Ecological issues related to ozone: agricultural issues

Growth and photosynthetic responses to ozone of Siebold's beech seedlings grown under elevated CO2 and soil nitrogen supply

Ozone (O₃) is a phytotoxic air pollutant, the adverse effects of which on growth and photosynthesis are modified by other environmental factors. In this study, we examined the combined effects of O₃, elevated CO₂, and soil nitrogen supply on Siebold's beech seedlings. Seedlings were grown under combinations of two levels of O₃ (low and two times ambient O₃ concentration), two levels of CO₂ (ambient and 700 ppm), and three levels of soil nitrogen supply (0, 50, and 100 kg N ha^-1 year^-1) during two growing seasons (2019 and 2020), with leaf photosynthetic traits being determined during the second season. We found that elevated CO₂ ameliorated O₃-induced reductions in photosynthetic activity, whereas the negative effects of O₃ on photosynthetic traits were enhanced by soil nitrogen supply. We observed three-factor interactions in photosynthetic traits, with the ameliorative effects of elevated CO₂ on O₃-induced reductions in the maximum rate of carboxylation being more pronounced under high than under low soil nitrogen conditions in July. In contrast, elevated CO₂-induced amelioration of the effects of O₃ on stomatal function-related traits was more pronounced under low soil nitrogen conditions. Although we observed several two- or three-factor interactions of gas and soil treatments with respect to leaf photosynthetic traits, the shoot to root dry mass (S/R) ratio was the only parameter for which a significant interaction was detected among seedling growth parameters. O₃ caused a significant increase in S/R under ambient CO₂ conditions, whereas no similar effects were observed under elevated CO₂ conditions. Collectively, our findings reveal the complex interactive effects of elevated CO₂ and soil nitrogen supply on the detrimental effects of O₃ on leaf photosynthetic traits, and highlight the importance of taking into consideration differences between the responses of CO₂ uptake and growth to these three environmental factors.

The Spectral Compositions of Light Changes Physiological Response of Chinese Cabbage to Elevated Ozone Concentration

The effects of ozone combined with other environmental factors remain an important topic of the research, both in connection with climate change and the possibility of using modern solutions in horticulture. In our experiment, we compared the influence of ozone (100 ppb) on photosynthesis and changes in the pigment composition of Chinese cabbage (Brassica rapa subsp. pekinensis) leaves depending on the spectral composition of light. We used white LED light (WL), a combination of red + green + blue (RGBL) with a dominant red component and white +blue (WBL) with a dominant blue component in comparison with the classic sodium lamp lighting (yellow light—YL). The values of the parameters describing the light-dependent phase of photosynthesis and the parameters of the gas exchange, as well as non-photosynthesis pigment contents, show that the spectral composition strongly differentiates the response of Chinese cabbage leaves to ozone. In general, the efficiency of photochemical reactions was the highest in YL, but after O₃ fumigation, it decreased. In plants growing in WL and WBL, the increase of O₃ concentration stimulated light photosynthesis reactions and led to the enhancement of transpiration, stomatal conductance and intracellular CO₂ concentration. Changes in photosynthetic activity were accompanied by an increase in the content of anthocyanins and flavonols.

Increasing co-occurrence of fine particulate matter and ground-level ozone extremes in the western United States

Wildfires and meteorological conditions influence the co-occurrence of multiple harmful air pollutants including fine particulate matter (PM_2.5) and ground-level ozone. We examine the spatiotemporal characteristics of PM_2.5/ozone co-occurrences and associated population exposure in the western United States (US). The frequency, spatial extent, and temporal persistence of extreme PM_2.5/ozone co-occurrences have increased significantly between 2001 and 2020, increasing annual population exposure to multiple harmful air pollutants by ~25 million person-days/year. Using a clustering methodology to characterize daily weather patterns, we identify significant increases in atmospheric ridging patterns conducive to widespread PM_2.5/ozone co-occurrences and population exposure. We further link the spatial extent of co-occurrence to the extent of extreme heat and wildfires. Our results suggest an increasing potential for co-occurring air pollution episodes in the western US with continued climate change.

First observation-based study on surface O3 trend in Indo-Gangetic Plain: Assessment of its impact on crop yield

Tropospheric ozone (O₃) is an important air pollutant which causes substantial losses in crop production. Increasing O₃ levels in India particularly in Indo-Gangetic Plain (IGP) is a major issue as it is reducing the crop yield. The present study is an attempt to determine the O₃ and its precursor trend using continuous ground-based observations at a suburban site in IGP. The study focuses on the overall characteristics of annual, monthly, diurnal and hourly measurements of O₃. Annual mean values of O₃ have shown an increment of 19.2% from 2010 to 2015. Similarly, nitrogen oxide (NO_x) levels increased by 30.2%. O₃ levels at the study site showed a significant increasing trend of 0.7 ppb/yr. The observed O₃ trend was analyzed in terms of changes in NO_x levels and meteorological parameters. No significant difference in meteorological parameters was observed during 2010-15, however, NO_x levels have shown an increasing trend of 0.9 ppb/yr. Further to quantify the impact of increasing O₃ on crops, ozone-related crop yield losses for rice and wheat crop were determined for the period 2010-15. AOT40 (accumulated ozone exposure over a threshold of 40 ppb) and M7 (mean 7-h O₃ mixing ratio from 09:00 to 15:59 LT) O₃ exposure metrics were used to calculate the reduction in crop yield during major crop growing seasons: Rabi and Kharif.

Spatiotemporal distribution of ground-level ozone in China at a city level

In recent years, ozone (O3) pollution in China has shown a worsening trend. Due to the vast territory of China, O3 pollution is a widespread and complex problem. It is vital to understand the current spatiotemporal distribution of O3 pollution in China. In this study, we collected hourly data on O3 concentrations in 338 cities from January 1, 2016, to February 28, 2019, to analyze O3 pollution in China from a spatiotemporal perspective. The spatial analysis showed that the O3 concentrations exceeded the limit in seven geographical regions of China to some extent, with more serious pollution in North, East, and Central China. The O3 concentrations in the eastern areas were usually higher than those in the western areas. The temporal analysis showed seasonal variations in O3 concentration, with the highest O3 concentration in the summer and the lowest in the winter. The weekend effect, which occurs in other countries (such as the USA), was found only in some cities in China. We also found that the highest O3 concentration usually occurred in the afternoon and the lowest was in the early morning. The comprehensive analysis in this paper could improve our understanding of the severity of O3 pollution in China.

