Search

Ground-level ozone (O3) is a widespread air pollutant causing extensive injuries in plants. However, its effects on perennial energy crops remain poorly understood due to technical difficulties in cultivating fast-growing shrubs for biomass production under O3 treatment on the field. Here we present the results of a two-year evaluation in the framework of which willow (Salix sachalinensis F. Schmid) shrubs were exposed to ambient (AOZ) or elevated (EOZ) O3 in two successive growing seasons (2014, 2015) and treated with 0 (EDU0) or 400 mg L−1 (EDU400) ethylenediurea spray in the second growing season. In 2014, EOZ altered the chemical composition of both top young and fallen leaves, and a novel mechanism of decreasing Mg in fallen leaves while highly enriching it in young top leaves was revealed in shrubs exposed to EOZ. In 2015, EDU400 alleviated EOZ-induced decreases in leaf fresh mass to dry mass ratio (FM/DM) and leaf mass per area (LMA). While EDU400 protected against EOZ-induced suppression of the maximum rate at which leaves can fix carbon (Amax) in O3-asymptomatic leaves, it did not alleviate EOZ-induced suppression of the maximum rates of carboxylation (VCmax) and electron transport (Jmax) and chlorophylls a, b, and a + b in the same type of leaves. In O3-symptomatic leaves, however, EDU400 alleviated EOZ-induced suppression of chlorophylls a and a + b, indicating different mode of action of EDU between O3-asymptomatic and O3-symptomatic leaves. Extensive herbivory occurred only in AOZ-exposed plants, leading to suppressed biomass production, while EOZ also led to a similar suppression of biomass production (EDU0 × EOZ vs. EDU400 × EOZ). In 2016, carry-over effects were also evaluated following cropping and transplantation into new ambient plots. Effects of EOZ in the preceding growing seasons extended to the third growing season in the form of suppressed ratoon biomass production, indicating carry-over effect of EOZ. Although EDU400 protected against EOZ-induced suppression of biomass production when applied in 2015, there was no carry-over effect of EDU in the absence of EDU treatment in 2016. The results of this study provide novel mechanistic understandings of O3 and EDU modes of action and can enlighten cultivation of willow as energy crop. [ABSTRACT FROM AUTHOR]

Ground-level ozone (O3) pollution is a persistent environmental issue that can lead to adverse effects on trees and wood production, thus indicating a need for forestry interventions to mediate O3 effects. We treated hybrid larch (Larix gmelinii var. japonica × L. kaempferi) saplings grown in nutrient-poor soils with 0 or 400 mg L−1 water solutions of the antiozonant ethylenediurea (EDU0, EDU400) and exposed them to ambient O3 (AOZ; 08:00 − 18:00 ≈ 30 nmol mol−1) or elevated O3 (EOZ; 08:00 − 18:00 ≈ 60 nmol mol−1) over three growing seasons. We found that EDU400 protected saplings against most effects of EOZ, which included extensive visible foliar injury, premature senescence, decreased photosynthetic pigment contents and altered balance between pigments, suppressed gas exchange and biomass production, and impaired leaf litter decay. While EOZ had limited effects on plant growth (suppressed stem diameter), it decreased the total number of buds per plant, an effect that was not observed in the first growing season. These results indicate that responses to EOZ might have implications to plant competitiveness, in the long term, as a result of decreased potential for vegetative growth. However, when buds were standardized per unit of branches biomass, EOZ significantly increased the number of buds per unit of biomass, suggesting a potentially increased investment to bud development, in an effort to enhance growth potential and competitiveness in the next growing season. EDU400 minimized most of these effects of EOZ, significantly enhancing plant health under O3-induced stress. The effect of EDU was attributed mainly to a biochemical mode of action. Therefore, hybrid larch, which is superior to its parents, can be significantly improved by EDU under long-term elevated O3 exposure, providing a perspective for enhancing afforestation practices. [ABSTRACT FROM AUTHOR]

Statistical relationships between surface ozone (O3) concentration, precursor species and meteorological conditions in continental South Africa were examined from data obtained from measurement stations in north-eastern South Africa. Three multivariate statistical methods were applied in the investigation, i.e. multiple linear regression (MLR), principal component analysis (PCA) and –regression (PCR), and generalised additive model (GAM) analysis. The daily maximum 8-h moving average O3 concentrations were considered in these statistical models (dependent variable). MLR models indicated that meteorology and precursor species concentrations are able to explain ~50% of the variability in daily maximum O3 levels. MLR analysis revealed that atmospheric carbon monoxide (CO), temperature and relative humidity were the strongest factors affecting the daily O3 variability. In summer, daily O3 variances were mostly associated with relative humidity, while winter O3 levels were mostly linked to temperature and CO. PCA indicated that CO, temperature and relative humidity were not strongly collinear. GAM also identified CO, temperature and relative humidity as the strongest factors affecting the daily variation of O3. Partial residual plots found that temperature, radiation and nitrogen oxides most likely have a non-linear relationship with O3,while the relationship with relative humidity and CO is probably linear. An inter-comparison between O3 levels modelled with the three statistical models compared to measured O3 concentrations showed that the GAM model offered a slight improvement over the MLR model. These findings emphasise the critical role of regional-scale O3 precursors coupled with meteorological conditions in daily variances of O3 levels in continental South Africa.

