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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.)

Increased concentrations of atmospheric CO2 are predicted to reduce the content of essential elements such as protein, zinc, and iron in C3 grains and legumes, threatening the nutrition of billions of people in the next 50 years. However, this prediction has mostly been limited to grain crops, and moreover, we have little information about either the underlying mechanism or an effective intervention to mitigate these reductions. Here, we present a broader picture of the reductions in elemental content among crops grown under elevated CO2 concentration. By using a new approach, flow analysis of elements, we show that lower absorption and/or translocation to grains is a key factor underlying such elemental changes. On the basis of these findings, we propose two effective interventions-namely, growing C4 instead of C3 crops, and genetic improvements-to minimize the elemental changes in crops, and thereby avoid an impairment of human nutrition under conditions of elevated CO2., Competing Interests: The authors have declared that no competing interests exist.

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.)

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.

Background and Aims: Influences of rising global CO(2) concentration and temperature on plant growth and ecosystem function have become major concerns, but how photosynthesis changes with CO(2) and temperature in the field is poorly understood. Therefore, studies were made of the effect of elevated CO(2) on temperature dependence of photosynthetic rates in rice (Oryza sativa) grown in a paddy field, in relation to seasons in two years., Methods: Photosynthetic rates were determined monthly for rice grown under free-air CO(2) enrichment (FACE) compared to the normal atmosphere (570 vs 370 micromol mol(-1)). Temperature dependence of the maximum rate of RuBP (ribulose-1,5-bisphosphate) carboxylation (V(cmax)) and the maximum rate of electron transport (J(max)) were analysed with the Arrhenius equation. The photosynthesis-temperature response was reconstructed to determine the optimal temperature (T(opt)) that maximizes the photosynthetic rate., Key Results and Conclusions: There was both an increase in the absolute value of the light-saturated photosynthetic rate at growth CO(2) (P(growth)) and an increase in T(opt) for P(growth) caused by elevated CO(2) in FACE conditions. Seasonal decrease in P(growth) was associated with a decrease in nitrogen content per unit leaf area (N(area)) and thus in the maximum rate of electron transport (J(max)) and the maximum rate of RuBP carboxylation (V(cmax)). At ambient CO(2), T(opt) increased with increasing growth temperature due mainly to increasing activation energy of V(cmax). At elevated CO(2), T(opt) did not show a clear seasonal trend. Temperature dependence of photosynthesis was changed by seasonal climate and plant nitrogen status, which differed between ambient and elevated CO(2).

An increase in atmospheric CO(2) concentration ( [CO(2)]) is generally expected to enhance photosynthesis and biomass. Rice plants (Oryza sativa L.) were grown in ambient CO(2) (AMB) or free-air CO(2)-enrichment (FACE), in which the target [CO(2)] was 200 micromol mol(-1) above AMB. (13)CO(2) was fed to the plants at different stages so we could examine the partitioning of photosynthates. Furthermore, canopy photosynthesis and respiration were measured at those stages. The ratio of (13)C content in the whole plant to the amount of fixed (13)C under FACE was similar to that under AMB at the vegetative stage. However, the ratio under FACE was greater than the ratio under AMB at the grain-filling stage. At the vegetative stage, plants grown under FACE had a larger biomass than those grown under AMB owing to enhancement of canopy photosynthesis by the increased [CO(2)]. On the other hand, at the grain-filling stage, CO(2) enrichment promoted the partitioning of photosynthate to ears, and plants grown under FACE had a greater weight of ears. However, enhancement of ear weight by CO(2) enrichment was not as great as that of biomass at the vegetative stage. Plants grown under FACE did not necessarily show higher canopy photosynthetic rates at the grain-filling stage. Therefore, we concluded that the ear weight did not increase as much as biomass at the vegetative stage owing to a loss of the advantage in CO(2) gain during the grain-filling period.

Abstract: 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. [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]

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. [ABSTRACT FROM AUTHOR]

Understanding of leaf stomatal responses to the atmospheric CO2 concentration, [CO2], is essential for accurate prediction of plant water use under future climates. However, limited information is available for the diurnal and seasonal changes in stomatal conductance ( gs) under elevated [CO2]. We examined the factors responsible for variations in gs under elevated [CO2] with three rice cultivars grown in an open-field environment under flooded conditions during two growing seasons (a total of 2140 individual measurements). Conductance of all cultivars was generally higher in the morning and around noon than in the afternoon, and elevated [CO2] decreased gs by up to 64% over the 2 years (significantly on 26 out of 38 measurement days), with a mean gs decrease of 23%. We plotted the gs variations against three parameters from the Ball-Berry model and two revised versions of the model, and all parameters explained the gs variations well at each [CO2] in the morning and around noon ( R2 > 0.68), but could not explain these variations in the afternoon ( R2 < 0.33). The present results provide an important basis for modelling future water use in rice production. [ABSTRACT FROM AUTHOR]

Maturity group (based on the number of days to maturity) is an important growth trait for determining crop productivity, but there has been no attempt to examine the effects of elevated [CO2] on yield enhancement of rice cultivars with different maturity groups. Since early-maturing cultivars generally show higher plant N concentration than late-maturing cultivars, it is hypothesized that [CO2]-induced yield enhancement might be larger for early-maturing cultivars than late-maturing cultivars. To test this hypothesis, the effects of elevated [CO2] on yield components, biomass, N uptake, and leaf photosynthesis of cultivars with different maturity groups were examined for 2 years using a free-air CO2 enrichment (FACE). Elevated [CO2] significantly increased grain yield and the magnitude significantly differed among the cultivars as detected by a significant [CO2]×cultivar interaction. Two cultivars (one with early and one with late maturity) responded more strongly to elevated [CO2] than those with intermediate maturity, resulting mainly from increases in spikelet density. Biomass and N uptake at the heading stage were closely correlated with grain yield and spikelet density over [CO2] and cultivars. Our 2 year field trial rejected the hypothesis that earlier cultivars would respond more to elevated [CO2] than later cultivars, but it is revealed that the magnitude of the growth enhancement before heading is a useful criterion for selecting rice cultivars capable of adapting to elevated [CO2]. [ABSTRACT FROM PUBLISHER]

