As cities strive for ambitious increases in tree canopy cover and reductions in anthropogenic volatile organic compound (AVOC) emissions, accurate assessments of the impacts of biogenic VOCs (BVOCs) on air quality become more important. In this study, we aim to quantify the impact of future urban greening on ozone production. BVOC emissions in dense urban areas are often coarsely represented in regional models. We set up a high-resolution (30 m) MEGAN (The Model of Emissions of Gases and Aerosols from Nature version 3.2) to estimate summertime biogenic isoprene emissions in the New York City metro area (NYC-MEGAN). Coupling an observation-constrained box model with NYC-MEGAN isoprene emissions successfully reproduced the observed isoprene concentrations in the city core. We then estimated future isoprene emissions from likely urban greening scenarios and evaluated the potential impact on future ozone production. NYC-MEGAN predicts up to twice as much isoprene emissions in NYC as the coarse-resolution (1.33 km) Biogenic Emission Inventory System version 3.61 (BEIS) on hot summer days. We find that BVOCs drive ozone production on hot summer days, even in the city core, despite large AVOC emissions. If high isoprene emitting species (e.g., oak trees) are planted, future isoprene emissions could increase by 1.4-2.2 times in the city core, which would result in 8-19 ppbv increases in peak ozone on ozone exceedance days with current NOx concentrations. We recommend planting non- or low-isoprene emitting trees in cities with high NOx concentrations to avoid an increase in the frequency and severity of future ozone exceedance events.

China implemented continuous forestation and experienced significant greening tendency in the past several decades. While the ecological project brings benefits to regional carbon assimilation, it also affects surface ozone (O3) pollution level through perturbations in biogenic emissions and dry deposition. Here, we use a coupled chemistry-vegetation model to assess the impacts of land use and land cover change (LULCC) on summertime surface O3 in China during 2000-2019. The LULCC is found to enhance O3 by 1-2 ppbv in already-polluted areas. In contrast, moderate reductions of -0.4 to -0.8 ppbv are predicted in southern China where the largest forest cover changes locate. Such inconsistency is attributed to the background chemical regimes with positive O3 changes over VOC-limited regions but negative changes in NOx-limited regions. The net contribution of LULCC to O3 budget in China is 24.17 Kg/s, in which the positive contribution by more isoprene emissions almost triples the negative effects by the increased dry deposition. Although the LULCC-induced O3 perturbation is much lower than the effects of anthropogenic emissions, forest expansion has exacerbated regional O3 pollution in North China Plain and is expected to further enhance surface O3 with continuous forestation in the future.

Isoprenoid metabolism and its derivatives took part in photosynthesis, growth regulation, signal transduction, and plant defense to biotic and abiotic stresses. However, how aluminum (Al) stress affects the isoprenoid metabolism and whether isoprenoid metabolism plays a vital role in the Citrus plants in coping with Al stress remain unclear. In this study, we reported that Al-treatment-induced alternation in the volatilization rate of monoterpenes (α-pinene, β-pinene, limonene, α-terpinene, γ-terpinene and 3-carene) and isoprene were different between Citrus sinensis (Al-tolerant) and C. grandis (Al-sensitive) leaves. The Al-induced decrease of CO2 assimilation, maximum quantum yield of primary PSII photochemistry (Fv/Fm), the lower contents of glucose and starch, and the lowered activities of enzymes involved in the mevalonic acid (MVA) pathway and 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway might account for the different volatilization rate of isoprenoids. Furthermore, the altered transcript levels of genes related to isoprenoid precursors and/or derivatives metabolism, such as geranyl diphosphate (GPP) synthase (GPPS) in GPP biosynthesis, geranylgeranyl diphosphate synthase (GGPPS), chlorophyll synthase (CHS) and GGPP reductase (GGPPR) in chlorophyll biosynthesis, limonene synthase (LS) and α-pinene synthase (APS) in limonene and α-pinene synthesis, respectively, might be responsible for the different contents of corresponding products in C. grandis and C. sinensis. Our data suggested that isoprenoid metabolism was involved in Al tolerance response in Citrus, and the alternation of some branches of isoprenoid metabolism could confer different Al-tolerance to Citrus species.