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. [ABSTRACT FROM AUTHOR]

Abstract Tropospheric ozone is a major air pollutant that significantly damages crop production. Crop metabolic responses to rising chronic ozone stress have not been well studied in the field, especially in C4 crops. In this study, we investigated the metabolomic profile of leaves from two diverse maize (Zea mays) inbred lines and the hybrid cross during exposure to season‐long elevated ozone (~100 nl L−1) in the field using free air concentration enrichment (FACE) to identify key biochemical responses of maize to elevated ozone. Senescence, measured by loss of chlorophyll content, was accelerated in the hybrid line, B73 × Mo17, but not in either inbred line (B73 or Mo17). Untargeted metabolomic profiling further revealed that inbred and hybrid lines of maize differed in metabolic responses to ozone. A significant difference in the metabolite profile of hybrid leaves exposed to elevated ozone occurred as leaves aged, but no age‐dependent difference in leaf metabolite profiles between ozone conditions was measured in the inbred lines. Phytosterols and α‐tocopherol levels increased in B73 × Mo17 leaves as they aged, and to a significantly greater degree in elevated ozone stress. These metabolites are involved in membrane stabilization and chloroplast reactive oxygen species (ROS) quenching. The hybrid line also showed significant yield loss at elevated ozone, which the inbred lines did not. This suggests that the hybrid maize line was more sensitive to ozone exposure than the inbred lines, and up‐regulated metabolic pathways to stabilize membranes and quench ROS in response to chronic ozone stress.

Tropospheric ozone is a major air pollutant that significantly damages crop production. Crop metabolic responses to rising chronic ozone stress have not been well studied in the field, especially in C4 crops. In this study, we investigated the metabolomic profile of leaves from two diverse maize (Zea mays) inbred lines and the hybrid cross during exposure to season‐long elevated ozone (~100 nl L−1) in the field using free air concentration enrichment (FACE) to identify key biochemical responses of maize to elevated ozone. Senescence, measured by loss of chlorophyll content, was accelerated in the hybrid line, B73 × Mo17, but not in either inbred line (B73 or Mo17). Untargeted metabolomic profiling further revealed that inbred and hybrid lines of maize differed in metabolic responses to ozone. A significant difference in the metabolite profile of hybrid leaves exposed to elevated ozone occurred as leaves aged, but no age‐dependent difference in leaf metabolite profiles between ozone conditions was measured in the inbred lines. Phytosterols and α‐tocopherol levels increased in B73 × Mo17 leaves as they aged, and to a significantly greater degree in elevated ozone stress. These metabolites are involved in membrane stabilization and chloroplast reactive oxygen species (ROS) quenching. The hybrid line also showed significant yield loss at elevated ozone, which the inbred lines did not. This suggests that the hybrid maize line was more sensitive to ozone exposure than the inbred lines, and up‐regulated metabolic pathways to stabilize membranes and quench ROS in response to chronic ozone stress. [ABSTRACT FROM AUTHOR]

Statistical relationships between surface ozone (O3) concentration, precursor species and meteorological conditions in continental South Africa were examined from data obtained from measurement stations in north-eastern South Africa. Three multivariate statistical methods were applied in the investigation, i.e. multiple linear regression (MLR), principal component analysis (PCA) and –regression (PCR), and generalised additive model (GAM) analysis. The daily maximum 8-h moving average O3 concentrations were considered in these statistical models (dependent variable). MLR models indicated that meteorology and precursor species concentrations are able to explain ~50% of the variability in daily maximum O3 levels. MLR analysis revealed that atmospheric carbon monoxide (CO), temperature and relative humidity were the strongest factors affecting the daily O3 variability. In summer, daily O3 variances were mostly associated with relative humidity, while winter O3 levels were mostly linked to temperature and CO. PCA indicated that CO, temperature and relative humidity were not strongly collinear. GAM also identified CO, temperature and relative humidity as the strongest factors affecting the daily variation of O3. Partial residual plots found that temperature, radiation and nitrogen oxides most likely have a non-linear relationship with O3,while the relationship with relative humidity and CO is probably linear. An inter-comparison between O3 levels modelled with the three statistical models compared to measured O3 concentrations showed that the GAM model offered a slight improvement over the MLR model. These findings emphasise the critical role of regional-scale O3 precursors coupled with meteorological conditions in daily variances of O3 levels in continental South Africa. [ABSTRACT FROM AUTHOR]

