Use of the antiozonant ethylenediurea (EDU) in Italy: verification of the effects of ambient ozone on crop plants and trees and investigation of EDU's mode of action

Twenty-four experiments where EDU was used to protect plants from ozone (O₃) in Italy are reviewed. Doses of 150 and 450 ppm EDU at 2-3 week intervals were successfully applied to alleviate O₃-caused visible injury and growth reductions in crop and forest species respectively. EDU was mainly applied as soil drench to crops and by stem injection or infusion into trees. Visible injury was delayed and reduced but not completely. In investigations on mode of action, EDU was quickly (<2 h) uptaken and translocated to the leaf apoplast where it persisted long (>8 days), as it cannot move via phloem. EDU did not enter cells, suggesting it does not directly affect cell metabolism. EDU delayed senescence, did not affect photosynthesis and foliar nitrogen content, and stimulated antioxidant responses to O₃ exposure. Preliminary results suggest developing an effective soil application method for forest trees is warranted.     

Cutleaf coneflower (Rudbeckia laciniata L.) response to ozone and ethylenediurea (EDU)

Cutleaf coneflower (Rudbeckia laciniata L.) seedlings were placed into open-top chambers in May, 2004 and fumigated for 12 wks. Nine chambers were fumigated with either carbon-filtered air (CF), non-filtered air (NF) or twice-ambient (2×) ozone (O₃). Ethylenediurea (EDU) was applied as a foliar spray weekly at 0 (control), 200, 400 or 600 ppm. Foliar injury occurred at ambient (30%) and elevated O₃ (100%). Elevated O₃ resulted in significant decreases in biomass and nutritive quality. Ethylenediurea reduced percent of leaves injured, but decreased root and total biomass. Foliar concentrations of cell-wall constituents were not affected by EDU alone; however, EDU × O₃ interactions were observed for total cell-wall constituents and lignocellulose fraction. Our results demonstrated that O₃ altered the physiology and productivity of cutleaf coneflower, and although reducing visible injury EDU may be phytotoxic at higher concentrations.     

A comparison of North American and Asian exposure–response data for ozone effects on crop yields

Modelling-based studies to assess the extent and magnitude of ozone (O₃) risk to agriculture in Asia suggest that yield losses of 5–20% for important crops may be common in areas experiencing elevated O₃ concentrations. These assessments have relied on European and North American dose–response relationships and hence assumed an equivalent Asian crop response to O₃ for local cultivars, pollutant conditions and climate. To test this assumption we collated comparable dose–response data derived from fumigation, filtration and EDU experiments conducted in Asia on wheat, rice and leguminous crop species. These data are pooled and compared with equivalent North American dose–response relationships. The Asian data show that at ambient O₃ concentrations found at the study sites (which vary between ～35–75 ppb 4–8 h growing season mean), yield losses for wheat, rice and legumes range between 5–48, 3–47 and 10–65%, respectively. The results indicate that Asian grown wheat and rice cultivars are more sensitive to O₃ than the North American dose–response relationships would suggest. For legumes the scatter in the data makes it difficult to reach any equivalent conclusion in relative sensitivities. As such, existing modelling-based risk assessments may have substantially underestimated the scale of the problem in Asia through use of North American derived dose–response relationships.     

Protection of palak (Beta vulgaris L. var Allgreen) plants from ozone injury by ethylenediurea (EDU): Roles of biochemical and physiological variations in alleviating the adverse impacts

