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Ground-level ozone (O 3 ) concentration is rising in Asia, which accommodates the world's top-two wheat producers (China and India). Because wheat is among the species of high O 3 sensitivity, yield loss due to rising O 3 in Asia is a major threat to global wheat supply. We estimated the relationships between O 3 dose on AOT40 (accumulated daytime O 3 concentrations above 40 ppb for 90 days) and relative wheat yield for four wheat producing regions: China, India, Europe and North America using results of O 3 elevation experiments conducted therein. When compared on the same AOT40, the estimated yield loss was greatest in China followed by India, Europe, and North America in this order. In China, Europe and North America, the yield loss was primarily due to the reduction of single grain weight, whereas in India reduction of the number of grains contributed more to the yield loss than single grain weight. The greater response of the number of grains to O 3 in India can be explained by the earlier start of O 3 elevation, but the seasonal change in O 3 concentrations cannot explain the lower yield loss in North America than China and India. Referring to the past reports of lower yield sensitivity to O 3 in older cultivars, we compared the year of release of cultivars between the regions. In North America, they used cultivars released in 1980s or earlier, whereas in China they used cultivars released in 2000s. In Europe and India, most cultivars were released between those in North America and China. The difference in cultivars could therefore be a cause the differential yield response among the regions. We argue that the O 3 -induced yield loss should be quantified using the dose-response relationships for each region accounting for the effects of seasonal change in O 3 concentrations, cultivars and climate on the yield response., 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 © 2023 Elsevier B.V. All rights reserved.)

The rising concentration of ground-level ozone (O 3 ) reduces crop yield via increased oxidative stress. Application of ethylenediurea (EDU) protects plants from O 3 and could thereby serve as a means to estimate the crop yield losses due to ambient O 3 (AO 3 ). However, no study but a few exceptions has ever compared the yield loss estimates from EDU application with those from O 3 elevation experiments. Here, we estimated yield loss to AO 3 in rice cultivars across the 3 types, indica, japonica, and hybrid, by an EDU application in the field, and compared the yield losses with those estimated with dose-response relationships based on O 3 elevation experiments. Relative yield loss (RYL) in the EDU application was estimated at 16% across the rice types on an assumption of a 100% efficiency for protection of crop yield by EDU. This estimate of RYL was close to the 15% RYL estimated from the O 3 elevation experiments when a common sensitivity to O 3 is assumed across the cultivars. The rice yield loss due to AO 3 was thus consistent between the two approaches supporting the idea of EDU application for the yield loss estimation. When only hybrids are focused, however, the RYL from EDU application (16%) was much lower than the 34% RYL from the O 3 elevation experiments, which indicates only a 37% yield protection by EDU in the hybrid rice. The incomplete protection by EDU and its genetic variability indicates the need to quantify the efficiency of protection from AO 3 -induced yield loss as estimated with O 3 manipulating experiments., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The increasing emission of nitrogen oxides exerts large impacts on vegetation by raising surface ozone (O 3 ) concentrations and enhancing atmospheric nitrogen (N) deposition. We established a free-air O 3 concentration elevation and enhanced N deposition system (O 3 -N-FACE) in Beijing, China, to investigate long-term effects of elevated O 3 and N deposition on poplar plantation. Eight square plots with a side length of 16 m were randomly allocated to elevated O 3 (E-O 3 ) and ambient air (AA) treatments. Ozone generated by electric discharge in pure oxygen is mixed with clean and dry air, and released from small holes on the tubes installed above the plant canopy at a rate controlled to keep O 3 concentration in E-O 3 plots by 50% higher than that in AA plots. Each O 3 treatment plot consisted of four subplots with a factorial combination of 2 lines of poplar clones and 2 levels of N deposition rate. In enhanced N deposition subplots, we sprayed urea solution on the plantation floor at a rate of 60 kg ha -1 year -1 . We hereby present the system performances during the growing seasons of 2018 and 2019: the first 2 years of experiment. The mean daytime O 3 concentrations of E-O 3 plots were 38% and 31% higher than AA plots in 2018 and 2019, respectively. And, in 2019, the accumulated O 3 exposure over 40 ppb (AOT40) in E-O 3 plots was 70% higher than that in AA plots. The hourly mean O 3 concentrations in E-O 3 plots were within 20% of the target for 83% of time on average across the four E-O 3 plots. Within the E-O 3 plots, spatial distribution of the hourly O 3 concentration exhibited the maximum deviation at 24% in 2019. We concluded that performance of this system is better than other similar facilities for trees and suitable for a long-term experiment of enhanced O 3 and N., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Ascorbate in leaf apoplast (ASC apo ) reacts with ozone (O 3 ) and thereby reduces O 3 flux reaching plasmalemma (F pl ). Some studies have shown significant protection of cells from O 3 by ASC apo , while others have questioned its efficacy. Hypothesizing that the protection by ASC apo depends on other variables, we quantified determinants of O 3 detoxification with a model of O 3 transport and reaction in apoplast. The model determines ascorbic acid concentration in apoplast (AA apo ) using measured values of O 3 concentration (c o ), leaf tissue ascorbic acid concentration (AA leaf ), cell wall thickness (L 3 ), apoplastic pH (pH apo ), and stomatal conductance (G sw ). We compared the measured and model-estimated AA apo in leaves of peach (Prunus persica) grown in open-top chambers under non-filtered air (NF) and elevated (EO 3 : NF + 80 ppb) O 3 concentrations. The estimated AA apo in individual leaves agreed well with the measured values (R 2  = .91). Analyses of the simulation results yielded the following findings: (a) The efficacy of O 3 reduction with ASC apo as quantified by fractional reduction (ϕ 3 ) of O 3 flux at the surface of plasmalemma (F pl ) was lowered from 70% in NF to 40% in EO 3 due to the reduction of L 3 . The EO 3 reduced AA apo , but the lower G sw and L 3 in EO 3 increased AA apo resulting in no significant change in AA apo due to EO 3 . ϕ 3 can be calculated with measured values of AA apo and L 3 , and F pl can be estimated with the measurement-based ϕ 3 . (b) When c 0 is increased, F pl increased curvilinearly with the increase of F st : nominal O 3 flux via stomatal diffusion, exhibiting apparent threshold on F st . The deviation of F pl from F st became greater when L 3 , pH apo , and AA leaf were increased. The quantification of ϕ 3 and F pl using leaf traits shall facilitate the understanding of the mechanisms of differential plant sensitivity to O 3 and improve quantification of the O 3 impacts on plants., (© 2020 John Wiley & Sons Ltd.)