Evaluating the effects of surface O3 on three main food crops across China during 2015-2018

In order to tackle China's severe air pollution issue, the government has released the "Air Pollution Prevention and Control Action Plan" (known simply as the "Action Plan") since 2013. A recent study reported a decreased trend in PM_2.5 concentrations over 2013-2017, but O₃ pollution has become more serious. However, the effects of surface O₃ on crops are unclear after the implementation of the "Action Plan". Here, we evaluated the potential negative effects of surface O₃ on three main food crops (winter wheat, maize and rice) across China during 2015-2018 using nationwide O₃ monitoring data and AOT40-yield response functions. Results suggested that mean O₃ concentration, AOT40 and relative yield loss in China showed an overall upward trend from 2015 to 2018. During winter wheat, maize, single rice, double-early rice, and double-late rice growing seasons, mean O₃ concentration in recent years ranged from 38.6 to 46.9 ppb, 40.2-43.9 ppb, 39.3-42.2 ppb, 33.8-40.0 ppb, and 35.9-39.1 ppb, respectively, and AOT40 mean values ranged from 8.5 to 14.3 ppm h, 10.5-13.4 ppm h, 9.8-11.9 ppm h, 5.2-9.2 ppm h, and 8.0-9.5 ppm h, respectively. O₃-induced yield reductions were estimated to range from 20.1 to 33.3% for winter wheat, 5.0-6.3% for maize, 7.3-8.8% for single rice, 3.9-6.8% for double-early rice and 5.9-7.1% for double-late rice. O₃-induced production losses for winter wheat, maize, single rice, double-early rice, and double-late rice totaled 39.5-88.2 million metric tons, 12.6-21.0 million metric tons, 9.5-11.3 million metric tons, 1.2-1.8 million metric tons, and 2.2-2.7 million metric tons, respectively, and the corresponding economic losses totaled 14.3-32.0 billion US$, 3.9-6.5 billion US$, 3.9-4.6 billion US$, 0.5-0.7 billion US$, and 0.9-1.1 billion US$, respectively. Our results suggested that the government should take effective measures to reduce O₃ pollution and its effects on agricultural production.

Interdecadal Variations of the Midlatitude Ozone Valleys in Summer

Using the ERA-Interim total column ozone data, the spatial distributions of the long-term mean of the global total ozone in summer are analyzed. The results demonstrate that there are three midlatitude ozone “valleys” on earth—they are centered over the Tibetan Plateau (TIP), the Rocky Mountains (ROM), and the Southwest Pacific (SWP), respectively. The interdecadal variations of the three ozone valleys are positively modulated by the solar radiation, and the TIP ozone’s correlation with the solar radiation gets maximized with a two-year lag. The interdecadal variation of the SWP ozone valley has a significantly negative relationship with the Pacific Decadal Oscillation (PDO) and the South Pacific quadrupole (SPQ). Warm sea surface temperature anomalies (SSTAs) associated with the SPQ strengthen the vertical ascending motion, which dilutes the high concentration ozone at high altitudes. The interdecadal variation of the ROM ozone valley is positively correlated with the PDO, leading by three years. The ROM ozone content is also modulated by SSTAs in the Indian Ocean basin (IOB) by the circumglobal teleconnection (CGT). The observed regional SSTAs can exert a significant impact on the regional and even global circulation, via which the ozone content in midlatitudes also varies.

Bibliometric Review of Research on Knowledge Management and Sustainability, 1994–2018

Even though Knowledge Management (KM) is already widely used in business and public sector organisations, it also has potentially important implications when applied to the concept of sustainability. This research review aimed to examine the topography of research on KM and Sustainability. A total of 3025 articles from 1994 to 2018 were selected and analysed using bibliometric analysis to identify the growth trajectory of this literature, identify influential researchers and documents, explore the intellectual structure of the knowledge base and identify topical trends. The review found a knowledge of moderate but rapidly growing size. Key authors and documents were identified who can serve as guiding references for scholars entering this field of sustainability studies. Author co-citation analysis yielded a network map visualising the intellectual structure of this knowledge base which consisted of four Schools of Thought: Knowledge Management for Sustainability, Socio-Ecological System, Sustainability Science, KM for Sustainability Application. Keyword analysis highlighted climate change, learning, communities of practice and socio-economic management as topical trends emerging in the research front of this knowledge base. As the first bibliometric review of the KM and Sustainability literature, the findings from this paper establish a baseline for scholarship in this field which can be as a benchmark as the field continues to evolve in the future.

Leaf Traits That Contribute to Differential Ozone Response in Ozone-Tolerant and Sensitive Soybean Genotypes

Ozone (O₃) is a phytotoxic air pollutant that limits crop productivity. Breeding efforts to improve yield under elevated O₃ conditions will benefit from understanding the mechanisms that contribute to O₃ tolerance. In this study, leaf gas exchange and antioxidant metabolites were compared in soybean genotypes (Glycine max (L.) Merr) differing in ozone sensitivity. Mandarin (Ottawa) (O₃-sensitive) and Fiskeby III (O₃-tolerant) plants grown under charcoal-filtered (CF) air conditions for three weeks were exposed for five days to either CF conditions or 70 ppb O₃ in continuously stirred tank reactors (CSTRs) in a greenhouse. In the CF controls, stomatal conductance was approximately 36% lower for Fiskeby III relative to Mandarin (Ottawa) while the two genotypes exhibited similar levels of photosynthesis. Ozone exposure induced significant foliar injury on leaves of Mandarin (Ottawa) associated with declines in both stomatal conductance (by 77%) and photosynthesis (by 38%). In contrast, O₃ exposure resulted in minimal foliar injury on leaves of Fiskeby III with only a small decline in photosynthesis (by 5%), and a further decline in stomatal conductance (by 30%). There was a general trend towards higher ascorbic acid content in leaves of Fiskeby III than in Mandarin (Ottawa) regardless of treatment. The results confirm Fiskeby III to be an O₃-tolerant genotype and suggest that reduced stomatal conductance contributes to the observed O₃ tolerance through limiting O₃ uptake by the plant. Reduced stomatal conductance was associated with enhanced water-use efficiency, providing a potential link between O₃ tolerance and drought tolerance.

