O3 Effect Research Articles

New ozone–nitrogen model shows early senescence onset is the primary cause of ozone-induced reduction in grain quality of wheat

Abstract. Ozone (O3) air pollution is well known to adversely affect both the grain and protein yield of wheat, an important staple crop. This study aims to identify and model the key plant processes influencing the effect of O3 on wheat protein. The DO3SE-Crop model was modified in this work to incorporate nitrogen (N) processes, and we parameterised the O3 effect on stem, leaf, and grain N using O3 fumigation datasets spanning 3 years and four O3 treatments. These modifications mean that the newly developed DO3SE-CropN model is the first crop model to include O3 effects on N processes, making it a valuable tool for understanding O3 effects on wheat quality. Our results show that the new model captures the O3 effect on grain N concentrations and the anthesis leaf and stem concentrations well, with an R2 of 0.6 for the increase in grain N concentration and an R2 of 0.3 for the decrease in grain N content under O3 exposure. However, the O3 effect on harvest leaf and stem N is exaggerated. Overestimations of harvest leaf N range from ∼20 % to 120 %, while overestimations of harvest stem N range from ∼40 % to 120 %. Further, a sensitivity analysis revealed that, irrespective of O3 treatment, early senescence onset (simulated as being ∼13 d earlier in the treatment with very high O3 vs. the low-O3 treatment) was the primary plant process affecting grain N. This finding has implications for the breeding of stay-green cultivars for maintaining yield, as well as quality, under O3 exposure. This modelling study therefore demonstrates the capability of the DO3SE-CropN model to simulate processes by which O3 affects N content and, thereby, determines that senescence onset is the main driver of O3 reductions in grain protein yield. The implication of the sensitivity analysis is that breeders should focus their efforts on stay-green cultivars that do not experience a protein penalty when developing O3-tolerant lines, to maintain both wheat yield and nutritional quality under O3 exposure. This work supports the second phase of the Tropospheric Ozone Assessment Report (TOAR) by investigating the impacts of tropospheric O3 on wheat, with a focus on wheat quality impacts that will subsequently affect human nutrition.

Drought mitigates the adverse effects of O3 on plant photosynthesis rather than growth: A global meta-analysis considering plant functional types.

Tropospheric ozone (O3 ) is a phytotoxic air pollutant adversely affecting plant growth. High O3 exposures are often concurrent with summer drought. The effects of both stresses on plants are complex, and their interactions are not yet well understood. Here, we investigate whether drought can mitigate the negative effects of O3 on plant physiology and growth based on a meta-analysis. We found that drought mitigated the negative effects of O3 on plant photosynthesis, but the modification of the O3 effect on the whole-plant biomass by drought was not significant. This is explained by a compensatory response of water-deficient plants that leads to increased metabolic costs. Relative to water control condition, reduced water treatment decreased the effects of O3 on photosynthetic traits, and leaf and root biomass in deciduous broadleaf species, while all traits in evergreen coniferous species showed no significant response. This suggested that the mitigating effects of drought on the negative impacts of O3 on the deciduous broadleaf species were more extensive than on the evergreen coniferous ones. Therefore, to avoid over- or underestimations when assessing the impact of O3 on vegetation growth, soil moisture should be considered. These results contribute to a better understanding of terrestrial ecosystem responses under global change.

An assessment of ozone risk for date palm suggests that phytotoxic ozone dose nonlinearly affects carbon gain

Tropospheric ozone (O3) is a significant phytotoxic air pollutant that has a negative impact on plant carbon gain. Although date palm (Phoenix dactylifera L.) is a globally important crop in arid or semi-arid regions, so far O3 risk assessment for this species has not been reported. This study estimated leaf- and plant-level photosynthetic CO2 uptake for understanding how elevated levels of O3 affects date palm biomass growth. Ozone risks to date palm plants were assessed based on exposure- (AOT40) or flux-based indices (Phytotoxic Ozone Dose, PODy, where y is a threshold of uptake). For this purpose, plants were exposed to three levels of O3 [ambient air, AA (45 ppb as daily average); 1.5 × AA; 2.0 × AA] for 92 days in an O3 Free-Air Controlled Exposure facility. According to the model simulations, the negative effects of O3 on plant-level net photosynthetic CO2 uptake were attributed to reduced gross photosynthetic carbon gain and increased respiratory carbon loss. Season-long O3 exposure and elevated temperatures promoted the negative O3 effect because of a further increase of respiratory carbon loss, which was caused by increased leaf temperature due to stomatal closure. POD1 nonlinearly affected the photosynthetic CO2 uptake, which was closely related to the variation of dry mass increment during the experiment. Although the dose-response relationship suggested that a low O3 dose (POD1 < 5.2 mmol m−2) may even positively affect photosynthetic CO2 uptake in date palms, stomatal O3 uptake at the current ambient O3 levels has potentially a negative impact on date palm growth. The results indicate 5.8 mmol m−2 POD1 or 21.1 ppm h AOT40 as critical levels corresponding to a 4% reduction of net CO2 uptake for date palm, suggesting that this species can be identified as a species moderately sensitive to O3.

