-rich forest, the effect of surface litter layer change on soil GHG emissions should be considered in assessing forest GHG budgets and future climate scenario modeling.

Essential oils, asthma, thunderstorms, and plant gases: a prospective study of respiratory response to ambient biogenic volatile organic compounds (BVOCs)

Purpose: Prevailing opinion is that wind-pollinated plants affect asthma negatively and that insect- pollinated ones do not. "Thunderstorm" asthma, too, is attributed to bursting grass pollens. Additional biogenic volatile organic compounds (BVOCs) are identified here. Essential oils' BVOCs are inhaled from plants, oil diffusers, candles, room "fresheners", perfumes, and hygiene products. Claims of BVOC "safety" for sensitive respiratory systems are questioned. Methods: Fourteen volunteers, of mixed-age and gender, with seasonal asthma recorded peak expiratory flow (PEF) and 11 symptom scores. BVOCs were collected on Tenax tubes from ambient air in autumn and spring, as were live flower emissions, before and after a thunderstorm. Gas chromatography-mass spectrometry analysis identified frequently occurring BVOCs. Air spora, meteorological, outdoor air pollution variables, and BVOCs predict respiratory symptoms in univariate linear regression models, seasonally. Results: Increased pinene, camphor, linalool, linalyl acetate, benzaldehyde, and benzoic acid predict respiratory symptoms, including reduced PEF, and increased nasal congestion; day length, atmospheric pressure and temperature predict symptoms in both seasons, differently; other variables predict a range of symptoms (0.0001≤p≤0.05). Thunder predicts different BVOC emissions in spring, compared to autumn (p≤0.05). An uncut Grevillea flower emitted linalool and hexenal before a storm; the latter is also emitted from cut grass. Increased nitrogen oxides and pinene in autumn may combine to form harmful oxidation products. Conclusion: This research supports BVOCs as contributors to seasonal asthma and allergic rhinitis, and "thunderstorm" asthma. Pinene emissions from Myrtaceae species (Eucalyptus, Melaleuca, Leptospermum, Callistemon), Brassicaceae (canola), and conifers, worldwide, may induce respiratory inflammation and maintain it, by inhibiting eosinophilic apoptosis. Widely used essential oil products containing BVOCs, like linalool, are associated here with respiratory symptoms. Lagged responses suggest that users' cognitive associations between exposure and response are unlikely, increasing potential for impaired health for vulnerable children.

Spruce budworm feeding and oviposition are stimulated by monoterpenes in white spruce epicuticular waxes

Monoterpenes, source of the distinctive odor of conifers, are generally considered plant defensive compounds. However, they are also known to act as long-range insect attractants, as they are volatile and permeate forest airspaces. Moreover, they are lipid soluble and can be absorbed into plant epicuticular waxes. We test their role in short-range host plant choice by both adult females and larvae of a folivorous forest pest (Choristoneura fumiferana). We conducted laboratory assays testing the responses of Eastern spruce budworm to an artificial monoterpene mix (α-pinene, β-pinene, limonene, myrcene) and to white spruce (Picea glauca) epicuticular waxes in closed arenas. Ovipositing females preferred filter paper discs treated with P. glauca waxes to controls, and preferred the waxes + monoterpenes treatment to waxes alone. However, females showed no preference between the monoterpene-treated disc and the control when presented without waxes. Feeding larvae prefered wax discs to control discs. They also consumed discs treated with realistic monoterpene concentrations and wax preferentially over wax-only discs, but showed no preference between extremely high monoterpene concentrations and wax-only controls. In an insect-free assay, P. glauca epicuticular wax decreased monoterpene volatilization. These results suggest that P. glauca waxes and realistic concentrations of monoterpenes are stimulatory to both egg-laying females and feeding larvae, and that their effects are synergistic.

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

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

A fully integrated isoprenoid emissions model coupling emissions to photosynthetic characteristics

The lack of a mechanistic basis has hampered modelling isoprene emission responses to environmental drivers, in particular the simulation of isoprene emissions under different CO₂ concentrations. Here, we advance previous semi-mechanistic model formulations by introducing a model that explicitly links electron availability for other purpose than carbon assimilation (or available energy for secondary metabolism processes; supply-constraint) and enzyme activity (capacity-constraint) to emissions. We furthermore investigate the sensitivity of the model to variations in photosynthetic and emission-specific parameters. By comparing species-specific simulations with experimental data, we demonstrate that differences in photosynthetic characteristics can explain inter-species differences in emissions. Interestingly, the seasonal development of emissions could also be explained to some degree by the change in energy supply from photosynthesis throughout the season. In addition, we show that the principal responses are not limited to isoprene but can be formulated to describe the emission of other light-dependent volatile species. The proposed model is suitable for implementation into regional and global models, particularly those that already provide species-specific photosynthesis estimates.

