BVOCs and global change

Isoprenoid emissions from Schima superba and Cunninghamia lanceolata: Their responses to elevated temperature by two warming facilities

Isoprenoids (including isoprene (ISO) and monoterpenes (MTs)) are the majority of biogenic volatile organic compounds (BVOCs) which are important carbon-containing secondary metabolites biosynthesized by organisms, especially plant in terrestrial ecosystem. Results of the warming effects on isoprenoid emissions vary within species and warming facilities, and thus conclusions remain controversial. In this study, two typical subtropical tree species seedlings of Schima superba and Cunninghamia lanceolata were cultivated under three conditions, namely no warming (CK) and two warming facilities (with infrared radiators (IR) and heating wires (HW)) in open top chamber (OTC), and the isoprenoid emissions were measured with preconcentor-GC-MS system after warming for one, two and four months. The results showed that the isoprenoid emissions from S. superba and C. lanceolata exhibited uniformity in response to two warming facilities. IR and HW both stimulated isoprenoid emissions in two plants after one month of treatment, with increased ratios of 16.3 % and 72.5 % for S. superba, and 2.47 and 5.96 times for C. lanceolata. However, the emissions were suppressed after four months, with more pronounced effect for HW. The variation in isoprenoid emissions was primarily associated with the levels of Pn, Tr, monoterpene synthase (MTPS) activity. C. lanceolata predominantly released MTs (mainly α-pinene, α-terpene, γ-terpene, and limonene), with 39.7 % to 99.6 % of the total isoprenoid but ISO was only a very minor constituent. For S. superba, MTs constituted 24.7 % to 96.1 % of total isoprenoid. It is noteworthy that HW generated a greater disturbance to physiology activity in plants. Our study provided more comprehensive and more convincing support for integrating temperature-elevation experiments of different ecosystems and assessing response and adaptation of forest carbon cycle to global warming.

Drought induces moderate, diverse changes in the odour of grassland species

Plants react to drought stress with numerous changes including altered emissions of volatile organic compounds (VOC) from leaves, which provide protection against oxidative tissue damage and mediate numerous biotic interactions. Despite the share of grasslands in the terrestrial biosphere, their importance as carbon sinks and their contribution to global biodiversity, little is known about the influence of drought on VOC profiles of grassland species. Using coupled gas chromatography-mass spectrometry, we analysed the odorants emitted by 22 European grassland species exposed to an eight-week-lasting drought treatment (DT; 30% water holding capacity, WHC). We focused on the odorants emitted during the light phase from whole plant shoots in their vegetative stage. Emission rates were standardised to the dry weight of each shoot. Well-watered (WW) plants (70% WHC) served as control. Drought-induced significant changes included an increase in total emission rates of plant VOC in six and a decrease in three species. Diverging effects on the number of emitted VOC (chemical richness) or on the Shannon diversity of the VOC profiles were detected in 13 species. Biosynthetic pathways-targeted analyses revealed 13 species showing drought-induced higher emission rates of VOC from one, two, three, or four major biosynthetic pathways (lipoxygenase, shikimate, mevalonate and methylerythritol phosphate pathway), while six species exhibited reduced emission rates from one or two of these pathways. Similarity trees of odorant profiles and their drought-induced changes based on a biosynthetically informed distance metric did not match species phylogeny. However, a phylogenetic signal was detected for the amount of terpenoids released by the studied species under WW and DT conditions. A comparative analysis of emission rates of single compounds released by WW and DT plants revealed significant VOC profile dissimilarities in four species only. The moderate drought-induced changes in the odorant emissions of grassland species are discussed with respect to their impact on trophic interactions across the food web. (294 words).

Plant secondary metabolism in a fluctuating world: climate change perspectives

Climate changes have unpredictable effects on ecosystems and agriculture. Plants adapt metabolically to overcome these challenges, with plant secondary metabolites (PSMs) being crucial for plant-environment interactions. Thus, understanding how PSMs respond to climate change is vital for future cultivation and breeding strategies. Here, we review PSM responses to climate changes such as elevated carbon dioxide, ozone, nitrogen deposition, heat and drought, as well as a combinations of different factors. These responses are complex, depending on stress dosage and duration, and metabolite classes. We finally identify mechanisms by which climate change affects PSM production ecologically and molecularly. While these observations provide insights into PSM responses to climate changes and the underlying regulatory mechanisms, considerable further research is required for a comprehensive understanding.

Potential pre-industrial-like new particle formation induced by pure biogenic organic vapors in Finnish peatland

Pure biogenic new particle formation (NPF) induced by highly oxygenated organic molecules (HOMs) could be an important mechanism for pre-industrial aerosol formation. However, it has not been unambiguously confirmed in the ambient due to the scarcity of truly pristine continental locations in the present-day atmosphere or the lack of chemical characterization of NPF precursors. Here, we report ambient observations of pure biogenic HOM-driven NPF over a peatland in southern Finland. Meteorological decoupling processes formed an "air pocket" (i.e., a very shallow surface layer) at night and favored NPF initiated entirely by biogenic HOM from this peatland, whose atmospheric environment closely resembles that of the pre-industrial era. Our study sheds light on pre-industrial aerosol formation, which represents the baseline for estimating the impact of present and future aerosol on climate, as well as on future NPF, the features of which may revert toward pre-industrial-like conditions due to air pollution mitigation.

Ozone alters the chemical signal required for plant - insect pollination: The case of the Mediterranean fig tree and its specific pollinator

Tropospheric ozone (O3) is likely to affect the chemical signal emitted by flowers to attract their pollinators through its effects on the emission of volatile organic compounds (VOCs) and its high reactivity with these compounds in the atmosphere. We investigated these possible effects using a plant-pollinator interaction where the VOCs responsible for pollinator attraction are known and which is commonly exposed to high O3 concentration episodes: the Mediterranean fig tree (Ficus carica) and its unique pollinator, the fig wasp (Blastophaga psenes). In controlled conditions, we exposed fig trees bearing receptive figs to a high-O3 episode (5 h) of 200 ppb and analyzed VOC emission. In addition, we investigated the chemical reactions occurring in the atmosphere between O3 and pollinator-attractive VOCs using real-time monitoring. Finally, we tested the response of fig wasps to the chemical signal when exposed to increasing O3 mixing ratios (0, 40, 80, 120 and 200 ppb). The exposure of the fig tree to high O3 levels induced a significant decrease in leaf stomatal conductance, a limited change in the emission by receptive figs of VOCs not involved in pollinator attraction, but a major change in the relative abundances of the compounds among pollinator-attractive VOCs in O3-enriched atmosphere. Fig VOCs reacted with O3 in the atmosphere even at the lowest level tested (40 ppb) and the resulting changes in VOC composition significantly disrupted the attraction of the specific pollinator. These results strongly suggest that current O3 episodes are probably already affecting the interaction between the fig tree and its specific pollinator.

The Effects of Heavy Metal Pollution on Soil Nitrogen Transformation and Rice Volatile Organic Compounds under Different Water Management Practices

One of the most concerning global environmental issues is the pollution of agricultural soils by heavy metals (HMs), especially cadmium, which not only affects human health through Cd-containing foods but also impacts the quality of rice. The soil's nitrification and denitrification processes, coupled with the release of volatile organic compounds by plants, raise substantial concerns. In this review, we summarize the recent literature related to the deleterious effects of Cd on both soil processes related to the N cycle and rice quality, particularly aroma, in different water management practices. Under both continuous flooding (CF) and alternate wetting and drying (AWD) conditions, cadmium has been observed to reduce both the nitrification and denitrification processes. The adverse effects are more pronounced in alternate wetting and drying (AWD) as compared to continuous flooding (CF). Similarly, the alteration in rice aroma is more significant in AWD than in CF. The precise modulation of volatile organic compounds (VOCs) by Cd remains unclear based on the available literature. Nevertheless, HM accumulation is higher in AWD conditions compared to CF, leading to a detrimental impact on volatile organic compounds (VOCs). The literature concludes that AWD practices should be avoided in Cd-contaminated fields to decrease accumulation and maintain the quality of the rice. In the future, rhizospheric engineering and plant biotechnology can be used to decrease the transport of HMs from the soil to the plant's edible parts.