Predicting ozone levels from climatic parameters and leaf traits of Bel-W3 tobacco variety

Air pollution has been identified as a major cause of environmental and human health damage. O3 is an oxidative pollutant that causes leaf symptoms in sensitive plants. This study aims to adjust a multilinear model for the monitoring of O3 in subtropical climatic conditions by associating O3 concentrations with measurements of morphological leaf traits in tobacco plants and different environmental variables. The plants were distributed into five areas (residential, urban or industrial) in the southern region of Brazil and exposed during 14 periods, of 14 days each, during the years of 2014 and 2015. The environmental variables and leaf traits during the exposure periods were described by mean, median, standard deviation and minimum and maximum values. Spearman correlation and multiple linear regression analyses were applied on data from exposure periods. Leaf injury index, leaf area, leaf dry mass, temperature, relative humidity, global solar radiation and accumulated rainfall were used in the regression analyses to select the best models for predicting O3 concentrations. Leaf injury characteristically caused by O3 was verified in all areas and periods of plant exposure. Higher values of leaf injury (24.5% and 27.7%) were registered in the 13th and 12th exposure periods during spring and in areas influenced by urban and industrial clutches. The VPD, temperature, global solar radiation and O3 were correlated to leaf injury. Environmental variables [leaf area, leaf dry mass, global solar radiation and accumulated rainfall] and primarily the VPD were fundamental to improve the adjustments done in the bioindicator model (R2 ≥ 0.73). Our research shows that biomonitoring employing the tobacco "Bel-W3" can be improved by measuring morphological leaf traits and meteorological parameters. Additionally, O3 fumigation experiment should be performed with biomonitoring as conducted in this study, which are useful in understanding the role of other environmental factors.

Growth and nutrition of Agelastica coerulea (Coleoptera: Chrysomelidae) larvae changed when fed with leaves obtained from an O3-enriched atmosphere

A series of laboratory no-choice assays were performed to test changes in the feeding, growth, and nutrition of leaf beetle (Agelastica coerulea) larval instars on O₃-treated leaves of Japanese white birch (Betula platyphylla var. japonica). Larvae fed with O₃-treated leaves grew and developed significantly faster throughout their developmental cycle than the corresponding controls. The growth rate (GR) and consumption index (CI) were mostly decreased with age for both control and O₃-treated leaves. Efficiency of conversion of both ingested and digested food (ECI, ECD) showed an increase from the 2nd to the 4th instar, after which they decreased significantly and reached the lowest value in the last larval instars (7th). GR, CI, ECI, and ECD were greater and approximate digestibility (AD) was lower in larvae fed with O₃-treated leaves than those fed with control leaves. This indicated that the greater rate of growth on fumigated leaves was due primarily to a greater rate of consumption (i.e., O₃ increased the "acceptability" of the host more than "suitability") and efficiency in converting food into body mass. Overall, larval performance seemed to have improved when fed with O₃-treated leaves in these assays. This study suggests that insects may be more injurious to O₃-treated plants and warrants further investigations on birch-beetle interactions under field conditions.

Impact of Ethylene diurea (EDU) on growth, yield and proteome of two winter wheat varieties under high ambient ozone phytotoxicity

The present study evaluated the impact of high ambient O₃ on morphological, physiological and biochemical traits and leaf proteome in two high-yielding varieties of wheat using ethylene diurea (EDU) as foliar spray (200 and 300 ppm). Average ambient ozone concentration was 60 ppb which was more than sufficient to cause phytotoxic effects. EDU treatment resulted in less lipid peroxidation along with increased chlorophyll content, biomass and yield. EDU alleviated the negative effects of ozone by enhancing activities of antioxidants and antioxidative enzymes. Two dimensional electrophoresis (2DGE) analysis revealed massive changes in protein abundance in Kundan at vegetative stage (50% proteins were increased, 20% were decreased) and at flowering stage (25% increased, 18% decreased). In PBW 343 at both the developmental stages about 15% proteins were increased whereas 20% were decreased in abundance. Higher abundance of proteins related to carbon metabolism, defense and photorespiration conferred tolerance to EDU treated Kundan. In PBW343, EDU provided incomplete protection as evidenced by low abundance of many primary metabolism related proteins. Proteomic changes in response to EDU treatment in two varieties are discussed in relation to growth and yield.

Assessment of ozone toxicity among 14 Indian wheat cultivars under field conditions: growth and productivity

Tropospheric ozone (O₃) 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 O₃. In this study, 14 wheat cultivars widely grown in India were exposed to 30 ppb elevated O₃ above ambient level using open top chambers to evaluate their response against O₃ 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 O₃, 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 O₃ 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 O₃-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 O₃ 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 O₃.

Measurement of hydrogen peroxide and organic hydroperoxide concentrations during autumn in Beijing, China

Gaseous peroxides play important roles in atmospheric chemistry. To understand the pathways of the formation and removal of peroxides, atmospheric peroxide concentrations and their controlling factors were measured from 7:00 to 20:00 in September, October, and November 2013 at a heavily trafficked residential site in Beijing, China, with average concentrations of hydrogen peroxide (H₂O₂) and methyl hydroperoxide (MHP) at 0.55ppb and 0.063ppb, respectively. H₂O₂ concentrations were higher in the afternoon and lower in the morning and evening, while MHP concentrations did not exhibit a regular diurnal pattern. Both H₂O₂ and MHP concentrations increased at dusk in most cases. Both peroxides displayed monthly variations with higher concentrations in September. These results suggested that photochemical activity was the main controlling factor on variations of H₂O₂ concentrations during the measurement period. Increasing concentrations of volatile organic compounds emitted by motor vehicles were important contributors to H₂O₂ and MHP enrichment. High levels of H₂O₂ and MHP concentrations which occurred during the measurement period probably resulted from the transport of a polluted air mass with high water vapor content passing over the Bohai Bay, China.

Ozone alters the feeding behavior of the leaf beetle Agelastica coerulea (Coleoptera: Chrysomelidae) into leaves of Japanese white birch (Betula platyphylla var. japonica)

High mixing ratios of ground-level O₃ threaten trophic interactions. In the present study, we conducted laboratory assays, where insect larvae and adults were not directly exposed to O₃, to test the feeding behavior and attraction of the coleopteran leaf beetle Agelastica coerulea to early and late leaves of Japanese white birch (Betula platyphylla var. japonica) treated with ambient or elevated O₃ levels. We found that overwintered adults were not deterred from grazing elevated O₃-treated leaves, but rather preferred them than ambient O₃-treated ones. We also found that the feeding behavior of 2nd instar larvae fed on early or late leaves was not influenced by the O₃ treatment of the leaves when larvae could choose leaves. These observations of the adults and larvae feeding preferences contradict prior observations in the field conditions where the insects avoided leaves in O₃-enriched atmosphere. Since adults preferred elevated O₃-exposed leaves in the present laboratory assays, it is worthy of further investigations whether adults change their grazing preference so as to ensure the leaf palatability as a feeding source for their larvae. Hence, new direction towards detailed ovipositional behavior surveys under field conditions is encouraged.