Seasonal variations in isoprene emission from tropical deciduous tree species

Isoprene is a dominant constituent of the global biogenic volatile organic compounds budget. It plays an important role in regulating the atmospheric trace gas composition including tropospheric ozone concentrations. In this study, monthly measurements of isoprene emission rates were carried out over a 1-year period (December 2002-November 2003) from four Indian deciduous tree species, namely Ficus relegiosa, Ficus infectoria, Pongamia pinnata, and Morus alba, using branch enclosure method. Significantly high monthly variations in isoprene emission rates were observed in all four-plant species. Also, each plant species exhibited pronounced seasonal variation in isoprene emission. Maximum isoprene emissions were observed during summer and minimum during the winter or spring months.

Release of trace organic compounds during the decomposition of municipal solid waste components

Landfill gas contains numerous speciated organic compounds (SOCs) including alkanes, aromatics, chlorinated aliphatic hydrocarbons, alcohols, ketones, terpenes, chlorofluoro compounds, and siloxanes. The source, rate and extent of release of these compounds are poorly understood. The objective of this study was to characterize the release of SOCs and the regulated parameter, non-methane organic compounds (NMOCs) during the decomposition of residential refuse and its major biodegradable components [paper (P), yard waste (YW), food waste (FW)]. Work was conducted under anaerobic conditions in 8-L reactors operated to maximize decomposition. Refuse and YW were also tested under aerobic conditions. NMOC release during anaerobic decomposition of refuse, P, YW, and FW was 0.151, 0.016, 0.038, and 0.221 mg-C dry g(-1), respectively, while release during aerobic decomposition of refuse and YW was 0.282 and 0.236 mg-C dry g(-1), respectively. The highest NMOC release was measured under abiotic conditions (3.01 mg-C dry g(-1)), suggesting the importance of gas stripping. NMOC release was faster than CH4 production in all treatments. Terpenes and ketones accounted for 32-96% of SOC release in each treatment, while volatile fatty acids were not a significant contributor. Release in aerobic systems points to the potential importance of composting plants as an emissions source.

Adverse health effects of outdoor air pollutants

Much research on the health effects of outdoor air pollution has been published in the last decade. The goal of this review is to concisely summarize a wide range of the recent research on health effects of many types of outdoor air pollution. A review of the health effects of major outdoor air pollutants including particulates, carbon monoxide, sulfur and nitrogen oxides, acid gases, metals, volatile organics, solvents, pesticides, radiation and bioaerosols is presented. Numerous studies have linked atmospheric pollutants to many types of health problems of many body systems including the respiratory, cardiovascular, immunological, hematological, neurological and reproductive/ developmental systems. Some studies have found increases in respiratory and cardiovascular problems at outdoor pollutant levels well below standards set by such agencies as the US EPA and WHO. Air pollution is associated with large increases in medical expenses, morbidity and is estimated to cause about 800,000 annual premature deaths worldwide [Cohen, A.J., Ross Alexander, H., Ostro, B., Pandey, K.D., Kryzanowski, M., Kunzail, N., et al., 2005. The global burden of disease due to outdoor air pollution. J Toxicol Environ Health A. 68: 1-7.]. Further research on the health effects of air pollution and air pollutant abatement methods should be very helpful to physicians, public health officials, industrialists, politicians and the general public.

Foliar phenolics in sugar maple (Acer saccharum) as a potential indicator of tropospheric ozone pollution

Tropospheric O3 has been implicated in the declining health of forest ecosystems in Europe and North America and has been shown to have negative consequences on human health. We have measured tropospheric ozone (O3) in the lower canopy through the use of passive monitors located in five woodlots along a 150 km urban-rural transect, originating in the large urban complex of Toronto, Canada. We also sampled foliage from 10 mature sugar maple trees in each woodlot and measured the concentration of a number of phenolic compounds and macronutrients. O3 concentrations were highest in the two rural woodlots, located approximately 150 km downwind of Toronto, when compared to the woodlots found within the Greater Toronto Area. Foliar concentrations of three flavonoids, avicularin, isoquercitrin, and quercitrin, were significantly greater and nitrogen concentrations significantly lower at these same rural woodlots, suggesting some physiological disruption is occurring in those sites where exposure to tropospheric O3 is greater. We suggest that foliar phenolics of sugar maple may be a biochemical indicator of tropospheric ozone exposure.

