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

Can ethylenediurea (EDU) alter the effects of ozone on the source-sink regulation of nitrogen uptake and remobilization during grain filling period in rice?

Increased surface ozone (O3) pollution seriously threatens crop production, and ethylenediurea (EDU) can alleviate crop yield reduction caused by O3. However, the reason for the decrease in grain nitrogen (N) accumulation caused by O3 and whether EDU serves as N fertilizer remain unclear. An experiment was conducted to investigate the impacts of factorial combinations of O3 enrichment (ambient air plus 60 ppb) and EDU (foliage spray with 450 ppm solutions) on N concentration, accumulation and remobilization in hybrid rice seedlings. Compared to ambient condition, elevated O3 significantly inhibited the N accumulation in vegetative organs during anthesis and grain N accumulation during the maturity stage. Elevated O3 significantly decreased the total N accumulation during anthesis and maturity stages, with a greater impact at the latter stage. The decrease in grain N accumulation caused by O3 was attributed to a decrease in N remobilization of vegetative organs during the grain filling period as well as to a decrease in post-anthesis N uptake. However, there was no significant change in the proportion of N remobilization and N uptake in grain N accumulation. The inhibitory effect of O3 on N remobilization in the upper canopy leaves was greater than that in the lower canopy leaves. In addition, elevated O3 increased the N accumulation of panicles at the anthesis stage, mainly by resulting in earlier heading of rice. EDU only increased N accumulation at the maturity stage, which was mainly attributed to an increase in rice biomass by EDU. EDU had no significant effect on N concentration, N remobilization process, and N harvest index. The findings are helpful to better understand the utilization of N fertilizer by rice under O3 pollution, and can also provide a theoretical basis for sustainable nutrient management to alleviate the negative impact of O3 on crop yield and quality.

Ozone-induced oxidative stress alleviation by biogenic silver nanoparticles and ethylenediurea in mung bean (Vigna radiata L.) under high ambient ozone

Ground-level ozone (O3) is the most phytotoxic secondary air pollutant in the atmosphere, severely affecting crop yields worldwide. The role of nanoparticles (NP) in the alleviation of ozone-induced yield losses in crops is not known. Therefore, in the present study, we investigated the effects of biogenicB-AgNPs on the mitigation of ozone-induced phytotoxicity in mung bean and compared its results with ethylenediurea (EDU) for the first time. Two mung bean cultivars (Vigna radiata L., Cv. SML-668 and PDM-139) were foliar sprayed with weekly applications of B-AgNPs (0 = control, 10 and 25 ppm) and EDU (0 = control, 200 and 300 ppm) until maturation phase. Morphological, physiological, enzymatic, and non-enzymatic antioxidant data were collected 30 and 60 days after germination (DAG). The mean O3 and AOT40 values (8 h day-1) during the cultivation period were approximately 52 ppb and 4.4 ppm.h, respectively. More biomass was accumulated at the vegetative phase due to the impact of B-AgNPs and EDU, and more photosynthates were transported to the reproductive phase, increasing yield. We observed that the 10 ppm B-AgNPs treatment had a more noticeable impact on yield parameters and lower Ag accumulation in seeds for both cultivars. Specifically, SML-668 cultivar treated with 10 ppm B-AgNPs (SN1) showed greater increases in seed weight plant-1 (124.97%), hundred seed weight (33.45%), and harvest index (37.53%) in comparison to control. Our findings suggest that B-AgNPs can enhance growth, biomass, yield, and seed quality, and can improve mung bean ozone tolerance. Therefore, B-AgNPs may be a promising protectant for mung bean.

Exogenous application of melatonin protects bean and tobacco plants against ozone damage by improving antioxidant enzyme activities, enhancing photosynthetic performance, and preventing membrane damage

Ozone (O3) pollution is harmful to plants and ecosystems. Several chemicals have been evaluated to protect plants against O3 deleterious effects. However, they are not adequately efficient and/or the environmental safety of their application is questioned. Hence, new chemicals that provide sufficient protection while being safer for environmental application are needed. This study investigates the response of two O3-sensitive plant species (Phaseolus vulgaris L. cv. Pinto and Nicotiana tabacum L. cv. Bel-W3) leaf-sprayed with deionized water (W, control), ethylenediurea (EDU, 1 mM) or melatonin at lower (1 mM) or higher (3 mM) concentrations (Mel_L and Mel_H, respectively), and then exposed to a square wave of 200 ppb O3, lasting 1 day (5 h day-1) for bean and 2 days (8 h day-1) for tobacco. In both species, the photosynthetic activity of O3-exposed plants was about halved. O3-induced membrane damage was also confirmed by increased malondialdehyde (MDA) byproducts compared to control (W). In EDU- and Mel-treated bean plants, the photosynthetic performance was not influenced by O3, leading to reduction of the incidence and severity of O3 visible injury. In bean plants, Mel_L mitigated the detrimental effect of O3 by boosting antioxidant enzyme activities or osmoprotectants (e.g. abscisic acid, proline, and glutathione transferase). In Mel_L-sprayed tobacco plants, O3 negatively influenced the photosynthetic activity. Conversely, Mel_H ameliorated the O3-induced oxidative stress by preserving the photosynthetic performance, preventing membrane damage, and reducing the visible injuries extent. Although EDU performed better, melatonin protected plants against O3 phytotoxicity, suggesting its potential application as a bio-safer and eco-friendlier phytoprotectant against O3. It is worth noting that the content of melatonin in EDU-treated plants remained unchanged, indicating that the protectant mode of action of EDU is not Mel-related.

Evidence for tropospheric ozone effects on rice production in Bangladesh

Although Bangladesh is known to be burdened with elevated tropospheric ozone levels, little is known about its effects on food security. We conducted field experiments in four highly polluted rice growing environments of Bangladesh in three cropping seasons (2020-2022), in which we grew 20 different rice varieties with or without application of the ozone protectant ethylene diurea (EDU). The average daytime ozone concentrations at the study sites during the rice growing seasons ranged from 53 ppb to 84 ppb, with the lowest concentrations occurring in the year 2020. EDU increased rice grain yields significantly by an average of 10.4 % across all seasons and locations, indicating that plants were stressed under ambient ozone concentrations. EDU was effective in distinguishing ozone-tolerant from ozone-sensitive varieties, in which yield increased by up to 21 %. Likewise, the EDU treatment positively affected vegetation indices representing chlorophyll (NDVI), the chorophyll:carotenoid ratio (Lic2), and pigments of the xanthophyll cycle (PRI). Stomatal conductance was increased significantly by an average of around 10 % among all varieties when plants were treated with EDU. In all physiological traits, significant genotype by treatment interactions occurred, indicating that different varieties varied in their responses to ozone stress. Our study demonstrates that rice production in Bangladesh is severely affected by tropospheric ozone, and calls for the breeding of tolerant rice varieties as well as mitigation measures to reduce air pollution.

Inhibitory effect of exogenous mineral elements (Si, P, Zn, Ca, Mn, Se, Fe, S) on rice Cd accumulation and soil Cd bioavailability in Cd-contaminated farmlands: A meta-analysis

A promising strategy for safely remediating Cd-contaminated farmland has been the application of mineral elements, which can reduce Cd accumulation in rice and inhibit its bioavailability in Cd-contaminated farmlands. However, there is still a lack of systematic and quantitative evaluations regarding how different mineral elements affect rice Cd accumulation and soil Cd bioavailability. Here, a meta-analysis was conducted based on 1062 individual observations from 137 published works to explore the effects of Si, P, Zn, Ca, Mn, Se, Fe and S in rice Cd accumulation and soil Cd bioavailability, we aimed to identify key factors that control the reduction of Cd concentration in rice grains. The results showed that the presence of exogenous elements had dramatically reduced rice grains Cd concentrations in the following decreasing order: Fe (43.03%) > P (38.45%) > Si (33.24%) > Ca (31.90%) > Se (29.83%) > Zn (25.95%) > Mn (23.26%) > S (18.78%). The elements of Ca, P and Si had strongly reduced Cd bioavailability in soils by 29.87%, 27.80% and 22.70%, respectively. The effects of these elements on Cd bioavailability appeared to be controlled by soil physio-chemical properties, such as pH, soil organic carbon (SOC) but also water management, application amounts and elemental forms. Overall, this study provides valuable insights into the potential of using exogenous mineral elements to mitigate Cd contamination in rice and farmlands, and facilitates the selection and application of mineral elements for the safe utilization of Cd-contaminated farmlands, taking into account soil properties and other factors that affect their effect.