Evaluation of urinary limonene metabolites as biomarkers of exposure to greenness

Exposure to plants is known to improve physical and mental health and living in areas of high vegetation is associated with better health. The addition of quantitative measures of greenness exposure at individual-level to other objective and subjective study measures will help establish cause-and-effect relationships between greenspaces and human health. Because limonene is one of the most abundant biogenic volatile organic compounds emitted by plants, we hypothesized that urinary metabolites of inhaled limonene can serve as biomarkers of exposure to greenness. To test our hypothesis, we analyzed urine samples collected from eight human volunteers after limonene inhalation or after greenness exposure using liquid chromatography-high resolution mass spectrometry-based profiling. Eighteen isomers of nine metabolites were detected in urine after limonene inhalation, and their kinetic parameters were estimated using nonlinear mixed effect models. Urinary levels of most abundant limonene metabolites were elevated after brief exposure to a forested area, and the ratio of urinary limonene metabolites provided evidence of recent exposure. The identities and structures of these metabolites were validated using stable isotope tracing and tandem mass spectral comparison. Together, these data suggest that urinary metabolites of limonene, especially uroterpenol glucuronide and dihydroperillic acid glucuronide, could be used as individualized biomarkers of greenness exposure.

Localized biogenic volatile organic compound emission inventory in China: A comprehensive review

Volatile organic compounds (VOCs) are the precursors of forming ozone (O3) and fine particulate matter (PM2.5). Accurate estimates of biogenic VOC (BVOC) emissions is essential for understanding the formation mechanism of O3 and PM2.5 pollution and precise reduction on anthropogenic emissions and thereby mitigating O3 and PM2.5 pollution. To gain comprehensive knowledge of BVOC emissions and improve the accuracy of their estimation, this study reviewed localized national, regional, and municipal emission estimations in China. From their comparisons, BVOC emission characteristics and deficiencies in the inventory compilation methodology were also investigated. The estimated BVOC emissions in China ranged between 10 and 58.9 Tg yr-1 and 10.9-18.9 Tg C yr-1, with diverse contributions for different BVOC categories. The simulated historical and future BVOC emissions exhibited an increasing trend. The uncertainty of the BVOC estimates was mainly from the applications of incomplete emission models, less localized accurate emission factors, deficient vegetation cover information, and low-resolution meteorological data in the inventory compilation. The regional and municipal BVOC emission inventories mainly focused on the Beijing-Tianjin-Hebei, Pearl River Delta, Sichuan Basin, and Yangtze River Delta regions, as well as the cities therein. For the same area, different studies reported diverse BVOC emissions by a maximum of two orders of magnitude. There is usually a lack of basic data with more detailed investigations and higher precision for estimation of BVOC emissions. By summarizing the measurements on terrestrial and marine BVOC emission fluxes, they are mainly focused on the Guangdong, Zhejiang and Jiangxi provinces, and Yellow Sea, East China Sea, and South China Sea, respectively. Expanding the temporal and spatial scales of observations is encouraged to enhance our understanding on the emissions and improve the emission estimates.

Process-evaluation of forest aerosol-cloud-climate feedback shows clear evidence from observations and large uncertainty in models

Natural aerosol feedbacks are expected to become more important in the future, as anthropogenic aerosol emissions decrease due to air quality policy. One such feedback is initiated by the increase in biogenic volatile organic compound (BVOC) emissions with higher temperatures, leading to higher secondary organic aerosol (SOA) production and a cooling of the surface via impacts on cloud radiative properties. Motivated by the considerable spread in feedback strength in Earth System Models (ESMs), we here use two long-term observational datasets from boreal and tropical forests, together with satellite data, for a process-based evaluation of the BVOC-aerosol-cloud feedback in four ESMs. The model evaluation shows that the weakest modelled feedback estimates can likely be excluded, but highlights compensating errors making it difficult to draw conclusions of the strongest estimates. Overall, the method of evaluating along process chains shows promise in pin-pointing sources of uncertainty and constraining modelled aerosol feedbacks.

Is tree planting an effective strategy for climate change mitigation?

The world's forests store large amounts of carbon (C), and growing forests can reduce atmospheric CO2 by storing C in their biomass. This has provided the impetus for world-wide tree planting initiatives to offset fossil-fuel emissions. However, forests interact with their environment in complex and multifaceted ways that must be considered for a balanced assessment of the value of planting trees. First, one needs to consider the potential reversibility of C sequestration in trees through either harvesting or tree death from natural factors. If carbon storage is only temporary, future temperatures will actually be higher than without tree plantings, but cumulative warming will be reduced, contributing both positively and negatively to future climate-change impacts. Alternatively, forests could be used for bioenergy or wood products to replace fossil-fuel use which would obviate the need to consider the possible reversibility of any benefits. Forests also affect the Earth's energy balance through either absorbing or reflecting incoming solar radiation. As forests generally absorb more incoming radiation than bare ground or grasslands, this constitutes an important warming effect that substantially reduces the benefit of C storage, especially in snow-covered regions. Forests also affect other local ecosystem services, such as conserving biodiversity, modifying water and nutrient cycles, and preventing erosion that could be either beneficial or harmful depending on specific circumstances. Considering all these factors, tree plantings may be beneficial or detrimental for mitigating climate-change impacts, but the range of possibilities makes generalisations difficult. Their net benefit depends on many factors that differ between specific circumstances. One can, therefore, neither uncritically endorse tree planting everywhere, nor condemn it as counter-productive. Our aim is to provide key information to enable appropriate assessments to be made under specific circumstances. We conclude our discussion by providing a step-by-step guide for assessing the merit of tree plantings under specific circumstances.

Correlation between microbial communities and volatile organic compounds in an urban soil provides clues on soil quality towards sustainability of city flowerbeds

Soil functionality is critical to the biosphere as it provides ecosystem services relevant for a healthy planet. The soil microbial composition is significantly impacted by anthropogenic activities, including urbanization. In this context, the study of soil microorganisms associated to urban green spaces has started to be crucial toward sustainable city development. Microbes living in the soil produce and degrade volatile organic compounds (VOCs). The VOC profiles may be used to distinguish between soils with various characteristics and management practices, reflecting variations in the activity of soil microbes that use a variety of metabolic pathways. Here, a combined approach based on DNA metabarcoding and GC-MS analysis was used to evaluate the soil quality from urban flowerbeds in Prato (Tuscany, Italy) in terms of microbial biodiversity and VOC emission profiles, with the final aim of evaluating the possible correlation between composition of microbial community and VOC patterns. Results showed that VOCs in the considered soil originated from anthropic and biological activity, and significant correlations between specific microbial taxa and VOCs were detected. Overall, the study demonstrated the feasibility of the use of microbe-VOC correlation as a proxy for soil quality assessment in urban soils.

Targeted rainfall enhancement as an objective of forestation

Forestation efforts are accelerating across the globe in the fight against global climate change, in order to restore biodiversity, and to improve local livelihoods. Yet, so far the non-local effects of forestation on rainfall have largely remained a blind spot. Here we build upon emerging work to propose that targeted rainfall enhancement may also be considered in the prioritization of forestation. We show that the tools to achieve this are rapidly becoming available, but we also identify drawbacks and discuss which further developments are still needed to realize robust assessments of the rainfall effects of forestation in the face of climate change. Forestation programs may then mitigate not only global climate change itself but also its adverse effects in the form of drying.

GLV reveal species differences and responses to environment in alpine shrub Rosa sericea complex

Plant Volatile components are an ecological adaptation mechanism of plants that can reflect species differences and environment information where it is located. The alpine shrub Rosa sericea complex consists of several allied species, which are morphologically similar and difficult to distinguish, they are typical distribution along the elevation in the Himalayas and the Transverse Ranges. We selected two typical areas to find that the different species could be distinguished by their "green leaf volatile components" (GLV) composition as well as their geographical location, and it was evident that species with glands had higher sesquiterpene content. Correlation analysis revealed the relation between volatile components and ecology factors (climate factors, soil factors, phyllospheric microorganisms). Our study adds a new perspective and basis for the environmental adaptations of different species in the alpine shrub Rosa sericea complex from a chemical ecology perspective.

Climate change, air quality, and respiratory health: a focus on particle deposition in the lungs

This review article delves into the multifaceted relationship between climate change, air quality, and respiratory health, placing a special focus on the process of particle deposition in the lungs. We discuss the capability of climate change to intensify air pollution and alter particulate matter physicochemical properties such as size, dispersion, and chemical composition. These alterations play a significant role in influencing the deposition of particles in the lungs, leading to consequential respiratory health effects. The review paper provides a broad exploration of climate change's direct and indirect role in modifying particulate air pollution features and its interaction with other air pollutants, which may change the ability of particle deposition in the lungs. In conclusion, climate change may play an important role in regulating particle deposition in the lungs by changing physicochemistry of particulate air pollution, therefore, increasing the risk of respiratory disease development.