Nitrogen deficiency increases volicitin-induced volatile emission, jasmonic acid accumulation, and ethylene sensitivity in maize

Insect herbivore-induced plant volatile emission and the subsequent attraction of natural enemies is facilitated by fatty acid-amino acid conjugate (FAC) elicitors, such as volicitin [N-(17-hydroxylinolenoyl)-L-glutamine], present in caterpillar oral secretions. Insect-induced jasmonic acid (JA) and ethylene (E) are believed to mediate the magnitude of this variable response. In maize (Zea mays) seedlings, we examined the interaction of volicitin, JA, and E on the induction of volatile emission at different levels of nitrogen (N) availability that are known to influence E sensitivity. N availability and volicitin-induced sesquiterpene emission are inversely related as maximal responses were elicited in N-deficient plants. Plants with low N availability demonstrated similar volatile responses to volicitin (1 nmol plant(-1)) and JA (100 nmol plant(-1)). In contrast, plants with medium N availability released much lower amounts of volicitin-induced sesquiterpenes compared with JA, suggesting an alteration in volicitin-induced JA levels. As predicted, low N plants exhibited greater sustained increases in wound- and volicitin-induced JA levels compared with medium N plants. N availability also altered volicitin-E interactions. In low N plants, E synergized volicitin-induced sesquiterpene and indole emission 4- to 12-fold, with significant interactions first detected at 10 nL L(-1) E. Medium N plants demonstrated greatly reduced volicitin-E interactions. Volicitin-induced sesquiterpene emission was increased by E and was decreased by pretreatment the E perception inhibitor 1-methylcyclopropene without alteration in volicitin-induced JA levels. N availability influences plant responses to insect-derived elicitors through changes in E sensitivity and E-independent JA kinetics.

Monoterpene levels in needles of Douglas fir exposed to elevated CO2 and temperature

Monoterpene levels in current year needles of Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were measured at the end of 4 years of exposure to ambient or elevated CO2 (+179 micro mol mol-1), and ambient or elevated temperature (+0.3.5;C). Eleven monoterpenes were identified and quantified using gas chromatography/flame ionization detector/mass spectroscopy, with eight of these compounds regularly occurring in all trees examined. Elevated CO2 exposure significantly reduced the levels for four of the eight main compounds in needles. Total monoterpene production was reduced by 52% (P < 0.05). Elevated temperature also reduced monoterpene levels (P < 0.07). The combination of elevated temperature and elevated CO2 resulted in a 64% reduction in total monoterpenes compared with needles on ambient temperature trees. Two-way anova showed no significant temperature-CO2 interaction. It is hypothesized that seasonal reductions in needle monoterpene pools under elevated CO2 and temperature conditions may be due to a combination of competing carbon sinks, including increased carbon flux through the roots.

Responses of spruce seedlings (Picea abies) to exhaust gas under laboratory conditions--II. Ultrastructural changes and stomatal behaviour

This study examines the effects of exhaust gas exposure on the epistomatal wax structure and mesophyll ultrastructure in needles of Norway spruce (Picea abies (L.) Karst.) seedlings. Stomatal diffusive resistance was also measured. Two independent exhaust gas fumigations were performed: 100 and 200 ppb measured as NO(x), for 10 days and 50, 100 and 200 ppb NO(x) for 19 days. The obstructive effect of exhaust gas exposure on epistomatal wax tubules was apparent. The stomata became covered by flat and solid wax resulting from the structural degradation of the wax crystalloids. Increasing the exhaust gas concentration in the chamber atmosphere exacerbated the degradation of the wax structure. Exhaust gas exposure induced aggregation and electron translucence of plastoglobuli, swelling of thylakoids, increase of cytoplasmic lipids and slight increase of vesiculation of cytoplasm in mesophyll cells of current and previous year needles. These changes were exemplified in current year needles. Damage to the epicuticular waxes and mesophyll ultrastructure of spruce needles most likely reflects the NO(x) and volatile hydrocarbon fraction. The alterations in epicuticular waxes and mesophyll ultrastructure can be related to accelerated senescence of the youngest, photosynthetically active, needle generation. The exhaust gas also resulted in decreased diffusive stomatal resistance at night which indicates that the exhaust gas exposure disturbed the gas exchange of spruce seedlings. The results show that even relatively short-term exposure to realistic concentrations of exhaust gas in the atmosphere can induce rather severe injuries to the needle surface structure as well as ultrastructure at the cellular level.