Ozone is an important air pollutant that affects growth, transpiration, and water use efficiency (WUE) in plants. Integrated models of photosynthesis (A n ) and stomatal conductance (G s ) (A n -G s ) are useful tools to consistently assess the impacts of ozone on plant growth, transpiration, and WUE. However, there is no information on how to incorporate the influence of ozone into A n -G s integrated models for crops. We focused on the Ball-Woodrow-Berry (BWB) relationship, which is a key equation in A n -G s integrated models, and aimed to address the following questions: (i) how does ozone change the BWB relationship for crops?; (ii) are there any difference in the changes in the BWB relationship among cultivars?, and (iii) how do the changes in the BWB relationship increase or decrease WUE for crops? We grew four rice cultivars in a field under ambient or Free-Air Concentration Enrichment (FACE) of ozone in China and measured A n and G s using a portable photosynthesis analyzer. We simulated WUE in individual leaves during the ripening period under different BWB relationships. The results showed that ozone significantly changed the BWB relationship only for the most sensitive cultivar, which showed an increase in the intercept of the BWB relationship under FACE conditions. These results imply that changes in the BWB relationship are related to the ozone sensitivity of the cultivar. Simulations of an A n -G s integrated model showed that increases in the intercept of the BWB relationship from 0.01 to 0.1 mol(H 2 O) m -2  s -1 indicated decreases in WUE by 22%. Since a reduction in WUE indicates increases in water demand per unit of crop growth, air pollution from ozone could be a critical issue in regions where agricultural water is limited, such as in rainfed paddy fields., (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.)

Increasing both crop productivity and the tolerance of crops to abiotic and biotic stresses is a major challenge for global food security in our rapidly changing climate. For the first time, we show how the spatial variation and severity of tropospheric ozone effects on yield compare with effects of other stresses on a global scale, and discuss mitigating actions against the negative effects of ozone. We show that the sensitivity to ozone declines in the order soybean > wheat > maize > rice, with genotypic variation in response being most pronounced for soybean and rice. Based on stomatal uptake, we estimate that ozone (mean of 2010-2012) reduces global yield annually by 12.4%, 7.1%, 4.4% and 6.1% for soybean, wheat, rice and maize, respectively (the "ozone yield gaps"), adding up to 227 Tg of lost yield. Our modelling shows that the highest ozone-induced production losses for soybean are in North and South America whilst for wheat they are in India and China, for rice in parts of India, Bangladesh, China and Indonesia, and for maize in China and the United States. Crucially, we also show that the same areas are often also at risk of high losses from pests and diseases, heat stress and to a lesser extent aridity and nutrient stress. In a solution-focussed analysis of these results, we provide a crop ideotype with tolerance of multiple stresses (including ozone) and describe how ozone effects could be included in crop breeding programmes. We also discuss altered crop management approaches that could be applied to reduce ozone impacts in the shorter term. Given the severity of ozone effects on staple food crops in areas of the world that are also challenged by other stresses, we recommend increased attention to the benefits that could be gained from addressing the ozone yield gap., (© 2018 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.)

Introduction of high-performing crop cultivars and crop/soil water management practices that increase the stomatal uptake of carbon dioxide and photosynthesis will be instrumental in realizing the United Nations Sustainable Development Goal (SDG) of achieving food security. To date, however, global assessments of how to increase crop yield have failed to consider the negative effects of tropospheric ozone, a gaseous pollutant that enters the leaf stomatal pores of plants along with carbon dioxide, and is increasing in concentration globally, particularly in rapidly developing countries. Earlier studies have simply estimated that the largest effects are in the areas with the highest ozone concentrations. Using a modelling method that accounts for the effects of soil moisture deficit and meteorological factors on the stomatal uptake of ozone, we show for the first time that ozone impacts on wheat yield are particularly large in humid rain-fed and irrigated areas of major wheat-producing countries (e.g. United States, France, India, China and Russia). Averaged over 2010-2012, we estimate that ozone reduces wheat yields by a mean 9.9% in the northern hemisphere and 6.2% in the southern hemisphere, corresponding to some 85 Tg (million tonnes) of lost grain. Total production losses in developing countries receiving Official Development Assistance are 50% higher than those in developed countries, potentially reducing the possibility of achieving UN SDG2. Crucially, our analysis shows that ozone could reduce the potential yield benefits of increasing irrigation usage in response to climate change because added irrigation increases the uptake and subsequent negative effects of the pollutant. We show that mitigation of air pollution in a changing climate could play a vital role in achieving the above-mentioned UN SDG, while also contributing to other SDGs related to human health and well-being, ecosystems and climate change., (© 2018 The Authors. Global Change Biology Published by John Wiley & Sons Ltd.)

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.)