Emission of marine volatile organic compounds (VOCs) by phytoplankton- a review

Oceans cover over 71% of the Earth's surface and play crucial roles in regulating the global climate. In the marine boundary layer, the levels of volatile organic compounds (VOCs) have been shown to have positive relations with the marine algal biomass, indicating that the marine biological activities can be an important biogenic VOCs (BVOCs) source. The emitted BVOCs will enhance the formation of secondary organic aerosols, and perturb the radiative forcing, which ultimately affects the climate. To date, knowledge on the emission processes (i.e., synthesis processes and emission rates) of BVOCs from marine phytoplankton is still lacking compared to the more well-known BVOCs released from terrestrial plants. In this review, we focus on the BVOCs emissions from the marine phytoplankton. Based on the available literature from field and laboratory studies, we listed the types of BVOCs being emitted by different marine phytoplankton species, summarized the diversity of BVOCs related to phytoplankton taxonomy and physiology and abiotic factors affecting their emissions in various marine environments, and discussed the biosynthesis and ecological function of important marine VOCs such as DMS, terpenoids and VHCs from phytoplankton. Finally, we highlighted the existing gaps in the current knowledge and the needs of future study for better understanding the physiological and ecological roles of BVOCs emission from marine phytoplankton.

Essential Oils of Artemisia frigida Plants (Asteraceae): Conservatism and Lability of the Composition

Plants of arid regions have adapted to harsh environments during the long span of their evolution and have developed a set of features necessary for their survival in water-limited conditions. Artemisia frigida Willd. (Asteraceae) is a widely distributed species possessing significant cenotic value in steppe ecosystems due to its high frequency and abundance. This study examines different patterns of formation of essential oil composition in A. frigida plants under the influence of heterogeneous factors, including climate and its integral characteristics (HTC, Cextr, SPEI and others). The work is based on the results of our research conducted in Russia (Republic of Buryatia, Irkutsk region), Mongolia, and China, from 1998 to 2021. A total of 32 constant compounds have been identified in the essential oil of A. frigida throughout its habitat range in Eurasia, from Kazakhstan to Qinghai Province, China. Among them, camphor, 1,8-cineol and bornyl acetate are the dominant components, contained in 93-95% of the samples. Among the sesquiterpenoids, germacrene D is the dominant component in 67% of the samples. The largest variability within the composition of the essential oils of A. frigida is associated with significant differences in the climatic parameters when plants grow in high-altitude and extrazonal conditions.

Exogenous monoterpenes mitigate H2O2-induced lipid damage but do not attenuate photosynthetic decline during water deficit in tomato

Although monoterpenes are suggested to mediate oxidative status, their role in abiotic stress responses is currently unclear. Here, a foliar spray of monoterpenes increased antioxidant capacity and decreased oxidative stress of Solanum lycopersicum under water deficit stress. The foliar content of monoterpenes increased with spray concentration indicating foliar uptake of exogenous monoterpenes. Exogenous monoterpene application substantially decreased foliar accumulation of hydrogen peroxide (H2O2) and lipid peroxidation (malondialdehyde). However, it appears that monoterpenes prevent the accumulation of reactive oxygen species rather than mitigating subsequent reactive oxygen species-induced damage. Low spray concentration (1.25 mM) proved most effective in decreasing oxidative stress but did not up-regulate the activity of key antioxidant enzymes (superoxide dismutase and ascorbate peroxidase) even though higher (2.5 and 5 mM) spray concentrations did, suggesting a complex role for monoterpenes in mediating antioxidant processes. Furthermore, soil drying caused similar photosynthetic limitations in all plants irrespective of monoterpene treatments, apparently driven by strong reductions in stomatal conductance as photosystem II efficiency only decreased in very dry soil. We suggest that exogenous monoterpenes may mitigate drought-induced oxidative stress by direct quenching and/or up-regulating endogenous antioxidative processes. The protective properties of specific monoterpenes and endogenous antioxidants require further investigation.

The Impact of Increased CO2 and Drought Stress on the Secondary Metabolites of Cauliflower (Brassica oleracea var. botrytis) and Cabbage (Brassica oleracea var. capitata)

Elevated carbon dioxide and drought are significant stressors in light of climate change. This study explores the interplay between elevated atmospheric CO2, drought stress, and plant physiological responses. Two Brassica oleracea varieties (cauliflowers and cabbage) were utilized as model plants. Our findings indicate that elevated CO2 accelerates assimilation rate decline during drought. The integrity of photosynthetic components influenced electron transport, potentially due to drought-induced nitrate reductase activation changes. While CO2 positively influenced photosynthesis and water-use efficiency during drought, recovery saw decreased stomatal conductance in high-CO2-grown plants. Drought-induced monoterpene emissions varied, influenced by CO2 concentration and species-specific responses. Drought generally increased polyphenols, with an opposing effect under elevated CO2. Flavonoid concentrations fluctuated with drought and CO2 levels, while chlorophyll responses were complex, with high CO2 amplifying drought's effects on chlorophyll content. These findings contribute to a nuanced understanding of CO2-drought interactions and their intricate effects on plant physiology.

Secondary metabolites responses of plants exposed to ozone: an update

Tropospheric ozone (O3) is a secondary pollutant that causes oxidative stress in plants due to the generation of excess reactive oxygen species (ROS). Phenylpropanoid metabolism is induced as a usual response to stress in plants, and induction of key enzyme activities and accumulation of secondary metabolites occur, upon O3 exposure to provide resistance or tolerance. The phenylpropanoid, isoprenoid, and alkaloid pathways are the major secondary metabolic pathways from which plant defense metabolites emerge. Chronic exposure to O3 significantly accelerates the direction of carbon flows toward secondary metabolic pathways, resulting in a resource shift in favor of the synthesis of secondary products. Furthermore, since different cellular compartments have different levels of ROS sensitivity and metabolite sets, intracellular compartmentation of secondary antioxidative metabolites may play a role in O3-induced ROS detoxification. Plants' responses to resource partitioning often result in a trade-off between growth and defense under O3 stress. These metabolic adjustments help the plants to cope with the stress as well as for achieving new homeostasis. In this review, we discuss secondary metabolic pathways in response to O3 in plant species including crops, trees, and medicinal plants; and how the presence of this stressor affects their role as ROS scavengers and structural defense. Furthermore, we discussed how O3 affects key physiological traits in plants, foliar chemistry, and volatile emission, which affects plant-plant competition (allelopathy), and plant-insect interactions, along with an emphasis on soil dynamics, which affect the composition of soil communities via changing root exudation, litter decomposition, and other related processes.

Assessing volatile organic compounds exposure and chronic obstructive pulmonary diseases in US adults

Background

Volatile organic compounds (VOCs) are a large group of chemicals widely used in People's Daily life. There is increasing evidence of the cumulative toxicity of VOCs. However, the association between VOCs and the risk of COPD has not been reported.

Objective

We comprehensively evaluated the association between VOCs and COPD.

Methods

Our study included a total of 1,477 subjects from the National Health and Nutrition Examination Survey, including VOCs, COPD, and other variables in the average US population. Multiple regression models and smooth-curve fitting (penalty splines) were constructed to examine potential associations, and stratified analyses were used to identify high-risk groups.

Results

We found a positive association between blood benzene and blood o-xylene concentrations and COPD risk and identified a concentration relationship between the two. That is, when the blood benzene and O-xylene concentrations reached 0.28 ng/mL and 0.08 ng/mL, respectively, the risk of COPD was the highest. In addition, we found that gender, age, and MET influence the relationship, especially in women, young people, and people with low MET.

Significance

This study revealed that blood benzene and blood o-xylene were independently and positively correlated with COPD risk, suggesting that long-term exposure to benzene and O-xylene may cause pulmonary diseases, and providing a new standard of related blood VOCs concentration for the prevention of COPD.

Improved monitoring of cryptogam gas-exchange and volatile emissions during desiccation-rehydration cycles with a within-chamber hydration method

Desiccation-rehydration studies in cryptogams constitute an important tool to understand the relation of key physiological traits with species stress tolerance and environmental adaptability. Real-time monitoring of responses has been limited by the design of commercial or custom measuring cuvettes and difficulties in experimental manipulation. We developed a within-chamber rehydration method that allows to rewater the samples rapidly, without the need to open the chamber and take out the sample for manual rehydration by the investigator. Data is collected in real-time and simultaneously with an infrared gas-analyzer (LICOR-7000), a chlorophyll fluorometer (Maxi Imaging-PAM) and a proton transfer reaction time-of-flight mass-spectrometer (PTR-TOF-MS) for volatile organic compound emissions. The system was tested on four cryptogam species with contrasting ecological distributions. No major errors or kinetics disruptions were found during system testing and measurements. Our within-chamber rehydration method improved accuracy, as measurement periods were not lacking, and repeatability of the protocol by reducing error variance in sample manipulation. This method provides an improved technique to conduct desiccation-rehydration measurements, contributing to the standardization and accuracy of current existing methodologies. A close real-time and simultaneous monitoring of photosynthesis, chlorophyll fluorescence and volatile organic compound emission data, offers a novel perspective in the analysis of the cryptogam stress responses that is yet to be fully explored.

