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Although ozone (O 3 ) pollution affects plant growth and monoterpene (MT) emissions, the responses of MT emission rates to elevated O 3 and the related mechanisms are not entirely understood. To gain an insight into these effects and mechanisms, we evaluated physiological (leaf MT synthesis ability, including precursor availability and enzyme kinetics) and physicochemical limiting factors (e.g. leaf thickness of the lower and upper epidermis, palisade and spongy tissue, and size of resin ducts and stomatal aperture) affecting MT emissions simultaneously from two broad-leaved and two coniferous species after one growing season of field experiment. The effects of elevated O 3 on MT emissions and the related mechanisms differed between plant functional types. Specifically, long-term moderate O 3 exposure significantly reduced MT emissions in broad-leaved species, primarily attributed to a systematic decrease in MT synthesis ability, including reductions in all MT precursors, geranyl diphosphate content, and MT synthase protein levels. In contrast, the same O 3 exposure significantly enhanced MT emissions in coniferous species. However, the change in MT emissions in coniferous species was not due to modifications in leaf MT synthesis ability but rather because of alterations in leaf anatomical structure characteristics, particularly the size of resin ducts and stomatal aperture. These findings provide an important understanding of the mechanisms driving MT emissions from different tree functional groups and can enlighten the estimation of MT emissions in the context of O 3 pollution scenarios as well as the development of MT emission algorithms., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Industrialization-driven surface ozone (O 3 ) pollution significantly impairs plant growth. This study evaluates the effectiveness of exogenous protectants [3 mg L⁻ 1 abscisic acid (ABA), 400 mg L⁻ 1 ethylenediurea (EDU), and 80 mg L⁻ 1 spermidine (Spd)] on Trifolium repens subjected to O 3 stress in open-top chambers, focusing on plant growth and dynamics of culturable endophytic fungal communities. Results indicate that O 3 exposure adversely affects photosynthesis, reducing root biomass and altering root structure, which further impacts the ability of plant to absorb essential nutrients such as potassium (K), magnesium (Mg), and zinc (Zn). Conversely, the application of ABA, EDU, and Spd significantly enhanced total biomass and chlorophyll content in T. repens. Specifically, ABA and Spd significantly improved root length, root surface area, and root volume, while EDU effectively reduced leaves' malondialdehyde levels, indicating decreased oxidative stress. Moreover, ABA and Spd treatments significantly increased leaf endophytic fungal diversity, while root fungal abundance declined. The relative abundance of Alternaria in leaves was substantially reduced by these treatments, which correlated with enhanced chlorophyll content and photosynthesis. Concurrently, EDU and Spd treatments increased the abundance of Plectosphaerella, enhance the absorption of K, Ca, and Mg. In roots, ABA treatment increased the abundance of Paecilomyces, while Spd treatment enhanced the presence of Stemphylium, linked to improved nitrogen (N), phosphorus (P), and K uptake. These findings suggest that specific symbiotic fungi mitigate O 3 -induced stress by enhancing nutrient absorption, promoting growth. This study highlights the potential of exogenous protectants to enhance plant resilience against O 3 pollution through modulating interactions with endophytic fungal communities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Masson SAS. All rights reserved.)

Poplars are economically important tree crops and biologically important model plants, which are known to be sensitive to ozone (O 3 ). Although surface O 3 is considered as a significant global environmental issue because of its phytotoxicity and greenhouse effect, the knowledge of the dose-response (DR) relationships in poplars for the assessment of O 3 risk is still limited. Hence, this study aimed at collecting data of studies with manipulative O 3 exposures of poplars within FACE (Free Air Concentration Enhancement) and OTC (Open-Top Chamber) facilities. The datasets contain studies on hybrid poplar clones and a non-hybrid native poplar (Populus nigra L.) reporting both AOT40 (Accumulated exposure Over a Threshold of 40 ppb) and POD1 (Phytotoxic Ozone Dose above a threshold of 1 nmol m -2 Projected Leaf Area [PLA] s -1 ) to compare exposure- and flux-based indices. As a result, linear regression analysis showed that the flux-based POD1 was better than the exposure-based AOT40 to explain the biomass response of poplars to O 3 . From the DR relationships, a critical level (CL) of 5.7 mmol m -2 POD1 has been derived corresponding to 4% biomass growth reduction for hybrid poplar clones, which can be considered very sensitive to O 3 , while the non-hybrid native poplar was less sensitive to O 3 (CL: 10.3 mmol m -2 POD1), although the potential risk of O 3 for this taxon is still high due to very high stomatal conductance. Moreover, the different experimental settings (OTC vs. FACE) have affected the AOT40-based DR relationships but not the POD1-based DR relationships, suggesting that poplar responses to O 3 were principally explained by stomatal O 3 uptake regardless of the different experimental settings and exposure patterns. These results highlight the importance of the flux-based approach, especially when scaling up from experimental datasets to the O 3 risk assessment for poplars at the regional or global scale., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

The present experiment was done to study the interactive effects of soil nitrogen (N) amendments and elevated ozone (O 3 ) (N-O 3 ) on a medicinal plant, lemongrass [Cymbopogon flexuosus (Steud.) (Wats.)]. The experiment used two doses of inorganic soil nitrogen (N 1 , recommended and N 2 , 1.5-times recommended dose) in open-top chambers under ambient and elevated (ambient + 15 ppb and ambient + 30 ppb) O 3 conditions. To analyze various characteristics, samples were collected at 45 and 90 days after transplantation (DAT). Additionally, at 110 days after transplantation (DAT), the metabolite contents of the leaves and essential oils were analyzed. The present study aims to investigate the mechanistic approach involving the crosstalk between antioxidant production and secondary metabolite biosynthesis in lemongrass upon N-O 3 interactions. The present experiment showed that N amendments can be an efficient measure to manage O 3 injury in plants, along with ensuring a balance between primary and secondary metabolic pathways, thus sustaining the plant defense and production of bioactive compounds, simultaneously. Under N-O 3 , not only the Halliwell asada pathway was stimulated resulting in the increased activities and concentrations of antioxidant pools; the shikimate, phenylpropanoid and mevalonic acid pathways were also invigorated, producing more number and contents of secondary metabolites (SMs), compared with plants that were not treated with N doses. This study suggests that soil nitrogen amendments will improve the therapeutic qualities of lemongrass, along with the strengthening of its antioxidant machinery, upon exposure to O 3 stress., Competing Interests: Declaration of competing interest The authors declare that they have no conflicts of interest., (Copyright © 2024 Elsevier Masson SAS. All rights reserved.)

Ozone (O 3 ) is one of the most harmful and widespread air pollutants, affecting crop yield and plant health worldwide. There is evidence that O 3 reduces the major limiting factor of photosynthesis, namely CO 2 mesophyll conductance (g m ), but there is little quantitative information of O 3 -caused changes in key leaf anatomical traits and their impact on g m . We exposed two O 3 -responsive clones of the economically important tree species Populus × canadensis Moench to 120 ppb O 3 for 21 days. An anatomical diffusion model within the leaf was used to analyse the entire CO 2 diffusion pathway from substomatal cavities to carboxylation sites and determine the importance of each structural and subcellular component as a limiting factor. g m decreased substantially under O 3 and was found to be the most important limitation of photosynthesis. This decrease was mostly driven by an increased cell wall thickness and length of subcellular diffusion pathway caused by altered interchloroplast spacing and chloroplast positioning. By contrast, the prominent leaf integrative trait leaf dry mass per area was neither affected nor related to g m under O 3 . The observed relationship between g m and anatomy, however, was clone-dependent, suggesting that mechanisms regulating g m may differ considerably between closely related plant lines. Our results confirm the need for further studies on factors constraining g m under stress conditions., (© 2024 John Wiley & Sons Ltd.)

The mitigation mechanisms of a kind of controlled-release nitrogen fertilizer (sulfur-coated controlled-release nitrogen fertilizer, SCNF) in response to O 3 stress on a winter wheat ( Triticum aestivum L.) variety (Nongmai-88) were studied in crop physiology and soil biology through the ozone-free-air controlled enrichment (O 3 -FACE) simulation platform and soil microbial metagenomics. The results showed that SCNF could not delay the O 3 -induced leaf senescence of winter wheat but could enhance the leaf size and photosynthetic function of flag leaves, increase the accumulation of nutrient elements, and lay the foundation for yield by regulating the release rate of nitrogen (N). By regulating the soil environment, SCNF could maintain the diversity and stability of soil bacterial and archaeal communities, but there was no obvious interaction with the soil fungal community. By alleviating the inhibition effects of O 3 on N-cycling-related genes ( ko00910 ) of soil microorganisms, SCNF improved the activities of related enzymes and might have great potential in improving soil N retention. The results demonstrated the ability of SCNF to improve leaf photosynthetic function and increase crop yield under O 3 -polluted conditions in the farmland ecosystem, which may become an effective nitrogen fertilizer management measure to cope with the elevated ambient O 3 and achieve sustainable production.