Elevated ozone effects on potato leaf physiology, growth, and yield: a meta-analysis

Potato is an important crop worldwide and threatened by various environmental stresses, including elevated ozone (e[O3]). Here, we conducted a meta-analysis to quantify the effect of e[O3] on potato plants and how it varies depending upon different experimental conditions. Regarding plant growth and biomass, e[O3] significantly decreased shoot biomass by 18% and belowground biomass by 35%, while it increased the leaf area index by 19% and total number of injured leaves by 146%. As for yield, e[O3] significantly decreased the total tuber number by 21%. A relatively pronounced effect of e[O3] on the stomatal conductance was observed when exposure lasted 31-60 days, which was significantly greater than that after exposure lasted 96-311 days. The overall quantity of leaves was mainly decreased by higher (100-150 ppb) than lower (30-80 ppb) concentrations of e[O3] compared to ambient O3. The effect of e[O3] on the total tuber number was significant mainly when exposure lasted 31-90 days and was greater in plants grown in growth chambers than those planted in open-top chambers and glasshouses. The effect of e[O3] stress on physiology, growth, and yield varied among cultivars, with some cultivars showing marked tolerance relative to other cultivars. The findings can guide strategies to manage the negative impacts of e[O3] stress on potato production.

Rebuilding high-quality near-surface ozone data based on the combination of WRF-Chem model with a machine learning method to better estimate its impact on crop yields in the Beijing-Tianjin-Hebei region from 2014 to 2019

In recent years, the problem of surface ozone pollution in China has been of great concern. According to observation data from monitoring stations, the concentration of near-surface ozone (O3) in China has gradually increased in recent years, and ozone concentration often exceeds the contaminant limit standard, especially in the Beijing-Tianjin-Hebei (BTH) region. High O3 concentration pollution will adversely affect crop growth, which can cause crop yield losses. Therefore, it is urgent to recognize the situation of ozone pollution in the BTH region and quantitatively evaluate the crop yield losses caused by ozone pollution to develop more effective pollution prevention and control policies. However, the monitoring of ozone concentration in China started relatively late compared with some developed countries, and currently, long-time series data covering the BTH region cannot be obtained, which makes it difficult to evaluate the impact of ozone on crop yield. Therefore, a new method (WRFC-XGB) was proposed in this study to establish a high-precision near-surface O3 concentration dataset covering the whole BTH region from 2014 to 2019 by integrating the Weather Research and Forecasting with Chemistry (WRF-Chem) model with the extreme gradient boosting (XGBoost) machine learning algorithm. Through verification with ground observation station data, the results of WRFC-XGB are satisfactory, and R2 can reach 0.78-0.91. Compared with other algorithms, the accuracy of the near-surface ozone concentration dataset is greatly improved, which can be used to estimate the impact of surface ozone on crop yield. Based on this dataset, the yield loss of winter wheat, rice, and maize caused by O3 pollution was estimated by using the response equation of the relative yield and ozone dose index. The results showed that the total yield losses of winter wheat, rice and maize from 2014 to 2019 were 2659.21 million tons, 49.23 million tons and 1721.56 million tons due to ozone pollution in the BTH region, respectively, and the highest relative yield loss of crops caused by O3 pollution could be 29.37% during 2014-2019, which indicated that the impact of ozone pollution on crop yield cannot be ignored, and effective measures need to be developed to control ozone pollution, prevent crop production loss, and ensure people's food security.

A quantitative review of the effects of Se application on the reduction of Hg concentration in plant: a meta-analysis

Mercury (Hg) is a highly toxic heavy metal entering the human body through the food chain after absorption by plant. Exogenous selenium (Se) has been suggested as a potential solution to reduce Hg concentration in plants. However, the literature does not provide a consistent picture of the performance of Se on the accumulation of Hg in plant. To obtain a more conclusive answer on the interactions of Se and Hg, 1,193 data records were collected from 38 publications for this meta-analysis, and we tested the effects of different factors on Hg accumulation by meta-subgroup analysis and meta-regression model. The results highlighted a significant dose-dependent effect of Se/Hg molar ratio on the reduction of Hg concentration in plants, and the optimum condition for inhibiting Hg accumulation in plants is at a Se/Hg ratio of 1-3. Exogenous Se significantly reduced Hg concentrations in the overall plant species, rice grains, and non-rice species by 24.22%, 25.26%, and 28.04%, respectively. Both Se(IV) and Se(VI) significantly reduced Hg accumulation in plants, but Se(VI) had a stronger inhibiting effect than Se(IV). Se significantly decreased the BAF_Grain in rice, which indicated that other physiological processes in rice may be involved in restricting uptake from soil to rice grain. Therefore, Se can effectively reduce Hg accumulation in rice grain, which provides a strategy for effectively alleviating the transfer of Hg to the human body through the food chain.

Elevated O3 concentrations alter the compartment-specific microbial communities inhabiting rust-infected poplars

Elevated ozone (O₃ ) can affect the susceptivity of plants to rust pathogens. However, the collective role of microbiomes involved in such interaction remains largely elusive. We exposed two cultivated poplar clones exhibiting differential O₃ sensitivities, to non-filtered ambient air (NF), NF + 40 ppb or NF + 60 ppb O₃ -enriched air in field open-top chambers and then inoculated Melampsora larici-populina urediniospores to study their response to rust infection and to investigate how microbiomes inhabiting four compartments (phyllosphere, rhizosphere, root endosphere, bulk soil) are involved in this response. We found that hosts with higher O₃ sensitivity had significantly lower rust severity than hosts with lower sensitivity. Furthermore, the effect of increased O₃ on the diversity and composition of microbial communities was highly dependent on poplar compartments, with the microbial network complexity patterns being completely opposite between the two clones. Notably, microbial source analysis estimated that phyllosphere fungal communities predominately derived from root endosphere and vice versa, suggesting a potential transmission mechanism between plant above- and below-ground systems. These promising results suggest that further investigations are needed to better understand the interactions of abiotic and biotic stresses on plant performance and the role of the microbiome in driving these changes.

Mechanisms of cerium-induced stress in plants: A meta-analysis

A comprehensive evaluation of the effects of cerium on plants is lacking even though cerium is extensively applied to the environment. Here, the effects of cerium on plants were meta-analyzed using a newly developed database consisting of approximately 8500 entries of published data. Cerium affects plants by acting as oxidative stressor causing hormesis, with positive effects at low concentrations and adverse effects at high doses. Production of reactive oxygen species and its linked induction of antioxidant enzymes (e.g. catalase and superoxide dismutase) and non-enzymatic antioxidants (e.g. glutathione) are major mechanisms driving plant response mechanisms. Cerium also affects redox signaling, as indicated by altered GSH/GSSG redox pair, and electrolyte leakage, Ca²⁺, K⁺, and K⁺/Na⁺, indicating an important role of K⁺ and Na⁺ homeostasis in cerium-induced stress and altered mineral (ion) balance. The responses of the plants to cerium are further extended to photosynthesis rate (A), stomatal conductance (g_s), photosynthetic efficiency of PSII, electron transport rate, and quantum yield of PSII. However, photosynthesis response is regulated not only by physiological controls (e.g. g_s), but also by biochemical controls, such as via changed Hill reaction and RuBisCO carboxylation. Cerium concentrations <0.1-25 mg L^-1 commonly enhance chlorophyll a and b, g_s, A, and plant biomass, whereas concentrations >50 mg L^-1 suppress such fitness-critical traits at trait-specific concentrations. There was no evidence that cerium enhances yields. Observations were lacking for yield response to low concentrations of cerium, whereas concentrations >50 mg Kg^-1 suppress yields, in line with the response of chlorophyll a and b. Cerium affects the uptake and tissue concentrations of several micro- and macro-nutrients, including heavy metals. This study enlightens the understanding of some mechanisms underlying plant responses to cerium and provides critical information that can pave the way to reducing the cerium load in the environment and its associated ecological and human health risks.

Assessing the impact of current tropospheric ozone on yield loss and antioxidant defense of six cultivars of rice using ethylenediurea in the lower Gangetic Plains of India

Climate change influences the current tropospheric ozone (O₃) budget due to industrialization and urbanization processes. In recent years, the impact of elevated O₃ on crop development and yield loss has emerged as one of the most important environmental issues, particularly in rural and suburban areas of the lower Indo-Gangetic Plains of India. The impact of the current tropospheric ozone (O₃) on the crop yield, photosynthetic yield, and enzymatic antioxidants of six rice (Oryza sativa L.) cultivars (IR 36, MTU 1010, GB 3, Khitish, IET 4786, and Ganga Kaveri) was investigated with and without the application of ethylenediurea (EDU). The results revealed that O₃ stress significantly affected crop yield, photosynthetic yield, and antioxidant enzymes. The findings showed that O₃ toxicity induces oxidative stress biomarkers, i.e., malondialdehyde (MDA) content, and was manifested by increasing the enzymatic antioxidants, i.e., superoxidase dismutase (SOD) and catalase (CAT) in four rice cultivars (IR 36, GB 3, IET 4786, and Ganga Kaveri). At the same time, the results also illustrated that the rice cultivars MTU 1010 and Khitish are more tolerant to O₃ stress as they had less oxidative damage, greater photosynthetic SPAD value, SOD and CAT activities, and lower MDA activity. The results also elucidated that the application of EDU decreased O₃ toxicity in sensitive cultivars of rice by increasing antioxidant defense systems. The current O₃ level is likely to show an additional increase in the near future, and the use of tolerant genotypes of rice may reduce the negative impacts of O₃ on rice production.