Assessment of greenhouse emissions of the green bean through the static enclosure technique

Urban green installations are extensively promoted to increase sustainable and accessible food production and simultaneously improve the environmental performance and liveability of city buildings. In addition to the multiple benefits of plant retrofitting, these installations may lead to a consistent increase in biogenic volatile organic compounds (BVOCs) in the urban environment, especially indoors. Accordingly, health concerns could limit the implementation of building-integrated agriculture. In a building-integrated rooftop greenhouse (i-RTG), throughout the whole hydroponic cycle, green bean emissions were dynamically collected in a static enclosure. Four representative BVOCs, α-pinene (monoterpene), β-caryophyllene (sesquiterpene), linalool (oxygenated monoterpene) and cis-3-hexenol (LOX derivate), were investigated in the samples collected from two equivalent sections of a static enclosure, one empty and one occupied by the i-RTG plants, to estimate the volatile emission factor (EF). Throughout the season, extremely variable BVOC levels between 0.04 and 5.36 ppb were found with occasional but not significant (P > 0.05) variations between the two sections. The highest emission rates were observed during plant vegetative development, with EFs equivalent to 78.97, 75.85 and 51.34 ng g^-1 h^-1 for cis-3-hexenol, α-pinene, and linalool, respectively; at plant maturity, all volatiles were either close to the LLOQ (lowest limit of quantitation) or not detected. Consistent with previous studies significant relationships (r ≥ 0.92; P < 0.05) were individuated within volatiles and temperature and relative humidity of the sections. However, correlations were all negative and were mainly attributed to the relevant effect of the enclosure on the final sampling conditions. Overall, levels found were at least 15 folds lower than the given Risk and LCI values of the EU-LCI protocol for indoor environments, suggesting low BVOC exposure in the i-RTG. Statistical outcomes demonstrated the applicability of the static enclosure technique for fast BVOC emissions survey inside green retrofitted spaces. However, providing high sampling performance over entire BVOCs collection is recommended to reduce sampling error and incorrect estimation of the emissions.

Insect Infestation Increases Viscosity of Biogenic Secondary Organic Aerosol

Plant stress alters emissions of volatile organic compounds. However, little is known about how this could influence climate-relevant properties of secondary organic aerosol (SOA), particularly from complex mixtures such as real plant emissions. In this study, the chemical composition and viscosity were examined for SOA generated from real healthy and aphid-stressed Canary Island pine (Pinus canariensis) trees, which are commonly used for landscaping in Southern California. Healthy Canary Island pine (HCIP) and stressed Canary Island pine (SCIP) aerosols were generated in a 5 m³ environmental chamber at 35-84% relative humidity and room temperature via OH-initiated oxidation. Viscosities of the collected particles were measured using an offline poke-flow method, after conditioning the particles in a humidified air flow. SCIP particles were consistently more viscous than HCIP particles. The largest differences in particle viscosity were observed in particles conditioned at 50% relative humidity where the viscosity of SCIP particles was an order of magnitude larger than that of HCIP particles. The increased viscosity for the aphid-stressed pine tree SOA was attributed to the increased fraction of sesquiterpenes in the emission profile. The real pine SOA particles, both healthy and aphid-stressed, were more viscous than α-pinene SOA particles, demonstrating the limitation of using a single monoterpene as a model compound to predict the physicochemical properties of real biogenic SOA. However, synthetic mixtures composed of only a few major compounds present in emissions (<10 compounds) can reproduce the viscosities of SOA observed from the more complex real plant emissions.

Water availability and plant-herbivore interactions

Water is essential to plant growth and drives plant evolution and interactions with other organisms such as herbivores. However, water availability fluctuates, and these fluctuations are intensified by climate change. How plant water availability influences plant-herbivore interactions in the future is an important question in basic and applied ecology. Here we summarize and synthesize the recent discoveries on the impact of water availability on plant antiherbivore defense ecology and the underlying physiological processes. Water deficit tends to enhance plant resistance and escape traits (i.e. early phenology) against herbivory but negatively affects other defense strategies, including indirect defense and tolerance. However, exceptions are sometimes observed in specific plant-herbivore species pairs. We discuss the effect of water availability on species interactions associated with plants and herbivores from individual to community levels and how these interactions drive plant evolution. Although water stress and many other abiotic stresses are predicted to increase in intensity and frequency due to climate change, we identify a significant lack of study on the interactive impact of additional abiotic stressors on water-plant-herbivore interactions. This review summarizes critical knowledge gaps and informs possible future research directions in water-plant-herbivore interactions.

Dynamic environmental interactions shaped by vegetative plant volatiles

Covering: up to November 2022Plants shape terrestrial ecosystems through physical and chemical interactions. Plant-derived volatile organic compounds in particular influence the behavior and performance of other organisms. In this review, we discuss how vegetative plant volatiles derived from leaves, stems and roots are produced and released into the environment, how their production and release is modified by abiotic and biotic factors, and how they influence other organisms. Vegetative plant volatiles are derived from different biosynthesis and degradation pathways and are released via distinct routes. Both biosynthesis and release are regulated by other organisms as well as abiotic factors. In turn, vegetative plant volatiles modify the physiology and the behavior of a wide range of organisms, from microbes to mammals. Several concepts and frameworks can help to explain and predict the evolution and ecology of vegetative plant volatile emission patterns of specific pathways: multifunctionality of specialized metabolites, chemical communication displays and the information arms race, and volatile physiochemistry. We discuss how these frameworks can be leveraged to understand the evolution and expression patterns of vegetative plant volatiles. The multifaceted roles of vegetative plant volatiles provide fertile grounds to understand ecosystem dynamics and harness their power for sustainable agriculture.

Floral scent of the Mediterranean fig tree: significant inter-varietal difference but strong conservation of the signal responsible for pollinator attraction

For thousands of years, humans have domesticated different plants by selecting for particular characters, often affecting less-known traits, including the volatile organic compounds (VOCs) emitted by these plants for defense or reproduction. The fig tree Ficus carica has a very wide range of varieties in the Mediterranean region and is selected for its traits affecting fruits, including pollination, but the effect of human-driven diversification on the VOCs emitted by the receptive figs to attract their pollinator (Blastophaga psenes) is not known. In the present study, VOCs from receptive figs of eight varieties in northern Morocco, were collected at different times within the manual pollination period and analyzed by gas chromatography-mass spectrometry. Genetic analyses using microsatellite loci were performed on the same varieties. Despite strong inter-varietal differences in the quantity and relative proportions of all VOCs, the relative proportions of the four pollinator-attractive VOCs showed limited variation among varieties. There was no significant correlation between genetic markers and chemical profiles of the different varieties. While diversification driven by humans has led to differences between varieties in VOC profiles, this paper suggests that throughout the process of domestication and varietal diversification, stabilizing selection has maintained a strong signal favoring pollinator attraction.

Oxylipins and Reactive Carbonyls as Regulators of the Plant Redox and Reactive Oxygen Species Network under Stress

Reactive oxygen species (ROS), and in particular H2O2, serve as essential second messengers at low concentrations. However, excessive ROS accumulation leads to severe and irreversible cell damage. Hence, control of ROS levels is needed, especially under non-optimal growth conditions caused by abiotic or biotic stresses, which at least initially stimulate ROS synthesis. A complex network of thiol-sensitive proteins is instrumental in realizing tight ROS control; this is called the redox regulatory network. It consists of sensors, input elements, transmitters, and targets. Recent evidence revealed that the interplay of the redox network and oxylipins–molecules derived from oxygenation of polyunsaturated fatty acids, especially under high ROS levels–plays a decisive role in coupling ROS generation and subsequent stress defense signaling pathways in plants. This review aims to provide a broad overview of the current knowledge on the interaction of distinct oxylipins generated enzymatically (12-OPDA, 4-HNE, phytoprostanes) or non-enzymatically (MDA, acrolein) and components of the redox network. Further, recent findings on the contribution of oxylipins to environmental acclimatization will be discussed using flooding, herbivory, and establishment of thermotolerance as prime examples of relevant biotic and abiotic stresses.