An economic assessment of the health effects and crop yield losses caused by air pollution in mainland China

Air pollution is severe in China, and pollutants such as PM_2.5 and surface O₃ may cause major damage to human health and crops, respectively. Few studies have considered the health effects of PM_2.5 or the loss of crop yields due to surface O₃ using model-simulated air pollution data in China. We used gridded outputs from the WRF-Chem model, high resolution population data, and crop yield data to evaluate the effects on human health and crop yield in mainland China. Our results showed that outdoor PM_2.5 pollution was responsible for 1.70-1.99 million cases of all-cause mortality in 2006. The economic costs of these health effects were estimated to be 151.1-176.9 billion USD, of which 90% were attributed to mortality. The estimated crop yield losses for wheat, rice, maize, and soybean were approximately 9, 4.6, 0.44, and 0.34 million tons, respectively, resulting in economic losses of 3.4 billion USD. The total economic losses due to ambient air pollution were estimated to be 154.5-180.3 billion USD, accounting for approximately 5.7%-6.6% of the total GDP of China in 2006. Our results show that both population health and staple crop yields in China have been significantly affected by exposure to air pollution. Measures should be taken to reduce emissions, improve air quality, and mitigate the economic loss.

Bulk C, H, O, and fatty acid C stable isotope analyses for purity assessment of vegetable oils from the southern and northern hemispheres

RATIONALE

The carbon, hydrogen and oxygen stable isotope composition (δ¹³ C, δ² H, and δ¹⁸ O values) of plants and their products is linked to photosynthetic fractionation, environmental factors and agricultural practices. Therefore, they contribute to determining the purity of commercial vegetable oils and may provide information on their geographical origin.

METHODS

Maize, olive, sunflower, groundnut, soybean and rice oils differing in sites of growth in the southern and northern hemispheres were characterized by bulk oil stable isotope ratios (δ¹³ C_bulk , δ² H_bulk , and δ¹⁸ O_bulk values), fatty acid (FA) concentrations and δ¹³ C_FA values using elemental analysis/isotope ratio mass spectrometry, gas chromatography/mass spectrometry, gas chromatography/flame ionization detection and gas chromatography/combustion/isotope ratio mass spectrometry. Principal component analysis was applied to examine the inherent structure of the data.

RESULTS

The δ¹³ C_bulk values of maize oils (-18.4 to -14.9 ‰) are typical for C₄ plants, and those of olive (-30.2 to -28.2 ‰), sunflower (-30.2 to -29.2 ‰), groundnut (-29.3 ‰), soybean (-30.6 ‰), and rice (-34.5 ‰) oils are typical for C₃ plants. The δ² H_bulk values vary from -161 to -132 ‰ for maize oils and -171 to -109 ‰ for C₃ oils. The δ¹⁸ O_bulk values of all oils vary between 15.2 and 38.9 ‰. The major δ¹³ C_FA differences (>5 ‰) within plant species render the inter-C₃ -species comparison difficult. These differences are explained in terms of variations in the lipid biosynthetic pathways and blend of vegetable oils of different FA composition and δ¹³ C_FA values. The samples from the southern hemisphere are generally enriched in ¹³ C compared with those from the northern hemisphere. Differences between the southern and northern hemispheres were observed in δ² H (p < 0.001) and δ¹⁸ O_bulk (p = 0.129) values for all C₃ oils, and in δ¹³ C_18:1 (p = 0.026) and δ¹⁸ O_bulk (p = 0.160) values for maize oils.

CONCLUSIONS

The results of this study show that combining bulk and molecular stable isotope ratios, FA compositions and their statistical analysis helps the characterization of the geographic origin of oils. This methodology can be used to detect and source impurities in valuable vegetable oils commercialized worldwide. Copyright © 2016 John Wiley & Sons, Ltd.

Assessment of rice yield loss due to exposure to ozone pollution in Southern Vietnam

The study domain covered the Eastern region of Southern of Vietnam that includes Ho Chi Minh City (HCMC) and five other provinces. Rice production in the domain accounted for 13% of the national total with three crop cycles per year. We assessed ozone (O3) induced rice production loss in the domain for 2010 using simulated hourly surface O3 concentrations (WRF/CAMx; 4km resolution). Simulated O3 was higher in January-February (largely overlaps the first crop) and September-December (third crop), and lower in March-June (second crop). Spatially, O3 was higher in downwind locations of HCMC and were comparable with observed data. Relative yield loss (RYL) was assessed for each crop over the respective growing period (105days) using three metrics: AOT40, M7 and flux-based O3 dose of POD10. Higher RYL was estimated for the downwind of HCMC. Overall, the rice production loss due to O3 exposure in the study domain in 2010 was the highest for the first crop (up to 25,800metrictons), the second highest for the third crop (up to 21,500tons) and the least for the second crop (up to 6800tons). The low RYL obtained for the second crop by POD10 may be due to the use of a high threshold value (Y=10nmolm(-2)s(-1)). Linear regression between non-null radiation POD0 and POD10 had similar slopes for the first and third crop when POD0 was higher and very low slope for the second crop when POD0 was low. The results of this study can be used for the rice crop planning to avoid the period of potential high RYL due to O3 exposure.

Spatiotemporal trends in ground-level ozone concentrations and metrics in France over the time period 1999-2012

The hourly ozone (O3) data from 332 background monitoring stations, spread in France, were analyzed over the period 1999-2012 and short-term trends were calculated. In the current climate change context, the calculation of human health- and vegetation-relevant metrics, and of associated trends, provides a consistent method to establish proper and effective policies to reduce the adverse O3 effects. The generation of optimal O3 maps, for risk and exposure assessment, is challenging. To overcome this issue, starting from a set of stations, a hybrid regression-interpolation approach was proposed. Annual surface O3 metrics, O3 human health metrics (number of exceedances of daily maximum 8-h values greater than 60 ppb and SOMO35) and O3 vegetation impact metrics (AOT40 for vegetation and forests) were investigated at individual sites. Citizens are more exposed to high O3 levels in rural areas than people living in the cities. The annual mean concentrations decreased by -0.12ppbyear(-1) at rural stations, and the significant reduction at 67% of stations, particularly during the warm season, in the number of episodic high O3 concentrations (e.g. 98th percentile, -0.19ppbyear(-1)) can be associated with the substantial reductions in NOx and VOCs emissions in the EU-28 countries since the early 1990s Inversely, the O3 background level is rising at 76% of urban sites (+0.14ppbyear(-1)), particularly during the cold period. This rise can be attributed to increases in imported O3 by long-range transport and to a low O3 titration by NO due to the reduction in local NOx emissions. The decrease in health-related and vegetation-relevant O3 metrics, at almost all stations, is driven by decreases in regional photochemical O3 formation and in peak O3 concentrations. The short-term trends highlight that the threat to population and vegetation declined between 1999 and 2012 in France, demonstrating the success of European control strategies over the last 20 years. However, for all exposure metrics, the issue of non-attainment of the target value for O3 persists in comparison with the objectives of air quality directives. The region at highest O3 risk is the South-eastern France. This study contains new information on the i) spatial distribution of surface O3 concentration, ii) exceedances and iii) trends to define more suitable standards for human health and environmental protection in France.