Ethylenediurea offers moderate protection against ozone-induced rice yield loss under high ozone pollution

Tropospheric ozone (O₃) is the main phytotoxic air pollutant threatening food security, while ethylenediurea (EDU) can effectively mitigate O₃-induced crop yield loss. EDU's mode of action, however, remains unclear, and the underlying physiological mechanisms of mitigating O₃-induced crop yield loss are poorly understood. We cultivated hybrid rice seedlings under two O₃ treatments (NF, nonfiltered ambient air; and NF60, ambient air plus 60 ppb O₃) and sprayed foliage with 0 or 450 ppm EDU every ten days and determine photosynthesis-related traits, biomass indicators, and yield components. We found that EDU significantly increased the leaf nitrogen (N) allocation to photosynthesis (N_P) and the grain N accumulation, while the grain N accumulation was positively correlated with N_P and root biomass. EDU significantly increased the rice yield mainly by increasing the individual grain weight rather than the number of panicles and grains. While EDU protected from yield loss, the degree of protection was only 31% under NF60 treatment, thus EDU was unable to offer complete protection under high O₃ pollution. These results will be conducive to a better understanding of the EDU protection mechanism and better application of EDU under high O₃ pollution in the future.

Ozone does not diminish the beneficial effects of arbuscular mycorrhizas on Medicago sativa L. in a low phosphorus soil

Enriched surface ozone (O₃) can impose harmful effects on plants. Conversely, arbuscular mycorrhizal (AM) symbiosis can enhance plant tolerance to various environmental stresses and facilitate plant growth. The interaction of AM fungi and O₃ on plant performance, however, seldom has been investigated. In this study, alfalfa (Medicago sativa L.) was used as a test plant to study the effects of O₃ and AM symbiosis on plant physiology and growth under two O₃ levels (ambient air and elevated O₃ with 60 nmol·mol^-1 O₃ enrichment) and three AM inoculation treatments (inoculation with exogenous or indigenous AM fungi and non-inoculation control). The results showed that elevated O₃ decreased plant net photosynthetic rate and biomass, and increased malondialdehyde concentration, while AM inoculation (with both exogenous and indigenous AM fungi) could promote plant nutrient acquisition and growth irrespective of O₃ levels. The positive effects of AM symbiosis on plant nutrient acquisition and antioxidant enzyme (superoxide dismutase and peroxidase) activities were most likely offset by increased stomatal conductance and O₃ intake. As a result, AM inoculation and O₃ generally showed no significant interactions on plant performance: although elevated O₃ did not diminish the beneficial effects of AM symbiosis on alfalfa plants, AM symbiosis also did not alleviate the harmful effects of O₃ on plants.

Ethylenediurea (EDU) protects inbred but not hybrid cultivars of rice from yield losses due to surface ozone

The rising concentration of ground-level ozone (O₃) reduces crop yield via increased oxidative stress. Application of ethylenediurea (EDU) protects plants from O₃ and could thereby serve as a means to estimate the crop yield losses due to ambient O₃ (AO₃). However, no study but a few exceptions has ever compared the yield loss estimates from EDU application with those from O₃ elevation experiments. Here, we estimated yield loss to AO₃ in rice cultivars across the 3 types, indica, japonica, and hybrid, by an EDU application in the field, and compared the yield losses with those estimated with dose-response relationships based on O₃ elevation experiments. Relative yield loss (RYL) in the EDU application was estimated at 16% across the rice types on an assumption of a 100% efficiency for protection of crop yield by EDU. This estimate of RYL was close to the 15% RYL estimated from the O₃ elevation experiments when a common sensitivity to O₃ is assumed across the cultivars. The rice yield loss due to AO₃ was thus consistent between the two approaches supporting the idea of EDU application for the yield loss estimation. When only hybrids are focused, however, the RYL from EDU application (16%) was much lower than the 34% RYL from the O₃ elevation experiments, which indicates only a 37% yield protection by EDU in the hybrid rice. The incomplete protection by EDU and its genetic variability indicates the need to quantify the efficiency of protection from AO₃-induced yield loss as estimated with O₃ manipulating experiments.

Exogenous application of melatonin to plants, algae, and harvested products to sustain agricultural productivity and enhance nutritional and nutraceutical value: A meta-analysis

Melatonin is produced by plants, algae, and animals. Worldwide studies show diverse positive effects of exogenous melatonin on plants, edible plant products, and algae, but the potential of melatonin to enhance food and feed systems through these positive effects remains largely unexplored. Through a meta-analysis of about 25,000 observations, we show for the first time that exogenous application of melatonin significantly increases crop productivity and yields, and enhances the nutritional and nutraceutical value of edible plant products and algae by regulating diverse biological functions. We demonstrate that melatonin can improve plants, edible plant products, and algae under various current climate change scenarios, environmental pollution factors, and other stresses by about 7% to nearly 30%, on average, depending on the stressor. We also analyze various technical/methodological factors influencing the desired outcomes and identify conditions that offer optimal enhancement. We show that the positive effect of melatonin on plants and edible plant products varies among species, genera, and families, and strongly depends on the concentration of melatonin and treatment duration. The effect of melatonin is slightly lower on the monocot clade Commelinids than on the eudicot clades Asterids and Rosids. We also show that its stimulatory effect on plants depends on cultivation system, with a larger effect obtained in hydroponic systems. However, it does not depend on application stage (seed or vegetative), application route (foliage, roots, or seed), and whether the cultivation system is ex vivo or in vivo. This is the first meta-analysis examining the effects of melatonin on plants, edible plant products, and algae, and offers a scientific and technical roadmap facilitating sustainable food and feed production through the application of exogenous melatonin.

Exogenous application of chemicals for protecting plants against ambient ozone pollution: What should come next?

Elevated ground-level ozone (O₃) pollution can adversely affect plants and inhibit plant growth and productivity, threatening food security and ecological health. It is therefore essential to develop measures to protect plants against O₃-induced adverse effects. Here we summarize the current status of phytoprotection against O₃-induced adverse effects and consider recent scientific and engineering advances, to provide a novel perspective for maximizing plant health while reducing environmental/ecological risks in an O₃-polluted world. We suggest that nanoscience and nanotechnology can provide a new dimension in the protection of plants against O₃-induced adverse effects, and recommend that new studies are based upon a green chemistry perspective.

Effect of elevated ozone and carbon dioxide interaction on growth, yield, nutrient content and wilt disease severity in chickpea grown in Northern India

Wilt caused by Fusarium oxysporum, sp. Ciceris (FOC) is an important disease causing losses up to 10% in chickpea yield. Experiments were conducted growing chickpea in free air ozone and carbon dioxide enrichment rings under four treatments of elevated ozone (O3) (EO:60 ± 10 ppb), elevated carbon dioxide (CO2) (ECO2:550 ± 25 ppm), combination of elevated CO2 and O3 (EO + ECO2) and ambient control for quantifying the effect on growth, yield, biochemical and nutrient content of chickpea. For studying the impact on wilt disease, chickpea was grown additionally in pots with soil containing FOC in these rings. The incidence of Fusarium wilt reduced significantly (p < 0.01) under EO as compared to ambient and ECO2. The activities of pathogenesis-related proteins chitinase and β-1,3- glucanase, involved in plant defense mechanism were enhanced under EO. The aboveground biomass and pod weight declined by 18.7 and 15.8% respectively in uninnoculated soils under EO, whereas, in FOC inoculated soil (diseased plants), the decline under EO was much less at 8.6 and 9.9% as compared to the ambient. Under EO, the activity of super oxide dismutase increased significantly (p < 0.5, 40%) as compared to catalase (12.5%) and peroxidase (17.5%) without any significant increase under EO + ECO2. The proline accumulation was significantly (p < 0.01) higher in EO as compared to EO + ECO2, and ECO2. The seed yield declined under EO due to significant reduction (p < 0.01) in the number of unproductive pods and seed weight. No change in the protein, total soluble sugars, calcium and phosphorus content was observed in any of the treatments, however, a significant decrease in potassium (K) content was observed under EO + ECO2. Elevated CO2 (554ppm) countered the impacts of 21.1 and 14.4 ppm h (AOT 40) O3 exposure on the seed yield and nutrient content (except K) in the EO + CO2 treatment and reduced the severity of wilt disease in the two years' study.