Spatialized temporal dynamics of daily ozone concentrations: Identification of the main spatial differences

Ground-level ozone (O₃) is one of the most worrisome air pollutants regarding environmental and health impacts. There is a need for a deeper understanding of its spatial and temporal dynamics. Models are needed to provide continuous temporal and spatial coverage in ozone concentration data with a fine resolution. However, the simultaneous influence of each determinant of ozone dynamics, their spatial and temporal variations, and their interaction make the resulting dynamics of O₃ concentrations difficult to understand. This study aimed to i) identify different classes of temporal dynamics of O₃ at daily and 9 km² resolution over a long-term period of 12 years, ii) identify the potential determinants of these dynamics and, iii) explore the spatial distribution of the potential classes of temporal dynamics on a spatial continuum and over about 1000 km². Thus, 126 time series of 12-year daily ozone concentrations were classified using dynamic time warping (DTW) and hierarchical clustering (study area centered on Besançon, eastern France). The different temporal dynamics obtained differed on elevation, ozone levels, proportions of urbanized and vegetated surfaces. We identified different daily ozone temporal dynamics, spatially structured, that overlapped areas called urban, suburban and rural. Urbanization, elevation and vegetation acted as determinants simultaneously. Individually, elevation and vegetated surface were positively correlated with O₃ concentrations (r = 0.84 and r = 0.41, respectively), while the proportion of urbanized area was negatively correlated with O₃ (r = -0.39). An increasing ozone concentration gradient was observed from urban to rural areas and was reinforced by the elevation gradient. Rural areas were both subject to higher ozone levels (p < 0.001), least monitoring and lower predictability. We identified main determinants of the temporal dynamics of ozone concentrations. The joint influence of determinants was also synthesized. This study proposed a systematic, and reproducible way to build exposure area mapping.

On-Site Detection of Volatile Organic Compounds (VOCs)

Volatile organic compounds (VOCs) are of interest in many different fields. Among them are food and fragrance analysis, environmental and atmospheric research, industrial applications, security or medical and life science. In the past, the characterization of these compounds was mostly performed via sample collection and off-site analysis with gas chromatography coupled to mass spectrometry (GC-MS) as the gold standard. While powerful, this method also has several drawbacks such as being slow, expensive, and demanding on the user. For decades, intense research has been dedicated to find methods for fast VOC analysis on-site with time and spatial resolution. We present the working principles of the most important, utilized, and researched technologies for this purpose and highlight important publications from the last five years. In this overview, non-selective gas sensors, electronic noses, spectroscopic methods, miniaturized gas chromatography, ion mobility spectrometry and direct injection mass spectrometry are covered. The advantages and limitations of the different methods are compared. Finally, we give our outlook into the future progression of this field of research.

Volatile responses of dwarf birch to mimicked insect herbivory and experimental warming at two elevations in Greenlandic tundra

Plants release a complex blend of volatile organic compounds (VOCs) in response to stressors. VOC emissions vary between contrasting environments and increase with insect herbivory and rising temperatures. However, the joint effects of herbivory and warming on plant VOC emissions are understudied, particularly in high latitudes, which are warming fast and facing increasing herbivore pressure. We assessed the individual and combined effects of chemically mimicked insect herbivory, warming, and elevation on dwarf birch (Betula glandulosa) VOC emissions in high-latitude tundra ecosystems in Narsarsuaq, South Greenland. We hypothesized that VOC emissions and compositions would respond synergistically to warming and herbivory, with the magnitude differing between elevations. Warming increased emissions of green leaf volatiles (GLVs) and isoprene. Herbivory increased the homoterpene, (E)-4,8-dimethyl-1,3,7-nonatriene, emissions, and the response was stronger at high elevation. Warming and herbivory had synergistic effects on GLV emissions. Dwarf birch emitted VOCs at similar rates at both elevations, but the VOC blends differed between elevations. Several herbivory-associated VOC groups did not respond to herbivory. Harsher abiotic conditions at high elevations might not limit VOC emissions from dwarf birch, and high-elevation plants might be better at herbivory defense than assumed. The complexity of VOC responses to experimental warming, elevation, and herbivory are challenging our understanding and predictions of future VOC emissions from dwarf birch-dominated ecosystems.

A review of the factors affecting the emission of the ozone chemical precursors VOCs and NOx from the soil

The soil environment is one of the main places for the generation, emission, and absorption of various atmospheric pollutants, including nitrogen oxides (NO_x) and volatile organic compounds (VOCs), which are the main chemical precursors for the formation of ground-level ozone. Ground-level ozone pollution has become a concerning environmental problem because of the harm it poses to human health and the surrounding ecological environment. However, current studies on chemical precursors of ozone mainly focus on emissions from industrial sources, forest vegetation, and urban vehicle exhaust; by contrast, few studies have examined the role of the soil environment on NO_x and VOCs emissions. In addition, the soil environment is complex and heterogeneous. Agricultural activities (fertilization) and atmospheric deposition provide nutrients for the soil environment, with a significant effect on NO_x and VOCs emissions. There is thus a need to study the environmental factors related to the release of NO_x and VOCs in the soil to enhance our understanding of emission fluxes and the types of NO_x and VOCs in the soil environment and aid efforts to control ground-level ozone pollution through appropriate measures such as management of agricultural activities. This paper reviews the generation of NO_x and VOCs in the soil environment and the effects of various environmental factors on this process. Some suggestions are provided for future research on the regulation of NO_x and VOCs emissions in the soil environment and the ability of the soil environment to contribute to ground-level ozone pollution.

Effects of drought-induced holm oak dieback on BVOCs emissions in a Mediterranean forest

Climate change is impairing tree physiology and growth, causing an increase in tree dieback in many Mediterranean forests. These desiccation phenomena are leading to changes in land cover and plant community composition. Mediterranean plants are capable to emit large amount of Biogenic Volatile Organic Compounds (BVOCs), whose emission and biosynthesis is strongly affected by environmental conditions. This study evaluates the seasonal changes in understory species composition in two forest stands in Southern Tuscany characterized by different levels of Quercus ilex L. crown defoliation (low and high defoliation, LD and HD) and the relationship with BVOCs emissions over three years. We found significant changes in the understory plant community following Q. ilex crown defoliation and mortality, observing an increment in the number of shrubs both in HD and LD stands. The environmental sampling of BVOCs fully reflected the changes in vegetation cover and composition, with a reduction in the amount of monoterpene emissions due to the increasing rates of defoliation and mortality of Q. ilex trees. Our results suggest that terpene emissions from Mediterranean forests would be modified by an increase of Q. ilex dieback, with important consequences for functioning of this forest ecosystem and its atmospheric chemistry.

Contrasting terpene emissions from canopy and understory vegetation in response to increases in nitrogen deposition and seasonal changes in precipitation

Given global change and shifts in climate are expected to increase BVOC emissions, the quantification of links between environmental conditions, plant physiology, and terpene emission dynamics is required to improve model predictions of ecosystem responses to increasing nitrogen deposition and changes in precipitation regimes. Here, we conducted a two-factor field experiment in sub-tropical forest plots to determine effects of N addition (N), precipitation change (PC), and NP (N and PC combined treatment) on wet and dry season terpene emissions and leaf photosynthetic parameters from canopy and understory species. Changes of β-ocimene and sabinene under PC and NP in the wet season (0.4-5.6-fold change) were the largest contributor to changes in total terpene emissions. In the dry season, the standardized total terpene emission rate was enhanced by 144.9% under N addition and 185.7% under PC for the understory species, while the total terpene emission rate was lower under NP than N addition and PC, indicating that N addition tended to moderate increases in PC-induced understory total terpene emissions. In the wet season, the total terpene emission rate under N and PC was close to ambient conditions for the canopy species, while the total terpene emission rate was enhanced by 54.6% under NP, indicating that N and PC combined treatment had an additive effect on canopy total terpene emissions. Total terpene emission rates increased with rates of net leaf photosynthesis (P_n) and transpiration (Tr) and there was a decoupling between terpene emission rates and P_n under NP, indicating that complex effects between PC and N decreased the regularity of single-factor effects. We recommend that N and PC interaction effects are included in models for the prediction of terpene emissions, particularly from canopy vegetation during the wet season as a major source of forest ecosystem terpene emissions.

The research hotspots and trends of volatile organic compound emissions from anthropogenic and natural sources: A systematic quantitative review

Volatile organic compound (VOC) emissions have attracted wide attention due to their impacts on atmospheric quality and public health. However, most studies reviewed certain aspects of natural VOCs (NVOCs) or anthropogenic VOCs (AVOCs) rather than comprehensively quantifying the hotspots and evolution trends of AVOCs and NVOCs. We combined the bibliometric method with the evolution tree and Markov chain to identify research focus and uncover the trends in VOC emission sources. This study found that research mainly focused on VOC emission characteristics, effects on air quality and health, and VOC emissions under climate change. More studies concerned on AVOCs than on NVOCs, and AVOC emissions have shifted with a decreasing proportion of transport emissions and an increasing share of solvent utilization in countries with high emissions and publications (China and the USA). Research on AVOCs is imperative to develop efficient and economical abatement techniques specific to solvent sources or BTEX species to mitigate the detrimental effects. Research on NVOCs originating from human sources risen due to their application in medicine, while studies on sources sensitive to climate change grew slowly, including plants, biomass burning, microbes, soil and oceans. Research on the long-term responses of NVOCs derived from various sources to climate warming is warranted to explore the evolution of emissions and the feedback on global climate. It is worthwhile to establish an emission inventory with all kinds of sources, accurate estimation, high spatial and temporal resolution to capture the emission trends in the synergy of industrialization and climate change as well as to simulate the effects on air quality. We review VOC emissions from both anthropogenic and natural sources under climate change and their effects on atmospheric quality and health to point out the research directions for the comprehensive control of global VOCs and mitigation of O₃ pollution.