Ameliorative effects of ethylenediurea (N-[2-(2-oxo-1-imidazolinidyl) ethyl]-N′ phenylurea, abbreviated as EDU) against ozone stress were studied on selected growth, biochemical, physiological and yield characteristics of palak (Beta vulgaris L. var Allgreen) plants grown in field at a suburban site of Varanasi, India. Mean eight hourly ozone concentration varied from 52 to 73 ppb which was found to produce adverse impacts on plant functioning and growth characteristics. The palak plants were treated with 300 ppm EDU at 10 days after germination at 10 days interval up to the plant maturity. Lipid peroxidation in EDU treated plants declined significantly as compared to non-EDU treated ones. Significant increment in F_v/F_m ratio in EDU treated plants as compared to non-EDU treated ones was recorded. EDU treated plants showed significant increment in ascorbic acid contents and reduction in peroxidase activity as compared to non-EDU treated ones. As a result of the protection provided by EDU against ozone induced stress on biochemical and physiological characteristics of palak, the morphological parameters also responded positively. Significant increments were recorded in shoot length, number of leaves plant⁻¹, leaf area and root and shoot biomass of EDU treated plants as compared to non-EDU treated ones. Contents of Na, K, Ca, Mg and Fe were higher in EDU treated plants as compared to non-EDU treated ones. The present investigation proves the usefulness of EDU in partially ameliorating ozone injury in ambient conditions.     

Effects of ozone on growth, yield and leaf gas exchange rates of two Bangladeshi cultivars of wheat (Triticum aestivum L.)

To clarify the effects of O₃ on crop plants cultivated in Bangladesh, two Bangladeshi wheat cultivars (Sufi and Bijoy) were grown in plastic boxes filled with Andisol and exposed daily to charcoal-filtered air or O₃ at 60 and 100 nl l⁻¹ (10:00-17:00) from 13 March to 4 June 2008. The whole-plant dry mass and grain yield per plant of the two cultivars at the final harvest were significantly reduced by the exposure to O₃. Although there was no significant effect of O₃ on stomatal diffusive conductance to H₂O of flag leaf, net photosynthetic rate of the leaf was significantly reduced by the exposure to O_3. The sensitivity of growth, yield, yield components and leaf gas exchange rates to O₃ was not significantly different between the two cultivars. The results obtained in the present study suggest that ambient levels of O₃ may detrimentally affect wheat production in Bangladesh.     

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.     

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.     

Establishing ozone flux–response relationships for winter wheat: Analysis of uncertainties based on data for UK and Polish genotypes

The work outlined in this paper had three objectives. The first was to explore the effects of ozone pollution on grain yield and quality of commercially-grown winter wheat cultivars. The second was to derive a stomatal ozone flux model for winter wheat and compare with those already developed for spring wheat. The third was to evaluate exposure- versus flux–response approaches from a risk assessment perspective, and explore the implications of genetic variation in modelled ozone flux.Fifteen winter wheat cultivars were grown in open-top chambers where they were exposed to four levels of ozone. During fumigation, stomatal conductance measurements were made over the lifespan of the flag leaf across a range of environmental conditions. Although significant intra-specific variation in ‘ozone sensitivity’ (in terms of impacts on yield) was identified, yield was inversely related (R² = 0.63, P < 0.001) to the accumulated hourly averaged ozone exposure above 40 ppb during daylight hours (AOT40) across the dataset. The adverse effect of ozone on yield was principally due to a decline in seed weight. Algorithms defining the influence of environmental variables on stomatal uptake were subtly different from those currently in use, based on data for spring wheat, to map ozone impacts on pan-European cereal yield. Considerable intra-specific variation in phenological effects was identified. This meant that an ‘average behaviour’ had to be derived which reduced the predictive capability of the derived stomatal flux model (R² = 0.49, P < 0.001, 15 cultivars included). Indeed, given the intra-specific variability encountered, the flux model that was derived from the full dataset was no better in predicting O₃ impacts on wheat yield than was the AOT40 index. The study highlights the need to use ozone risk assessment tools appropriate to specific vegetation types when modelling and mapping ozone impacts at the regional level.     

Ethylenediurea (EDU): a research tool for assessment and verification of the effects of ground level ozone on plants under natural conditions

Ethylenediurea (EDU) has been widely used to prevent ozone (O₃) injury and crop losses in crop plants and growth reductions in forest trees. Successful use requires establishing a dose/response curve for EDU and the proposed plant in the absence of O₃ and in the presence of O₃ before initiating multiple applications to prevent O₃ injury. EDU can be used to verify foliar O₃ symptoms in the field, and to screen plants for sensitivity to O₃ under ambient conditions. Despite considerable research, the mode of action of EDU remains elusive. Additional research on the mode of action of EDU in suppressing O₃ injury in plants may also be helpful in understanding the mode of action of O₃ in causing injury in plants.     