Volatile organic compounds (VOCs) emitted by plants may help in understanding the status of a plant\'s physiology and its coping with mild to severe stress. Future climatic projections reveal that shifts in temperature and CO2 availability will occur, and plants may incur the uncoupling of carbon assimilation and synthesis of key molecules. This study explores the patterns of emissions of key VOCs (isoprene, methanol, acetaldehyde, and acetic acid) emitted by poplar leaves (more than 350) under a combined gradient of temperature (12-42 °C) and air CO2 concentration (400-1500 ppm), along with measurements of photosynthetic rates and stomatal conductance. Isoprene emission exhibited a rise with temperature and CO2 availability, peaking at 39 °C, the temperature at which methanol emission started to peak, illustrating the limit of stress tolerance to severe damage. Isoprene emission was uncoupled from the photosynthesis rate, indicating a shift from the carbon source for isoprene synthesis, while assimilation was decreased. Methanol and acetaldehyde emissions were correlated with stomatal conductance and peaked at 25 °C and 1200 ppm CO2. Acetic acid emissions lacked a clear correlation with stomatal conductance and the emission pattern of its precursor acetaldehyde. This study offers crucial insights into the limitations of photosynthetic carbon and stress tolerance.

The plastidic 2-C-methylerythritol 4-phosphate (MEP) pathway supplies the precursors of a large variety of essential plant isoprenoids, but its regulation is still not well understood. Using metabolic control analysis (MCA), we examined the first enzyme of this pathway, 1-deoxyxylulose 5-phosphate synthase (DXS), in multiple grey poplar (Populus × canescens) lines modified in their DXS activity. Single leaves were dynamically labeled with 13CO2 in an illuminated, climate-controlled gas exchange cuvette coupled to a proton transfer reaction mass spectrometer, and the carbon flux through the MEP pathway was calculated. Carbon was rapidly assimilated into MEP pathway intermediates and labeled both the isoprene released and the IDP+DMADP pool by up to 90%. DXS activity was increased by 25% in lines overexpressing the DXS gene and reduced by 50% in RNA interference lines, while the carbon flux in the MEP pathway was 25-35% greater in overexpressing lines and unchanged in RNA interference lines. Isoprene emission was also not altered in these different genetic backgrounds. By correlating absolute flux to DXS activity under different conditions of light and temperature, the flux control coefficient was found to be low. Among isoprenoid end products, isoprene itself was unchanged in DXS transgenic lines, but the levels of the chlorophylls and most carotenoids measured were 20-30% less in RNA interference lines than in overexpression lines. Our data thus demonstrate that DXS in the isoprene-emitting grey poplar plays only a minor part in controlling flux through the MEP pathway.

In the breath research community\'s search for volatile organic compounds that can act as non-invasive biomarkers for various diseases, hundreds of endogenous volatiles have been discovered. Whilst these systemic chemicals result from normal and abnormal metabolic activities or pathological disorders, to date very few are of any use for the development of clinical breath tests that could be used for disease diagnosis or to monitor therapeutic treatments. The reasons for this lack of application are manifold and complex, and these complications either limit or ultimately inhibit the analytical application of endogenous volatiles for use in the medical sciences. One such complication is a lack of knowledge on the biological origins of the endogenous volatiles. A major exception to this is isoprene. Since 1984, i.e. for 40 years, it has been generally accepted that the pathway to the production of human isoprene, and hence the origin of isoprene in exhaled breath, is through cholesterol biosynthesis via the mevalonate (MVA) pathway within the liver. However, various studies between 2001 and 2012 provide compelling evidence that human isoprene is produced in skeletal muscle tissue. A recent multi-omic investigation of genes and metabolites has revealed that this proposal is correct by showing that human isoprene predominantly results from muscular lipolytic cholesterol metabolism. Despite the overwhelming proof for a muscular pathway to isoprene production in the human body, breath research papers still reference the hepatic MVA pathway. The major aim of this perspective is to review the evidence that leads to a correct interpretation for the origins of human isoprene, so that the major pathway to human isoprene production is understood and appropriately disseminated. This is important, because an accurate attribution to the endogenous origins of isoprene is needed if exhaled isoprene levels are to be correctly interpreted and for assessing isoprene as a clinical biomarker.