Effect of ozone exposure on the foraging behaviour of Bombus terrestris

Tropospheric ozone (O₃) mixing ratios have increased substantially since preindustrial times and high O₃ peaks are increasingly common. Plant-pollinator interactions are central to natural ecosystem functioning and food production systems but could be negatively affected by unfavourable environmental conditions such as elevated O₃. Ecosystem functioning is threatened by O₃, which can degrade floral volatile organic compounds (VOCs) used by pollinators as olfactory cues during foraging. It can also exert oxidative stress on VOC-emitting plants and receiving organisms, potentially disturbing the sending and receiving of VOC signals. The aim of this study was to determine the effects of elevated ozone on the foraging behaviour of Bombus terrestris on three species of the Brassicaceae, with a particular focus on bumblebee choices and the mechanisms underpinning differences observed. Moreover, the study was designed to fill a gap between observations in small-scale laboratory experiments and large-scale modelling through empirical observations in polytunnels that represent a medium-large-scale artificial environment. Using 10 × 3 × 2 m polytunnels the effects of O₃ on pollinator foraging parameters on Sinapis alba, Sinapis arvensis and Raphanus raphanistrum were assessed. Significant effects of elevated O₃ (100 ± 10 ppb) on the time taken for the first bee to alight on a flower and the cumulative amount of time spent on flowers was observed. To further investigate the underlying mechanisms, a laboratory test was conducted to determine the effects of ozone on the VOC blend composition of S. alba flowers. Synthetic VOC blends representing O₃-altered and unaltered profiles were reconstituted and utilized in polytunnel and olfactometry experiments. The results indicated that a reduction of olfaction-mediated orientation, probably via VOC-degradation or direct effects of O₃ on bees, was responsible for the altered foraging parameters of B. terrestris, suggesting that the presence of elevated O₃ could have negative effects on the foraging efficiency of important pollinator species.

Impacts of Drought and Rehydration Cycles on Isoprene Emissions in Populus nigra Seedlings

The volatile organic compounds emitted by plants significantly impact the atmospheric environment. The impacts of drought stress on the biogenic volatile organic compound (BVOC) emissions of plants are still under debate. In this study, the effects of two drought-rehydration cycle groups with different durations on isoprene emissions from Populus nigra (black poplar) seedlings were studied. The P. nigra seedlings were placed in a chamber that controlled the soil water content, radiation, and temperature. The daily emissions of isoprene and physiological parameters were measured. The emission rates of isoprene (F_iso) reached the maximum on the third day (D3), increasing by 58.0% and 64.2% compared with the controlled groups, respectively, and then F_iso significantly decreased. Photosynthesis decreased by 34.2% and 21.6% in D3 in the first and second groups, respectively. After rehydration, F_iso and photosynthesis recovered fully in two groups. However, F_iso showed distinct inconsistencies in two groups, and the recovery rates of F_iso in the second drought group were slower than the recovery rates of F_iso in the first groups. The response of BVOC emissions during the drought-rehydration cycle was classified into three phases, including stimulated, inhibited, and restored after rehydration. The emission pattern of isoprene indicated that isoprene played an important role in the response of plants to drought stress. A drought-rehydration model was constructed, which indicated the regularity of BVOC emissions in the drought-rehydration cycle. BVOC emissions were extremely sensitive to drought, especially during droughts of short duration. Parameters in computational models related to BVOC emissions of plants under drought stress should be continuously improved.

Biological control needs evolutionary perspectives of ecological interactions

While ecological interactions have been identified as determinant for biological control efficiency, the role of evolution remains largely underestimated in biological control programs. With the restrictions on the use of both pesticides and exotic biological control agents (BCAs), the evolutionary optimization of local BCAs becomes central for improving the efficiency and the resilience of biological control. In particular, we need to better account for the natural processes of evolution to fully understand the interactions of pests and BCAs, including in biocontrol strategies integrating human manipulations of evolution (i.e., artificial selection and genetic engineering). In agroecosystems, the evolution of BCAs traits and performance depends on heritable phenotypic variation, trait genetic architecture, selection strength, stochastic processes, and other selective forces. Humans can manipulate these natural processes to increase the likelihood of evolutionary trait improvement, by artificially increasing heritable phenotypic variation, strengthening selection, controlling stochastic processes, or overpassing evolution through genetic engineering. We highlight these facets by reviewing recent studies addressing the importance of natural processes of evolution and human manipulations of these processes in biological control. We then discuss the interactions between the natural processes of evolution occurring in agroecosystems and affecting the artificially improved BCAs after their release. We emphasize that biological control cannot be summarized by interactions between species pairs because pests and biological control agents are entangled in diverse communities and are exposed to a multitude of deterministic and stochastic selective forces that can change rapidly in direction and intensity. We conclude that the combination of different evolutionary approaches can help optimize BCAs to remain efficient under changing environmental conditions and, ultimately, favor agroecosystem sustainability.

Secondary Organic Aerosol Mass Yields from NO3 Oxidation of α-Pinene and Δ-Carene: Effect of RO2 Radical Fate

Dark chamber experiments were conducted to study the SOA formed from the oxidation of α-pinene and Δ-carene under different peroxy radical (RO₂) fate regimes: RO₂ + NO₃, RO₂ + RO₂, and RO₂ + HO₂. SOA mass yields from α-pinene oxidation were <1 to ∼25% and strongly dependent on available OA mass up to ∼100 μg m^-3. The strong yield dependence of α-pinene oxidation is driven by absorptive partitioning to OA and not by available surface area for condensation. Yields from Δ-carene + NO₃ were consistently higher, ranging from ∼10-50% with some dependence on OA for <25 μg m^-3. Explicit kinetic modeling including vapor wall losses was conducted to enable comparisons across VOC precursors and RO₂ fate regimes and to determine atmospherically relevant yields. Furthermore, SOA yields were similar for each monoterpene across the nominal RO₂ + NO₃, RO₂ + RO₂, or RO₂ + HO₂ regimes; thus, the volatility basis sets (VBS) constructed were independent of the chemical regime. Elemental O/C ratios of ∼0.4-0.6 and nitrate/organic mass ratios of ∼0.15 were observed in the particle phase for both monoterpenes in all regimes, using aerosol mass spectrometer (AMS) measurements. An empirical relationship for estimating particle density using AMS-derived elemental ratios, previously reported in the literature for non-nitrate containing OA, was successfully adapted to organic nitrate-rich SOA. Observations from an NO₃^- chemical ionization mass spectrometer (NO₃-CIMS) suggest that Δ-carene more readily forms low-volatility gas-phase highly oxygenated molecules (HOMs) than α-pinene, which primarily forms volatile and semivolatile species, when reacted with NO₃, regardless of RO₂ regime. The similar Δ-carene SOA yields across regimes, high O/C ratios, and presence of HOMs, suggest that unimolecular and multistep processes such as alkoxy radical isomerization and decomposition may play a role in the formation of SOA from Δ-carene + NO₃. The scarcity of peroxide functional groups (on average, 14% of C₁₀ groups carried a peroxide functional group in one test experiment in the RO₂ + RO₂ regime) appears to rule out a major role for autoxidation and organic peroxide (ROOH, ROOR) formation. The consistently substantially lower SOA yields observed for α-pinene + NO₃ suggest such pathways are less available for this precursor. The marked and robust regime-independent difference in SOA yield from two different precursor monoterpenes suggests that in order to accurately model SOA production in forested regions the chemical mechanism must feature some distinction among different monoterpenes.