Ozone sensitivity of the Mediterranean terophyte Trifolium striatum is modulated by soil nitrogen content

The influence of nitrogen (N) fertilization on the sensitivity to ozone (O₃) has been studied using the O₃ sensitive species Trifolium striatum, an annual species frequently found in therophitic grasslands of the dehesas in the central Iberian Peninsula. The experiment was carried out in open-top chambers using three different O₃ exposure treatments: charcoal-filtered air (CFA), non-filtered air (NFA) and non-filtered air plus 40 nl l⁻¹ added over ambient concentrations (NFA+). After 30 days of exposure to the different treatments, plants were placed under ambient conditions until seed ripeness was completed. Three N fertilization treatments were established receiving final doses of 10 (low), 30 (medium) or 60 (high) kg N ha⁻¹ throughout the growing period divided into four proportional doses at every 15 days. Ozone affected phenology and reduced total aerial and flower biomass and seed production in NFA and NFA+ treatments. Carry-over effects of O₃ on the reproductive ability of this species were found resulting in reductions in flower biomass and seed production detected 1 month after O₃ exposure. By contrast, N fertilization increased aerial and flower biomass. Significant O₃×N interactive effects were detected since N fertilization counterbalanced O₃-induced effects only when plants were exposed to moderate O₃ levels (NFA) but not under high O₃ concentrations (NFA+). The observed O₃ effects on reproductive ability of T. striatum might determine changes in species viability and future diversity of the ecosystem.     

Ozone,antioxidant spray and meloidogyne hapla effects on tobacco

The relationship between ozone and the northern root-knot nematode on tobacco was investigated. Seedlings of tobacco (Nicotiana tabacum L.) cv. Virginia 115 were inoculated and not inoculated with root-knot (Meloidogyne hapla (Chitwood) prior to transplanting to a field plot. One-half the plants were sprayed at weekly intervals with an antioxidant, EDU at the rate of 1 kg ha⁻¹ to protect against oxidant injury. O₃ concentrations in excess of 80 ppb were recorded 14 times during the summer of 1982. Ambient ozone inhibited growth and yield of tobacco inoculated and not inoculated with M. hapla. Tobacco inoculated with nematode alone developed significantly more ozone injury than other treatments indicating that tobacco infected with M. hapla is more susceptible to ambient O₃. Significantly 20% more galls developed on plants with nematode inoculation compared to plants with nematode inoculation + EDU indicating that EDU indirectly reduced gall development in tobacco. Plants protected with EDU also showed an increase in dry weight of shoot, root and biomass.     

Cadmium accumulation in and tolerance of rice (Oryza sativa L.) varieties with different rates of radial oxygen loss

Cadmium (Cd) uptake and tolerance were investigated among 20 rice cultivars based on a field experiment (1.2 mg Cd kg⁻¹ in soil) and a soil pot trial (control, 100 mg Cd kg⁻¹), and rates of radial oxygen loss (ROL) were measured under a deoxygenated solution. Significant differences were found among the cultivars in: (1) brown rice Cd concentrations (0.11-0.29 mg kg⁻¹) in a field soil, (2) grain Cd tolerance (34-113%) and concentrations (2.1-6.5 mg kg⁻¹) in a pot trial, and (3) rates of ROL (15-31 mmol O₂ kg⁻¹ root d.w. h⁻¹). Target hazard quotients were calculated for the field experiment to assess potential Cd risk. Significant negative relationships were found between rates of ROL and concentrations of Cd in brown rice or straw under field and greenhouse conditions, indicating that rice cultivars with higher rates of ROL had higher capacities for limiting the transfer of Cd to rice and straw.     

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.     