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 13C pulse-labeling experiment was conducted under ambient CO2 and free-air CO2 enrichment (FACE) conditions to understand how elevated CO2 affects the CH4 in soil bubbles and CH4 emissions from rice paddies. Two hills of rice plants enclosed by frames in ambient CO2 and FACE plots were labeled with 13CO2 at the panicle formation stage, and plants and soil bubbles were collected 2 and 51 days after the pulse labeling. CH4 and 13CH4 emissions were also measured by the closed-chamber method between the 2 bubble samplings. Conversion of photosynthate carbon to CH4 entrapped in soil bubbles and CH4 emission to the atmosphere occurred quickly, suggesting that recent photosynthates can be an important source of carbon for methanogenesis. About 1% of the 13C-labeled C taken up through photosynthesis was emitted as 13CH4 during the 7 weeks of measurement, most during the first 3 weeks after labeling. Total CH4 and 13CH4 emissions did not differ between the ambient CO2 and FACE treatments, because the entrapped CH4 in the soil and the root biomass were not affected by elevated CO2 levels in this study. [ABSTRACT FROM AUTHOR]

A comprehensive biogeochemistry model, DNDC, was revised to simulate crop growth and soil processes more explicitly and improve its ability to estimate methane (CH4) emission from rice paddy fields under a wide range of climatic and agronomic conditions. The revised model simulates rice growth by tracking photosynthesis, respiration, C allocation, tillering, and release of organic C and O2 from roots. For anaerobic soil processes, it quantifies the production of electron donors [H2 and dissolved organic carbon (DOC)] by decomposition and rice root exudation, and simulates CH4 production and other reductive reactions based on the availability of electron donors and acceptors (NO3−, Mn4+, Fe3+, and SO42−). Methane emission through rice is simulated by a diffusion routine based on the conductance of tillers and the CH4 concentration in soil water. The revised DNDC was tested against observations at three rice paddy sites in Japan and China with varying rice residue management and fertilization, and produced estimates consistent with observations for the variation in CH4 emission as a function of residue management. It also successfully predicted the negative effect of (NH4)2SO4 on CH4 emission, which the current model missed. Predicted CH4 emission was highly sensitive to the content of reducible soil Fe3+, which is the dominant electron acceptor in anaerobic soils. The revised DNDC generally gave acceptable predictions of seasonal CH4 emission, but not of daily CH4 fluxes, suggesting the model's immaturity in describing soil heterogeneity or rice cultivar-specific characteristics of CH4 transport. It also overestimated CH4 emission at one site in a year with low temperatures, suggesting uncertainty in root biomass estimates due to the model's failure to consider the temperature dependence of leaf area development. Nevertheless, the revised DNDC explicitly reflects the effects of soil electron donors and acceptors, and can be used to quantitatively estimate CH4 emissions from rice fields under a range of conditions. [ABSTRACT FROM AUTHOR]

Summary • Season-long effects of elevated CO2 concentration ([CO2 ]) on the carbon balance of the rice (Oryza sativa ) canopy are reported here. • The experiment was conducted in six sunlit, semiclosed growth chambers for an entire growing season. Rice plants (cv. Nipponbare) were grown at 350 µmol mol-1 [CO2 ] (ambient) in three chambers, or at 650 µmol mol-1 (elevated) in the other three chambers. Canopy net photosynthesis and night-time respiration were determined in the chambers by mass balance. • Both canopy gross photosynthesis and total respiration, through the entire growing season, were increased by the CO2 enrichment. But CO2 -induced variations in canopy carbon gain were mainly caused by changes in canopy photosynthesis. The enhancement of daily canopy gross photosynthesis by elevated [CO2 ] was 33.4% for the first 3 week, but it declined gradually and disappeared by heading. Enhancement of daily net carbon gain also decreased as rice plants grew. • These results show that the increase in rice biomass by elevated [CO2 ] results more from the increase in carbon gain at early rather than later stages of growth. [ABSTRACT FROM AUTHOR]

Summary • Season-long effects of elevated CO2 concentration ([CO2 ]) on the carbon balance of the rice (Oryza sativa ) canopy are reported here. • The experiment was conducted in six sunlit, semiclosed growth chambers for an entire growing season. Rice plants (cv. Nipponbare) were grown at 350 µmol mol-1 [CO2 ] (ambient) in three chambers, or at 650 µmol mol-1 (elevated) in the other three chambers. Canopy net photosynthesis and night-time respiration were determined in the chambers by mass balance. • Both canopy gross photosynthesis and total respiration, through the entire growing season, were increased by the CO2 enrichment. But CO2 -induced variations in canopy carbon gain were mainly caused by changes in canopy photosynthesis. The enhancement of daily canopy gross photosynthesis by elevated [CO2 ] was 33.4% for the first 3 week, but it declined gradually and disappeared by heading. Enhancement of daily net carbon gain also decreased as rice plants grew. • These results show that the increase in rice biomass by elevated [CO2 ] results more from the increase in carbon gain at early rather than later stages of growth. [ABSTRACT FROM AUTHOR]