Urban trees possess different capacities to mitigate ozone (O 3 ) pollution through stomatal uptake. Stomatal closure protects trees from oxidative damage but limits their growth. To date, it is unclear how plant hydraulic function affect stomatal behaviour and determine O 3 resistance. We assessed gas exchange and hydraulic traits in three subtropical urban tree species, Celtis sinensis, Quercus acutissima, and Q. nuttallii, under nonfiltered ambient air (NF) and elevated O 3 (NF60). NF60 decreased photosynthetic rate (A n ) and stomatal conductance (g s ) only in Q. acutissima and Q. nuttallii. Maintained A n in C. sinensis suggested high O 3 resistance and was attributed to higher leaf capacitance at the full turgor. However, this species exhibited a reduced stomatal sensitivity to vapour pressure deficit and an increased minimal g s under NF60. Such stomatal dysfunction did not decrease intrinsic water use efficiency (WUE) due to a tight coupling of A n and g s . Conversely, Q. acutissima and Q. nuttallii showed maintained stomatal sensitivity and increased WUE, primarily correlated with g s and leaf water relations, including relative water content and osmotic potential at turgor loss point. Our findings highlight a trade-off between O 3 resistance and stomatal functionality, with efficient stomatal control reducing the risk of hydraulic failure under combined stresses., (© 2024 John Wiley & Sons Ltd.)

Dwarf bamboo (Indocalamus decorus) is an O 3 -tolerant plant species. To identify the possible mechanism and response of leaf morphological, antioxidant, and anatomical characteristics to elevated atmospheric O 3 (EO 3 ) concentrations, we exposed three-year-old I. decorus seedlings to three O 3 levels (low O 3 -LO: ambient air; medium O 3 -MO: Ambient air+70 ppb high O 3 -HO: Ambient air+140 ppb O 3 ) over a growing season using open-top chambers. Leaf shape and stomatal characteristics, and leaf microscopic structure of I. decorus were examined. The results indicated that 1) the stomata O 3 flux (F st ) of HO decreased more rapidly under EO 3 as the exposure time increased. The foliar O 3 injury of HO and MO occurred when AOT40 was 26.62 ppm h and 33.20 ppm h, respectively, 2) under EO 3 , leaf number, leaf mass per area, leaf area, and stomata length/width all decreased, while leaf thickness, stomatal density, width, and area increased compared to the control, 3) MDA and total soluble protein contents all showed significantly increase under HO (36.57% and 32.77%) and MO(31.91% and 19.52%) while proline contents only increased under HO(33.27%). 4) MO and HO increased bulliform cells numbers in the leaves by 6.28% and 23.01%, respectively. HO reduced the transverse area of bulliform cells by 13.73%, while MO treatments had no effect, and 5) the number of fusoid cells interspace, the transverse area of fusoid cells interspace, and mesophyll thickness of HO significantly increased by 11.16%, 28.58%, and 13.42%, respectively. In conclusion, I. decorus exhibits strong O 3 tolerance characteristics, which stem from adaptions in the leaf's morphological, structural, antioxidant, and anatomical features. One critical attribute was the enlargement of the bulliform cell transverse area and the transverse area of fusoid cells interspace that drove this resistance to O 3 . Local bamboo species with high resistance to O 3 pollution thus need to be promoted for sustained productivity and ecosystem services in areas with high O 3 pollution., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

An experimental study was conducted to assess the detrimental effect of ground-level ozone (O 3 ) on garlic physiology and to find out appropriate control measures against ground-level O 3 , at TNAU-Horticultural Research farm, Udhagamandalam. Elevated ground ozone levels significantly decreased garlic leaf chlorophyll, photosynthetic rate, stomatal conductance, total soluble solids and pungency. The garlic chlorophyll content was highest in ambient ozone level and lowest in elevated ozone@200 ppb, highest stomatal conductance was recorded in ambient ozone with foliar spray of 3%Panchagavya, and the lowest was observed in elevated ozone@200 ppb. Since the elevated O 3 had reduced in garlic photosynthetic rate significantly the lowest was observed in elevated O 3 @200 ppb and the highest photosynthetic rate was observed in ambient Ozone with foliar spray 3% of panchagavya after a week. The antioxidant enzymes of garlic were increased with increased concentration of tropospheric ozone. The highest catalase (60.97 µg of H 2 O 2 /g of leaf) and peroxidase (9.13 ΔA/min/g of leaf) concentration was observed at 200 ppb elevated ozone level. Garlic pungency content was highest in ambient ozone with foliar spray of 0.1% ascorbic acid and the lowest was observed under elevated O 3 @200 ppb. Highest total soluble solids were observed in ambient ozone with foliar spray of 3%Panchagavya and the lowest observed in elevated ozone@200 ppb. Thus, tropospheric ozone has a detrimental impact on the physiology of crops, which reduced crop growth and yield. Under elevated O 3 levels, ascorbic acid performed well followed by panchagavya and neem oil. The antioxidant such as catalase and peroxidase had positive correlation among themselves and had negative correlation with chlorophyll content, stomatal conductance, photosynthetic rate, pungency and TSS. The photosynthetic rate has high positive correlation with chlorophyll content, pungency and TSS. Correlation analysis confirmed the negative effects of tropospheric ozone and garlic gas exchange parameters and clove quality. The ozone protectants will reduce stomatal opening by which the entry of O 3 in to the cell will be restricted and other hand they also will alleviate ROS and allied stresses., (© 2024. The Author(s) under exclusive licence to International Society of Biometeorology.)

Ozone (O 3 ), an oxidizing toxic air pollutant, is ubiquitous in industrialized and developing countries. To understand the effects of O 3 exposure on apple (Malus) and to explore its defense mechanisms, we exposed 'Hongjiu' crabapple to O 3 and monitored its responses using physiological, transcriptomics, and metabolomics analyses. Exposure to 300 nL L -1 O 3 for 3 h caused obvious damage to the leaves of Malus crabapple, affected chlorophyll and anthocyanin contents, and activated antioxidant enzymes. The gene encoding phospholipase A was highly responsive to O 3 in Malus crabapple. McWRKY75 is a key transcription factor in the response to O 3 stress, and its transcript levels were positively correlated with those of flavonoid-related structural genes (McC4H, McDFR, and McANR). The ethylene response factors McERF019 and McERF109-like were also up-regulated by O 3 . Exogenous methyl jasmonate (MeJA) decreased the damaging effects of O 3 on crabapple and was most effective at 200 μmol L -1 . Treatments with MeJA altered the metabolic pathways of crabapple under O 3 stress. In particular, MeJA activated the flavonoid metabolic pathway in Malus, which improved its resistance to O 3 stress., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Inc. All rights reserved.)

High-throughput and large-scale measurements of chlorophyll a fluorescence (ChlF) are of great interest to investigate the photosynthetic performance of plants in the field. Here, we tested the capability to rapidly, precisely, and simultaneously estimate the number of pulse-amplitude-modulation ChlF parameters commonly calculated from both dark- and light-adapted leaves (an operation which usually takes tens of minutes) from the reflectance of hyperspectral data collected on light-adapted leaves of date palm seedlings chronically exposed in a FACE facility to three ozone (O 3 ) concentrations (ambient air, AA; target 1.5 × AA O 3 , named as moderate O 3 , MO; target 2 × AA O 3 , named as elevated O 3 , EO) for 75 consecutive days. Leaf spectral measurements were paired with reference measurements of ChlF, and predictive spectral models were constructed using partial least squares regression. Most of the ChlF parameters were well predicted by spectroscopic models (average model goodness-of-fit for validation, R 2 : 0.53-0.82). Furthermore, comparing the full-range spectral profiles (i.e., 400-2400 nm), it was possible to distinguish with high accuracy (81% of success) plants exposed to the different O 3 concentrations, especially those exposed to EO from those exposed to MO and AA. This was possible even in the absence of visible foliar injury and using a moderately O 3 -susceptible species like the date palm. The latter view is confirmed by the few variations of the ChlF parameters, that occurred only under EO. The results of the current study could be applied in several scientific fields, such as precision agriculture and plant phenotyping.

The increasing concentration of surface ozone (O 3 ) was observed during recent decades in the world, which affects tree roots and forest soils. Meanwhile, the impact of ozone on tree roots is greatly affected by soil condition. However, there is a lack of knowledge about the possible effects of ozone on tree roots and soil processes. In this study, The influences of surface ozone (O 3 ) stress on the root biomass, morphology, nutrients, soil properties, and soil enzyme activity of Elaeocarpus sylvestris and Michelia chapensis seedlings were examined at four O 3 concentrations (charcoal-filtered air, 1 × O 3 air, 2 × O 3 air, and 4 × O 3 air). Elevated O 3 concentrations were found to significantly increase the root C content, N content, C/P ratio, and N/P ratio, and significantly decrease the root biomass, number of root tips, and root C/N ratio of both species. The soil organic matter content, pH, total N content, and urease and catalase activities of both species tended to increase. The limitation in root growth and responses in the root structure of E. sylvestris induced by elevated O 3 concentrations led to increased bulk density and decreased soil porosity and void ratio. These profound effects of O 3 concentrations on the roots and soil characteristics of these two species underscore the importance of research in O 3 science.