Ethylenediurea (EDU) effects on Japanese larch: an one growing season experiment with simulated regenerating communities and a four growing season application to individual saplings

Japanese larch (Larix kaempferi (Lamb.) Carr.) and its hybrid are economically important coniferous trees widely grown in the Northern Hemisphere. Ground-level ozone (O₃) concentrations have increased since the pre-industrial era, and research projects showed that Japanese larch is susceptible to elevated O₃ exposures. Therefore, methodologies are needed to (1) protect Japanese larch against O₃ damage and (2) conduct biomonitoring of O₃ in Japanese larch forests and, thus, monitor O₃ risks to Japanese larch. For the first time, this study evaluates whether the synthetic chemical ethylenediurea (EDU) can protect Japanese larch against O₃ damage, in two independent experiments. In the first experiment, seedling communities, simulating natural regeneration, were treated with EDU (0, 100, 200, and 400 mg L^-1) and exposed to either ambient or elevated O₃ in a growing season. In the second experiment, individually-grown saplings were treated with EDU (0, 200 and 400 mg L^-1) and exposed to ambient O₃ in two growing seasons and to elevated O₃ in the succeeding two growing seasons. The two experiments revealed that EDU concentrations of 200-400 mg L^-1 could protect Japanese larch seedling communities and individual saplings against O₃-induced inhibition of growth and productivity. However, EDU concentrations ≤ 200 mg L^-1 did offer only partial protection when seedling communities were coping with higher level of O₃-induced stress, and only 400 mg EDU L^-1 fully protected communities under higher stress. Therefore, we conclude that among the concentrations tested the concentration offering maximum protection to Japanese larch plants under high competition and O₃-induced stress is that of 400 mg EDU L^-1. The results of this study can provide a valuable resource of information for applied forestry in an O₃-polluted world.

Effects of ethylenediurea (EDU) on regulatory proteins in two maize (Zea mays L.) varieties under high tropospheric ozone phytotoxicity

Rising tropospheric ozone is a major threat to the crops in the present climate change scenario. To investigate the EDU induced changes in proteins, two varieties of maize, the SHM3031 and the PEHM5, (hereafter S and P respectively) were treated with three EDU applications (0= control, 50 and 200 ppm) (hereafter 0= A, 1 and 2 respectively) (SA, S1, S2, PA, P1, P2 cultivar X treatments). Data on the morpho-physiology, enzymatic activity, and protein expression (for the first time) were collected at the vegetative (V, 45 DAG) and flowering (F, 75 DAG) developmental stages. The tropospheric ozone was around 53 ppb enough to cause phytotoxic effects. Protective effects of EDU were recorded in morpho-physiologically and biochemically. SOD, CAT and APX together with GR performed better under EDU protection in SHM3031 variety than PEHM5. The protein expression patterns in SHM3031 at the vegetative stage (28% proteins were increased, 7% were decreased), and at the flowering stage (17% increased, 8% decreased) were found. In PEHM5, a 14% increase and an 18% decrease (vegetative stage) whereas a 16% increase and a 20% decrease (flowering stage) were recorded in protein expression. Some protein functional categories, for instance, photosynthesis, carbon metabolism, energy metabolism, and defense were influenced by EDU. Rubisco expression was increased in SHM3031 whereas differentially expressed in PEHM5. Germin like protein, APX, SOD, and harpin binding proteins have enhanced defense regulatory mechanisms under EDU treatment during prevailing high tropospheric O₃. The present study showed EDU protective roles in C4 plants as proven in C3.

Ozone affects plant, insect, and soil microbial communities: A threat to terrestrial ecosystems and biodiversity

Elevated tropospheric ozone concentrations induce adverse effects in plants. We reviewed how ozone affects (i) the composition and diversity of plant communities by affecting key physiological traits; (ii) foliar chemistry and the emission of volatiles, thereby affecting plant-plant competition, plant-insect interactions, and the composition of insect communities; and (iii) plant-soil-microbe interactions and the composition of soil communities by disrupting plant litterfall and altering root exudation, soil enzymatic activities, decomposition, and nutrient cycling. The community composition of soil microbes is consequently changed, and alpha diversity is often reduced. The effects depend on the environment and vary across space and time. We suggest that Atlantic islands in the Northern Hemisphere, the Mediterranean Basin, equatorial Africa, Ethiopia, the Indian coastline, the Himalayan region, southern Asia, and Japan have high endemic richness at high ozone risk by 2100.

Growth, physiological and proteomic responses in field grown wheat varieties exposed to elevated CO2 under high ambient ozone

The present study investigated growth, biochemical, physiological, yield and proteomic changes in 3 wheat varieties exposed to elevated CO₂ (515 ppm) in a background of high ambient ozone in field. Ethylenediurea (EDU) was used as antiozonant. Average ozone concentration was 59 ppb and was sufficient enough to exert phytotoxic effects. Elevated carbon dioxide (eCO₂) and EDU application individually or in combination negated the adverse effects of ozone by modulating antioxidants and antioxidative enzymes. Differential leaf proteomics revealed that at vegetative stage major changes in protein abundance were due to EDU treatment (47, 52 and 41 proteins in PBW-343, LOK1 and HD-2967, respectively). Combined treatment of eCO₂ and EDU was more responsible for changes in 37 proteins during flowering stage of PBW-343 and LOK1. Functional categorization revealed more than 60% differentially abundant protein collectively belonging to carbon metabolism, protein synthesis assembly and degradation and photosynthesis. At both the growth stages, LOK1 was more responsive to eCO₂ and combined treatment (eCO₂ + EDU). HD-2967 was more positively responsive to EDU and combined treatment. eCO₂ in combination of EDU protected these varieties against high ambient O₃.

Effects of warming and elevated O3 concentrations on N2O emission and soil nitrification and denitrification rates in a wheat-soybean rotation cropland

The effects of warming and elevated ozone (O3) concentrations on nitrous oxide (N2O) emission from cropland has received increasing attention; however, the small number of studies on this topic impedes understanding. A field experiment was performed to explore the role of warming and elevated O3 concentrations on N2O emission from wheat-soybean rotation cropland from 2012 to 2013 using open-top chambers (OTCs). Experimental treatments included ambient temperature (control), elevated temperature (+2 °C), elevated O3 (100 ppb), and combined elevated temperature (+2 °C) and O3 (100 ppb). Results demonstrate that warming significantly increased the accumulative amount of N2O (AAN) emitted from the soil-winter wheat system due to enhanced nitrification rates in the wheat farmland and nitrate reductase activity in wheat leaves. However, elevated O3 concentrations significantly decreased AAN emission from the soil-soybean system owing to reduced nitrification rates in the soybean farmland. The combined treatment of warming and elevated O3 inhibited the emission of N2O from the soybean farmland. Additionally, both the warming and combined treatments significantly increased soil nitrification rates in winter wheat and soybean croplands and decreased denitrification rates in the winter wheat cropping system. Our results suggest that global warming and elevated O3 concentrations will strongly affect N2O emission from wheat-soybean rotation croplands.

Ethylenediurea (EDU) pretreatment alleviated the adverse effects of elevated O3 on Populus alba "Berolinensis" in an urban area

Ethylenediurea (EDU) has been used as a chemical protectant against ozone (O₃). However, its protective effect and physiological mechanisms are still uncertain. The present study aimed to investigate the changes of foliar visible injury, physiological characteristics and emission rates of volatile organic compounds (VOCs) in one-year-old Populus alba "Berolinensis" saplings pretreated with EDU and exposed to elevated O₃ (EO, 120 μg/m³). The results showed that foliar visible injury symptoms under EO were significantly alleviated in plants with EDU application (p < 0.05). Under EO, net photosynthetic rate, the maximum photochemical efficiency of PSII and the photochemical efficiency of PSII of plants pretreated with 300 and 600 mg/L EDU were similar to unexposed controls and significantly higher compared to EO-stressed plants without EDU pretreatment, respectively. Malondialdehyde content was highest in EO without EDU and decreased significantly by 14.9% and 21.3% with 300 and 600 mg/L EDU pretreatment, respectively. EDU pretreatment alone increased superoxide dismutase activity by 10-fold in unexposed plants with further increases of 88.4% and 37.5% in EO plants pretreated with 300 and 600 mg/L EDU pretreatment, respectively (p < 0.05). Abscisic acid content declined under EO relative to unexposed controls with the effect partially reversed by EDU pretreatments. Similarly, VOCs emission rate declined under EO relative to unexposed plants with a recovery of emission rate observed with 300 and 600 mg/L EDU pretreatment. These findings provided significant evidence that EDU exerted a beneficial effect and protection on the tested plants against O₃ stress.