The impacts of surface ozone pollution on winter wheat productivity in China--An econometric approach

The impact of surface ozone pollution on winter wheat yield is empirically estimated by considering socio-economic and weather determinants. This research is the first to use an economic framework to estimate the ozone impact, and a unique county-level panel is employed to examine the impact of the increasing surface ozone concentration on the productivity of winter wheat in China. In general, the increment of surface ozone concentration during the ozone-sensitive period of winter wheat is determined to be harmful to its yield, and a conservative reduction of ozone pollution could significantly increase China's wheat supply.

Diel trends in stomatal response to ozone and water deficit: a unique relationship of midday values to growth and allometry in Pima cotton?

Plant responses to ozone (O3 ) and water deficit (WD) are commonly observed, although less is known about their interaction. Stomatal conductance (gs ) is both an impact of these stressors and a protective response to them. Stomatal closure reduces inward flux of O3 and outward flux of water. Stomatal measurements are generally obtained at midday when gas exchange is maximal, but these may not be adequate surrogates for stomatal responses observed at other times of day, nor for non-stomatal responses. Here, we find in Pima cotton that stomatal responses to O3 observed at midday do not reflect responses at other times. Stomata were more responsive to O3 and WD near midday, despite being at quasi-steady state, than during periods of active opening or closing in morning or evening. Stomatal responsivity to O3 was not coincident with maximum gas exchange or with periods of active regulation, but coincident with plant sensitivity to O3 previously determined in this cultivar. Responses of pigmentation and shoot productivity were more closely related to stomatal responses at midday than to responses at other times of day under well-watered (WW) conditions, reflecting higher stomatal responsivity, sensitivity to O3 , and magnitude of midday gs . Under WD conditions, shoot responses were more closely related to early morning gs. Root responses were more closely related to early morning gs under both WW and WD. Responses of stomata to O3 at midday were not good surrogates for stomatal responses early or late in the day, and may not adequately predicting O3 flux under WD or when maximum ambient concentrations do not occur near midday.

Biochemical and physiological characteristics of tropical mung bean (Vigna radiata L.) cultivars against chronic ozone stress: an insight to cultivar-specific response

Surface-level ozone (O3) has been regarded as one of the most significant phytotoxic pollutants worldwide. Investigations addressing adverse impacts of elevated O3 on mung bean (Vigna radiata L.), an important leguminous crop of the Indian subcontinent, are still limited. The present study analyzed the differences on the foliar injury, reactive oxygen species (ROS) generation, antioxidative defense system, physiology, and foliar protein profile of two tropical mung bean cultivars (HUM-2 and HUM-6) exposed to elevated O3 under near-natural conditions. Both cultivars were negatively affected by the pollutant, but the response was cultivar-specific. Results revealed that elevated O3 induced higher levels of ROS (O2 (·-) and H2O2) and lipid peroxidation leading to greater foliar injury in HUM-2 compared to HUM-6. Photosynthetic pigments, photosynthetic rate, stomatal conductance, and photochemical efficiency reduced under elevated O3 exposure and the extent of reduction was higher in HUM-2. Principal component analysis revealed that photosynthetic performance and quantum yield were drastically affected in HUM-2 as compared to HUM-6. Activities of antioxidative enzymes were also stimulated, suggesting generation of oxidative stress under elevated O3. HUM-6 showed higher induction of antioxidative enzymes than HUM-2. One-dimensional gel electrophoresis analysis showed drastic reductions in the abundantly present ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) large and small subunits and the decrease was higher in HUM-2. Altogether, results suggested that higher accumulation of ROS and limited induction of antioxidant defense system led to more leaf injury and impairment of photosynthesis in HUM-2 than HUM-6 depicting its higher sensitivity towards elevated O3.

Effects of elevated ozone concentration on CH4 and N2O emission from paddy soil under fully open-air field conditions

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.

Fructans, ascorbate peroxidase, and hydrogen peroxide in ryegrass exposed to ozone under contrasting meteorological conditions

Ozone (O3) is the most abundant tropospheric oxidant as well as an important component of photochemical pollution. Once inside the plant, ozone can produce reactive oxygen species that change the antioxidative pool and the carbohydrate metabolism. The current study aimed to analyze whether the contents and the composition of the fructan, the ascorbate peroxidase activity, and the H2O2 accumulation were changed in Lolium multiflorum ssp. italicum cv. Lema plants as response to short-term exposure to ozone and/or to different meteorological conditions, in two contrasting seasons (winter and summer). Results showed that higher solar radiation tends to decrease fructose content and, along with temperature, increases the ascorbate peroxidase (APX) activity. Such activity and levels of fructans practically did not vary during the time the experiment was being done, but APX daylight variation was modified by the ozone. Thus, the higher levels of this pollutant decreased the APX activity and increased fructose content, as well as changed the size of the fructan chains. Hydrogen peroxide (H2O2) accumulation was higher in plants that were fumigated with ozone when compared to the control, and it decreased throughout the day. As a conclusion, fructan contents increased when the APX activity decreased. It suggested that fructans could also help the defense system when there is a reduction on the APX activity in the plant.

Elevated tropospheric ozone increased grain protein and amino acid content of a hybrid rice without manipulation by planting density

BACKGROUND

Rising tropospheric ozone affects crop yield and quality. Rice protein concentration, which is closely associated with eating/cooking quality, is of critical importance to nutritional quality. The ozone effect on amino acids of rice grains was little known, especially grown under different cultivation conditions. A hybrid rice cultivar Shanyou 63 was grown in 2010 and 2011 to investigate the interactive effect of ozone exposure and planting density on rice protein quality in a free-air ozone enrichment system.

RESULTS

The content of protein, total amino acids (TAA), total essential (TEAA) and non-essential amino acids (TNEAA) in rice grain was increased by 12-14% with elevated ozone. A similar significant response to ozone was observed for concentrations of the seven essential and eight non-essential amino acids. In contrast, elevated ozone caused a small but significant decrease in percentage of TEAA to TAA. The year effect was significant for all measured traits; however, interactions of ozone with year or planting density were not detected.

CONCLUSION

The study suggested that season-long elevation of ozone concentration to projected 2050 levels will increase protein and amino acids of Shanyou 63, and crop management such as changing planting density might not alter the impact.