DNA damage in Populus tremuloides clones exposed to elevated O3

The effects of elevated concentrations of atmospheric tropospheric ozone (O₃) on DNA damage in five trembling aspen (Populus tremuloides Michx.) clones growing in a free-air enrichment experiment in the presence and absence of elevated concentrations of carbon dioxide (CO₂) were examined. Growing season mean hourly O₃ concentrations were 36.3 and 47.3 ppb for ambient and elevated O₃ plots, respectively. The 4th highest daily maximum 8-h ambient and elevated O₃ concentrations were 79 and 89 ppb, respectively. Elevated CO₂ averaged 524 ppm (+150 ppm) over the growing season. Exposure to O₃ and CO₂ in combination with O₃ increased DNA damage levels above background as measured by the comet assay. Ozone-tolerant clones 271 and 8L showed the highest levels of DNA damage under elevated O₃ compared with ambient air; whereas less tolerant clone 216 and sensitive clones 42E and 259 had comparably lower levels of DNA damage with no significant differences between elevated O₃ and ambient air. Clone 8L was demonstrated to have the highest level of excision DNA repair. In addition, clone 271 had the highest level of oxidative damage as measured by lipid peroxidation. The results suggest that variation in cellular responses to DNA damage between aspen clones may contribute to O₃ tolerance or sensitivity.     

Degradation kinetics of anthracene by ozone on mineral oxides

To further understand the role of substrates on the heterogeneous reactions of polycyclic aromatic hydrocarbons, the reactions of ozone with anthracene adsorbed on different mineral oxides (SiO₂, α-Al₂O₃ and α-Fe₂O₃) and on Teflon disc were investigated in dark at 20 °C. No reaction between ozone and anthracene on Teflon disc was observed when the ozone concentration was ～1.18 × 10¹⁴ molecules cm^?3. The reactions on mineral oxides exhibited pseudo-first-order kinetics for anthracene loss, and the pseudo-first-order rate constant (k_1,obs) displayed a Langmuir–Hinshelwood dependence on the gas-phase ozone concentration. The adsorption equilibrium constants for ozone (K_O3) on SiO₂-1, SiO₂-2, α-Al₂O₃ and α-Fe₂O₃ were (0.81 ± 0.26) × 10^?15 cm³, (2.83 ± 1.17) × 10^?15 cm³, (2.48 ± 0.77) × 10^?15 cm³ and (1.66 ± 0.45) × 10^?15 cm³, respectively; and the maximum pseudo-first-order rate constant (k_1,max) on these oxides were (0.385 ± 0.058) s^?1, (0.101 ± 0.0138) s^?1, (0.0676 ± 0.0086) s^?1 and (0.0457 ± 0.004) s^?1, respectively. Anthraquinone was identified as the main surface product of anthracene reacted with ozone. Comparison with previous research and the results obtained in this study suggest that the reactivity of anthracene with ozone and the lifetimes of anthracene adsorbed on mineral dust in the atmosphere are determined by the nature of the substrate.     

Assessing the impact of ambient ozone on growth and productivity of two cultivars of wheat in India using three rates of application of ethylenediurea (EDU)

Three rates of ethylenediurea were used to assess the impact of ambient ozone on growth and productivity of wheat (Triticum aestivum L) cultivars "Malviya 533" (M 533) and "Malviya 234" (M 234) at a suburban site near Varanasi, India, beginning in December. Wheat plants were treated with EDU at 0, 150, 300 and 450 ppm as soil drenches at 10-day intervals. EDU treatment affected plant growth, with effects varying with cultivar, age, and EDU concentration. Seed yield was improved for M 533 at 150 ppm EDU, while yield improved for M 234 at 300 and 450 ppm EDU. M 533 appears to be more resistant to ozone than M 234. Overall results confirmed that EDU is very useful in assessing the effect of ambient ozone in India.     

Assessing the impacts of current and future concentrations of surface ozone on crop yield with meta-analysis

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

Surface ozone-temperature relationships in the eastern US: A monthly climatology for evaluating chemistry-climate models