Effect of Warming and Elevated O3 Concentration on CO2 Emissions in a Wheat-Soybean Rotation Cropland

A deeper understanding of the effects of experimental warming and elevated ozone (O3) concentration on carbon dioxide (CO2) fluxes is imperative for reducing potential CO2 emissions in agroecosystems, but are less understood particularly in rotational wheat (Triticum aestivum)-soybean (Glycine max) croplands. In order to understand such effects on CO2 fluxes from winter wheat-soybean rotation, a field experiment was conducted by using the open-top chamber (OTCs) during the growing seasons of 2012 and 2013 at an agro-ecological station in southeast China. The experimental treatments included the control (CK), experimental warming (T, crop canopy temperature increased by ~2 °C), elevated O3 concentration (O, O3 concentration about 100 ppb) along with temperature enhancement (OT, elevated ~2 °C temperature plus 100 ppb O3). The results showed that warming significantly increased the mean CO2 fluxes (MCF) and the cumulative amount of CO2 (CAC) from soil and soil-crop systems, while elevated O3 and warming enhancement (OT) significantly reduced MCF and CAC. Besides, warming significantly reduced the biomass of winter-wheat, but it insignificantly decreased the biomass of soybean in the harvest period. The O and OT treatments significantly reduced the biomass of winter-wheat and soybean cropping systems in the harvest time. Both warming and elevated O3 concentration decreased the temperature sensitivity coefficients (Q10) in soil respiration during the experimental period. Overall, our results indicate that elevated O3 concentration compensates the effect of warming on CO2 emission to some extents, which has a positive feedback impact on the climate system.

Assessment of Ozone Sensitivity in Three Wheat Cultivars Using Ethylenediurea

Three wheat (Triticum aestivum L.) cultivars [HD 2987 (ozone (O₃) sensitive), PBW 502 (intermediately sensitive) and Kharchiya 65 (O₃ tolerant)] with known sensitivity to O₃ were re-evaluated using ethylenediurea (EDU; 400 ppm) to ascertain the use of EDU in determiningO₃ sensitivity under highly O₃-polluted tropical environments. EDU treatment helped in improving the growth, biomass, photosynthetic pigments and the antioxidative defense system of all the wheat cultivars. Under EDU treatment, PBW 502 retained more biomass, while HD 2987 showed better performance and ultimately the greatest increment in yield. Cultivar Kharchiya 65 also showed a positive response to EDU as manifested with an increase in pigment contents, total biomass and enzymatic antioxidants; however, this increment was comparatively lower compared to the other two cultivars. The results indicated that EDU did not have many physiological effects on cultivars but helped in counteracting O₃ primarily by scavenging reactive oxygen species and enhancing the antioxidative defense system where superoxide dismutase emerged as the major responsive biochemical parameter against ambient O₃. The observed results clearly indicated that differential O₃ sensitivity in three wheat cultivars established by the previous study is in accordance with the present study using EDU as a sensitivity tool, which is an easy and efficient technology in comparison to chamber and Free-Air Carbon dioxide Enrichment (FACE) experiments although its mechanistic understanding needs to be further validated.

High Variation in Resource Allocation Strategies among 11 Indian Wheat (Triticum aestivum) Cultivars Growing in High Ozone Environment

Eleven local cultivars of wheat (Triticum aestivum) were chosen to study the effect of ambient ozone (O3) concentration in the Indo-Gangetic Plains (IGP) of India at two high-ozone experimental sites by using 300 ppm of Ethylenediurea (EDU) as a chemical protectant against O3. The O3 level was more than double the critical threshold reported for wheat grain production (AOT40 8.66 ppm h). EDU-grown plants had higher grain yield, biomass, stomatal conductance and photosynthesis, less lipid peroxidation, changes in superoxide dismutase and catalase activities, changes in content of oxidized and reduced glutathione compared to non-EDU plants, thus indicating the severity of O3 induced productivity loss. Based on the yield at two different growing sites, the cultivars could be addressed in four response groups: (a) generally well-adapted cultivars (above-average yield); (b) poorly-adapted (below-average yield); (c) adapted to low-yield environment (below-average yield); and (d) sensitive cultivars (adapted to high-yield environment). EDU responses were dependent on the cultivar, the developmental phase (vegetative, flowering and harvest) and the experimental site.

Ethylenediurea (EDU) mitigates the negative effects of ozone in rice: Insights into its mode of action

Monitoring of ozone damage to crops plays an increasingly important role for the food security of many developing countries. Ethylenediurea (EDU) could be a tool to assess ozone damage to vegetation on field scale, but its physiological mode of action remains unclear. This study investigated mechanisms underlying the ozone-protection effect of EDU in controlled chamber experiments. Ozone sensitive and tolerant rice genotypes were exposed to ozone (108 ppb, 7 hr day^-1 ) and control conditions. EDU alleviated ozone effects on plant morphology, foliar symptoms, lipid peroxidation, and photosynthetic parameters in sensitive genotypes. Transcriptome profiling by RNA sequencing revealed that thousands of genes responded to ozone in a sensitive variety, but almost none responded to EDU. Significant interactions between ozone and EDU application occurred mostly in ozone responsive genes, in which up-regulation was mitigated by EDU application. Further experiments documented ozone degrading properties of EDU, as well as EDU deposits on leaf surfaces possibly related to surface protection. EDU application did not mitigate the reaction of plants to other abiotic stresses, including iron toxicity, zinc deficiency, and salinity. This study provided evidence that EDU is a surface protectant that specifically mitigates ozone stress without interfering directly with the plants' stress response systems.

Closing the global ozone yield gap: Quantification and cobenefits for multistress tolerance

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

Intraspecific variation in sensitivity of winter wheat (Triticum aestivum L.) to ambient ozone in northern China as assessed by ethylenediurea (EDU)

Wheat is a major staple food and its sensitivity to the gas pollutant ozone (O₃) depends on the cultivar. However, few chamber-less studies assessed current ambient O₃ effects on a large number of wheat cultivars. In this study, we used ethylenediurea (EDU), an O₃ protectant whose protection mechanisms are still unclear, to test photosynthetic pigments, gas exchange, antioxidants, and yield of 15 cultivars exposed to 17.4 ppm h AOT40 (accumulated O₃ over an hourly concentration threshold of 40 ppb) over the growing season at Beijing suburb, China. EDU significantly increased light-saturated photosynthesis rate (A_sat), photosynthetic pigments (i.e., chlorophyll and carotenoid), and total antioxidant capacity, while reduced malondialdehyde and reduced ascorbate contents. In comparison with EDU-treated plants (control), plants treated with water (no protection from ambient O₃) significantly decreased yield, weight of 1000 grains, and harvest index by 20.3%, 15.1%, and 14.2%, respectively, across all cultivars. There was a significant interaction between EDU and cultivars in all tested variables with exception of A_sat, chlorophyll, and carotenoid. The cultivar-specific sensitivity to O₃ was ranked from highly sensitive (> 25% change) to less sensitive (< 10% change) by comparing the difference of the average grain yield of plants applied with and without EDU. Neither stomatal conductance nor antioxidant capacity contributed to the different response of the cultivars to EDU, suggesting that another mechanism contributes to the large variation in response to O₃ among cultivars. Generally, the results indicate that present O₃ concentration is threatening wheat production in Northern China, highlighting the urgent need for policy-making actions to protect this critical staple food.

Effects of elevated ozone concentration and nitrogen addition on ammonia stomatal compensation point in a poplar clone

The stomatal compensation point of ammonia (χ_s) is a key factor controlling plant-atmosphere NH₃ exchange, which is dependent on the nitrogen (N) supply and varies among plant species. However, knowledge gaps remain concerning the effects of elevated atmospheric N deposition and ozone (O₃) on χ_s for forest species, resulting in large uncertainties in the parameterizations of NH₃ incorporated into atmospheric chemistry and transport models (CTMs). Here, we present leaf-scale measurements of χ_s for hybrid poplar clone '546' (Populusdeltoides cv. 55/56 x P. deltoides cv. Imperial) growing in two N treatments (N0, no N added; N50, 50 kg N ha^-1 yr^-1 urea fertilizer added) and two O₃ treatments (CF, charcoal-filtered air; E-O₃, non-filtered air plus 40 ppb) for 105 days. Our results showed that χ_s was significantly reduced by E-O₃ (41%) and elevated N (19%). The interaction of N and O₃ was significant, and N can mitigate the negative effects of O₃ on χ_s. Elevated O₃ significantly reduced the light-saturated photosynthetic rate (A_sat) and chlorophyll (Chl) content and significantly increased intercellular CO₂ concentrations (Ci), but had no significant effect on stomatal conductance (g_s). By contrast, elevated N did not significantly affect all measured photosynthetic parameters. Overall, χ_s was significantly and positively correlated with A_sat, g_s and Chl, whereas a significant and negative relationship was observed between χ_s and Ci. Our results suggest that O₃-induced changes in A_sat, Ci and Chl may affect χ_s. Our findings provide a scientific basis for optimizing parameterizations of χ_s in CTMs in response to environmental change factors (i.e., elevated N deposition and/or O₃) in the future.