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.

Terpenoids have long been known to originate from natural sources. However, there is growing evidence for emissions from anthropogenic activities in cities, in particular from the production, manufacturing, and use of household solvents. Here, as part of the DATAbASE (Do Anthropogenic Terpenoids mAtter in AtmoSpheric chEmistry?) project, we investigate for the first time the potential role of industrial activities on the terpenoid burden in the urban atmosphere. This study is based on continuous VOC observations from an intensive field campaign conducted in July 2014 at an industrial-urban background site located in Dunkirk, Northern France. More than 80 VOCs including oxygenated and terpenoid compounds were measured by on-line Thermal Desorption Gas Chromatography with a Flame Ionization Detection (TD-GC-FID) and Proton Transfer Reaction-Time of Flight Mass Spectrometry (PTR-ToFMS). Isoprene, α-pinene, limonene and the sum of monoterpenes were the terpenoids detected at average mixing ratios of 0.02 ± 0.02 ppbv, 0.02 ± 0.02 ppbv, 0.01 ± 0.01 ppbv and 0.03 ± 0.05 ppbv, respectively. Like other anthropogenic VOCs, the mixing ratios of terpenoids significantly increase downwind the industrial plumes by one order of magnitude. Positive Matrix Factorization (PMF) was performed to identify the different emission sources of VOCs and their contribution. Six factors out of the eight factors extracted (r2 = 0.95) are related to industrial emissions such as solvent use, chemical and agrochemical storage, metallurgy, petrochemical, and coal-fired industrial activities. From the correlations between the industrial-type PMF factors, sulfur dioxide, and terpenoids, we determined their emissions ratios and we quantified for the first time their industrial emissions. The highest emission ratio is related to the alkene-dominated factor and is related to petrochemical, metallurgical and coal-fired industrial activities. The industrial emissions of monoterpenes equal 8.1 ± 4.3 tons/year. Those emissions are as significant as the non-industrialized anthropogenic ones estimated for the Paris megacity.

A family of pyridine-oxazoline-ligated cobalt complexes L2CoCl23a-h were synthesized and characterized. Determined via single-crystal X-ray diffraction, complexes 3a and 3d, ligated by two ligands, displayed a distorted tetrahedral coordination of a cobalt center. The X-ray structure indicated the pyridine-oxazoline ligands acted as unusual mono-dentate ligands by coordinating only to Noxazoline. Upon activation with AlEt2Cl (diethylaluminum chloride), these cobalt complexes all exhibited high catalytic activity (up to 2.5 × 106 g·molCo-1·h-1), affording cis-1,4-co-3,4-polyisoprene with molecular weights of 4.4-176 kg mol-1 and a narrow Ð of 1.79-3.42, suggesting a single-site nature of the active sites. The structure of cobalt catalysts and reaction parameters, especially co-catalysts and the reaction temperature, all have significant influence on the polymerization activity but not on the microstructure of polyisoprene.

Climate change profoundly affects the timing of seasonal activities of organisms, known as phenology. The impact of climate change is not unidirectional; it is also influenced by plant phenology as plants modify atmospheric composition and climatic processes. One important aspect of this interaction is the emission of biogenic volatile organic compounds (BVOCs), which link the Earth\'s surface, atmosphere, and climate. BVOC emissions exhibit significant diurnal and seasonal variations and are therefore considered essential phenological traits. To understand the dynamic equilibrium arising from the interplay between plant phenology and climate, this review presents recent advances in comprehending the molecular mechanisms underpinning plant phenology and its interaction with climate. We provide an overview of studies investigating molecular phenology, genome-wide gene expression analyses conducted in natural environments, and how these studies revolutionize the concept of phenology, shifting it from observable traits to dynamic molecular responses driven by gene-environment interactions. We explain how this knowledge can be scaled up to encompass plant populations, regions, and even the globe by establishing connections between molecular phenology, changes in plant distribution, species composition, and climate.