We use long-term, coincident O₃ and temperature measurements at the regionally representative US Environmental Protection Agency Clean Air Status and Trends Network (CASTNet) over the eastern US from 1988 through 2009 to characterize the surface O₃ response to year-to-year fluctuations in weather, for the purpose of evaluating global chemistry-climate models. We first produce a monthly climatology for each site over all available years, defined as the slope of the best-fit line (m_O3-T) between monthly average values of maximum daily 8-hour average (MDA8) O₃ and monthly average values of daily maximum surface temperature (T_max). Applying two distinct statistical approaches to aggregate the site-specific measurements to the regional scale, we find that summer time m_O3-T is 3–6 ppb K^?1 (r = 0.5–0.8) over the Northeast, 3–4 ppb K^?1 (r = 0.5–0.9) over the Great Lakes, and 3–6 ppb K^?1 (r = 0.2–0.8) over the Mid-Atlantic. The Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model version 3 (AM3) global chemistry-climate model generally captures the seasonal variations in correlation coefficients and m_O3-T despite biases in both monthly mean summertime MDA8 O₃ (up to +10 to +30 ppb) and daily T_max (up to +5 K) over the eastern US. During summer, GFDL AM3 reproduces m_O3-T over the Northeast (m_O3-T = 2–6 ppb K^?1; r = 0.6–0.9), but underestimates m_O3-T by 4 ppb K^?1 over the Mid-Atlantic, in part due to excessively warm temperatures above which O₃ production saturates in the model. Combining T_max biases in GFDL AM3 with an observation-based m_O3-T estimate of 3 ppb K^?1implies that temperature biases could explain up to 5–15 ppb of the MDA8 O₃ bias in August and September though correcting for excessively cool temperatures would worsen the O₃ bias in June. We underscore the need for long-term, coincident measurements of air pollution and meteorological variables to develop process-level constraints for evaluating chemistry-climate models used to project air quality responses to climate change.     

An examination of oxidant amounts on secondary organic aerosol formation and aging

The effect of HO_x radicals (OH and HO₂) and ozone (O₃) on aerosol formation and aging has been studied. Experiments were performed in presence as well as in absence of oxygen in a flow-through chamber at 299 K for three organic precursor gases, isoprene, α-pinene and m-xylene. The HO_x source was the UV photolysis of humidified air or nitrogen and was measured with a GTHOS (Ground-based Tropospheric Hydrogen Oxides Sensor). The precursor gases concentration was monitored with an online GC-FID. The aerosol mass was then quantified by a Tapered Element Oscillating Microbalance (TEOM). Typical oxidant mixing ratios were (0–4.5) ppm for O₃, 200 pptv for OH and 3 ppbv for HO₂. A simple kinetics model is used to infer the aerosol production mechanism. In the present of O₃ (or O₂), the SOA yields were 0.46, 0.036 and 0.12 for α-pinene with an initial concentration of 100 ppbv (RH = 37%), isoprene with an initial concentration of 177 ppbv (RH = 50%) and m-xylene with an initial concentration of 100 ppbv (RH = 37%), respectively. When the chosen precursor gases reacted with HO_x in the absence of O₃, the maximum SOA yields were significantly increased by factors of 1.6 for isoprene 1.1 for α-pinene, and 3 for m-xylene respectively. The comparison of the calculated and measured potential aerosol mass concentrations as function of time shows that presence of ozone or oxygen can influence the aerosol yield and the absence of ozone or oxygen in the system resulted in high concentrations of its organic aerosol products.     

Leaf size and surface characteristics of Betula papyrifera exposed to elevated CO2 and O3

Betula papyrifera trees were exposed to elevated concentrations of CO₂ (1.4 × ambient), O₃ (1.2 × ambient) or CO₂ + O₃ at the Aspen Free-air CO₂ Enrichment Experiment. The treatment effects on leaf surface characteristics were studied after nine years of tree exposure. CO₂ and O₃ increased epidermal cell size and reduced epidermal cell density but leaf size was not altered. Stomatal density remained unaffected, but stomatal index increased under elevated CO₂. Cuticular ridges and epicuticular wax crystallites were less evident under CO₂ and CO₂ + O₃. The increase in amorphous deposits, particularly under CO₂ + O_3, was associated with the appearance of elongated plate crystallites in stomatal chambers. Increased proportions of alkyl esters resulted from increased esterification of fatty acids and alcohols under elevated CO₂ + O₃. The combination of elevated CO₂ and O₃ resulted in different responses than expected under exposure to CO₂ or O₃ alone.