Protecting the photosynthetic performance of snap bean under free air ozone exposure

Tropospheric ozone (O₃) is a major air pollutant and causes serious injury to vegetation. To protect sensitive plants from O₃ damage, several agrochemicals have been assessed, including cytokinin (e.g., kinetin, KIN) and ethylenediurea (EDU) with cytokinin-like activity. In higher plant, leaves are primarily injured by O₃ and protective agrochemicals are often applied by leaf spraying. To our knowledge, the mitigating abilities of EDU and KIN have not been compared directly in a realistic setup. In the present research, impacts of elevated O₃ (2× ambient O₃, 24hr per day, for 8days) on an O₃ sensitive line (S156) of snap bean (Phaseolus vulgaris), which is often used for biomonitoring O₃ pollution, were studied in a free air controlled exposure system. The day before starting the O₃ exposure, plants were sprayed with a solution of EDU (300ppm), KIN (1mmol/L) or distilled water, to compare their protective abilities. The results demonstrated that 2× ambient O₃ inhibited net photosynthetic rate and stomatal conductance, increased the minimal fluorescence yield of the dark-adapted state, decreased the maximal quantum yield of PSII photochemistry, and led to visible injury. KIN and EDU alleviated the reduction of the photosynthetic performance, and visible injury under O₃ fumigation. The plants sprayed with EDU showed greater ability to mitigate the O₃ damage than those sprayed with KIN. Chlorophyll fluorescence imaging may have detected more precisely the differences in O₃ response across the leaf than the conventional fluorometer.

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.

Large variability in ambient ozone sensitivity across 19 ethylenediurea-treated Chinese cultivars of soybean is driven by total ascorbate

The sensitivity of Chinese soybean cultivars to ambient ozone (O3) in the field is unknown, although soybean is a major staple food in China. Using ethylenediurea (EDU) as an O3 protectant, we tested the gas exchange, pigments, antioxidants and biomass of 19 cultivars exposed to 28ppm·hr AOT40 (accumulated O3 over an hourly concentration threshold of 40ppb) over the growing season at a field site in China. By comparing the average biomass with and without EDU, we estimated the cultivar-specific sensitivity to O3 and ranked the cultivars from very tolerant (<10% change) to highly sensitive (>45% change), which helps in choosing the best-suited cultivars for local cultivation. Higher lipid peroxidation and activity of the ascorbate peroxidase enzyme were major responses to O3 damage, which eventually translated into lower biomass production. The constitutional level of total ascorbate in the leaves was the most important parameter explaining O3 sensitivity among these cultivars. Surprisingly, the role of stomatal conductance was insignificant. These results will guide future breeding efforts towards more O3-tolerant cultivars in China, while strategies for implementing control measures of regional O3 pollution are being implemented. Overall, these results suggest that present ambient O3 pollution is a serious concern for soybean in China, which highlights the urgent need for policy-making actions to protect this critical staple food.

Use of Ethylenediurea (EDU) in identifying indicator cultivars of Indian clover against ambient ozone

Three clover (Trifolium alexandrium L.) cultivars (Bundel, Wardan and JHB-146) were assessed for their responses to ambient ozone (O₃) with respect to growth, physiological and biochemical parameters at two rural sites (R1 and R2) using ethylenediurea (EDU). EDU solution (300ppm) was applied as soil drench, 10 days after germination (DAG) at an interval of 10 days up to 80 DAG. The average O₃ concentrations were 52.76 and 60.86 ppb at R1 and R2 sites, respectively during the experimental period. Ambient O₃ induced visible symptoms in all the cultivars at both the sites, with more at R2 site having high ambient O₃ levels. Visible injury was observed first in non-EDU treated plants of Wardan at R2 site. Wardan also showed maximum reduction in leaf injury under EDU treatment at both the sites with more at R2. Under EDU treatment, better adaptation to ambient O₃ at initial age of observation and higher acquisition of resources at later ages of observation at both the sites led to better physiological and biochemical adaptations in Wardan. Bundel retained more biomass in shoot as is reflected with higher shoot/root ratio and thus focused more on repair and defense. Shoot/root ratio of JHB-146 did not respond to EDU treatment and thus showed insignificant variations except at initial age of observation at R1 site. This study clearly suggests that Wardan and Bundel are sensitive to ambient O₃ and can be used as bioindicator species in areas having higher O₃ levels using EDU as a research tool.

High doses of ethylenediurea (EDU) as soil drenches did not increase leaf N content or cause phytotoxicity in willow grown in fertile soil

Ground-level ozone (O₃) levels are nowadays elevated in wide regions of the Earth, causing significant effects on plants that finally lead to suppressed productivity and yield losses. Ethylenediurea (EDU) is a chemical compound which is widely used in research projects as phytoprotectant against O₃ injury. The EDU mode of action remains still unclear, while there are indications that EDU may contribute to plants with nitrogen (N) when the soil is poor in N and the plants have relatively small leaf area. To reveal whether the N content of EDU acts as a fertilizer to plants when the soil is not poor in N and the plants have relatively large total plant leaf area, willow plants (Salix sachalinensis Fr. Schm) were exposed to low ambient O₃ levels and treated ten times (9-day interval) with 200mL soil drench containing 0, 800 or 1600mg EDU L^-1. Fertilizer was added to a nutrient-poor soil, and the plants had an average plant leaf area of 9.1m² at the beginning of EDU treatments. Indications for EDU-induced hormesis in maximum electron transport rate (J_max) and ratio of intercellular to ambient CO₂ concentration (C_i:C_a) were observed at the end of the experiment. No other EDU-induced effects on leaf greenness and N content, maximum quantum yield of photosystem II (F_v/F_m), gas exchange, growth and matter production suggest that EDU did not act as N fertilizer and did not cause toxicity under these experimental conditions.

Diagnosing ozone stress and differential tolerance in rice (Oryza sativa L.) with ethylenediurea (EDU)

Rising tropospheric ozone concentrations in Asia necessitate the breeding of adapted rice varieties to ensure food security. However, breeding requires field-based evaluation of ample plant material, which can be technically challenging or very costly when using ozone fumigation facilities. The chemical ethylenediurea (EDU) has been proposed for estimating the effects of ozone in large-scale field applications, but controlled experiments investigating constitutive effects on rice or its suitability to detect genotypic differences in ozone tolerance are missing. This study comprised a controlled open top chamber experiment with four treatments (i) control (average ozone concentration 16 ppb), (ii) control with EDU application, (iii) ozone stress (average 77 ppb for 7 h daily throughout the season), and (iv) ozone stress with EDU application. Three contrasting rice genotypes were tested, i.e. the tolerant line L81 and the sensitive Nipponbare and BR28. The ozone treatment had significant negative effects on plant growth (height and tillering), stomatal conductance, SPAD value, spectral reflectance indices such as the normalized difference vegetation index (NDVI), lipid peroxidation, as well as biomass and grain yields. These negative effects were more pronounced in the a priori sensitive varieties, especially the widely grown Bangladeshi variety BR28, which showed grain yield reductions by 37 percent. EDU application had almost no effects on plants in the absence of ozone, but partly mitigated ozone effects on foliar symptoms, lipid peroxidation, SPAD value, stomatal conductance, several spectral reflectance parameters, panicle number, grain yield, and spikelet sterility. EDU responses were more pronounced in sensitive genotypes than in the tolerant L81. In conclusion, EDU had no constitutive effects on rice and partly offset negative ozone effects, especially in sensitive varieties. It can thus be used to diagnose ozone damage in field grown rice and for distinguishing tolerant (less EDU-responsive) and sensitive (more EDU-responsive) genotypes.

Effects of the Antiozonant Ethylenediurea (EDU) on Fraxinus ornus L.: The Role of Drought

Ethylenediurea (EDU) is a synthetic chemical known to protect plants from the phytotoxic effects of tropospheric ozone (O3). Although many studies have proposed the use of EDU for studying the O3 effects under field conditions, its mechanism of action is not fully understood, and it is unclear whether it exerts a specific antiozonant action, or if it may also interact with other oxidative stresses. The aim of this work was to evaluate the effect of EDU on forest species in a Mediterranean environment where, during summer, vegetation is exposed to multiple oxidative stresses, such as O3 and drought. The experiment was conducted on Fraxinus ornus L. (Manna ash) plants growing in six mesocosms, three maintained under full irrigation, while the other three were subjected to drought for 84 days. In each mesocosm, three plants were sprayed every 15 days with 450 ppm EDU. Gas exchange and chlorophyll “a” fluorescence measurements carried out through the experimental period highlighted that EDU did not affect stomatal conductance and had an ameliorative effect on the functionality of drought-stressed plants, thus suggesting that it may act as a generic antioxidant. The implications of these findings for the applicability of EDU in field studies are discussed.