Five winter wheat cultivars were exposed to ambient (A-O 3 ) and elevated (E-O 3 , 1.5 ambient) O 3 in a fully open-air fumigation system in China. Ozone exposure- and flux based response relationships were established for seven physiological variables related to photosynthesis. The performance of the fitting of the regressions in terms of R 2 increased when second order regressions instead of first order ones were used, suggesting that effects of O 3 were more pronounced towards the last developmental stages of the wheat. The more robust indicators were those related with CO 2 assimilation, Rubisco activity and RuBP regeneration capacity (A sat , J max and Vc max ), and chlorophyll content (Chl). Flux-based metrics (POD y , Phytotoxic O 3 Dose over a threshold ynmolO 3 m -2 s -1 ) predicted slightly better the responses to O 3 than exposure metrics (AOTX, Accumulated O 3 exposure over an hourly Threshold of X ppb) for most of the variables. The best performance was observed for metrics POD 1 ( A sat , J max and Vc max ) and POD 3 (Chl). For this crop, the proposed response functions could be used for O 3 risk assessment based on physiological effects and also to include the influence of O 3 on yield or other variables in models with a photosynthetic component., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Five modern cultivars of winter wheat (Triticum aestivum L.): Yangmai16 (Y16), Yangmai 15 (Y15), Yangfumai 2 (Y2), Yannong 19 (Y19) and Jiaxing 002 (J2) were investigated to determine the impacts of elevated ozone concentration (E-O 3 ) on photosynthesis-related parameters and the antioxidant system under fully open-air field conditions in China. The plants were exposed to E-O 3 at 1.5 times the ambient ozone concentration (A-O 3 ) from the initiation of tillering to final harvest. Pigments, gas exchange rates, chlorophyll a fluorescence, antioxidants contents, antioxidative enzyme activity and lipid oxidation were measured in three replicated plots throughout flag leaf development. Results showed that significant O 3 effects on most variables were only found during the mid-grain filling stage. Across five cultivars, E-O 3 significantly accelerated leaf senescence, as indicated by increased lipid oxidation as well as faster declines in pigment amounts and photosynthetic rates. The lower photosynthetic rates were mainly due to non-stomatal factors, e.g. lower maximum carboxylation capacity and electron transport rates. There were strong interactions between O 3 and cultivar in photosynthetic pigments, light-saturated photosynthesis rate and chlorophyll a fluorescence with O 3 -sensitive (Y19, Y2 and Y15) and O 3 -tolerant (J2, Y16) cultivars being clearly differentiated in their responses to E-O 3 . E-O 3 significantly influenced the antioxidative enzymes but not antioxidant contents. Significant interactions between O 3 and cultivar were found in antioxidative enzymes, such as SOD and CAT, but not in stomatal conductance (g s ). Therefore, it can be concluded that antioxidative enzymes rather than g s or antioxidants are responsible for the differential responses to E-O 3 among cultivars. These findings provide important information for the development of accurate modeling O 3 effects on crops, especially with respect to the developmental stage when O 3 damage to photosynthesis becomes manifest., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Besides stomatal closure, biological detoxification is an important protection mechanism for plants against ozone (O3). This study investigated the diurnal changes of ascorbate (a major detoxification agent) in the apoplast and leaf tissues of winter wheat grown under ambient air field conditions. Results showed the reduced ascorbate in the apoplast (ASCapo) exhibited a peak in late morning or midday, mismatching with either the maximum external O3 concentrations in mid-afternoon or the maximum stomatal O3 uptake between late morning and mid-afternoon. In contrast, the ASC in leaf tissues remained stable throughout the day. The investigations conducted in a Free-Air Concentration Elevation of O3 system confirmed that the diurnal variations of the ASCapo were induced more by the daily variations of O3 concentrations rather than the cumulative O3 effects. In conclusion, the O3-stress detoxification should be a dynamic variable rather than a fixed threshold as assumed in the stomatal flux-based O3 dose metrics., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

We investigated the effects of elevated ozone concentration (E-O3) on CH4 and N2O emission from paddies with two rice cultivars: an inbred Indica cultivar Yangdao 6 (YD6) and a hybrid one II-you 084 (IIY084), under fully open-air field conditions in China. A mean 26.7% enhancement of ozone concentration above the ambient level (A-O3) significantly reduced CH4 emission at tillering and flowering stages leading to a reduction of seasonal integral CH4 emission by 29.6% on average across the two cultivars. The reduced CH4 emission is associated with O3-induced reduction in the whole-plant biomass (-13.2%), root biomass (-34.7%), and maximum tiller number (-10.3%), all of which curbed the carbon supply for belowground CH4 production and its release from submerged soil to atmosphere. Although no significant difference was detected between the cultivars in the CH4 emission response to E-O3, a larger decrease in CH4 emission with IIY084 (-33.2%) than that with YD6 (-7.0%) was observed at tillering stage, which may be due to the larger reduction in tiller number in IIY084 by E-O3. Additionally, E-O3 reduced seasonal mean NOx flux by 5.7% and 11.8% with IIY084 and YD6, respectively, but the effects were not significant statistically. We found that the relative response of CH4 emission to E-O3 was not significantly different from those reported in open-top chamber experiments. This study has thus confirmed that increasing ozone concentration would mitigate the global warming potential of CH4 and suggested consideration of the feedback mechanism between ozone and its precursor emission into the projection of future ozone effects on terrestrial ecosystem., (© 2014 John Wiley & Sons Ltd.)