Screening of Bangladeshi winter wheat (Triticum aestivum L.) cultivars for sensitivity to ozone

The sensitivity to ozone of ten Bangladeshi wheat cultivars was tested by exposing plants to eight ozone exposure regimes (50, 60, 80, 100, 120, 135, 150, and 200 ppb for 14, 11, 8, 6, 5, 4, 3, and 1 days, respectively, for 8 h/day) in controlled environment chambers. Visible leaf injury, dry weight, chlorophyll, carotenoid content, leaf greenness (SPAD value), quantum yield of photosynthesis, and stomatal resistance were measured to evaluate response. Shoot biomass, total chlorophyll, leaf greenness, and carotenoid content were reduced in ozone-exposed plants. Based on the results of principal component analysis (PCA)-biplot analysis, the order of sensitivity to ozone was: Akbar >> Sufi ≥ Bijoy ≥ Shatabdi > Bari-26 ≥ Gourab > Bari-25 ≥ Prodip ≥ Sourav >> Kanchan. The most important parameters to discriminate cultivars with respect to ozone sensitivity were visible injury and chlorophyll b/a ratio, whereas quantum yield of photosynthesis was less important. Differences in stomatal resistance were not a significant factor in ozone response. Regression of cultivars' PCA scores against year of release revealed no trend, suggesting that ozone tolerance was not incorporated during cultivar breeding.

Phenolic compounds and antioxidant ability responses to experimental free-air ozone exposure in two wheat cultivars

Effects of elevated ozone concentrations [O3] on two wheat (Triticum aestivum L.) cultivars [Yangmai16 (Y16) and Yannong19 (Y19)] were investigated to determine the different metabolic mechanisms of phenolic compounds under O3-FACE (free-air controlled enrichment) condition. This study specifically investigated changes of phenolic compounds content, secondary metabolism related enzymes activities, lipid peroxidation extent and reactive oxygen species (ROS) content in the leaves of two wheat cultivars. Results indicated that elevated [O3] (1.5 × ambient [O3]) induced different regulation mechanisms of secondary metabolism in different wheat cultivars. Lipid peroxidation and ROS content increased under O3 stress, and these results were more pronounced in the leaves of Y19 than in those of Y16, suggesting that Y19 is more sensitive to O3 than Y16.

Contrasting physiological responses of ozone-tolerant Phaseolus vulgaris and Nicotiana tobaccum varieties to ozone and nitric acid

Ozone (O3) and nitric acid (HNO3) are synthesized by the same atmospheric photochemical processes and are almost always co-pollutants. Effects of O3 on plants have been well-elucidated, yet less is known about the effects of HNO3 on plants. We investigated the physiological effects of experimental O3 and HNO3 fumigation on Phaseolus vulgaris (snap bean) and Nicotiana tobaccum (tobacco) varieties with known sensitivity to O3, but unknown responses to HNO3. Responses were measured as leaf absorptance, aboveground plant biomass, and photosynthetic CO2-response curve parameters. Our results demonstrate that O3 reduced absorptance, stomatal conductance and plant biomass in both species, and maximum photosynthetic rate in P. vulgaris, whereas the main effect of HNO3 was an increase in mesophyll conductance. Overall, the results suggest that HNO3 affects mesophyll conductance through increased nitrogen absorbed by leaves during HNO3 deposition which in turn increases photosynthetic demand for CO2, or that damage to epicuticular waxes on leaves increased diffusion of CO2 to sites of carboxylation.

Gas exchange and chlorophyll fluorescence of pea (Pisum sativum L.) plants in response to ambient ozone at a rural site in Egypt

Egyptian pea cultivars (Pisum sativum L. cultivars Little Marvel, Perfection and Victory) grown in open-top chambers were exposed to either charcoal-filtered (FA) or non-filtered air (NF) for five consecutive years (2009-2013) at a rural site in northern Egypt. Net photosynthetic rates (PN), stomatal conductance (gs), intercellular CO2 (Ci) and chlorophyll fluorescence were measured. Ozone (O3) was found to be the most prevalent pollutant common at the rural site and is suspected to be involved in the alteration of the physiological parameters measured in the present investigation. PN of different cultivars were found to respond similarly; decreases of 23, 29 and 39% were observed in the cultivars Perfection, Little Marvel and Victory, respectively (averaged over the five years) due to ambient O3. The maximum impairment in PN was recorded in the cultivar Victory (46%) in 2013 when the highest O3 levels were recorded (90 nL L(-1)). The average stomatal conductance decreased by 20 and 18% in the cultivars Little Marvel and Perfection, respectively, while the average stomatal conductance increased on average by 27% in the cultivar Victory. A significant correlation was found between PN and Ci, indicating the importance of non-stomatal limitations of photosynthesis, especially in the cultivar Victory. The PN vs. Ci curves were fitted to a non-rectangular hyperbolic model. The actual quantum yield (ΦPSII) and photochemical quenching coefficient (qP) were significantly decreased in the leaves of plants exposed to NF air. Non-photochemical quenching (NPQ) was increased in all cultivars. Exposure to NF air caused reductions in chlorophyll (Chl a) of 19, 16 and 30% in the Little Marvel, Perfection and Victory cultivars, respectively.

Contrasting effects of water salinity and ozone concentration on two cultivars of durum wheat (Triticum durum Desf.) in Mediterranean conditions

This paper reports the results of an Open-Top Chambers experiment on the responses of two durum wheat cultivars (Neodur and Virgilio) exposed to two different levels of ozone (charcoal-filtered air and ozone-enriched air) and irrigation water salinity (tap water as control and a 75 mM NaCl solution once a week). The stomatal conductance of the flag leaves was measured on four dates during May. Flag leaf samples were collected to detect ozone visible leaf injuries. At the end of the growing season, the yield/biomass and grain quality parameters were assessed. Saline irrigation caused significant reductions in gs, yield and grain quality in Neodur, while Virgilio was more tolerant. The yield response to ozone was almost negligible, with Virgilio, despite the higher susceptibility to visible leaf injuries, being more productive than Neodur. The responses to the combined stress were not consistent, with the main tendencies undoubtedly driven by the saline irrigation factor.

High tolerance of subalpine grassland to long-term ozone exposure is independent of N input and climatic drivers

In a seven-year study, we tested effects of increased N and O3 deposition and climatic conditions on biomass of subalpine grassland. Ozone risk was assessed as exposure (AOT40) and as stomatal flux (POD0,1). We hypothesized that productivity is higher under N- and lower under O3 deposition, with interactions with climatic conditions. Aboveground biomass was best correlated with growing-degree days for May (GDDMay). Nitrogen deposition increased biomass up to 60% in the highest treatment, and 30% in the lowest addition. Also belowground biomass showed a positive N-response. Ozone enrichment had no effect on biomass, and no interaction between O3 and N was observed. Growth response to N deposition was not correlated to GDDMay or precipitation, but indicated a cumulative effect over time. Productivity of subalpine grassland is tolerant to increasing ozone exposure, independent of N input and climatic drivers. N deposition rates at current critical loads, strongly increase the grassland yield.