Tropospheric ozone is a major atmospheric pollutant; it is phytotoxic and has a strong effect on phytochemicals, which are constitutively present in plant tissues, but also produced de novo in response to stress. It has been shown that ozone exposure can modify volatile phytochemical emissions from leaves, which could disturb interactions between plants and other organisms. However, there is a lack of knowledge on the effects of ozone on floral chemistry. The aim of this study was to determine the effects of two elevated ozone exposure scenarios (80 and 120 ppb during daylight hours for 5 consecutive days) on the floral volatile emissions and floral chemical (molecular size range C 6 -C 20 ) content of four Brassicaceae species: Sinapis alba, Sinapis arvensis, Brassica napus and Brassica nigra. The results showed that the emissions of individual compounds and their relative contributions to volatile blends are both affected by ozone exposure. In addition, for all four species studied, three diterpenes (neophytadiene, cis-phytol and trans-phytol) were present in significantly lower amounts and a fourth diterpene (hexahydrofarnesyl acetone) in significantly greater amounts in ozone-exposed plants. Consistent effects of ozone exposure on volatile emissions and terpene content were observed for each of the four species studied with no significant effect of exposure level. It appeared that B. napus is the most ozone-sensitive species, whereas B. nigra is the most ozone-tolerant. Since earlier studies have indicated that ratios of phytochemicals can have substantial effects on the efficacy of chemical use by pollinators, these changes may have ecological and biological relevance that should be the focus of further elucidation., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Increasing tropospheric ozone (O 3 ) concentrations in most regions of the world have led to significant phytotoxicity to all types of vegetation. Indo-Gangetic Plains of India is one of the hot spot areas with high O 3 concentrations throughout the year although O 3 phytotoxicity on grassland species in this region is not explored. Therefore the present study was conducted to assess the responses of a dominant species, Ischaemum rugosum Salisb, a C 4 grass and a co-dominant species Malvastrum coromandelianum (L.) Garcke, a C 3 forb under future elevated O 3 (non filtered ambient + 20 nl l -1 ; NFA + ) concentration compared to non filtered ambient (NFA; 48.7 nl l -1 , 8 h mean) for 9 weeks from 15th May to 15th July 2016 in mix-culture using open-top chambers (OTCs). Plants were assessed for physiological, biochemical and growth parameters including biomass accumulation during vegetative and reproductive stages to assess the O 3 induced responses. Under NFA + , higher reductions were observed in physiological parameters, growth and total biomass accumulation in M. coromandelianum compared to I. rugosum while both the species suffered membrane damage. Enhancement in contents of ascorbic acid and tannin in I. rugosum while proline and total phenolics in M. coromandelianum led to more protection of former species compared to later from oxidative damage. No significant change in stomatal conductance in I. rugosum while significant increase in M. coromandelianum might have led to more accumulation of O 3 inside the plant, thus more negatively affecting the performance of later species. The present study concludes that M. coromandelianum (C 3 photosynthetic pathway) will be relatively more negatively affected compared to I. rugosum (C 4 photosynthetic pathway) under future O 3 concentrations., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Two common tropical grassland species, Panicum maximum Jacq. (Guinea grass) and Cenchrus ciliaris (Buffel grass) of Indo-Gangetic plains were assessed for their responses under future level of O 3 (ambient +30 ppb) using open top chambers. Plants were assessed for foliar injuries, pigments, growth, biomass accumulation, histochemical localization of reactive oxygen species (ROS), antioxidant defense system and ROS scavenging activities at two stages. Foliar injuries were noticed at an early stage in P. maximum compared to C. ciliaris. Significant reductions were observed in total chlorophyll, growth and total biomass in both species. Significant increases in contents of melondialdehyde and ascorbic acid in P. maximum while total phenolics and thiols in C. ciliaris were found. Histochemical analysis showed more production of superoxide radicals and hydrogen peroxide in leaf tissues of P. maximum compared to C. ciliaris. It can be concluded that higher level of primary antioxidants (total phenolics and thiols) along with superoxide dismutase and ascorbate peroxidase scavenged O 3 effectively in C. ciliaris causing less reduction of biomass which is used as a feed for cattles. In P. maximum, more photosynthates were allocated for defense, leading to higher reduction in total biomass compared to C. ciliaris. The leaf area ratio was higher in P. maximum compared to C. ciliaris under elevated O 3 . The study further suggests higher susceptibility of P. maximum compared to C. ciliaris under future level of O 3 exposure.

Ethylenediurea (EDU) has been used as a chemical protectant against ozone (O 3 ). However, its protective effect and physiological mechanisms are still uncertain. The present study aimed to investigate the changes of foliar visible injury, physiological characteristics and emission rates of volatile organic compounds (VOCs) in one-year-old Populus alba "Berolinensis" saplings pretreated with EDU and exposed to elevated O 3 (EO, 120 μg/m 3 ). The results showed that foliar visible injury symptoms under EO were significantly alleviated in plants with EDU application (p < 0.05). Under EO, net photosynthetic rate, the maximum photochemical efficiency of PSII and the photochemical efficiency of PSII of plants pretreated with 300 and 600 mg/L EDU were similar to unexposed controls and significantly higher compared to EO-stressed plants without EDU pretreatment, respectively. Malondialdehyde content was highest in EO without EDU and decreased significantly by 14.9% and 21.3% with 300 and 600 mg/L EDU pretreatment, respectively. EDU pretreatment alone increased superoxide dismutase activity by 10-fold in unexposed plants with further increases of 88.4% and 37.5% in EO plants pretreated with 300 and 600 mg/L EDU pretreatment, respectively (p < 0.05). Abscisic acid content declined under EO relative to unexposed controls with the effect partially reversed by EDU pretreatments. Similarly, VOCs emission rate declined under EO relative to unexposed plants with a recovery of emission rate observed with 300 and 600 mg/L EDU pretreatment. These findings provided significant evidence that EDU exerted a beneficial effect and protection on the tested plants against O 3 stress., (Copyright © 2019. Published by Elsevier B.V.)

The impact of ozone (O 3 ) pollution events on the plant drought response needs special attention because spring O 3 episodes are often followed by summer drought. By causing stomatal sluggishness, O 3 could affect the stomatal dynamic during a subsequent drought event. In this context, we studied the impact of O 3 exposure and water deficit (in the presence or in the absence of O 3 episode) on the stomatal closure/opening mechanisms relative to irradiance or vapour pressure deficit (VPD) variation. Two genotypes of Populus nigra x deltoides were exposed to various treatments for 21 days. Saplings were exposed to 80 ppb/day O 3 for 13 days, and then to moderate drought for 7 days. The curves of the stomatal response to irradiance and VPD changes were determined after 13 days of O 3 exposure, and after 21 days in the case of subsequent water deficit, and then fitted using a sigmoidal model. The main responses under O 3 exposure were stomatal closure and sluggishness, but the two genotypes showed contrasting responses. During stomatal closure induced by a change in irradiance, closure was slower for both genotypes. Nonetheless, the genotypes differed in stomatal opening under light. Carpaccio stomata opened more slowly than control stomata, whereas Robusta stomata tended to open faster. These effects could be of particular interest, as stomatal impairment was still present after O 3 exposure and could result from imperfect recovery. Under water deficit alone, we observed slower stomatal closure in response to VPD and irradiance, but faster stomatal opening in response to irradiance, more marked in Carpaccio. Under the combined treatment, most of the parameters showed antagonistic responses. Our results highlight that it is important to take genotype-specific responses and interactive stress cross-talk into account to improve the prediction of stomatal conductance in response to various environmental modifications., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Tropospheric ozone (O 3 ) has been identified as the most damaging air pollutant to crop plants in terms of growth and yield reductions. Considering the negative effect of O 3 in tropical regions, fourteen commonly grown Indian wheat cultivars with known sensitivity to O 3 were tested for their sensitivity/tolerance with respect to two major antioxidants (ascorbic acid and thiols) and grain yield responses against elevated O 3 (ambient + 30 ppb) exposure. The objectives of the study were to assess the usefulness of the biochemical markers in the screening of wheat cultivars having differential level of sensitivity to O 3 and different release time (modern and old cultivars). Ozone exposure led to an upsurge of ascorbic acid, thiols as well as their ratio greatly in the tolerant group followed by the intermediately sensitive group while least in sensitive one. Both ascorbic acid and thiol contents offered more resistance to early released cultivars compared to modern ones. Ascorbic acid served to be the most influential parameter for determining varietal response under elevated O 3 stress and directly linked with O 3 tolerance. Overall, the sensitive group suffered maximum yield losses while the minimum was observed in the tolerant group due to the differential enhancement of tolerance offered by antioxidants. Higher concentrations of antioxidants at early growth stages were highly correlated with final yield responses suggesting the role of antioxidants as a determinant of final yield. Findings of this study will help in the identification of O 3 tolerant and sensitive wheat cultivars for future screening programs using ascorbic acid and thiols as important markers of O 3 tolerance., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Finite mesophyll conductance (g m ) reduces the rate of CO 2 diffusion from the leaf intercellular space to the chloroplast and constitutes a major limitation of photosynthesis in trees. While it is well established that g m is decreased by stressors such as drought and high temperature, few studies have investigated if the phytotoxic air pollutant ozone (O 3 ) affects g m . We quantified the relative importance of three different types of limitations of photosynthesis in poplar trees exposed to elevated O 3 : decreases in stomatal conductance, g m and biochemical photosynthetic capacity. The O 3 -induced reductions in light-saturated net photosynthesis were linked to significant declines in g m and biochemical photosynthetic capacity (in particular carboxylation). There was no significant effect of O 3 on stomatal conductance. Of the O 3 -induced limitations on photosynthesis, g m limitation was by far the most important (-16%) while biochemical limitation (-8%) was rather small. Both limitations grew in magnitude over the study period and varied in response to leaf-specific O 3 exposure. Our findings suggest that declines in g m may play a key role in limiting photosynthesis of plants exposed to elevated O 3 , an effect hitherto overlooked., (Copyright © 2018 Elsevier B.V. All rights reserved.)