Tropospheric ozone is an air pollutant harmful to plants and animals. Its rapid increase at the ground surface has raised serious concern over damage to the quality and yield of agricultural crops. Reactive oxygen species (ROS) are formed in plant cells when that are exposed to a high concentration of ozone, and the ROS are thought to alter gene expression and result in cellular death. Clarification of the ROS formation will provide us with a better understanding of the physiological responses to and signaling pathways of ozone stress in plants. In this study, we investigated the mechanisms of the ROS formation in rice (Oryza sativa L.), the premier crop in Asia. To determine ROS distribution in rice leaves under acute ozone stress, we analyzed superoxide dismutase (SOD) expression, lipid peroxidation, NADPH oxidase activity, and in vivo H2O2 formation. Interestingly, chloroplastic, peroxisomal and mitochondrial SODs down-regulated their expression levels under ozone stress, whereas cytosolic SODs maintained their expression level. Higher lipid peroxidation occurred after the end of ozone exposure, which suggests lipid peroxidation may not be due to ozone directly, but rather to metabolic changes caused by the ozone exposure. Activity of NADPH oxidase did not show significant change. The in vivo analysis indicated accelerated formation of H2O2 about 24 h after the onset of exposure, which suggests that cellular death occurred around this time., (Copyright © 2013 Elsevier Masson SAS. All rights reserved.)

Using a high-resolution (40 × 40 km) chemical transport model coupled with the Regional Emission inventory in Asia (REAS), we simulated surface ozone concentrations ([O3 ]) and evaluated O3 -induced wheat production loss in China and India for the years 2000 and 2020 using dose-response functions based on AOT40 (accumulated [O3 ] above 40 ppb) and PODY (phytotoxic O3 dose, accumulated stomatal flux of O3 above a threshold of Y nmol m(-2) s(-1) ). Two O3 dose metrics (90 days AOT40 and POD6 ) were derived from European experiments, and the other two (75 days AOT40 and POD12 ) were adapted from Asian studies. Relative yield loss (RYL) of wheat in 2000 was estimated to be 6.4-14.9% for China and 8.2-22.3% for India. POD6 predicted greater RYL, especially for the warm regions of India, whereas the 90 days AOT40 gave the lowest estimates. For the future projection, all the O3 dose metrics gave comparable estimates of an increase in RYL from 2000 to 2020 in the range 8.1-9.4% and 5.4-7.7% for China and India, respectively. The lower projected increase in RYL for India may be due to conservative estimation of the emission increase in 2020. Sensitivity tests of the model showed that the PODY -based estimates of RYL are highly sensitive to perturbations in the meteorological inputs, but that the estimated increase in RYL from 2000 to 2020 is much more robust. The projected increase in wheat production loss in China and India in the near future is substantially larger than the uncertainties in the estimation and indicates an urgent need for curbing the rapid increase in surface [O3 ] in these regions., (© 2013 John Wiley & Sons Ltd.)

By using a free-air controlled enrichment (FACE) system, this paper studied the effects of elevated atmospheric ozone (O3) concentration (150% of ambient O3) on the flag leaf photosynthetic pigment contents of wheat varieties Yannong 19, Yangmai 16, Jiaxin 002, Yangmai 15, and Yangfumai 2. For the test varieties, no significant differences were observed in the flag leaf chlorophyll a, chlorophyll b, chlorophyll (a+b), and carotenoid contents between treatments elevated O3 concentration and ambient O3 at booting and anthesis stages, but the photosynthetic pigment contents in treatment elevated O3 concentration all decreased after anthesis, with a significant decrease of chlorophyll a, chlorophyll b, and chlorophyll (a+b) contents, which indicated that elevated O3 had minor effects on the synthesis of photosynthetic pigments but accelerated their decline process. Different wheat varieties had genetic difference in the responses of flag leaf photosynthetic pigment contents to elevated O3, among which, Yangmai 15 and Jiaxin 002 had better tolerance to ozone stress. The flag leaf chlorophyll a, chlorophyll b, and chlorophyll (a+b) contents at grain-filling stage (about 21 days after anthesis) had a significant positive correlation with the 1000-grain mass.

By using FACE (Free-Air Controlled Environment)-ozone system, a field plot experiment was conducted in 2008-2009 to study the effects of elevated ozone (O3) concentration on the flag leaf microscopic structure, chlorophyll content, and grain weight of wheat. Two treatments were installed, i. e., ambient O3 and 150% of ambient O3, and four winter varieties, i. e., Yannong 19, Yangmai 16, Jiaxin 002, and Yangfumai 2, were taken as the test materials. At anthesis, elevated O3 concentration had a slight damage to the flag leaf microscopic structure. The mesophyll cell and chloroplast structure began destroying, and the grana lamellae started breaking and loosing. Twenty-one days after anthesis, the differences in the leaf microscopic structure between the two treatments became significant. Under elevated O3, the flag leaf senescence was accelerated, with the endomembrane system disintegrated, grana lamella disappeared, and corpus adiposum inside chloroplast broken down, resulting in a significant decrease of the chlorophyll content, photosynthesis rate, and grain weight at maturing stage. Significant difference was observed among the test varieties in their responses to elevated O3. Jiaxin 002 was tolerant, while Yangfumai 2 was sensitive to the ozone stress.

Stomatal ozone flux and flux-response relationships were derived for winter wheat (Triticum aestivum L.) grown under fully open-air ozone fumigation. A stomatal conductance (g(sto)) model developed for wheat in Europe was re-parameterized. Compared to European model parameterizations, the main changes were that the VPD and radiation response functions were made less and more restrictive, respectively, and that the temperature function was omitted. The re-parameterized g(sto) model performed well with an r(2) value of 0.76. The slope and intercept of the regression between observed and predicted g(sto) were not significantly different from 1 to 0, respectively. An ozone uptake threshold of 12 nmol m(-2) s(-1) was judged most reasonable for the wheat flux-response relationship in subtropical China. Judging from both flux- and concentration-based relationships, the cultivars investigated seem to be more sensitive to ozone than European cultivars. The new flux-response relationship can be applied to ozone risk assessment in subtropical regions., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

