Increased tropospheric ozone (O₃) concentrations in boreal forests affect the emission of biogenic volatile organic compounds (BVOCs), which play crucial roles in biosphere-atmosphere feedbacks. Although it has been well documented that BVOC emissions are altered in response to elevated O₃, consequent effects on the carbon budget have been largely unexplored. Here, we studied the effects of elevated O₃ (80 nmol mol⁻¹) on diurnal variation of BVOC emissions and gas exchange of CO₂ from above- and belowground parts of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) and further investigated effects on the carbon budget. In spring, elevated O₃ decreased BVOC emissions and net photosynthesis rate (Pn) from above-ground parts of both species. As BVOC emissions have a causal relationship with dormancy recovery, O₃-induced decreases in BVOC emissions indicated the inhibition of dormancy recovery. Contrary to the spring results, in summer BVOC emissions from aboveground parts were increased in response to elevated O₃ in both species. Decreases in Pn indicated O₃ stress. O₃-induced monoterpene emissions from aboveground were the main volatile defense response. Elevated O₃ had little effect on BVOC emissions from belowground parts of either species in spring or summer. In spring, elevated O₃ decreased the proportion of carbon emitted as BVOCs relative to that assimilated by photosynthesis (the proportion of BVOC-C loss) at the soil-plant system levels in both species. In summer, elevated O₃ resulted in a net CO₂–C loss at the soil-plant system level of Scots pine. During this process, O₃-induced BVOC-C loss can represent a significant fraction of carbon exchange between the atmosphere and Scots pine. In Norway spruce, the effects of O₃ were less pronounced. The current results highlight the need for prediction of BVOC emissions and their contributions to the carbon budget in boreal forests under O₃ stress.

Thirteen secondary organic aerosol (SOA) tracers of isoprene, monoterpenes and sesquiterpenes were measured for PM₂.₅ aerosols collected at the summit of Mt. Wuyi (1139 m, a.s.l.), to investigate their seasonality and formation mechanism. Concentrations of the isoprene and monoterpene SOA tracers were much higher in summer than those in other seasons. In contrast, β-caryophyllinic acid was found to be the lowest in summer. Concentrations of those BSOA tracers showed a positive correlation with temperature (R² = 0.52–0.70), and a negative correlation with relative humidity (R² = 0.43–0.78). Moreover, thermodynamic model (i.e., ISORROPIA-II) calculation results showed that acidity conditions are favorable for BSOA formation. Robust linear correlations between the BSOA tracers and anthropogenic pollutants such as SO₂ (R² = 0.53–0.7) and NO₂ (R² = 0.37–0.54) were observed for all the samples, suggesting that SO₂ and NOx can enhance BSOA production in the remote mountain area of southeast China, which is related to an acid-catalyzed heterogeneous chemistry. Moreover, we also found a significant correlation between the concentrations of the BSOA tracers and levoglucosan especially for β-caryophyllinic acid, indicating that biomass burning plumes from the distant lowland regions could influence the production of BSOA in the mountain free troposphere. Our results clearly demonstrated that anthropogenic emissions in China could enhance BSOA formation in the distant mountain regions.

Thirteen secondary organic aerosol (SOA) tracers of isoprene (SOAI), monoterpenes (SOAM), sesquiterpenes (SOAS) and aromatics (SOAA) in fine particulate matter (PM2.5) were measured at a Pearl River Delta (PRD) regional site for one year. The characteristics including their seasonal cycles and the factors influencing their formation in this region were studied. The seasonal patterns of SOAI, SOAM and SOAS tracers were characterized over three enhancement periods in summer (I), autumn (II) and winter (III), while the elevations of SOAA tracer (i.e., 2,3-dihydroxy-4-oxopentanoic acid, DHOPA) were observed in Periods II and III. We found that SOA formed from different biogenic precursors could be driven by several factors during a one-year seasonal cycle. Isoprene emission controlled SOAI formation throughout the year, while monoterpene and sesquiterpene emissions facilitated SOAM and SOAS formation in summer rather than in other seasons. The influence of atmospheric oxidants (Ox) was found to be an important factor of the formation of SOAM tracers during the enhancement periods in autumn and winter. The formation of SOAS tracer was influenced by the precursor emissions in summer, atmospheric oxidation in autumn and probably also by biomass burning in both summer and winter. In this study, we could not see the strong contribution of biomass burning to DHOPA as suggested by previous studies in this region. Instead, good correlations between observed DHOPA and Ox as well as [NO2][O3] suggest the involvement of both ozone (O3) and nitrogen dioxide (NO2) in the formation of DHOPA. The results showed that regional air pollution may not only increase the emissions of aromatic precursors but also can greatly promote the formation processes.