We investigated the effects of elevated ozone (O 3 ) concentration on leaf nitrogen (N), a key determinant of plant photosynthesis, with two clones of poplar grown in open-top chambers. We focus on the difference between mass-based leaf N concentration (N mass ) and area-based one (N area ) in their responses to elevated O 3 , and the allocation of N to different leaf components: photosynthetic apparatus, cell walls, and others under elevated O 3 level. Our results showed that elevated O 3 significantly increased N mass , but reduced N area and leaf mass per area (LMA). The two clones showed no difference in N mass response to O 3 , but the more sensitive clone showed greater reduction of N area and LMA due to O 3 . We also found positive relationships between N area and photosynthetic parameters, e.g. light-saturated photosynthetic rate (A sat ). Furthermore, elevated O 3 significantly reduced photosynthetic N-use efficiency (PNUE) and leaf N allocation to photosynthetic components, while increasing N allocation to cell walls and other components. We concluded that plants invested more N in cell walls and other components to resist O 3 damages at the expense of photosynthetic N. The change of N allocation in plant leaves in response to elevated O 3 could have an impact on ecological processes, e.g. leaf litter decomposition., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Passiflora edulis Sims is a liana species of high economic interest and is an interesting model plant for understanding ozone action on disturbed vegetation. In this work we hypothesized that P. edulis has adaptive responses to oxidative stress that enable it to tolerate ozone damage based on its capacity to grow under a diversity of environmental conditions and to dominate disturbed areas. We exposed seedlings to three levels of ozone in a Free-Air Controlled Exposure (FACE) system (22, 41 and 58 ppb h AOT40 and 13.52, 17.24 and 20.62 mmol m -2 POD0, over 97 days) for identifying its tolerance mechanisms. Anatomical (leaf blade structure and fluorescence emission of chloroplast metabolites), physiological (leaf gas exchange, growth rate and biomass production) and biochemical (pigments, total sugars, starch, enzymatic and non-enzymatic antioxidant metabolites, reactive oxygen species and lipid peroxidation derivatives) responses were assessed. Ozone caused decreased total number of leaves, hyperplasia and hypertrophy of the mesophyll cells, and accelerated leaf senescence. However, O 3 did not affect carbohydrates content, net photosynthetic rate, or total biomass production, indicating that the carboxylation efficiency and associated physiological processes were not affected. In addition, P. edulis showed higher leaf contents of ascorbic acid, glutathione (as well high ratio between their reduced and total forms), carotenoids, and flavonoids located in the chloroplast outer envelope membrane. Our results indicate that P. edulis is an O 3 -tolerant species due to morphological acclimation responses and an effective antioxidant defense system represented by non-enzymatic antioxidants, which maintained the cellular redox balance under ozone., (Copyright © 2018. Published by Elsevier B.V.)

The effects of current and future elevated O 3 concentrations (e[O 3 ]) were investigated by a meta-analysis for poplar, a widely distributed genus in the Northern Hemisphere with global economic importance. Current [O 3 ] has significantly reduced CO 2 assimilation rate (P n ) by 33% and total biomass by 4% in comparison with low O 3 level (charcoal-filtered air, CF). Relative to CF, an increase in future [O 3 ] would further enhance the reduction in total biomass by 24%, plant height by 17% and plant leaf area by 19%. Isoprene emissions could decline by 34% under e[O 3 ], with feedback implications in reducing the formation of secondary air pollutants including O 3 . Reduced stomatal conductance and lower foliar area might increase runoff and freshwater availability in O 3 polluted areas. Higher cumulated O 3 exposure over a threshold of 40 ppb (AOT40) induced larger reductions in P n , total biomass and isoprene emission. Relationships of light-saturated photosynthesis rates (A sat ), total biomass and chlorophyll content with AOT40 using a global dataset are provided. These relationships are expected to improve O 3 risk assessment and also to support the inclusion of the effect of O 3 in models addressing plantation productivity and carbon sink capacity., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Apoplastic ascorbate (ASC apo ) is an important contributor to the detoxification of ozone (O 3 ). The objective of the study is to explore whether ASC apo is stimulated by elevated O 3 concentrations. The detoxification of O 3 by ASC apo was quantified in tobacco (Nicotiana L), soybean (Glycine max (L.) Merr.) and poplar (Populus L), which were exposed to charcoal-filtered air (CF) and elevated O 3 treatments (E-O 3 ). ASC apo in the three species were significantly increased by E-O 3 compared with the values in the filtered treatment. For all three species, E-O 3 significantly increased the malondialdehyde (MDA) content and decreased light-saturated rate of photosynthesis (A sat ), suggesting that high O 3 has induced injury/damage to plants. E-O 3 significantly increased redox state in the apoplast (redox state apo ) for all species, whereas no effect on the apoplastic dehydroascorbate (DHA apo ) was observed. In leaf tissues, E-O 3 significantly enhanced reduced-ascorbate (ASC) and total ascorbate (ASC+DHA) in soybean and poplar, but significantly reduced these in tobacco, indicating different antioxidative capacity to the high O 3 levels among the three species. Total antioxidant capacity in the apoplast (TAC apo ) was significantly increased by E-O 3 in tobacco and poplar, but leaf tissue TAC was significantly enhanced only in tobacco. Leaf tissue superoxide anion (O 2 •- ) in poplar and hydrogen peroxide (H 2 O 2 ) in tobacco and soybean were significantly increased by E-O 3 . The diurnal variation of ASC apo , with maximum values occurring in the late morning and lower values experienced in the afternoon, appeared to play an important role in the harmful effects of O 3 on tobacco, soybean and poplar., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Ozone (O 3 ) pollution and the availability of nitrogen (N) and phosphorus (P) in the soil both affect plant photosynthesis and chlorophyll (Chl) content, but the interaction of O 3 and nutrition is unclear. We postulated that the nutritional condition changes plant photosynthetic responses to O 3 . An O 3 -sensitive poplar clone (Oxford) was subject to two N levels (N0, 0 kg N ha - 1 ; N80, 80 kg N ha - 1 ), two P levels (P0, 0 kg P ha - 1 ; P80, 80 kg P ha - 1 ) and three levels of O 3 exposure (ambient concentration, AA; 1.5 × AA; 2.0 × AA) over a growing season in an O 3 free air controlled exposure (FACE) facility. The daily change of leaf gas exchange and dark respiration (R d ) were investigated at mid-summer (August). Chl a fluorescence was measured three times in July, August and September. At the end of the growing season, Chl content was measured. It was found that Chl content, the maximum quantum yield (F v /F m ), Chl a fluorescence performance index (PI) and gas exchange were negatively affected by elevated O 3 . Phosphorus may mitigate the O 3 -induced reduction of the ratio of photosynthesis to stomatal conductance, while it exacerbated the O 3 -induced loss of F v /F m . Nitrogen alleviated negative effects of O 3 on F v /F m and PI in July. Ozone-induced loss of net photosynthetic rate was mitigated by N in medium O 3 exposure (1.5 × AA). However, such a mitigation effect was not observed in the higher O 3 level (2.0 × AA). Nitrogen addition exacerbated O 3 -induced increase of R d suggesting an increased respiratory carbon loss in the presence of O 3 and N. This may result in a further reduction of the net carbon gain for poplars exposed to O 3 .