We studied leaf apoplastic ascorbates in relation to ozone (O(3)) sensitivity in two winter wheat (Triticum aestivum L.) varieties: Yangfumai 2 (Y2) and Yangmai 16 (Y16). The plants were exposed to elevated O(3) concentration 27% higher than the ambient O(3) concentration in a fully open-air field from tillering stage until final maturity. The less sensitive variety Y16 had higher concentration of reduced ascorbate in the apoplast and leaf tissue by 33.5% and 12.0%, respectively, than those in the more sensitive variety Y2, whereas no varietal difference was detected in the decline of reduced ascorbate concentration in response to elevated O(3). No effects of O(3) or variety were detected in either oxidized ascorbate or the redox state of ascorbate in the apoplast and leaf tissue. The lower ascorbate concentrations in both apoplast and leaf tissue should have contributed to the higher O(3) sensitivity in variety Y2., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Context: Ozone concentrations near the land surface are rising in Asia while they are declining or stagnating in Europe and North America. Ozone is the most widespread air pollutant negatively affecting vegetation, and its increased concentrations pose a major threat to food quality and production and other ecosystem services in Asia.Method: In this review, we provide an overview of scientific challenges in the impacts of ozone pollution on Asian vegetation, and synthesize the challenges toward mitigation of the impacts.Result: We argue that new policy initiatives need to seek both reduction of ozone levels and enhancement of plant tolerance to ozone to maintain food quality and ensure food supplies.Conclusion: The scientific advancements must be transferred to actions by two types of institutions: a) environmental agencies for reducing ozone levels and b) agricultural research institutions for enhancing plant tolerance to ozone. In connecting the scientific advancements with the institutional actions, scientists in Asian countries should play the key role taking advantages of interdisciplinary and international collaborations. [ABSTRACT FROM AUTHOR]

Assessments of the impacts of ozone (O3) 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 O3 exposure and yield data for three major crop species--wheat, rice, and soybean--for which O3 experiments have been conducted with OTCs as well as the ecologically more realistic free-air O3 elevation (O3-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 O3 metric AOT40 (accumulated hourly O3 exposure above a cut-off threshold concentration of 40 ppb) significantly differed between OTC and O3-FACE experiments. In wheat and rice, O3 sensitivity was higher in O3-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 O3 flux when applying experimental data to assess O3 impacts on crops at large spatial scales. [ABSTRACT FROM AUTHOR]

We investigated the effects of elevated ozone concentration (E-O3) on CH4 and N2O emission from paddies with two rice cultivars: an inbred Indica cultivar Yangdao 6 ( YD6) and a hybrid one II-you 084 ( IIY084), under fully open-air field conditions in China. A mean 26.7% enhancement of ozone concentration above the ambient level (A-O3) significantly reduced CH4 emission at tillering and flowering stages leading to a reduction of seasonal integral CH4 emission by 29.6% on average across the two cultivars. The reduced CH4 emission is associated with O3-induced reduction in the whole-plant biomass (−13.2%), root biomass (−34.7%), and maximum tiller number (−10.3%), all of which curbed the carbon supply for belowground CH4 production and its release from submerged soil to atmosphere. Although no significant difference was detected between the cultivars in the CH4 emission response to E-O3, a larger decrease in CH4 emission with IIY084 (−33.2%) than that with YD6 (−7.0%) was observed at tillering stage, which may be due to the larger reduction in tiller number in IIY084 by E-O3. Additionally, E-O3 reduced seasonal mean NOx flux by 5.7% and 11.8% with IIY084 and YD6, respectively, but the effects were not significant statistically. We found that the relative response of CH4 emission to E-O3 was not significantly different from those reported in open-top chamber experiments. This study has thus confirmed that increasing ozone concentration would mitigate the global warming potential of CH4 and suggested consideration of the feedback mechanism between ozone and its precursor emission into the projection of future ozone effects on terrestrial ecosystem. [ABSTRACT FROM AUTHOR]

Four modern cultivars of winter wheat (Triticum aestivum L.) were grown under elevated ozone concentration (E-O3) in fully open-air field conditions in China for three consecutive growth seasons from 2007 to 2009. Results indicated that a mean 25% enhancement above the ambient ozone concentration (A-O3, 45.7 p.p.b.) significantly reduced the grain yield by 20% with significant variation in the range from 10% to 35% among the combinations of cultivar and season. The varietal difference in the yield response to E-O3 became nonsignificant when the ANOVA was done by omitting one cultivar which showed unstable response to E-O3 among the seasons. The reduction of individual grain mass accounted mostly for the yield loss by E-O3, and showed significant difference between the cultivars. The response of relative yield to E-O3 was not significantly different from those reported in China, Europe and India on the basis of experiments in open-top chambers. Our results thus confirmed the rising threat of surface O3 on wheat production worldwide in the near future. Various countermeasures are urgently needed against the crop losses due to O3 such as mitigation of the increase in surface O3 with stricter pollution control, and enhancement of the wheat tolerance against O3 by breeding and management. [ABSTRACT FROM AUTHOR]

Two modern cultivars [Yangmai16 (Y16) and Yangfumai 2 (Y2)] of winter wheat ( Triticum aestivum L.) with almost identical phenology were investigated to determine the impacts of elevated ozone concentration (E-O) on physiological characters related to photosynthesis under fully open-air field conditions in China. The plants were exposed from the initiation of tillering to final harvest, with E-O of 127% of the ambient ozone concentration (A-O). Measurements of pigments, gas exchange rates, chlorophyll a fluorescence and lipid oxidation were made in three replicated plots throughout flag leaf development. In cultivar Y2, E-O significantly accelerated leaf senescence, as indicated by increased lipid oxidation as well as faster declines in pigment amounts and photosynthetic rates. The lower photosynthetic rates were mainly due to nonstomatal factors, e.g. lower maximum carboxylation capacity, electron transport rates and light energy distribution. In cultivar Y16, by contrast, the effects of E-O were observed only at the very last stage of flag leaf ageing. Since the two cultivars had almost identical phenology and very similar leaf stomatal conductance before senescence, the greater impacts of E-O on cultivars Y2 than Y16 cannot be explained by differential ozone uptake. Our findings will be useful for scientists to select O-tolerant wheat cultivars against the rising surface [O] in East and South Asia. [ABSTRACT FROM AUTHOR]