Strong isoprene emission response to temperature in tundra vegetation

Emissions of biogenic volatile organic compounds (BVOCs) are a crucial component of biosphere-atmosphere interactions. In northern latitudes, climate change is amplified by feedback processes in which BVOCs have a recognized, yet poorly quantified role, mainly due to a lack of measurements and concomitant modeling gaps. Hence, current Earth system models mostly rely on temperature responses measured on vegetation from lower latitudes, rendering their predictions highly uncertain. Here, we show how tundra isoprene emissions respond vigorously to temperature increases, compared to model results. Our unique dataset of direct eddy covariance ecosystem-level isoprene measurements in two contrasting ecosystems exhibited Q₁₀ (the factor by which the emission rate increases with a 10 °C rise in temperature) temperature coefficients of up to 20.8, that is, 3.5 times the Q₁₀ of 5.9 derived from the equivalent model calculations. Crude estimates using the observed temperature responses indicate that tundra vegetation could enhance their isoprene emissions by up to 41% (87%)-that is, 46% (55%) more than estimated by models-with a 2 °C (4 °C) warming. Our results demonstrate that tundra vegetation possesses the potential to substantially boost its isoprene emissions in response to future rising temperatures, at rates that exceed the current Earth system model predictions.

Strategic roadmap to assess forest vulnerability under air pollution and climate change

Although it is an integral part of global change, most of the research addressing the effects of climate change on forests have overlooked the role of environmental pollution. Similarly, most studies investigating the effects of air pollutants on forests have generally neglected the impacts of climate change. We review the current knowledge on combined air pollution and climate change effects on global forest ecosystems and identify several key research priorities as a roadmap for the future. Specifically, we recommend (1) the establishment of much denser array of monitoring sites, particularly in the South Hemisphere; (2) further integration of ground and satellite monitoring; (3) generation of flux-based standards and critical levels taking into account the sensitivity of dominant forest tree species; (4) long-term monitoring of N, S, P cycles and base cations deposition together at global scale; (5) intensification of experimental studies, addressing the combined effects of different abiotic factors on forests by assuring a better representation of taxonomic and functional diversity across the ~73,000 tree species on Earth; (6) more experimental focus on phenomics and genomics; (7) improved knowledge on key processes regulating the dynamics of radionuclides in forest systems; and (8) development of models integrating air pollution and climate change data from long-term monitoring programs.

Desiccation-rehydration measurements in bryophytes: current status and future insights

Desiccation-rehydration experiments have been employed over the years to evaluate desiccation tolerance of bryophytes (Bryophyta, Marchantiophyta, and Anthocerotophyta). Researchers have applied a spectrum of protocols to induce desiccation and subsequent rehydration, and a wide variety of techniques have been used to study desiccation-dependent changes in bryophyte molecular, cellular, physiological, and structural traits, resulting in a multifaceted assortment of information that is challenging to synthesize. We analysed 337 desiccation-rehydration studies, providing information for 351 species, to identify the most frequent methods used, analyse the advances in desiccation studies over the years, and characterize the taxonomic representation of the species assessed. We observed certain similarities across methodologies, but the degree of convergence among the experimental protocols was surprisingly low. Out of 52 bryophyte orders, 40% have not been studied, and data are lacking for multiple remote or difficult to access locations. We conclude that for quantitative interspecific comparisons of desiccation tolerance, rigorous standardization of experimental protocols and measurement techniques, and simultaneous use of an array of experimental techniques are required for a mechanistic insight into the different traits modified in response to desiccation. New studies should also aim to fill gaps in taxonomic, ecological, and spatial coverage of bryophytes.

Modeling Biogenic Volatile Organic Compounds Emissions and Subsequent Impacts on Ozone Air Quality in the Sichuan Basin, Southwestern China

Biogenic volatile organic compounds (BVOCs) impact atmospheric oxidation capacity and regional air quality through various biogeochemistry processes. Accurate estimation of BVOC emissions is crucial for modeling the fate and transport of air pollutants in chemical transport models. Previous modeling characterizes the spatial variability of BVOCs while estimated BVOC emissions show large uncertainties, and the impacts of BVOC emissions on ozone (O3) air quality are not well understood. In this study, we estimate the BVOC emissions by model of emissions of gases and aerosols from nature (MEGAN) v2.1 and MEGAN v3.1 over the Sichuan Basin (SCB) situated in southwestern China for 2017. Further, the critical role of BVOC emissions on regional O3 pollution is illustrated with a CMAQ modeled O3 episode in summer 2017. Annual BVOC emissions over the SCB in 2017 are estimated to be 1.8 × 106 tons with isoprene emissions as high as 7.3 × 105 tons. Abundant BVOC emissions are depicted over the southern and southeastern SCB, in contrast to the relatively low emissions of BVOC over the Chengdu Plain and northeastern SCB. CMAQ simulations depict a strong influence of BVOC on ambient O3 formation over densely forested regions including southern SCB and Chongqing city, accounting for 10% of daily maximum hourly O3 concentration (DM1h O3) and 6% of daily maximum 8-h average O3 (MDA8h O3) concentrations in July 2017. Over the severe O3 episode in summer 2017, sensitivity experiments indicate that enhanced BVOC emissions contribute substantially to basin-wide O3 concentrations and elevate peak O3 levels by 36.5 and 31.2 μg/m3 for the southern SCB and Chengdu Plain, respectively. This work identifies robustly important effects of BVOC emissions on O3 exceedance events over the SCB and contributes insight into pursuing an O3 abatement strategy with full consideration of potential contributions from BVOC emissions.

Acute ozone exposure impairs detection of floral odor, learning, and memory of honey bees, through olfactory generalization

Air pollution stemming from human activities affects the environment in which plant and animal species live and interact. Similar to primary air pollutants which are emitted, secondary air pollutants, such as tropospheric ozone (O₃) formed from nitrogen oxides, are also harmful to human health and plant physiology. Yet, few reports studied the effects of O₃ on pollinators' physiology, despite that this pollutant, with its high oxidative potential, likely affects pollinators behaviors, especially the perception of signals they rely on to navigate their environment. Volatile Organic Compounds (VOCs) released by plants are used as signals by different animals. For pollination services, VOCs attract different insects to the flowers and strengthen these interactions. Here, we used the honey bee Apis mellifera as a model to characterize the effects of acute exposure to different realistic mixing ratios of O₃ (80-, 120-, and 200-ppb) on two crucial aspects: first, how exposed honey bees detect VOCs; and second, how O₃ affects these pollinators' learning and memory processes. With electroantennogram (EAG) recordings, we showed that increasing O₃ mixing ratios had a biphasic effect: an initial 25% decrease of the antennal activity when bees were tested directly after exposure (O₃ direct effect), followed by a 25% increase in activity and response when bees were allowed a two-hour rest after exposure (O₃ delayed effect). In parallel, during olfactory conditioning, increasing O₃ mixing ratios in both exposure protocols scarcely affected olfactory learning, followed by a decrease in recall of learned odors and an increase of response to new odors, leading to a higher generalization rate (i.e., discrimination impairment). These results suggest a link between O₃-related oxidative stress and olfactory coding disturbance in the honey bee brain. If ozone affects the pollinators' olfaction, foraging behaviors may be modified, in addition with a possible long-term harmful effect on pollination services.

Ozone Impact on Emission of Biogenic Volatile Organic Compounds in Three Tropical Tree Species From the Atlantic Forest Remnants in Southeast Brazil

Plants emit a broad number of Biogenic Volatile Organic Compounds (BVOCs) that can impact urban ozone (O₃) production. Conversely, the O₃ is a phytotoxic pollutant that causes unknown alterations in BVOC emissions from native plants. In this sense, here, we characterized the constitutive and O₃-induced BVOCs for two (2dO₃) and four (4dO₃) days of exposure (O₃ dose 80 ppb) and evaluated the O₃ response by histochemical techniques to detect programmed cell death (PCD) and hydrogen peroxide (H₂O₂) in three Brazilian native species. Croton floribundus Spreng, Astronium graveolens Jacq, and Piptadenia gonoacantha (Mart.) JF Macbr, from different groups of ecological succession (acquisitive and conservative), different carbon-saving defense strategies, and specific BVOC emissions. The three species emitted a very diverse BVOC composition: monoterpenes (MON), sesquiterpenes (SEQ), green leaf volatiles (GLV), and other compounds (OTC). C. floribundus is more acquisitive than A. graveolens. Their most representative BVOCs were methyl salicylate-MeSA (OTC), (Z) 3-hexenal, and (E)-2-hexenal (GLV), γ-elemene and (-)-β-bourbonene (SEQ) β-phellandrene and D-limonene (MON), while in A. graveolens were nonanal and decanal (OTC), and α-pinene (MON). Piptadenia gonoachanta is more conservative, and the BVOC blend was limited to MeSA (OTC), (E)-2-hexenal (GLV), and β-Phellandrene (MON). The O₃ affected BVOCs and histochemical traits of the three species in different ways. Croton floribundus was the most O₃ tolerant species and considered as an SEQ emitter. It efficiently reacted to O₃ stress after 2dO_3, verified by a high alteration of BVOC emission, the emergence of the compounds such as α-Ionone and trans-ß-Ionone, and the absence of H₂O₂ detection. On the contrary, A. graveolens, a MON-emitter, was affected by 2dO₃ and 4dO₃, showing increasing emissions of α-pinene and β-myrcene, (MON), γ-muurolene and β-cadinene (SEQ) and H₂O₂ accumulation. Piptadenia gonoachanta was the most sensitive and did not respond to BVOCs emission, but PCD and H₂O₂ were highly evidenced. Our results indicate that the BVOC blend emission, combined with histochemical observations, is a powerful tool to confirm the species' tolerance to O₃. Furthermore, our findings suggest that BVOC emission is a trade-off associated with different resource strategies of species indicated by the changes in the quality and quantity of BVOC emission for each species.