Screening crop plants under elevated ozone concentrations ([O3]) is a pre-requisite for identification of tolerant lines, but few studies have mapped maize responses to elevated [O3]. B73-Mo17 nearly isogenic lines (NILs) were screened in the field under ambient (~40 ppb) and elevated (~100 ppb) [O3] at the Free Air gas Concentration Enrichment (FACE) research facility in Champaign, IL to identify maize leaf damage QTL associated with variation in O3-induced oxidative stress response. In Mo17 NILs, a significant leaf damage QTL was identified at 161Mb on chromosome 2. To assess the feasibility of high-throughput phenotyping and fine mapping of early season O3 leaf damage QTL, a subset of the nested association mapping (NAM) founder lines were screened in a growth chamber experiment under ambient and elevated [O3]. Results showed that elevated [O3] decreased the number of green leaves while increasing the number of lesioned and dead leaves. Most lines showed the same general response to elevated [O3], but the degree of damage varied among lines. Next, tolerant and sensitive B73-Mo17 NILs identified from the FACE study, and hybrid crosses of the identified NILs with Mo17 (n = 20) were grown under elevated O3 (~150 ppb) in growth chambers (n = 7). In the chambers, O3-sensitive lines could be distinguished from tolerant lines based on leaf lesions, but there was not a continuous degree of damage like that seen in the field. This research identified a repeatable O3-induced leaf damage QTL and developed populations and markers that can be used in future growth chamber fine mapping experiments. These results demonstrate the feasibility of high-throughput phenotyping and fine mapping of O3 leaf damage QTL in a controlled environment.

Elevated levels of tropospheric ozone (O 3) are phytotoxic, inhibiting plant growth and production, and thus, compromising environmental health and sustainable crop production. It is therefore critical to devise strategies to protect plants from the negative effects of O 3. However, the efficacy of different chemical or non-chemical methods to protect plants against O 3 toxicities has not been critically reviewed. Hence, this study aimed at comprehensively reviewing various methods of crop protection against O 3 stress. Ethylenediurea (EDU) is the most investigated and efficient protectant in ameliorating O 3 -induced phytodamage. However, plant protectants (e.g. pesticides, fungicides), antitranspirants (e.g. di-1-p-menthene), antioxidants (e.g. ascorbic acid, diphenylamine), exogenously-applied plant hormones (e.g. ethylene, kinetin, abscisic acid), and nutrient management strategies (e.g. varied level of nitrogen fertilizers, application of calcium acetate) were also found to offer some protection against O 3. Hence, more studies are needed to comprehensively explore the potential of these methods, individually and in different combinations. Biological mechanisms that underlie the ameliorative effect of the different methods are discussed along with relevance of the concept of hormesis. This assessment also acknowledges major information gaps and suggests future options for dealing with O 3 pollution. New insights into the efficacy of additional protectants provide a new dimension to plant protection against O 3 -induced detrimental effects, and suggest that future research should use a green chemistry approach and an 'one health' perspective. • Application of protectants is widely adopted to alleviate O 3 phytotoxicity. • Review reveals that ethylene diurea (EDU) is the vastly studied protectant. • Besides EDU, antioxidants, plant nutrients, and growth regulators are also effective. • Protectants alleviate O 3 stress by enhancing physiological and biochemical traits. [ABSTRACT FROM AUTHOR]

Tropospheric ozone (O 3), a critically harmful greenhouse gas, has steadily increased over the last several decades, leading to significant soybean (Glycine max) yield loses worldwide. However, substantial efforts have focused on the effect of elevated O 3 concentration (eOZ) on shoots rather than the roots that support plant fitness and directly interact with soil ecosystems. To better assess the impact of eOZ on roots, this study investigated morphological and proteomic profiles of two soybean genotypes from the same genetic background, but with contrasting O 3 resilience, Fiskeby III (O 3 -tolerant) and Fiskeby 840–7–3 (O 3 -sensitive). Plants were treated either with sub-ambient O 3 or eOZ in a field-based air exclusion system (AES) and harvested at flowering and pod-filling stages. Our results established that the effect of eOZ on decreasing root biomass initiated at the flowering stage, while above-ground biomass was not altered. However, O 3 -caused biomass reduction was observed in both, roots and shoots, at the pod-filling stage. Season-long eOZ ultimately caused a 29 % seed yield reduction in Fiskeby III, and 50 % in Fiskeby 840–7–3. Root proteome analysis showed that the effect of O 3 in roots is complex, and distinct between flowering and pod-filling stages. Changes in the abundance of proteins correspond to glycolysis, TCA cycle, nitrogen metabolism, secondary metabolites, antioxidant, and stress response pathway, and differed between genotypes. Some of these changes may be in response to eOZ as an attempt to mitigate the effects of a challenging environment, and others are likely due to genetic differences that confer an adaptative advantage to the O 3 resilient genotype. These findings provide further knowledge of proteins and pathways that may confer O 3 -tolerance, which can be applied to develop O 3 -resistant, high-yielding soybean. • Exposure to tropospheric ozone impacts aboveground and underground organs. • Proteins and metabolism responses to ozone is distinct at early and late stages of development. • Ozone caused greater changes in protein expression in sensitive than in tolerant soybean. • Identification of ozone resilience traits in ancestral genotypes is important for improvement of soybean yields worldwide. [ABSTRACT FROM AUTHOR]