Assessment of competitive ability of two Indian wheat cultivars under ambient O3 at different developmental stages

The concentrations of O3 are increasing, which may have potential adverse effects on crop yield. This paper deals with assessing the intraspecific variability of two wheat cultivars (PBW 343 and M 533) at different growth stages using open top chambers. Mean O3 concentrations were 50.2 and 53.2 ppb, and AOT40 values were 9 and 12.1 ppm h, respectively, in 2008-2009 and 2009-2010. Reproductive stage showed higher AOT40 values (6.9 and 9.2 ppm h) compared to vegetative (2.23 and 2.9 ppm h). Critical levels of a 3-month AOT 40 of 3 ppm h led to 6% yield reduction in two wheat cultivars for two consecutive years. Variations in photosynthesis rate, stomatal conductance (gs), Fv/Fm ratio, photosynthetic pigments, primary and secondary metabolites, morphological parameters, and yield attributes were measured at vegetative and reproductive stages. Reductions in number of leaves, leaf area, total biomass, root/shoot ratio, RGR, photosynthetic pigments, protein content, and Fv/Fm ratio in PBW 343 were more than M 533 at reproductive stage. Photosynthetic rate did not vary between the cultivars, but gs was higher in PBW 343 compared to M 533 under ambient O3. Higher total phenolics and peroxidase activity were recorded in M 533 at reproductive stage conferring higher resistance at latter age. Results of O3 resistance showed that M 533 was sensitive compared to PBW 343 during vegetative stage but developed more resistance at reproductive stage. PBW 343 with larger leaf area and high gs is more sensitive than M 533 with smaller leaf area and low gs. The study suggests that the sensitivity varied with plant growth stage, and the plant showing higher sensitivity during vegetative period developed more resistance during reproductive period due to higher defense mechanism. Though the yield reductions were same in both cultivars under ambient O3, the mechanism of acquiring the resistance is different between the cultivars.

Signaling molecules and cell death in Melissa officinalis plants exposed to ozone

The study focuses on the interaction between reactive oxygen species and hormones that regulate the programmed cell death in plants of Melissa officinalis exposed to ozone. Interaction between hormone and redox signaling pathways has been investigated in ozone-stressed (200 ppb, 5 h) lemon balm to verify if the response resembles the biotic defense reactions. In comparison to controls, plants exhibited foliar injury and the cell death was induced by (1) biphasic production of hydrogen peroxide and superoxide radical; (2) hormonal regulation of ozone-induced lesion formation with a significant production of ethylene, salicylic, jasmonic and abscisic acid; (3) ozone degradation to reactive oxygen species and their detoxification by some enzymatic (such as superoxide dismutase) and non-enzymatic antioxidant systems (such as ascorbic acid, glutathione and carotenoids), that worked in cooperation without providing a defense against free radicals (such as confirmed by the modification of the antioxidant properties of leaf tissue). This integrated view showed that reactive oxygen species interact with hormonal signaling pathway regulating cell death and the sensitivity of lemon balm to ozone.

A projection of ozone-induced wheat production loss in China and India for the years 2000 and 2020 with exposure-based and flux-based approaches

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.

Stomata are less responsive to environmental stimuli in high background ozone in Dactylis glomerata and Ranunculus acris

Two mesotrophic grassland species, Ranunculus acris and Dactylis glomerata were exposed to a range of ozone treatments (16.2-89.5 ppb 24 h mean) and two watering regimes under naturally fluctuating photosynthetically active radiation (PAR), vapour pressure deficit (VPD) and temperature. Stomatal conductance was measured throughout the experiments, and the combined data set (>1000 measurements) was analysed for effects of low and high ozone on responses to environmental stimuli. We show that when D. glomerata and R. acris were grown in 72.6-89.5 ppb ozone the stomata consistently lose the ability to respond, or have reduced response, to naturally fluctuating environmental conditions in comparison to their response in low ozone. The maximum stomatal conductance (g(max)) was also significantly higher in the high ozone treatment for D. glomerata. We discuss the hypotheses for the reduced sensitivity of stomatal closure to a changing environment and the associated implications for ozone flux modelling.

Root and shoot gas exchange respond additively to moderate ozone and methyl jasmonate without induction of ethylene: ethylene is induced at higher O3 concentrations

The available literature is conflicting on the potential protection of plants against ozone (O(3)) injury by exogenous jasmonates, including methyl jasmonate (MeJA). Protective antagonistic interactions of O(3) and MeJA have been observed in some systems and purely additive effects in others. Here it is shown that chronic exposure to low to moderate O(3) concentrations (4-114 ppb; 12 h mean) and to MeJA induced additive reductions in carbon assimilation (A (n)) and root respiration (R (r)), and in calculated whole plant carbon balance. Neither this chronic O(3) regime nor MeJA induced emission of ethylene (ET) from the youngest fully expanded leaves. ET emission was induced by acute 3 h pulse exposure to much higher O(3) concentrations (685 ppb). ET emission was further enhanced in plants treated with MeJA. Responses of growth, allocation, photosynthesis, and respiration to moderate O(3) concentrations and to MeJA appear to be independent and additive, and not associated with emission of ET. These results suggest that responses of Pima cotton to environmentally relevant O(3) are not mediated by signalling pathways associated with ET and MeJA, though these pathways are inducible in this species and exhibit a synergistic O(3)×MeJA interaction at very high O(3) concentrations.

Implementation of a module for risk of ozone impacts assessment to vegetation in the Integrated Assessment Modelling system for the Iberian Peninsula. Evaluation for wheat and Holm oak

A module to estimate risks of ozone damage to vegetation has been implemented in the Integrated Assessment Modelling system for the Iberian Peninsula. It was applied to compute three different indexes for wheat and Holm oak; daylight AOT40 (cumulative ozone concentration over 40 ppb), cumulative ozone exposure index according to the Directive 2008/50/EC (AOT40-D) and POD(Y) (Phytotoxic Ozone Dose over a given threshold of Y nmol m(-2) s(-1)). The use of these indexes led to remarkable differences in spatial patterns of relative ozone risks on vegetation. Ozone critical levels were exceeded in most of the modelling domain and soil moisture content was found to have a significant impact on the results. According to the outputs of the model, daylight AOT40 constitutes a more conservative index than the AOT40-D. Additionally, flux-based estimations indicate high risk areas in Portugal for both wheat and Holm oak that are not identified by AOT-based methods.

A stomatal ozone flux-response relationship to assess ozone-induced yield loss of winter wheat in subtropical China

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.