An Overview of the Isoprenoid Emissions From Tropical Plant Species

Terrestrial vegetation is the largest contributor of isoprenoids (a group of biogenic volatile organic compounds (BVOCs)) to the atmosphere. BVOC emission data comes mostly from temperate regions, and less is known about BVOC emissions from tropical vegetation, even though it is estimated to be responsible for >70% of BVOC emissions. This review summarizes the available data and our current understanding of isoprenoid emissions from tropical plant species and the spatial and temporal variation in emissions, which are strongly species-specific and regionally variable. Emission models lacking foliar level data for tropical species need to revise their parameters to account for seasonal and diurnal variation due to differences in dependencies on temperature and light of emissions from plants in other ecosystems. More experimental information and determining how emission capacity varies during foliar development are warranted to account for seasonal variations more explicitly.

Responses in growth and emissions of biogenic volatile organic compounds in Scots pine, Norway spruce and silver birch seedlings to different warming treatments in a controlled field experiment

We investigated the responses in growth and emissions of biogenic volatile organic compounds (BVOCs) in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies [L.] Karst.) and silver birch (Betula pendula Roth) seedlings to a simulated climate warming of +2 °C (T2) and +4 °C (T4), compared to the ambient conditions, during two growing seasons (2019-2020) in a controlled field experiment in central Finland. In all seedlings, height was measured weekly. Diameter was measured continuously for one seedling from each tree species per plot. For shoot and root biomass measurements, half of the seedlings were harvested at end of the first growing season and the rest at the end of the second growing season. Foliage BVOC emission rates were measured at the end of the second growing season. Biomass, height, and diameter growth of silver birch did benefit the most from warming in both growing seasons. In the Scots pine and Norway spruce seedlings, height and diameter growth increased with increasing temperature in the second growing season, more so in Scots pine. Overall, the shoot and root biomass of conifer seedlings increased with increasing temperature. In the conifer seedlings, warming increased biomass and diameter growth more than height growth, due to their predetermined height growth pattern. The warming increased BVOC emissions more clearly in silver birch, whilst the BVOC emissions were in conifers less sensitive to temperature variation. Based on our findings, silver birch seedlings could be expected to benefit the most from warmer growing conditions and Norway spruce the least.

Seasonal variation influences flavonoid biosynthesis path and content, and antioxidant activity of metabolites in Tetrastigma hemsleyanum Diels & Gilg

Environmental conditions contribute to plant growth and metabolism. This study aimed to determine a suitable environment and climate for large-scale artificial cultivation of an endangered plant, Tetrastigma hemsleyanum, by investigating the seasonal variations influencing the flavonoid biosynthetic selectivity and antioxidant activity of its major metabolites. Under conditions of precipitation (2.0~6.6 mm), temperature (17.5~24.1°C), humidity (67.3~80.2%), and sunshine duration (3.4~5.8 h) from April to May, the total flavonoid content in T. hemsleyanum reached higher levels between 281.3 and 392.8 μg/g. In the second half of April, the production selectivity (PS) of isoorientin (IsoO), orientin (Or), rutin (Rut), isoquercitin (IsoQ), kaempferol-3-O-rutinoside (Km3rut), astragalin (Ast), quercetin (Qu), apigenin (Ap), and kaempferol (Km) were 0.30, 0.06, 0.07, 0.07, 0.00, 0.04, 0.38, 0.05, and 0.03, respectively. Naringenin was dehydrogenated or hydroxylated to initiate two parallel reaction pathways for flavonoid biosynthesis in T. hemsleyanum: path I subsequently generated flavone derivatives including apigenin, luteolin, orientin, and isoorientin, and path II subsequently generated flavonol derivatives including Km, Qu, IsoQ, Rut, Ast, and Km3rut. The reaction selectivity of path II (RPSII) from January 1 to September 30 was considerably higher than that of path I (RPSI), except for March 16-31. In addition, either the content or antioxidant activity of three major metabolites in T. hemsleyanum followed the order of phenolic compounds > polysaccharides > sterols, and exhibited dynamic correlations with environmental factors. Naringenin favored hydroxylation and derived six flavonol compounds from January to September, and favored dehydrogenation and derived three flavone compounds from October to December. In most months of a year, Km preferentially favored hydroxylation rather than glucosylation.

The Influence of Elevated CO2 on Volatile Emissions, Photosynthetic Characteristics, and Pigment Content in Brassicaceae Plants Species and Varieties

Climate change will determine a sharp increase in carbon dioxide in the following years. To study the influence of elevated carbon dioxide on plants, we grew 13 different species and varieties from the Brassicaceae family at three carbon dioxide concentrations: 400, 800, and 1200 ppmv. The photosynthetic parameters (assimilation rate and stomatal conductance to water vapor) increase for all species. The emission of monoterpenes increases for plants grown at elevated carbon dioxide while the total polyphenols and flavonoids content decrease. The chlorophyll content is affected only for some species (such as Lipidium sativum), while the β-carotene concentrations in the leaves were not affected by carbon dioxide.

Biogenic volatile organic compound emission patterns and secondary pollutant formation potentials of dominant greening trees in Chengdu, southwest China

Integral to the urban ecosystem, greening trees provide many ecological benefits, but the active biogenic volatile organic compounds (BVOCs) they release contribute to the production of ozone and secondary organic aerosols, which harm ambient air quality. It is, therefore, necessary to understand the BVOC emission characteristics of dominant greening tree species and their relative contribution to secondary pollutants in various urban contexts. Consequently, this study utilized a dynamic enclosure system to collect BVOC samples of seven dominant greening tree species in urban Chengdu, Southwest China. Gas chromatography/mass spectrometry was used to analyze the BVOC components and standardized BVOC emission rates of each tree species were then calculated to assess their relative potential to form secondary pollutants. We found obvious differences in the composition of BVOCs emitted by each species. Ficus virens displayed a high isoprene emission rate at 31.472 μgC/(gdw (g dry weight)•hr), while Cinnamomum camphora emitted high volumes of D-Limonene at 93.574 μgC/(gdw•hr). In terms of the BVOC emission rates by leaf area, C. camphora had the highest emission rate of total BVOCs at 13,782.59 μgC/(m²•hr), followed by Cedrus deodara with 5466.86 μgC/(m²•hr). Ginkgo biloba and Osmanthus fragrans mainly emitted oxygenated VOCs with lower overall emission rates. The high BVOC emitters like F. virens, C. camphora, and Magnolia grandiflora have high potential for significantly contributing to environmental secondary pollutants, so should be cautiously considered for future planting. This study provides important implications for improving urban greening efforts for subtropical Chinese urban contexts, like Chengdu.

Amplified Drought and Seasonal Cycle Modulate Quercus pubescens Leaf Metabolome

The intensification of summer drought expected with climate change can induce metabolism modifications in plants to face such constraints. In this experiment, we used both a targeted approach focused on flavonoids, as well as an untargeted approach, to study a broader fraction of the leaf metabolome of Quercus pubescens exposed to amplified drought. A forest site equipped with a rainfall exclusion device allowed reduction of natural rainfall by ~30% over the tree canopy. Leaves of natural drought (ND) and amplified drought (AD) plots were collected over three seasonal cycles (spring, summer, and autumn) in 2013 (the second year of rain exclusion), 2014, and 2015. As expected, Q. pubescens metabolome followed a seasonal course. In the summer of 2015, the leaf metabolome presented a shifted and early autumnal pattern because of harsher conditions during this year. Despite low metabolic modification at the global scale, our results demonstrated that 75% of Quercus metabolites were upregulated in springs when trees were exposed to AD, whereas 60 to 73% of metabolites (93% in summer 2015), such as kaempferols and quercetins, were downregulated in summers/autumns. Juglanin, a kaempferol pentoside, as well as rhododendrin derivatives, were upregulated throughout the year, suggesting an antioxidant ability of these metabolites. Those changes in terms of phenology and leaf chemistry could, in the end, affect the ecosystem functioning.