The effects of elevated O3 concentration ([O3]) on grain yield and photosynthetic characteristics of flag leaves in rice (Oryza sativa L.) were studied using a hybrid indica cultivar SY63 and a conventional Japonica cultivar WYJ3. Both cultivars were grown in the field under ambient (A-O3) and elevated [O3] (E-O3, ambient×1.5) using free-air O3 enrichment in Jiangdu city, Jiangsu province, China. The E-O3 significantly reduced above-ground biomass (p =0.047) and grain yield (p =0.0046), but had no significant effect on harvest index (p =0.18) across cultivars. The hybrid Indica cultivar SY63 was more sensitive to E-O3 than the conventional Japonica cultivar WYJ3. The above-ground biomass was reduced by 17.6% for SY63 and 6.6% for WYJ3, whereas the grain yield was reduced by 20.7% for SY63 and 6.3% for WYJ3. A barely non-significant (p =0.079) interaction between O3 and cultivar on grain yield suggested a higher sensitivity of the hybrid variety: SY63. In SY63, flag leaves exhibited an earlier and stronger response in photosynthetic characteristics to E-O3. Depression in light-saturated photosynthetic rate (A sat) was first observed at 237 day of year (DOY) in SY63, and the seasonal mean A sat was reduced by 23.1%. In contrast, for WYJ3, the conventional cultivar, the impact of E-O3 on A sat was negligible until 266 DOY, and seasonal mean decrease of A sat was only 9.4%. The same trend was found in chlorophyll a fluorescence parameters. In SY63, actual quantum yield of PSII (p =0.007) and q p (photochemical quenching) (p =0.002) were significantly decreased at 248 DOY and the downward trends persisted throughout the rest of the life span of flag leaves. No such changes were observed in WYJ3. In the ozonated flag leaves of SY63, necrotic damages occurred and chlorophyll contents declined significantly by 12.6¿43.6% through the entire functional duration of the leaf. As for WYJ3, chlorophyll remained unaffected until a 25.7% decrease appeared at 278 DOY under E-O3. The observed yield losses were compared with those estimated from two existing exposure¿yield loss relationships for rice. The yield loss in SY63 was much greater than either estimate, whereas that in WYJ3 was comparable to one estimate but was moderately larger than the other. This warrants further studies with a much larger number of varieties. Open-air O3 release would serve as the best platform for such a large-scale screening of rice varieties to increasing [O3]. [Copyright &y& Elsevier]

Meta-analysis was conducted to quantitatively assess the effects of rising ozone concentrations ([O3]) on yield and yield components of major food crops: potato, barley, wheat, rice, bean and soybean in 406 experimental observations. Yield loss of the crops under current and future [O3] was expressed relative to the yield under base [O3] (≤26ppb). With potato, current [O3] (31–50ppb) reduced the yield by 5.3%, and it reduced the yield of barley, wheat and rice by 8.9%, 9.7% and 17.5%, respectively. In bean and soybean, the yield losses were 19.0% and 7.7%, respectively. Compared with yield loss at current [O3], future [O3] (51–75ppb) drove a further 10% loss in yield of soybean, wheat and rice, and 20% loss in bean. Mass of individual grain, seed, or tuber was often the major cause of the yield loss at current and future [O3], whereas other yield components also contributed to the yield loss in some cases. No significant difference was found between the responses in crops grown in pots and those in the ground for any yield parameters. The ameliorating effect of elevated [CO2] was significant in the yields of wheat and potato, and the individual grain weight in wheat exposed to future [O3]. These findings confirm the rising [O3] as a threat to food security for the growing global population in this century. [Copyright &y& Elsevier]

We quantitatively evaluated the effects of elevated concentration of ozone (O3) on growth, leaf chemistry, gas exchange, grain yield, and grain quality relative to carbon-filtered air (CF) by means of meta-analysis of published data. Our database consisted of 53 peer-reviewed studies published between 1980 and 2007, taking into account wheat type, O3 fumigation method, rooting environment, O3 concentration ([O3]), developmental stage, and additional treatments such as drought and elevated carbon dioxide concentration ([CO2]). The results suggested that elevated [O3] decreased wheat grain yield by 29% (CI: 24–34%) and aboveground biomass by 18% (CI: 13–24%), where CI is the 95% confidence interval. Even in studies where the [O3] range was between 31 and 59 ppb (average 43 ppb), there was a significant decrease in the grain yield (18%) and biomass (16%) relative to CF. Despite the increase in the grain protein content (6.8%), elevated [O3] significantly decreased the grain protein yield (−18%). Relative to CF, elevated [O3] significantly decreased photosynthetic rates (−20%), Rubisco activity (−19%), stomatal conductance (−22%), and chlorophyll content (−40%). For the whole plant, rising [O3] induced a larger decrease in belowground (−27%) biomass than in aboveground (−18%) biomass. There was no significant response difference between spring wheat and winter wheat. Wheat grown in the field showed larger decreases in leaf photosynthesis parameters than wheat grown in < 5 L pots. Open-top chamber fumigation induced a larger reduction than indoor growth chambers, when plants were exposed to elevated [O3]. The detrimental effect was progressively greater as the average daily [O3] increased, with very few exceptions. The impact of O3 increased with developmental stages, with the largest detrimental impact during grain filling. Both drought and elevated [CO2] significantly ameliorated the detrimental effects of elevated [O3], which could be explained by a significant decrease in O3 uptake resulting from decreased stomatal conductance. [ABSTRACT FROM AUTHOR]