The effects of tropospheric ozone on net primary productivity and implications for climate change

Tropospheric ozone (O(3)) is a global air pollutant that causes billions of dollars in lost plant productivity annually. It is an important anthropogenic greenhouse gas, and as a secondary air pollutant, it is present at high concentrations in rural areas far from industrial sources. It also reduces plant productivity by entering leaves through the stomata, generating other reactive oxygen species and causing oxidative stress, which in turn decreases photosynthesis, plant growth, and biomass accumulation. The deposition of O(3) into vegetation through stomata is an important sink for tropospheric O(3), but this sink is modified by other aspects of environmental change, including rising atmospheric carbon dioxide concentrations, rising temperature, altered precipitation, and nitrogen availability. We review the atmospheric chemistry governing tropospheric O(3) mass balance, the effects of O(3) on stomatal conductance and net primary productivity, and implications for agriculture, carbon sequestration, and climate change.

Tropospheric ozone and plants: absorption, responses, and consequences

Ozone is now considered to be the second most important gaseous pollutant in our environment. The phytotoxic potential of O₃ was first observed on grape foliage by B.L. Richards and coworkers in 1958 (Richards et al. 1958). To date, unsustainable resource utilization has turned this secondary pollutant into a major component of global climate change and a prime threat to agricultural production. The projected levels to which O₃ will increase are critically alarming and have become a major issue of concern for agriculturalists, biologists, environmentalists and others plants are soft targets for O₃. Ozone enters plants through stomata, where it disolves in the apoplastic fluid. O₃ has several potential effects on plants: direct reaction with cell membranes; conversion into ROS and H₂O₂ (which alters cellular function by causing cell death); induction of premature senescence; and induction of and up- or down-regulation of responsive components such as genes , proteins and metabolites. In this review we attempt to present an overview picture of plant O₃ interactions. We summarize the vast number of available reports on plant responses to O₃ at the morphological, physiological, cellular, biochemical levels, and address effects on crop yield, and on genes, proteins and metabolites. it is now clear that the machinery of photosynthesis, thereby decreasing the economic yield of most plants and inducing a common morphological symptom, called the "foliar injury". The "foliar injury" symptoms can be authentically utilized for biomonitoring of O₃ under natural conditions. Elevated O₃ stress has been convincingly demonstrated to trigger an antioxidative defense system in plants. The past several years have seen the development and application of high-throughput omics technologies (transcriptomics, proteomics, and metabolomics) that are capable of identifying and prolifiling the O₃-responsive components in model and nonmodel plants. Such studies have been carried out ans have generated an inventory of O₃-Responsive components--a great resource to the scientific community. Recently, it has been shown that certain organic chemicals ans elevated CO₂ levels are effective in ameliorating O₃-generated stress. Both targeted and highthroughput approaches have advanced our knowledge concerning what O₃-triggerred signaling and metabolic pathways exist in plants. Moreover, recently generated information, and several biomarkers for O₃, may, in the future, be exploited to better screen and develop O₃-tolerant plants.

Protection of plants from ambient ozone by applications of ethylenediurea (EDU): a meta-analytic review

A meta-analysis was conducted to quantitatively assess the effects of ethylenediurea (EDU) on ozone (O3) injury, growth, physiology and productivity of plants grown in ambient air conditions. Results indicated that EDU significantly reduced O3-caused visible injury by 76%, and increased photosynthetic rate by 8%, above-ground biomass by 7% and crop yield by 15% in comparison with non-EDU treated plants, suggesting that ozone reduces growth and yield under current ambient conditions. EDU significantly ameliorated the biomass and yield of crops and grasses, but had no significant effect on tree growth with an exception of stem diameter. EDU applied as a soil drench at a concentration of 200-400 mg/L has the highest positive effect on crops grown in the field. Long-term research on full-grown tree species is needed. In conclusion, EDU is a powerful tool for assessing effects of ambient [O3] on vegetation.

Effects of ozone on growth, yield and leaf gas exchange rates of four Bangladeshi cultivars of rice (Oryza sativa L.)

To assess the effects of tropospheric O3 on rice cultivated in Bangladesh, four Bangladeshi cultivars (BR11, BR14, BR28 and BR29) of rice (Oryza sativa L.) were exposed daily to charcoal-filtered air or O3 at 60 and 100 nl l(-1) (10:00-17:00) from 1 July to 28 November 2008. The whole-plant dry mass and grain yield per plant of the four cultivars were significantly reduced by the exposure to O3. The exposure to O3 significantly reduced net photosynthetic rate of the 12th and flag leaves of the four cultivars. The sensitivity to O3 of growth, yield and leaf gas exchange rates was not significantly different among the four cultivars. The present study suggests that the sensitivity to O3 of yield of the four Bangladeshi rice cultivars is greater than that of American rice cultivars and is similar to that of Japanese rice cultivars and that O3 may detrimentally affect rice production in Bangladesh.

Leaf antioxidant fluctuations and growth responses in saplings of Caesalpinia echinata Lam. (brazilwood) under an urban stressing environment

We intended to establish how efficient the leaf antioxidant responses of C. echinata are against oxidative environmental conditions observed in an urban environment and their relations to growth and biomass parameters. Plants were grown for 15 months in four sites: Congonhas and Pinheiros, affected by pollutants from vehicular emissions; Ibirapuera, affected by high O(3) concentrations; and a greenhouse with filtered air. Fifteen plants were quarterly removed from each site for analysis of antioxidants, growth and biomass. Plants growing in polluted sites showed alterations in their antioxidants. They were shorter, had thicker stems and produced less leaf biomass than plants maintained under filtered air. The fluctuations in the levels of antioxidants were significantly influenced by combined effects of climatic and pollution variables. The higher were the antioxidant responses and the concentrations of pollutant markers of air contamination in each site the slower were the growth and biomass production.

Effects of enhanced UV-B radiation on the distribution of mineral elements in soybean (Glycine max) seedlings

In order to understand the effect of ultraviolet-B (UV-B) radiation on plant, the accumulated amount of dry matter and the distribution of the mineral elements in the different organs of soybean seedlings treated with UV-B radiation were investigated using the inductively coupled plasma-atomic emission spectrometry (ICP-AES). The results indicated that the accumulated amount of dry matter in root, stem and leaf of soybean seedlings treated with UV-B radiation during the stress and recovery period was lower than that of the control soybean. Moreover, the content of macroelements in the root, stem and leaf of soybean seedlings during the stress period and recovery period were decreased comparing with that of the control soybean. The change in the contents of microelements depended on the intensity of UV-B radiation, the organs of soybean and the treating period. Finally, the results from the stepwise regression analysis indicated that the content of specific microelements also affected the accumulation of dry matter in the soybean seedlings treated with UV-B radiation comparing with the contents of macroelements in the control soybean. The relationship between the contents of mineral elements and the accumulation of dry matter depended on the intensity of UV-B radiation and the organs of soybean. These results demonstrated that UV-B radiation induced the change in the distribution of mineral elements in root, stem and leaf, leading to the decrease in the accumulation of dry matter and then the inhibition of soybean growth. It was a possible effect mechanism of UV-B radiation on plant.