Perspectives for elucidating the ethylenediurea (EDU) mode of action for protection against O3 phytotoxicity

Ethylenediurea (EDU) has been widely studied for its effectiveness to protect plants against injuries caused by surface ozone (O₃), however its mode of action remains unclear. So far, there is not a unified methodological approach and thus the methodology is quite arbitrary, thereby making it more difficult to generalize findings and understand the EDU mode of action. This review examines the question of whether potential N addition to plants by EDU is a fundamental underlying mechanism in protecting against O₃ phytotoxicity. Yet, this review proposes an evidence-based hypothesis that EDU may protect plants against O₃ deleterious effects upon generation of EDU-induced hormesis, i.e. by activating plant defense at low doses. This hypothesis challenges the future research directions. Revealing a hormesis-based EDU mode of action in protecting plants against O₃ toxicity would have further implications to ecotoxicology and environmental safety. Furthermore, this review discusses the need for further studies on plant metabolism under EDU treatment through relevant experimental approach, and attempts to set the bases for approaching a unified methodology that will contribute in revealing the EDU mode of action. In this framework, focus is given to the main EDU application methods.

Ethylenediurea as a potential tool in evaluating ozone phytotoxicity: a review study on physiological, biochemical and morphological responses of plants

Present-day climate change scenario has intensified the problem of continuously increasing ground-level ozone (O₃), which is responsible for causing deleterious effects on growth and development of plants. Studies involving use of ethylenediurea (EDU), a chemical with antiozonant properties, have given some promising results in evaluating O₃ injury in plants. The use of EDU is especially advantageous in developing countries which face a more severe problem of ground-level O₃, and technical O₃-induced yield loss assessment techniques like open-top chambers cannot be used. Recent studies have detected a hormetic response of EDU on plants; i.e. treatment with higher EDU concentrations may or may not show any adverse effect on plants depending upon the experimental conditions. Although the mode of action of EDU is still debated, it is confirmed that EDU remains confined in the apoplastic regions. Certain studies indicate that EDU significantly affects the electron transport chain and has positive impact on the antioxidant defence machinery of the plants. However, the mechanism of protecting the yield of plants without significantly affecting photosynthesis is still questionable. This review discusses in details the probable mode of action of EDU on the basis of available data along with the impact of EDU on physiological, biochemical, growth and yield response of plants under O₃ stress. Data regarding the effect of EDU on plant 'omics' is highly insufficient and can form an important aspect of future EDU research.

Impacts of ethylenediurea (EDU) soil drench and foliar spray in Salix sachalinensis protection against O3-induced injury

It is widely accepted that elevated levels of surface ozone (O₃) negatively affect plants. Ethylenediurea (EDU) is a synthetic substance which effectively protects plants against O₃-caused phytotoxicity. Among other questions, the one still open is: which EDU application method is more appropriate for treating fast-growing tree species. The main aims of this study were: (i) to test if chronic exposure of Salix sachalinensis plants to 200-400mgEDUL^-1, the usually applied range for protection against O₃ phytotoxicity, is beneficial to plants; (ii) to evaluate the effects of chronic exposure to elevated O₃ on S. sachalinensis; (iii) to assess the efficacy of two methods (i.e. soil drench and foliar spray) of EDU application to plants; (iv) to investigate the appropriate concentration of EDU to protect against elevated O₃-induced damage in S. sachalinensis; and (v) to compare the two methods of EDU application in terms of effectiveness and EDU consumption. Current-year cuttings grown in infertile soil free from organic matter were exposed either to low ambient O₃ (AOZ, 10-h≈28.3nmolmol^-1) or to elevated O₃ (EOZ, 10-h≈65.8nmolmol^-1) levels during daylight hours. Over the growing season, plants were treated every nine days with 200mL soil drench of 0, 200 or 400mgEDUL^-1 or with foliar spray of 0, 200 or 400mgEDUL^-1 (in two separate experiments). We found that EDU per se had no effects on plants exposed to AOZ. EOZ practically significantly injured S. sachalinensis plants, and the impact was indifferent between the experiments. EDU did not protect plants against EOZ impact when applied as soil drench but it did protect them when applied as 200-400mgL^-1 foliar spray. We conclude that EDU may be more effective against O₃ phytotoxicity to fast-growing species when applied as a spray than when applied as a drench. Keymessage: Soil-drenched EDU was ineffective in protecting willow plants against O₃-induced injury, whereas foliar-sprayed EDU was effective even at the concentration of 200mgL^-1.

Moderate drought did not affect the effectiveness of ethylenediurea (EDU) in protecting Populus cathayana from ambient ozone

A field study was conducted to evaluate the effects of ambient ozone (O3) on an O3-sensitive poplar (Populus cathayana) by using ethylenediurea (EDU) as a chemical protectant under two soil water treatments (well-watered (WW) and moderate drought (MD, 50-60% of WW in volumetric soil water content). EDU was applied as foliar spray at 0, 300, 450, and 600ppm. Photosynthetic parameters, pigment contents, leaf nitrogen, antioxidant capacity, growth, and biomass were measured. The 8h (9:00-17:00) average ambient O3 concentration was 71.7ppb, and AOT40 was 29.2ppmh during the experimental period (9 June to 21 September), which was high enough to cause plant injury. MD had significantly negative effects on P. cathayana, as indicated by reduced photosynthesis, growth, and biomass, and higher MDA contents. On the other hand, EDU significantly increased photosynthesis rate, chlorophyll a fluorescence, Vcmax and Jmax, photosynthetic pigments, total antioxidant capacity, tree growth and biomass accumulation, and reduced lipid peroxidation, but there was no significant interaction between EDU and drought for most parameters, indicating that EDU can efficiently protect Populus cathayana against ambient O3 and the protection was not affected by soil water contents when soil water reached moderate drought level. Among all doses, EDU at 450ppm provided maximum protection. Comparison of EDU-treated and non-treated P. cathayana could be used as a biomarker system in risk assessment of the effects of ambient O3 on forest health.

High doses of ethylene diurea (EDU) are not toxic to willow and act as nitrogen fertilizer

Ethylene diurea (EDU) is synthetic chemical which protects plants against damage caused by ground level O3 and is used experimentally as a biomonitoring tool at doses usually ranging from 200 to 400mgL(-1) a.i. Although several studies have investigated the protective action of EDU, this mechanism remains unclear. Important uncertainties in EDU action are whether EDU acts as a source of nitrogen (N) to plants and whether high doses are phytotoxic. In order to answer these questions, we conducted an open-field experiment where potted willow (Salix sachalinensis Fr. Schm) plants were exposed to ambient O3 conditions and treated with 0, 800 or 1600mgL(-1) EDU as a soil drench, every nine days, for about 2.5months. We examined approximately 50 response variables. Based on N content in different plant organs, we found that (a) all EDU was transferred to the leaves and (b) high doses of EDU increased the leaf N content. However, EDU did not affect the C content and distribution within the plant body. Still, even at the highest dose, EDU was not toxic to this fast-growing species (however such a high dose should not be applied in uncontrolled environments); and there was no EDU persistence in the soil, as indicated by soil N content. Notably, our soil was free from organic matter and N-poor.

KEY MESSAGE

EDU per se does not cause toxicity to willow plants when applied as drench to a soil with no organic matter, rather, high EDU doses may act as nitrogen fertilizer in a nitrogen-poor soil.

The first toxicological study of the antiozonant and research tool ethylene diurea (EDU) using a Lemna minor L. bioassay: Hints to its mode of action

The antiozonant and research tool ethylene diurea (EDU) is widely studied as a phytoprotectant against the widespread pollutant ground-surface ozone. Although it has been extensively used, its potential toxicity in the absence of ozone is unknown and its mode of action is unclear. The purpose of this research was to toxicologically assess EDU and to further investigate its mode of action using Lemna minor L. as a model organism. Application of EDU concentrations greater than 593 mg L(-1) (practically 600 mg L(-1)) resulted in adverse inhibition of colony growth. As no-observed-toxic-effects concentration (NOEL) we recommend a concentration of 296 mg L(-1) (practically 300 mg L(-1)). A hormetic response was detected, i.e. stimulatory effects of low EDU concentrations, which may indicate overcompensation in response to disruption in homeostasis. Growth inhibition and suppressed biomass were associated with impacted chlorophyll a fluorescence (ΦPSII, qP and ETR). Furthermore, EDU increased mesophyll thickness, as indicated by frond succulence index. Applications of concentrations ≥593 mg L(-1) to uncontrolled environments should be avoided due to potential toxicity to sensitive organisms and the environment.