A field exposure chamber system was constructed in a paddy field. The system consisted of four ozone generators, five exposure chambers equipped with ventilation fans on both ends, and an ozone measurement and control system. Rice plants were exposed to ozone in the exposure chambers for the whole growing season. The ozone concentration in each chamber was maintained in a constant proportion to ambient ozone. The horizontal distribution of ozone concentration within a chamber showed ± 10% of variation with the lowest values at the centre and both ends of the chamber. Wind velocity showed a similar horizontal distribution as ozone but with a greater variation among the locations within a chamber. Diurnal as well as seasonal changes of ozone concentration in the chambers followed the targeted level rather closely except for several occasions of power failure or system malfunctioning. Temperature in the chambers was c. 1 °C higher in the daytime and 0.34 °C higher on daily average than in the field outside. Light flux density in the chambers was reduced to 75% of that outside with little seasonal variation. These results indicated a satisfactory performance of the field exposure chamber system for its intended use. [ABSTRACT FROM AUTHOR]

Wheat yield loss due to ambient ozone (O 3) and the associated economic losses in China were evaluated for years 2015 and 2016 using for the first time measured O 3 concentration ([O 3 ]) and meteorological data as well as phenological observations. Relative yield losses (RYL) were estimated using response functions based on both O 3 exposure and flux metrics: AOT40 (the accumulated hourly [O 3 ] over a threshold of 40 ppb) and POD 12 (Phytotoxic Ozone Dose over a threshold of 12 nmol O 3 m−2 s−1). Both metrics showed consistent spatial patterns being highest in the North China Plain, the largest wheat-producing area in China, followed by some provinces in Yangtze River region. The higher stomatal conductance in areas with high [O 3 ] in year 2015 contributed to higher POD 12 values than in 2016. The RYLs for the whole China estimated with AOT40 were 17.1% and 18.1% for years 2015 and 2016, respectively, whereas those with POD 12 were lower, 10.6% and 10.2%, respectively. Wheat production losses as translated to annual economic losses were 10 304 and 10 745 million USD (AOT40) or 5912 and 5554 million USD (POD 12), for 2015 and 2016, respectively. The O 3 impact estimated with monitoring data suggests its overestimation by some of the previous studies based on model estimates of surface [O 3 ]. The overestimation could be attributed to the uncertainties in estimating meteorological variables and [O 3 ], particularly the omission of the correction for the vertical gradient of [O 3 ] near crop canopy in some studies. Image 1 • O 3 impact on wheat yield was estimated using O 3 monitoring data for the first time. • The relative yield loss was assessed based on O 3 concentration flux metrics. • Previous modelling studies have overestimated O 3 impacts on yield of winter wheat. • The highest yield loss by O 3 was found in North China Plain. Previous simulation studies have overestimated the yield loss of winter wheat by ozone. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the impact of elevated ozone concentration ([O3]) on grain yield of rice in relation to the changes in spikelet formation, which plays a critical role in securing a sufficient number of spikelets per land area for a higher yield. Using a free air gas concentration enrichment (FACE) facility for O3 fumigation in China, two contrasting rice cultivars were exposed to either ambient (38ppb) or elevated [O3] (47ppb) from tillering stage to final harvest in 2008. A 23% increase in [O3] decreased grain yield of Yangdao6 and Shanyou63 by 6% and 27%, respectively. The yield loss was driven primarily by a decrease in the number of spikelets per panicle, rather than changes in the other yield components. The large reduction observed in panicle size of Shanyou63 under ozone stress resulted from both the inhibition of spikelet differentiation and promotion of spikelet degeneration, which was associated with decreased accumulation of nitrogen and biomass up to the heading stage. The results of this experiment indicated that the yield loss in rice under ozone exposure resulted primarily from negative effects on spikelet formation, and that a better understanding of spikelet formation process is indispensable for the assessment of rice yield response to future higher ground-level [O3]. [Copyright &y& Elsevier]

Air pollution and climate change are increasing threats to agricultural production and food security. Extensive studies have focused on the effect of climate change, but the interactive effects of multiple global change factors are poorly understood. Here, we incorporate the interactions between climate change, carbon dioxide (CO 2 ) and ozone (O 3 ) into an eco-physiological mechanistic model based on three years of O 3 Free-Air Concentration Elevation (O 3 -FACE) experiments. We then investigate the effects of climate change, elevated CO 2 concentration ([CO 2 ]) and rising O 3 concentration ([O 3 ]) on wheat growth and productivity in eastern China in 1996–2005 (2000s) and 2016–2025 (2020s) under two climate change scenarios, singly and in combination. We find the interactive effects of climate change, CO 2 and O 3 on wheat productivity have spatially explicit patterns; the effect of climate change dominates the general pattern, which is however subject to the large uncertainties of climate change scenarios. Wheat productivity is estimated to increase by 2.8–9.0% due to elevated [CO 2 ] however decline by 2.8–11.7% due to rising [O 3 ] in the 2020s, relative to the 2000s. The combined effects of CO 2 and O 3 are less than that of O 3 only, on average by 4.6–5.2%, however with O 3 damage outweighing CO 2 benefit in most of the region. This study demonstrates a more biologically meaningful and appropriate approach for assessing the interactive effects of climate change, CO 2 and O 3 on crop growth and productivity. Our findings promote the understanding on the interactive effects of multiple global change factors across contrasting climate conditions, cast doubt on the potential of CO 2 fertilization effect in offsetting possible negative effect of climate change on crop productivity as suggested by many previous studies. [ABSTRACT FROM AUTHOR]