Ozone is an air pollutant that negatively affects photosynthesis in woody plants. Previous studies suggested that ozone-induced reduction in photosynthetic rates is mainly attributable to a decrease of maximum carboxylation rate (V cmax ) and/or maximum electron transport rate (J max ) estimated from response of net photosynthetic rate (A) to intercellular CO 2 concentration (C i ) (A/C i curve) assuming that mesophyll conductance for CO 2 diffusion (g m ) is infinite. Although it is known that C i -based V cmax and J max are potentially influenced by g m , its contribution to ozone responses in C i -based V cmax and J max is still unclear. In the present study, therefore, we analysed photosynthetic processes including g m in leaves of Siebold's beech (Fagus crenata) seedlings grown under three levels of ozone (charcoal-filtered air or ozone at 1.0- or 1.5-times ambient concentration) for two growing seasons in 2016-2017. Leaf gas exchange and chlorophyll fluorescence were simultaneously measured in July and September of the second growing season. We determined the A, stomatal conductance to water vapor and g m, and analysed A/C i curve and A/C c curve (C c : chloroplast CO 2 concentration). We also determined the Rubisco and chlorophyll contents in leaves. In September, ozone significantly decreased C i -based V cmax . At the same time, ozone decreased g m , whereas there was no significant effect of ozone on C c -based V cmax or the contents of Rubisco and chlorophyll in leaves. These results suggest that ozone-induced reduction in C i -based V cmax is a result of the decrease in g m rather than in carboxylation capacity. The decrease in g m by elevated ozone was offset by an increase in C i , and C c did not differ depending on ozone treatment. Since C c -based V cmax was also similar, A was not changed by elevated ozone. We conclude that g m is an important factor for reduction in C i -based V cmax of Siebold's beech under elevated ozone.

Vegetation in the Arabian Peninsula is facing high and steadily rising tropospheric ozone pollution. However, little is known about the impacts of elevated ozone on date palms, one of the most important indigenous economic species. To elucidate the physiological responses of date palm to peak levels of acute ozone exposure, seedlings were fumigated with 200 ppb ozone for 8 h. Net CO 2 assimilation rate, stomatal conduction, total carbon, its isotope signature and total sugar contents in leaves and roots were not significantly affected by the treatment and visible symptoms of foliar damage were not induced. Ozone exposure did not affect hydrogen peroxide and thiol contents but diminished the activities of glutathione reductase and dehydroascorbate reductase, stimulated the oxidation of ascorbate, and resulted in elevated total ascorbate contents. Total nitrogen, soluble protein and lignin contents remained unchanged upon ozone exposure, but the abundance of low molecular weight nitrogen (LMWN) compounds such as amino acids and nitrate as well as other anions were strongly diminished in leaves and roots. Other nitrogen pools did not benefit from the decline of LMWN, indicating reduced uptake and/or enhanced release of these compounds into the soil as a systemic response to aboveground ozone exposure. Several phenolic compounds, concurrent with fatty acids and stearyl alcohol, accumulated in leaves, but declined in roots, whereas total phenol contents significantly increased in the roots. Together these results indicate that local and systemic changes in both, primary and secondary metabolism contribute to the high tolerance of date palms to short-term acute ozone exposure., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Tropospheric ozone (O 3 ) is a phytotoxic air pollutant causing a substantial damage to plants and agriculture worldwide. Plant productivity is affected by several environmental factors, which interact with each other. Studies related to interactions involving O 3 and different levels of nitrogen (N) are still rare and elusive. In the present study we grew two wheat cultivars (HD2967 and Sonalika) in open top chambers (OTC) under ambient (AO) and elevated O 3 (EO) (ambient + 20 ppb O 3 ) and provided two levels of N fertilization; (a) recommended nitrogen (RN), (b) 1.5 times the recommended N (HN). Growth (root/shoot ratio, leaf number and leaf area), biomass, gas-exchange (stomatal conductance (g s ), photosynthesis (A), transpiration (E), chlorophyll fluorescence (F v /F m ), physiological (chlorophyll and carotenoids), biochemical [antioxidant activity, lipid peroxidation (MDA)] parameters and leaf N content were measured at the vegetative and reproductive phases. Yield attributes (spike weight plant -1 , grain weight plant -1 , grain numbers plant -1 , husk weight plant -1 , straw weight plant -1 , 1000 grain weight, harvest index) and seed N content were analyzed at the final harvest stage. Grain yield plant -1 was decreased in Sonalika under EO irrespective of different levels of N fertilization. Seed N content decreased by 3.9% and 5.6% in HD2967 and Sonalika, respectively, under EO at RN treatment. Antioxidant defense played an important role in protecting the plants against O 3 stress which was enhanced under HN treatment. Response of antioxidants varied between the cultivar, growth phase (at the vegetative or reproductive phase) and the N levels (RN or HN). Cultivar HD2967 was characterized by higher biomass, g s and stronger antioxidant protection system, while, Sonalika showed early senescence response (decreased leaf number plant -1 , g s ) and greater resources allocation towards eco-physiological parameters (increased A and F v /F m ) at the vegetative phase, resulting in the significant decrease in the yield attributes. Further study warrants the need to screen a large number of cultivars in relation to their response to various levels of N fertilization to minimize the yield losses under highly O 3 polluted areas., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Ground-level ozone (O 3 ) concentrations have been elevating in the last century. While there has been a notable progress in understanding O 3 effects on vegetation, O 3 effects on ecological stoichiometry remain unclear, especially early in the oxidative stress. Ethyelenediurea (EDU) is a chemical compound widely applied in research projects as protectant of plants against O 3 injury, however its mode of action remains unclear. To investigate O 3 and EDU effects early in the stress, we sprayed willow (Salix sachalinensis) plants with 0, 200 or 400 mg EDU L -1 , and exposed them to either low ambient O 3 (AOZ) or elevated O 3 (EOZ) levels during the daytime, for about one month, in a free air O 3 controlled exposure (FACE); EDU treatment was repeated every nine days. We collected samples for analyses from basal, top, and shed leaves, before leaves develop visible O 3 symptoms. We found that O 3 altered the ecological stoichiometry, including impacts in nutrient resorption efficiency, early in the stress. The relation between P content and Fe content seemed to have a critical role in maintaining homeostasis in an effort to prevent O 3 -induced damage. Photosynthetic pigments and P content appeared to play an important role in EDU mode of action. This study provides novel insights on the stress biology which are of ecological and toxicological importance., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The stomatal compensation point of ammonia (χ s ) is a key factor controlling plant-atmosphere NH 3 exchange, which is dependent on the nitrogen (N) supply and varies among plant species. However, knowledge gaps remain concerning the effects of elevated atmospheric N deposition and ozone (O 3 ) on χ s for forest species, resulting in large uncertainties in the parameterizations of NH 3 incorporated into atmospheric chemistry and transport models (CTMs). Here, we present leaf-scale measurements of χ s for hybrid poplar clone '546' (Populusdeltoides cv. 55/56 x P. deltoides cv. Imperial) growing in two N treatments (N0, no N added; N50, 50 kg N ha -1 yr -1 urea fertilizer added) and two O 3 treatments (CF, charcoal-filtered air; E-O 3 , non-filtered air plus 40 ppb) for 105 days. Our results showed that χ s was significantly reduced by E-O 3 (41%) and elevated N (19%). The interaction of N and O 3 was significant, and N can mitigate the negative effects of O 3 on χ s . Elevated O 3 significantly reduced the light-saturated photosynthetic rate (A sat ) and chlorophyll (Chl) content and significantly increased intercellular CO 2 concentrations (Ci), but had no significant effect on stomatal conductance (g s ). By contrast, elevated N did not significantly affect all measured photosynthetic parameters. Overall, χ s was significantly and positively correlated with A sat , g s and Chl, whereas a significant and negative relationship was observed between χ s and Ci. Our results suggest that O 3 -induced changes in A sat , Ci and Chl may affect χ s . Our findings provide a scientific basis for optimizing parameterizations of χ s in CTMs in response to environmental change factors (i.e., elevated N deposition and/or O 3 ) in the future., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Assessments of the impacts of ozone (O 3 ) on regional and global food production are currently based on results from experiments using open-top chambers (OTCs). However, there are concerns that these impact estimates might be biased due to the environmental artifacts imposed by this enclosure system. In this study, we collated O 3 exposure and yield data for three major crop species-wheat, rice, and soybean-for which O 3 experiments have been conducted with OTCs as well as the ecologically more realistic free-air O 3 elevation (O 3 -FACE) exposure system; both within the same cultivation region and country. For all three crops, we found that the sensitivity of crop yield to the O 3 metric AOT40 (accumulated hourly O 3 exposure above a cut-off threshold concentration of 40 ppb) significantly differed between OTC and O 3 -FACE experiments. In wheat and rice, O 3 sensitivity was higher in O 3 -FACE than OTC experiments, while the opposite was the case for soybean. In all three crops, these differences could be linked to factors influencing stomatal conductance (manipulation of water inputs, passive chamber warming, and cultivar differences in gas exchange). Our study thus highlights the importance of accounting for factors that control stomatal O 3 flux when applying experimental data to assess O 3 impacts on crops at large spatial scales., (© 2018 John Wiley & Sons Ltd.)