Assessing ambient ozone injury in olive (Olea europaea L.) plants by using the antioxidant ethylenediurea (EDU) in Saudi Arabia

The antiozonant chemical, ethylenediurea (N-[2-(2-oxo-1-imidazolidinyl)ethyl]-N'-phenylurea, abbreviated as EDU), was applied as stem injections or soil drenches to 5-year-old containerized plants of olive (Olea europaea L. cultivar Kalamata) in growth chambers in order to assess its ameliorative effects against realistic ozone (O3) stress. Visible injury symptoms were reduced greatly in individuals treated with EDU, with injection applications having greater protection than soil drenches. EDU application caused increases in the measured ecophysiological parameters compared to untreated individuals. In particular, the stem injection protected plants against photosynthetic impairment (unchanged net photosynthetic rates and intercellular CO2 concentration, in comparison to plants grown in filtered air). EDU application increased the protection of PSII from ambient O3 oxidative stress, although it did not retain the proportion of redox state of QA, pigment composition of photosynthetic apparatus and size of light-harvesting complex of PSII. However, the stem injection of plants with EDU induced lower non-photochemical quenching (NPQ) values in comparison to ambient air (-2 %), indicating a better photoprotection of PSII in comparison to soil drench application. EDU application caused increases in the morphological and biometric parameters compared to individuals exposed to ambient air. To the best of our knowledge, this is the first study highlighting the protection of Kalamata olive trees due to EDU in terms of growth, yield, visible injury, and photosynthetic performance. Furthermore, this study proved that EDU could be a low-cost and a low-technology efficient tool for assessing O3 effects on plant performances in the field in Saudi Arabia.

Changes of paramagnetic species in cereal grains upon short-term ozone action as a marker of oxidative stress tolerance

The increase of the concentration of ozone in the atmosphere, being the direct source of reactive oxygen species, results in the yield loss of agronomic crops. On the other hand, ozone is also used as a protector against microorganisms, living in plants and present in materials obtained from them, dangerous for human and animal health. In this work it has been studied if ozone in doses similar to those used for removal of microorganisms can have significant influence on the generation of stable organic radicals and changes in the character of transition metal ions and in the antioxidative biochemical parameters of cereal grains. The aim of this work was to find if the response of grains of three cereals (wheat, oat and barley) to ozone depended on their oxidative stress tolerance. The influence of direct short-term ozone application on grains of these cereals, each represented by two genotypes with different oxidative stress tolerance, was studied by biochemical analyses and by electron paramagnetic resonance (EPR) technique. Whole grains as well as their parts: embryo, endosperm and seed coat were subjected to ozone treatment for 30 min. Biochemical investigation of control samples showed that their antioxidant activity increased in order: wheat<oat<barley. EPR method revealed that character and the number of paramagnetic species (transition metal ions: Fe(III), Cu(II), Mn(II) and stable organic radicals) changed upon ozone exposure, depending on the kind of cereal, stress tolerance of particular genotype and the part of grain. The control samples of whole grains and their parts originating from sensitive genotypes contained higher amounts of stable organic radicals (semiquinone, phenoxyl and carbohydrate types) than those from tolerant ones. In embryos of grains from sensitive genotypes their amount increased upon ozone treatment stronger than in embryos from grains of tolerant cultivars. In seed coats and endosperms such relation was not found and the changes in the content of the radicals during ozone application were correlated with the amount of transition metal ions and were more intensive in parts of grains richer in easily oxidized iron species Fe(II), located in inorganic structures. On the contrary, Fe(II) ions situated in embryos were stabilized by organic matrix and did not undergo oxidation by ozone.

Effects of long-term ambient ozone exposure on biomass and wood traits in poplar treated with ethylenediurea (EDU)

This is the longest continuous experiment where ethylenediurea (EDU) was used to protect plants from ozone (O3). Effects of long-term ambient O3 exposure (23 ppm h AOT40) on biomass of an O3 sensitive poplar clone (Oxford) were examined after six years from in-ground planting. Trees were irrigated with either water or 450 ppm EDU. Above (-51%) and below-ground biomass (-47%) was reduced by O3 although the effect was significant only for stem and coarse roots. Ambient O3 decreased diameter of the lower stem, and increased moisture content along the stem of not-protected plants (+16%). No other change in the physical wood structure was observed. A comparison with a previous assessment in the same experiment suggested that O3 effects on biomass partitioning to above-ground organs depend on the tree ontogenetic stage. The root/shoot ratios did not change, suggesting that previous short-term observations of reduced allocation to tree roots may be overestimated.

Searching for common responsive parameters for ozone tolerance in 18 rice cultivars in India: Results from ethylenediurea studies

Eighteen rice (Oryza sativa) cultivars were screened for ozone (O3) tolerance and for the most responsive parameters with ethylenediurea (EDU) treatments at two experimental sites experiencing high ambient O3 conditions in the Indo-Gangetic Plains (IGP) of India. EDU was applied at 15 day intervals until the final harvest phase as a foliar spray at 300 ppm in order to protect the plants from the adverse effects of O3. Antioxidant activity, malondialdehyde content (MDA), chlorophyll content, gas exchange, and chlorophyll fluorescence (Fv/Fm) at the vegetative and flowering phases and harvest-related parameters were studied, for a total of 24 parameters. Seven of the studied cultivars had higher than average grainweightplant(-1) in all site and treatment combinations and can be recommended for cultivation in areas suffering from high O3 concentrations. The most responsive parameters with EDU treatment in high O3 across all cultivars were superoxide dismutase (SOD) and catalase (CAT) activities, the contents of oxidised (GSSG) and reduced (GSH) glutathione and MDA, and shoot weight plant(-1). These results indicated that the O3 scavenging activity of EDU is mediated through an antioxidant defence system rather than a direct effect on physiological parameters, such as photosynthesis and stomatal conductance.

Assessing the effects of ambient ozone in China on snap bean genotypes by using ethylenediurea (EDU)

Four genotypes of snap bean (Phaseolus vulgaris L.) were selected to study the effects of ambient ozone concentration at a cropland area around Beijing by using 450 ppm of ethylenediurea (EDU) as a chemical protectant. During the growing season, the 8h (9:00-17:00) average ozone concentration was very high, approximately 71.3 ppb, and AOT40 was 29.0 ppm.h. All genotypes showed foliar injury, but ozone-sensitive genotypes exhibited much more injury than ozone-tolerant ones. Compared with control, EDU significantly alleviated foliar injury, increased photosynthesis rate and chlorophyll a fluorescence, Vcmax and Jmax, and seed and pod weights in ozone-sensitive genotypes but not in ozone-tolerant genotypes. EDU did not significantly affect antioxidant contents in any of the genotypes. Therefore, EDU effectively protected sensitive genotypes from ambient ozone damage, while protection on ozone-tolerant genotypes was limited. EDU can be regarded as a useful tool in risk assessment of ambient ozone on food security.

Ground-level O3 pollution and its impacts on food crops in China: a review

Ground-level ozone (O3) pollution has become one of the top environmental issues in China, especially in those economically vibrant and densely populated regions. In this paper, we reviewed studies on the O3 concentration observation and O3 effects on food crops throughout China. Data from 118 O3 monitoring sites reported in the literature show that the variability of O3 concentration is a function of geographic location. The impacts of O3 on food crops (wheat and rice) were studied at five sites, equipped with Open Top Chamber or O3-FACE (free-air O3 concentration enrichment) system. Based on exposure concentration and stomatal O3 flux-response relationships obtained from the O3-FACE experimental results in China, we found that throughout China current and future O3 levels induce wheat yield loss by 6.4-14.9% and 14.8-23.0% respectively. Some policies to reduce ozone pollution and impacts are suggested.

Screening agrochemicals as potential protectants of plants against ozone phytotoxicity

We tested seven contemporary agrochemicals as potential plant protectants against ozone phytotoxicity. In nine experiments, Bel-W3 tobacco plants were experienced weekly exposures to a) 80 nmol mol(-1) of ozone-enriched or ozone-free air in controlled environment chambers, b) an urban air polluted area, and c) an agricultural-remote area. Ozone caused severe leaf injury, reduced chlorophylls' and total carotenoids' content, and negatively affected photosynthesis and stomatal conductance. Penconazole, (35% ± 8) hexaconazole (28% ± 5) and kresoxim-methyl (28% ± 15) showed higher plants' protection (expressed as percentage; mean ± s.e.) against ozone, although the latter exhibited a high variability. Azoxystrobin (21% ± 15) showed lower protection efficacy and Benomyl (15% ± 9) even lower. Trifloxystrobin (7% ± 11) did not protect the plants at all. Acibenzolar-S-methyl + metalaxyl-M (Bion MX) (-6% ± 17) exhibited the higher variability and contrasting results: in some experiments it showed some protection while in others it intensified the ozone injury by causing phytotoxic symptoms on leaves, even in control plants.