Abstract: Rising tropospheric ozone concentration is currently the most important air pollutant which suppresses plant growth and thus results in yield loss of agronomic crops. However little is known about ozone effects on grain quality of crops. Using a free-air gas concentration enrichment (FACE) facility for ozone fumigation in paddy rice (Oryza Sativa L.), a Chinese hybrid indica cultivar Shanyou 63 was exposed to either ambient or elevated ozone concentration (ca 23.5% above ambient) for two consecutive growth seasons from 2007 to 2008. Harvested grain samples were subjected to various quality tests. In both seasons, the brown, milled and head rice yield all reduced by elevated ozone concentration, with this reduction being greater in 2008 (17–22%) than in 2007 (8–19%). Ozone elevation caused small but significant decrease in brown rice percentage, but greatly increased head rice percentage by 8.8%. Chalky grain percentage increased (5.8%) due to ozone elevation, while chalkiness area and chalkiness degree remaining unchanged. Although the amylose concentration of rice grains was marginally reduced, starch pasting properties demonstrated that grains in elevated ozone concentration had lower breakdown (7.7%) and higher setback value (25.2%) and gelatinization temperature (0.9°C) than those grown in ambient conditions. Nutrition evaluation indicated that ozone exposure tended to increase the concentrations of protein and all mineral elements analyzed (i.e., K, Mg, Ca, Fe, Zn, Mn and Cu), but the contents of protein and mineral elements in harvested grains were unchanged or reduced. For most traits of grain quality, the year effect was significant, however, its interaction with ozone was not detected. Our results suggested that long-term exposure to ozone-enriched atmospheres projected in the coming a few decades not only caused serious reductions in yield, but also tended to produce the deleterious effects upon grain quality of hybrid Shanyou 63 in terms of appearance and eating/cooking quality. [Copyright &y& Elsevier]

Abstract: A system for free-air concentration enrichment with ozone (FACE-O3) was installed in a field in Jiangsu Province of China to grow wheat and rice plants in either ambient [O3] (A-O3) or elevated [O3] (E-O3) without any enclosures. Ozone generated from pure O2 and mixed with compressed air was released into the E-O3 plots from a 14 m diameter octagon. The gas release was controlled for each E-O3 plot with an algorithm based on wind direction, wind speed and [O3] at the center of the plot. With 1-min mean [O3], the achieved elevation was within ±20% of the target, which is 50% above A-O3, for 94% of time, and within ±10% of the target for 73% of time on average across 4 years from 2007 to 2010. Ozone fumigation ran on daytime, but was withheld when ambient [O3] was below 20 ppb or leaves were wet. The discontinuity in O3 release resulted in the daily mean 7 h [O3] (M7, 900–1600 h Chinese Standard Time) in E-O3 by only 24% higher than that in A-O3. The average effective increase in AOT40 (accumulated [O3] above the threshold of 40 ppb) was 115%. Ozone exposure regime in E-O3 as characterized by M7 and AOT40 was compared with that in a scaled-up [O3] (S-O3), which was obtained by scaling A-O3 by 1.24: the ratio of M7 in E-O3 to that in A-O3. For the same M7, E-O3 had higher AOT40 than S-O3, because E-O3 had more high [O3] peaks than S-O3. The shift in AOT40 is only modest, however, and the [O3] regime in E-O3 was consistent with that in open-top chamber experiments in the past. This FACE-O3 system can thus maintain elevated [O3] in open field with modest alteration to [O3] regime to an extent comparable to open-top chambers. [Copyright &y& Elsevier]

Ozone is currently the most important air pollutant that negatively affects growth and yield of agricultural crops in most parts of the world, and rice is arguably the most important food crops on the planet. While a limited number of enclosure-based studies have examined the genotypic differences among rice (Oryza sativa L.) cultivars in response to increasing ozone concentration, no ozone experiment has been conducted to date under fully open-air field conditions to address this issue. In 2007, we conducted an experiment for the first time in the world with rice using free-air concentration enrichment (FACE) system at Xiaoji town, Jiangdu County, Jiangsu Province, China (119° 42′0″E, 32° 35′5″N). Four Chinese rice cultivars: Wujing 15 (WJ15, inbred japonica cultivar), Yangdao 6 (YD6, inbred indica cultivar), Shanyou 63 (SY63, three-line hybrid rice cultivar), Liangyoupeijiu (LYPJ, two-line hybrid rice cultivar), were grown at ambient or elevated (target at 50% above ambient) ozone concentration under nitrogen application rate of 15gNm−2. The ozone enhancement strongly accelerated phenologycal development of WJ15 and SY63, with maturity being reached by 4 and 8 days earlier, respectively, but only 1 day earlier for YD6 and LYPJ. Elevated ozone concentration reduced the number of mainstem leaves (ca. by half a leaf) and plant height at maturity (ca. by 3–5cm) of SY63 and LYPJ with no ozone effects detected in YD6 or WJ15. Among the cultivars tested, SY63 and LYPJ exhibited significant yield loss by exposure to ozone (−17.5%, −15%, respectively), while WJ15 and YD6 showed no responses. For all cultivars, no ozone effect was observed on panicle number per unit area as a result of no changes in both maximum tiller number or productive tiller ratio. However, the number of spikelets per panicle of SY63 and LYPJ showed a significant reduction due to ozone exposure, while those of WJ15 and YD6 remained unaffected. Meanwhile, ozone exposure also caused minor reductions in both filled spikelet percentage and individual grain mass. The results of this experiment indicated that yield loss due to ozone exposure differs among rice cultivars with hybrid cultivars (i.e., SY63 and LYPJ) exhibiting greater yield loss than inbred cultivars (i.e., WJ15 and YD6), which could be attributed to the suppression of spikelet formation in the hybrid cultivars under ozone stress. [Copyright &y& Elsevier]