Accelerated industrialization has been increasing releases of chemical precursors of ozone. Ozone concentration has risen nowadays, and it's predicted that this trend will continue in the next few decades. The yield of many ozone-sensitive crops suffers seriously from ozone pollution, and there are abundant reports exploring the damage mechanisms of ozone to these crops, such as winter wheat. However, little is known on how to alleviate these negative impacts to increase grain production under elevated ozone. Nitric oxide, as a bioactive gaseous, mediates a variety of physiological processes and plays a central role in response to biotic and abiotic stresses. In the present study, the accumulation of endogenous nitric oxide in wheat leaves was found to increase in response to ozone. To study the functions of nitric oxide, its precursor sodium nitroprusside was spayed to wheat leaves under ozone pollution. Wheat leaves spayed with sodium nitroprusside accumulated less hydrogen peroxide, malondialdehyde and electrolyte leakage under ozone pollution, which can be accounted for by the higher activities of superoxide dismutase and peroxidase than in leaves treated without sodium nitroprusside. Consequently, net photosynthetic rate of wheat treated using sodium nitroprusside was much higher, and yield reduction was alleviated under ozone fumigation. These findings are important for our understanding of the potential roles of nitric oxide in responses of crops in general and wheat in particular to ozone pollution, and provide a viable method to mitigate the detrimental effects on crop production induced by ozone pollution, which is valuable for keeping food security worldwide., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Tropospheric ozone (O 3 ) is a well-known threat to global agricultural production. Wheat (Triticum aestivum L.) is the second most important staple crop in India, although little is known about intra-specific variability of Indian wheat cultivars in terms of their sensitivity against O 3 . In this study, 14 wheat cultivars widely grown in India were exposed to 30 ppb elevated O 3 above ambient level using open top chambers to evaluate their response against O 3 stress. Different growth and physiological parameters, foliar injury and grain yield were evaluated to assess the sensitivity of cultivars and classified them on the basis of their cumulative stress response index (CSRI). Due to elevated O 3 , growth parameters, plant biomass, and photosynthetic rates were negatively affected, whereas variable reductions in yield were observed among the test cultivars. Based on CSRI values, HD 2987, DBW 50, DBW 77, and PBW 550 were classified as O 3 sensitive; HD 2967, NIAW 34, HD 3059, PBW 502, HUW 213, and HUW 251 as intermediately sensitive, while HUW12, KUNDAN, HUW 55, and KHARCHIYA 65 were found to be O 3 -tolerant cultivars. Cultivars released after year 2000 were found to be more sensitive compared to earlier released cultivars. Path analysis approach showed that leaf area, plant biomass, stomatal conductance, net assimilation rate, and absolute growth rate were the most important variables influencing yield under O 3 stress. Findings of the current study highlight the importance of assessing differential sensitivity and tolerance of wheat cultivars and response of different traits in developing resistance against elevated O 3 .

Numerous studies have documented the negative effects of ozone (O 3 ) on tree species in growing season, however, little is done in non-growing season. Three evergreen tree species, Phoebe bournei (Hemsl.) Yang (P. bournei), Machilus pauhoi Kanehira (M. pauhoi) and Taxus chinensis (Pilger) Rehd (T. chinensis), were exposed to non-filtered air, 100 nmol mol -1 O 3 air (E1) and 150 nmol mol -1 O 3 air (E2) in open-top chambers in subtropical China. In the entire period of experiment, O 3 fumigation decreased net photosynthesis rate (Pn) through stomatal limitation during the transition period from growing to non-growing season (TGN), and through non-stomatal limitation during the period of non-growing season (NGS) in all species tested. Meanwhile, O 3 fumigation reduced and delayed the resilience of Pn in all species tested during the transition period from non-growing to growing season (TNG). O 3 fumigation significantly decreased chlorophyll contents during NGS, whereas no obvious injury symptoms were observed till the end of experiment. O 3 fumigation induced increases in levels of malondialdehyde, superoxide dismutase, total phenolics and reduced ascorbic acid, and changes in four plant endogenous hormones as well in all species tested during NGS. During NGS, E1 and E2 reduced Pn by an average of 80.11% in P. bournei, 94.56% in M. pauhoi and 12.57% in T. chinensis, indicating that the O 3 sensitivity was in an order of M. pauhoi > P. bournei > T. chinensis. Overall, O 3 fumigation inhibited carbon fixation in all species tested during NGS. Furthermore, O 3 -induced physiological activities also consumed the dry matter. All these suggested that elevated O 3 , which is likely to come true during NGS in the future, will adversely affect the accumulation of dry matter and the resilience of Pn during TNG in evergreen tree species, and further inhibit their growth and development in the upcoming growing season., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The effects of elevated ozone on C (carbon), N (nitrogen) and P (phosphorus) ecological stoichiometry and nutrient resorption in different organs including leaves, stems and roots were investigated in poplar clones 546 (P. deltoides cv. '55/56' × P. deltoides cv. 'Imperial') and 107 (P. euramericana cv. '74/76') with a different sensitivity to ozone. Plants were exposed to two ozone treatments, NF (non-filtered ambient air) and NF60 (NF with targeted ozone addition of 60 ppb), for 96 days in open top chambers (OTCs). Significant ozone effects on most variables of C, N and P ecological stoichiometry were found except for the C concentration and the N/P in different organs. Elevated ozone increased both N and P concentrations of individual organs while for C/N and C/P ratios a reduction was observed. On these variables, ozone had a greater effect for clone 546 than for clone 107. N concentrations of different leaf positions ranked in the order upper > middle > lower, showing that N was transferred from the lower senescent leaves to the upper ones. This was also indicative of N resorption processes, which increased under elevated ozone. N resorption of clone 546 was 4 times larger than that of clone 107 under ambient air (NF). However, elevated ozone (NF60) had no significant effect on P resorption for both poplar clones, suggesting that their growth was only limited by N, while available P in the soil was enough to sustain growth. Understanding ecological stoichiometric responses under ozone stress is crucial to predict future effects on ecological processes and biogeochemical cycles., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The emission profile of volatile organic compounds (VOCs) and nitric oxide (NO) in young and mature leaves of Croton floribundus was assessed in plants exposed to filtered air (FA) and ozone-enriched filtered air (FA+O 3 ). After the period of exposure, leaves were enclosed in polyethylene terephthalate bags and VOCs were collected in young and mature leaves. Both young and mature leaves constitutively emitted the same VOC, but the concentrations were higher in young leaves. O 3 exposure induced the emission of sesquiterpenes (mainly β-caryophyllene) known as antioxidant compounds that may scavenge O 3 . Young leaves were the highest emitters of sesquiterpenes. O 3 induced a rapid accumulation of NO in different tissues and leaf developmental stages; this accumulation was marked in palisade and spongy parenchyma cells in young and mature leaves, respectively. O 3 altered the levels of the signaling compound methyl salicylate (MeSA). Moreover, our data showed that NO together with VOC emissions, such as geranyl acetate, α-cadiene, trans-farnesol, cis-β-farnesene, and MeSA, participate of plant defense mechanisms against the oxidative damage caused by O 3 .

Ozone is a strong oxidant and a key stress elicitor. The immediate and longer term impacts of ozone are poorly understood in species with emission of both de novo synthesized and stored volatiles, such a tobacco (Nicotiana tabacum), which has terpene-containing glandular trichomes on the leaf surface. In this study, we exposed N. tabacum 'Wisconsin' leaves to acute ozone doses of 0 (control), 400, 600, 800, and 1000 ppb for 30 min and studied the effects of ozone exposure on ozone uptake, gas-exchange characteristics, and emissions of lipoxygenase pathway volatiles, monoterpenes, and sesquiterpenes. Foliage emissions of lipoxygenase pathway volatiles were quantitatively related to the severity of ozone exposure, but the stress dose vs. emission relationship was weaker for terpenoids. Analysis of leaf terpene content and composition indicated that several monoterpenes and sesquiterpenes were not stored in leaves and were synthesized de novo upon ozone exposure. The highest degree of elicitation for each compound was observed immediately after ozone treatment and it declined considerably during recovery. Leaf ozone uptake was dominated by non-stomatal deposition, and the emissions of total lipoxygenase pathway volatiles and mono- and sesquiterpenes were positively correlated with non-stomatal ozone deposition. Overall, this study demonstrates remarkably high ozone resistance of the studied tobacco cultivar and indicates that ozone's effects on volatile emissions primarily reflect modifications in the release of stored volatiles and reaction of ozone with the leaf surface structure., (© The Author(s) 2017. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