Tropospheric ozone (O₃) affects isoprenoid emissions, and floral emissions in particular, which may result in potential impacts on the interactions of plants with other organisms. The effects of ozone (O₃) on isoprenoid emissions have been investigated for many years, while knowledge on O₃ effects on floral emissions is still scarce and the relevant mechanism has not been clarified so far. We investigated the effects of O₃ on floral and foliar isoprenoid emissions (mainly isoprene, monoterpenes and sesquiterpenes) and their synthase substrates from three rose varieties (CH, Rosa chinensis Jacq. var. chinensis; SA, R. hybrida ‘Saiun’; MO, R. hybrida ‘Monica Bellucci’) at different exposure durations. Results indicated that the O₃-induced stimulation after short-term exposure (35 days after the beginning of O₃ exposure) was significant only for sesquiterpene emissions from flowers, while long-term O₃ exposure (90 days after the beginning of O₃ exposure) significantly decreased both foliar and floral monoterpene and sesquiterpene emissions. In addition, the observed decline of emissions under long-term O₃ exposure resulted from the limitation of synthase substrates, and the responses of emissions and substrates varied among varieties, with the greatest variation in the O₃-sensitive variety. These findings provide important insights on plant isoprenoid emissions and species selection for landscaping, especially in areas with high O₃ concentration.

Plants can respond physiologically to damaging ultraviolet-B radiation by altering leaf chemistry, especially UV absorbing phenolic compounds. However, the effects on terpene emissions have received little attention. We conducted two field trials in plots with supplemented UV-B radiation and assessed the influence of feeding by pine weevils, Hylobius abietis L., on volatile emissions from 3-year old Norway spruce trees (Picea abies L. Karst.). We collected emissions from branch tips distal to the feeding weevils, and from whole branches including the damage sites. Weevil feeding clearly induced the emission of monoterpenes and sesquiterpenes, particularly linalool and (E)-β-farnesene, from branch tips, and the sums of monoterpenes and sesquiterpenes emitted by whole branches were substantially increased. We discovered little effect of UV-B radiation up to 30% above the ambient level on volatile emissions from branch tips distal to damage sites, but there was a possible effect on bark emissions from damage sites. Chronic exposure to enhanced UV-B radiation has little effect on volatile emissions of Norway spruce.

The effects of monoterpenes on the degradation of 14C-2,4-dichlorophenol (DCP) were investigated in soils collected from areas surrounding monoterpene and non-monoterpene-emitting vegetation. Indigenous microorganisms degraded 14C-2,4-DCP to 14CO2, after 1 d contact time. Degradation was enhanced by prior exposure of the soils to 2,4-DCP for 32 d, increasing extents of mineralisation up to 60%. Monoterpene amendments further enhanced 2,4-DCP degradation, but only following pre-exposure to both 2,4-DCP and monoterpene, with total 2,4-DCP mineralisation extents of up to 71%. Degradation was greatest at the higher monoterpene concentrations (>=1 μg kg-1). Total mineralisation extents were similar between concentrations, but higher than the control and the 0.1 μg kg-1 amendment, indicating that increases in monoterpene concentration has a diminishing enhancing effect. We suggest that monoterpenes can stimulate the biodegradation of 2,4-DCP by indigenous soil microorganisms and that monoterpene amendment in soils is an effective strategy for removing organic contaminants. A amendment of soils with monoterpenes may induce organic contaminant degradation by indigenous soil microorganisms.

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

This study is focused on the analysis of regional variation of the chemical compositions of three Clinopodium menthifolium subsp. ascendens (Jord.) Govaerts Tunisian accession, as well as their inhibition toward fungi and insect pests. The diversity of the chemical constituents and biological activities in front of the aforementioned variations was found to be remarkable. Essential oils were obtained by hydrodistillation of the aerial parts and analyzed by gas chromatography-mass spectrometry (GC-MS). A total of 41, 42, and 30 compounds were identified respectively from Clinopodium menthifolium essential oils harvested from three Tunisian regions, namely Ain-Draham (ADEO), Babouch (BEO), and Tabarka (TEO). All analyzed oils were rich in oxygenated monoterpenes with different major constituents. Piperitenone (34.5%), cis-piperitone oxide (26.1%), and pulegone (47.9%) were the dominant compounds in the three volatile oils, respectively. The antifungal activity was investigated in vitro using six targeted fungal strains (Aspergillus flavus, Aspergillus terreus, Candida albicans, Microsporum canis, Microsporum gypseum, and Trichophyton mentagrophytes). The toxicity and repellency of essential oils were evaluated against the stored product pest Tribolium confusum. The tested samples were differently effective toward the target fungi and the pest depending on the variability of their chemical compositions. BEO exhibited the highest fungitoxic properties toward A. terreus mold, M. canis dermatophyte, and C. albicans yeast (the MIC values ranged from 40 to 400 μg mL⁻¹). In addition, the data showed that TEO repelled T. confusum moderately (PR = 42.5% at 2 h after exposure). Concerning the contact treatment, both ADEO and BEO were proved to possess slightly toxic effects toward T. confusum pest (% of mortality 27.5–32.5% at 5% concentration). The results showed that the geographic origin greatly influenced the chemical composition and the associated bioactivities of Clinopodium menthifolium subsp. ascendens.