With the vigorous implementation of the Clean Air Action since 2013, the atmospheric particle pollution in China has been substantially reduced, but ozone concentrations have been increasing. Moreover, tropospheric ozone can make a difference in meteorology and air quality through its radiative forcing as an important greenhouse gas. A coupled regional meteorology-chemistry model (WRF-Chem) was used to reproduce an ozone pollution event that occurred in North China in June 2017. The impact of tropospheric ozone radiative forcing on local meteorological fields and its feedback effect on ozone air quality were analyzed through sensitivity experiments. The results revealed the excellent performance of the WRF-Chem model for meteorological parameters and ozone pollutant concentrations. Tropospheric ozone radiative forcing (TORF) increased the average near-surface temperature by 0.23 K in the Beijing-Tianjin-Hebei-Shandong Region (the maximum temperature increase could reach 0.8 K), reduced the relative humidity by 1.84%, and elevated the height of the boundary layer by 27.73 m. TORF had a weaker effect on wind speed (-0.02 m·s -1 ), but the generated anomalous southwestern wind was more liable to transport ozone and its precursors from upstream polluted areas to North China. Under the impacts of ozone radiation feedback, the ozone volume fraction in the study area increased by an average of 1.7% (1.23×10 -9 ), whereas in the heavily polluted Beijing and Tianjin areas, the increase reached up to 5×10 -9 . Furthermore, the enhanced gas phase chemical reactions were identified as the dominant cause worsening near-surface ozone pollution by progress diagnostic analysis.

Tropospheric ozone (O 3) is a phytotoxic pollutant that leads to a reduction in crop yield. Nanotechnology offers promising solutions to stem such yield losses against abiotic stresses. Silver nanoparticles are major nanomaterials used in consumer products however, their impact on crops under abiotic stress is limited. In this study, we evaluated the anti-ozonant efficacy of biogenic silver nanoparticles (B-AgNPs) and compared them with a model anti-ozonant ethylenediurea (EDU) against ozone phyto-toxicity. Growth, physiology, antioxidant defense, and yield parameters in two wheat cultivars (HD-2967 & DBW-17), treated with B-AgNPs (25 mg/L and 50 mg/L) and EDU (150 mg/L and 300 mg/L), were studied at both vegetative and reproductive stages. During the experimental period, the average ambient ozone concentration and accumulated dose of ozone over a threshold of 40 ppb (AOT40) (8 h day−1) were found to be 60 ppb and 6 ppm h, respectively, which were sufficient to cause ozone-induced phyto-toxicity in wheat. Growth and yield for B-AgNPs as well as EDU-treated plants were significantly higher in both the tested cultivars over control ones. However, 25 mg/L B-AgNPs treatment showed a more pronounced effect in terms of yield attributes and its lower accumulation in grains for both cultivars. DBW-17 cultivar responded better with B-AgNPs and EDU treatments as compared to HD-2967. Meanwhile, foliar exposure of B-AgNPs (dose; 25 mg/L) significantly enhanced grain weight plant−1, thousand-grain weight, and harvest index by 54.22 %, 29.46 %, and 14.21 %, respectively in DBW-17, when compared to control. B-AgNPs could enhance ozone tolerance in wheat by increasing biochemical and physiological responses. It is concluded that B-AgNPs at optimum concentrations were as effective as EDU, hence could be a promising ozone protectant for wheat. • Comparative efficacy of B-AgNP and EDU as ozone protectant was evaluated on Triticum aestivum L. under high tropospheric O 3. • Efficacy of B-AgNPs was found to be as good as EDU in terms of enhanced growth as well as yield in both wheat cultivars. • B-AgNPs at optimum concentration could be a promising anti-ozonant for Triticum aestivum L. experiencing high levels of O 3. [ABSTRACT FROM AUTHOR]