In southern Brazil, the recent increase in tropospheric ozone (O 3 ) concentrations poses an additional threat to the biodiverse but endangered and fragmented remnants of the Atlantic Forest. Given the mostly unknown sensitivity of tropical species to oxidative stress, the principal objective of this study was to determine whether the current O 3 levels in the Metropolitan Region of Campinas (MRC), downwind of São Paulo, affect the native vegetation of forest remnants. Foliar responses to O 3 of three tree species typical of the MRC forests were investigated using indoor chamber exposure experiments under controlled conditions and a field survey. Exposure to 70ppb O 3 reduced assimilation and leaf conductance but increased respiration in Astronium graveolens while gas exchange in Croton floribundus was little affected. Both A. graveolens and Piptadenia gonoacantha developed characteristic O 3 -induced injury in the foliage, similar to visible symptoms observed in >30% of trees assessed in the MRC, while C. floribundus remained asymptomatic. The underlying structural symptoms in both O 3 -exposed and field samples were indicative of oxidative burst, hypersensitive responses, accelerated cell senescence and, primarily in field samples, interaction with photo-oxidative stress. The markers of O 3 stress were thus mostly similar to those observed in other regions of the world. Further research is needed, to estimate the proportion of sensitive forest species, the O 3 impact on tree growth and stand stability and to detect O 3 hot spots where woody species in the Atlantic Forest are mostly affected., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Three clover (Trifolium alexandrium L.) cultivars (Bundel, Wardan and JHB-146) were assessed for their responses to ambient ozone (O 3 ) with respect to growth, physiological and biochemical parameters at two rural sites (R1 and R2) using ethylenediurea (EDU). EDU solution (300ppm) was applied as soil drench, 10 days after germination (DAG) at an interval of 10 days up to 80 DAG. The average O 3 concentrations were 52.76 and 60.86 ppb at R1 and R2 sites, respectively during the experimental period. Ambient O 3 induced visible symptoms in all the cultivars at both the sites, with more at R2 site having high ambient O 3 levels. Visible injury was observed first in non-EDU treated plants of Wardan at R2 site. Wardan also showed maximum reduction in leaf injury under EDU treatment at both the sites with more at R2. Under EDU treatment, better adaptation to ambient O 3 at initial age of observation and higher acquisition of resources at later ages of observation at both the sites led to better physiological and biochemical adaptations in Wardan. Bundel retained more biomass in shoot as is reflected with higher shoot/root ratio and thus focused more on repair and defense. Shoot/root ratio of JHB-146 did not respond to EDU treatment and thus showed insignificant variations except at initial age of observation at R1 site. This study clearly suggests that Wardan and Bundel are sensitive to ambient O 3 and can be used as bioindicator species in areas having higher O 3 levels using EDU as a research tool., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Tropospheric ozone is considered the most detrimental air pollutant for vegetation at the global scale, with negative consequences for both provisioning and climate regulating ecosystem services. In spite of recent developments in ozone exposure metrics, from a concentration-based to a more physiologically relevant stomatal flux-based index, large-scale ozone risk assessment is still complicated by a large and unexplained variation in ozone sensitivity among tree species. Here, we explored whether the variation in ozone sensitivity among woody species can be linked to interspecific variation in leaf morphology. We found that ozone tolerance at the leaf level was closely linked to leaf dry mass per unit leaf area (LMA) and that whole-tree biomass reductions were more strongly related to stomatal flux per unit leaf mass (r 2  = 0.56) than to stomatal flux per unit leaf area (r 2  = 0.42). Furthermore, the interspecific variation in slopes of ozone flux-response relationships was considerably lower when expressed on a leaf mass basis (coefficient of variation, CV = 36%) than when expressed on a leaf area basis (CV = 66%), and relationships for broadleaf and needle-leaf species converged when using the mass-based index. These results show that much of the variation in ozone sensitivity among woody plants can be explained by interspecific variation in LMA and that large-scale ozone impact assessment could be greatly improved by considering this well-known and easily measured leaf trait., (© 2017 John Wiley & Sons Ltd.)

Exposure to elevated tropospheric ozone concentration ([O 3 ]) accelerates leaf senescence in many C 3 crops. However, the effects of elevated [O 3 ] on C 4 crops including maize (Zea mays L.) are poorly understood in terms of physiological mechanism and genetic variation in sensitivity. Using free air gas concentration enrichment, we investigated the photosynthetic response of 18 diverse maize inbred and hybrid lines to season-long exposure to elevated [O 3 ] (~100 nl L -1 ) in the field. Gas exchange was measured on the leaf subtending the ear throughout the grain filling period. On average over the lifetime of the leaf, elevated [O 3 ] led to reductions in photosynthetic CO 2 assimilation of both inbred (-22%) and hybrid (-33%) genotypes. There was significant variation among both inbred and hybrid lines in the sensitivity of photosynthesis to elevated [O 3 ], with some lines showing no change in photosynthesis at elevated [O 3 ]. Based on analysis of inbred line B73, the reduced CO 2 assimilation at elevated [O 3 ] was associated with accelerated senescence decreasing photosynthetic capacity and not altered stomatal limitation. These findings across diverse maize genotypes could advance the development of more O 3 tolerant maize and provide experimental data for parameterization and validation of studies modeling how O 3 impacts crop performance., (© 2017 John Wiley & Sons Ltd.)

The present study investigated the response to ozone (O 3 ) of two cultivars (cv.'Romana' and cv. 'Canasta') of irrigated lettuce grown in an open-top chamber (OTC) experiment in Mediterranean conditions. Two different levels of O 3 were applied, ambient O 3 in non-filtered OTCs (NF-OTCs) and -40% of ambient O 3 in charcoal-filtered OTCs (CF-OTCs), during four consecutive growing cycles. At the end of each growing cycle, the marketable yield (fresh biomass) was assessed while during the growing periods, measurements of the stomatal conductance at leaf level were performed and used to define a stomatal conductance model for calculation of the phytotoxic ozone dose (POD) absorbed by the plants.Results showed that O 3 caused statistically significant yield reductions in the first and in the last growing cycle. In general, the marketable yield of the NF-OTC plants was always lower than the CF-OTC plants for both cultivars, with mean reductions of -18.5 and -14.5% for 'Romana' and 'Canasta', respectively. On the contrary, there was no statistically significant difference in marketable yield due to the cultivar factor or to the interaction between O 3 and cultivar in any of the growing cycle performed.Dose-response relationships for the marketable relative yield based on the POD values were calculated according to different flux threshold values (Y). The best regression fit was obtained using an instantaneous flux threshold of 6 nmol O 3 m -2  s -1 (POD 6 ); the same value was obtained also for other crops. According to the generic lettuce dose-response relationship, an O 3 critical level of 1 mmol O 3 m -2 of POD 6 for a 15% of marketable yield loss was found.

Tropospheric ozone (O 3 ) pollution frequently overlaps with drought episodes but the combined effects are not yet understood. We investigated the physiological and biomass responses of an O 3 sensitive hybrid poplar clone ('546') under three O 3 levels (charcoal-filtered ambient air, non-filtered ambient air (NF), and NF plus 40 ppb) and two watering regimes (well-watered (WW) and reduced watering (RW), i.e. 40% irrigation) for one growing season. Water stress increased chlorophyll and carotenoid contents, protecting leaves from pigment degradation by O 3 . Impairment of photosynthesis by O 3 was also reduced by stomatal closure due to water stress, which preserved light-saturated CO 2 assimilation rate, and the maximum carboxylation efficiency. Water stress increased water use efficiency of the leaves while O 3 decreased it, showing significant interactions. Effects were more evident in older leaves than in younger leaves. Water stress reduced biomass production, but the negative effects of O 3 were less in RW than in WW for total biomass per plant. A stomatal O 3 flux-based dose-response relationship was parameterized considering water stress effects, which explained biomass losses much better than a concentration-based approach. The O 3 critical level of Phytotoxic Ozone Dose over a threshold of 7 nmol O 3 .m -2 .s -1 (POD 7 ) for a 4% biomass loss in this poplar clone under different water regimes was 4.1 mmol m -2 . Our results suggest that current O 3 levels in most parts of China threaten poplar growth and that interaction with water availability is a key factor for O 3 risk assessment., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Open top chambers were used to study the changes in photosynthesis, physiology and stomata characteristics in 1-year-old Lonicera maackii seedlings exposed to drought (DT, 30%-35% soil saturated water content) or/and elevated ozone (EO, 80 ppb). The results showed that DT or/and EO significantly decreased net photosynthetic rate (Pn), stomatal conductance (gs), maximum photochemical efficiency (Fv/Fm), but increased the activity of superoxide dismutase (SOD), and malondialdehyde content (p < 0.05). Compared with EO alone, the combination of EO and DT caused higher values in Pn, Fv/Fm, SOD activity (p < 0.05), and smaller stomata size and lower visible injury rate. DT alleviated the adverse impact of EO on the shrub by increasing enzyme activity and decreasing stomatal size, particularly stomatal width. The study provided increasing evidence that moderate drought might exert a beneficial effect on the tested plants to adapt to the future climate change, particularly in high ozone regions.

Ground-level ozone (O 3 ) affects trees through visible leaf injury, accelerating leaf senescence, declining foliar chlorophyll content, photosynthetic activity, growth, carbon sequestration, predisposing to pests attack and a variety of other physiological effects. Tree crown defoliation is one of the most important parameters that is representative of forest health and vitality. Effects of air pollution on forests have been investigated through manipulative experiments that are not representative of the real environmental conditions observed in the field. In this work we investigated the role of O 3 concentration and other metrics (AOT40 and POD0) in affecting crown defoliation in temperate Romanian forests. The impacts of O 3 were estimated in combination with nitrogen pollutants, climatic factors and orographic conditions, by applying a non-linear modelling approach (Random Forest and Generalised Regression Models). Ozone concentration and AOT40 under Romanian conditions were more important than meteorological parameters in affecting crown defoliation. In these particular conditions, POD0 never exceeded the critical level suggested by previous literature for forest protection, and thus was not important in affecting crown defoliation., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The effects of nitrogen (N) deposition, tropospheric ozone (O3) and their interaction were investigated in two Mediterranean tree species, Fraxinus ornus L. (deciduous) and Quercus ilex L. (evergreen), having different leaf habits and resource use strategies. An experiment was conducted under controlled condition to analyse how nitrogen deposition affects the ecophysiological and biochemical traits, and to explore how the nitrogen-induced changes influence the response to O3. For both factors we selected realistic exposures (20 kg N ha-1 yr-1 and 80 ppb h for nitrogen and O3, respectively), in order to elucidate the mechanisms implemented by the plants. Nitrogen addition resulted in higher nitrogen concentration at the leaf level in F. ornus, whereas a slight increase was detected in Q. ilex. Nitrogen enhanced the maximum rate of assimilation and ribulose 1,5-bisphosphate regeneration in both species, whereas it influenced the light harvesting complex only in the deciduous F. ornus that was also affected by O3 (reduced assimilation rate and accelerated senescence-related processes). Conversely, Q. ilex developed an avoidance mechanism to cope with O3, confirming a substantial O3 tolerance of this species. Nitrogen seemed to ameliorate the harmful effects of O3 in F. ornus: the hypothesized mechanism of action involved the production of nitrogen oxide as the first antioxidant barrier, followed by enzymatic antioxidant response. In Q. ilex, the interaction was not detected on gas exchange and photosystem functionality; however, in this species, nitrogen might stimulate an alternative antioxidant response such as the emission of volatile organic compounds. Antioxidant enzyme activity was lower in plants treated with both O3 and nitrogen even though reactive oxygen species production did not differ between the treatments.

The carbon-sink strength of temperate and boreal forests at midlatitudes of the northern hemisphere is decreased by ozone pollution, but knowledge on subtropical evergreen broadleaved forests is missing. Taking the dataset from Chinese studies covering temperate and subtropical regions, effects of elevated ozone concentration ([O 3 ]) on growth, biomass, and functional leaf traits of different types of woody plants were quantitatively evaluated by meta-analysis. Elevated mean [O 3 ] of 116 ppb reduced total biomass of woody plants by 14% compared with control (mean [O 3 ] of 21 ppb). Temperate species from China were more sensitive to O 3 than those from Europe and North America in terms of photosynthesis and transpiration. Significant reductions in chlorophyll content, chlorophyll fluorescence parameters, and ascorbate peroxidase induced significant injury to photosynthesis and growth (height and diameter). Importantly, subtropical species were significantly less sensitive to O 3 than temperate ones, whereas deciduous broadleaf species were significantly more sensitive than evergreen broadleaf and needle-leaf species. These findings suggest that carbon-sink strength of Chinese forests is reduced by present and future [O 3 ] relative to control (20-40 ppb). Given that (sub)-tropical evergreen broadleaved species dominate in Chinese forests, estimation of the global carbon-sink constraints due to [O 3 ] should be re-evaluated., (© 2017 John Wiley & Sons Ltd.)

In this study, impacts of O 3 on four cultivars ('Rose', 'Pink', 'Blush' and 'White') of the polka dot plant with variegated leaves were investigated for the first time. Ozone fumigation [(120 ± 20 ppb) for 14 days (8 h day -1 , from 8:30 to 16:30)] resulted in visible foliar injuries, decreased contents of pigments (chlorophyll a and b, and carotenoid), the inhibition of photosynthesis, the increase of quantum yield of non-regulated heat dissipation and fluorescence emission (Y(NO)), and the damage of cell membrane. Elevated O 3 increased the content of anthocyanin (Ant). 'White' showed the highest, and 'Rose' the lowest amount of injured leaf area, indicating that the former was the most sensitive, and the latter the most tolerant to O 3 stress. After O 3 exposure, the highest Ant content was found in 'Rose', followed by 'Pink', 'Blush', and 'White'. Levels of Ant were likely responsible for the different sensitivities to O 3 due to their roles in photoprotection.

Concentration- and flux-based O 3 dose-responses of isoprene emission from single leaves and whole plants were developed. Two poplar clones differing in O 3 sensitivity were exposed to five O 3 levels in open-top chambers for 97 d: charcoal-filtered ambient air (CF), non-filtered ambient air (NF) and NF plus 20 ppb (NF + 20), 40 ppb (NF + 40) and 60 ppb (NF + 60). At both leaf and plant level, isoprene emission was significantly decreased by NF + 40 and NF + 60 for both clones. Although intra-specific variability was found when the emissions were up-scaled to the whole plant, both leaf- and plant-level emissions decreased linearly with increasing concentration-based (AOT40, cumulative exposure to hourly O 3 concentrations >40 ppb) and flux-based indices (POD Y , cumulative stomatal uptake of O 3  > Y nmol O 3 m -2 PLA s -1 ). AOT40- and POD 7 -based dose-responses performed equally well. The two clones responded differently to AOT40 and similarly to POD Y (with a slightly higher R 2 for POD 7 ) when the emission was expressed as change relative to clean air. We thus recommend POD 7 as a large-scale risk assessment metric to estimate isoprene emission responses to O 3 in poplar., (© 2017 John Wiley & Sons Ltd.)

Enhanced ultraviolet radiation (UV) and elevated tropospheric ozone (O3) may individually cause reductions in the growth and productivity of important agricultural crops. However, research regarding their combined effects on important agricultural crops is still scarce, especially on changes in secondary metabolites and endogenous hormones, which are important protective substances and signal components that control plant responses to environment stresses. In this study, using an experimental setup of open top chambers, we monitored the responses of seed yield per plant, leaf secondary metabolites and leaf endogenous hormones under the stress of elevated O3 and enhanced UV radiation individually, as well as their combined stress. The results indicated that elevated O3 (110 ± 10 nmol mol-1 for 8 hours per day) and enhanced UV radiation (1.73 kJ h-1 m-2) significantly decreased seed yield per plant. Concentrations of rutin, queretin and total flavonoids were significantly increased under the elevated O3 treatment or the enhanced UV radiation treatment or the combination treatment at flowering and podding stages, and concentrations of rutin, queretin and total flavonoids showed significant correlations with seed yield per plant. Concentrations of ABA and IAA decreased under the three treatments. There was a significant positive correlation between the ABA concentration and seed yield and a negative correlation between the IAA concentration and seed yield. We concluded that the combined stress of elevated O3 and UV radiation significantly decreased seed yield per plant. Yield reduction was associated with changes in the concentrations of flavonoids, ABA and IAA in soybean leaves. The effects of the combined O3 and UV stress were always greater than those of the individual stresses alone.

Background: Ozone is an air pollutant widely known to cause a decrease in productivity in many plant species, including soybean (Glycine max (L.) Merr). While the response of cultivated soybean to ozone has been studied, very little information is available regarding the ozone response of its wild relatives., Results: Ozone-resistant wild soybean accessions were identified by measuring the response of a genetically diverse group of 66 wild soybean (Glycine soja Zucc. and Sieb.) accessions to elevated ozone levels. RNA-Seq analyses were performed on leaves of different ages from selected ozone-sensitive and ozone-resistant accessions that were subjected to treatment with an environmentally relevant level of ozone. Many more genes responded to elevated ozone in the two ozone-sensitive accessions than in the ozone-resistant accessions. Analyses of the ozone response genes indicated that leaves of different ages responded differently to ozone. Older leaves displayed a consistent reduction in expression of genes involved in photosynthesis in response to ozone, while changes in expression of defense genes dominated younger leaf tissue in response to ozone. As expected, there is a substantial difference between the response of ozone-sensitive and ozone-resistant accessions. Genes associated with photosystem 2 were substantially reduced in expression in response to ozone in the ozone-resistant accessions. A decrease in peptidase inhibitors was one of several responses specific to one of the ozone resistant accessions., Conclusion: The decrease in expression in genes associated with photosynthesis confirms that the photosynthetic apparatus may be an early casualty in response to moderate levels of ozone. A compromise of photosynthesis would substantially impact plant growth and seed production. However, the resistant accessions may preserve their photosynthetic apparatus in response to the ozone levels used in this study. Older leaf tissue of the ozone-resistant accessions showed a unique down-regulation of genes associated with endopeptidase inhibitor activity. This study demonstrates the existence of significant diversity in wild soybean for ozone response. Wild soybean accessions characterized in this study can be used by soybean breeders to enhance ozone tolerance of this important food crop.