A three-year free-air experimental assessment of ozone risk on the perennial Vitis vinifera crop species

Tropospheric ozone (O3) is an oxidative air pollutant that promotes damage to several crops, including grapevine, which is considered moderately resistant to O3 stress. To study the O3 effect on this perennial crop species under realistic environmental conditions, a three-year experiment was performed using an innovative O3-FACE facility located in the Mediterranean climate region, where the target species, Vitis vinifera cv. “Cabernet sauvignon”, was exposed to three O3 levels: ambient (AA), 1.5 × ambient (×1.5), and 2 × ambient (×2.0). A stomatal conductance model parameterization was conducted, and O3-exposure (AOT40) and flux-based indices (PODy) were estimated. An assessment of O3-induced visible foliar injury (O3_VFI) was conducted by estimating VFI_Incidence (percentage of symptomatic leaves per branch) and VFI_Severity (average percentage of O3_VFI surface in symptomatic leaves). Biomass parameters were used to assess the cumulative O3 effect and calculate the most appropriate critical levels (CL) for a 5% yield loss and for the induction of 5, 10, and 15% of O3_VFI. We confirmed that the O3 effect on this grapevine variety VFI was cumulative and that POD0 values accumulated over the two or three years preceding the assessment were better related to the response variables than single-year values, with the response increasing with increasing O3 level. The estimated CL for 5% yield loss based on the O3-exposure index was 25 ppm h AOT40 and 21 or 23 ppm h for a 10% of VFI_Incidence or VFI_Severity, respectively. The suggested flux-based index value for 5% yield loss was 5.2 POD3 mmol m−2, and for 10% of VFI_Incidence or VFI_Severity, the values were 7.7 or 8.6 POD3 mmol m−2, respectively. The results presented in this study demonstrate that O3 risk assessment for this grapevine varietyproduces consistent and comparable results when using either yield or O3_VFI as response parameter.

Solar-induced chlorophyll fluorescence captures the effects of elevated ozone on canopy structure and acceleration of senescence in soybean.

Solar-induced chlorophyll fluorescence (SIF) provides an opportunity to rapidly and non-destructively investigate how plants respond to stress. Here, we explored the potential of SIF to detect the effects of elevated O3 on soybean in the field where soybean was subjected to ambient and elevated O3 throughout the growing season in 2021. Exposure to elevated O3 resulted in a significant decrease in canopy SIF at 760 nm (SIF760), with a larger decrease in the late growing season (36%) compared with the middle growing season (13%). Elevated O3 significantly decreased the fraction of absorbed photosynthetically active radiation by 8-15% in the middle growing season and by 35% in the late growing stage. SIF760 escape ratio (fesc) was significantly increased under elevated O3 by 5-12% in the late growth stage due to a decrease of leaf chlorophyll content and leaf area index. Fluorescence yield of the canopy was reduced by 5-11% in the late growing season depending on the fesc estimation method, during which leaf maximum carboxylation rate and maximum electron transport were significantly reduced by 29% and 20% under elevated O3. These results demonstrated that SIF could capture the elevated O3 effect on canopy structure and acceleration of senescence in soybean and provide empirical support for using SIF for soybean stress detection and phenotyping.

Sensitivity of isoprene emission rate to ozone in greening trees is concurrently determined by isoprene synthesis capacity and stomatal conductance

The sensitivity of isoprene emission rate (ISOrate) to ozone (O3) in plant suggests potentially large changes in future isoprene emissions, which will have important consequences for atmospheric chemistry. However, the interspecific variation of ISOrate sensitivity to O3 and its key drivers remain largely unknown. In this study, four urban greening tree species were exposed to two O3 treatments (charcoal-filtered air, CF; and non-filtered ambient air plus 60 ppb extra O3, EO3) in open-top chambers for one growing season. We aimed to compare the interspecific variation in O3 inhibitory effect on ISOrate and explore its physiological mechanism. EO3 decreased the ISOrate by on average 42.5 % across species. According to absolute effect size ranking, the highest ISOrate sensitivity to EO3 was observed in Salix matsudana, followed by Sophora japonica and hybrid poplar clone ‘546’, while Quercus mongolica ISOrate was the least sensitive. Leaf anatomical structures differed in tree species but did not respond to EO3. Furthermore, the ISOrate sensitivity to O3 was driven by the concurrent effects of O3 on ISO synthesis ability (i.e., dimethylallyl diphosphate and isoprene synthase contents) and stomatal conductance. Overall, the mechanistic understanding grained from this study may promote the integrity of O3 effect into process-based ISO emission models.

TransClim (v1.0): a chemistry–climate response model for assessing the effect of mitigation strategies for road traffic on ozone

Abstract. Road traffic emits not only carbon dioxide (CO2) and particulate matter, but also other pollutants such as nitrogen oxides (NOx), volatile organic compounds (VOCs) and carbon monoxide (CO). These chemical species influence the atmospheric chemistry and produce ozone (O3) in the troposphere. Ozone acts as a greenhouse gas and thus contributes to anthropogenic global warming. Technological trends and political decisions can help to reduce the O3 effect of road traffic emissions on climate. In order to assess the O3 response of such mitigation options on climate, we developed a chemistry–climate response model called TransClim (Modelling the effect of surface Transportation on Climate). The current version considers road traffic emissions of NOx, VOC and CO and determines the O3 change and its corresponding stratosphere-adjusted radiative forcing. Using a tagging method, TransClim is further able to quantify the contribution of road traffic emissions to the O3 concentration. Thus, TransClim determines the contribution to O3 as well as the change in total tropospheric O3 of a road traffic emission scenario. Both quantities are essential when assessing mitigation strategies. The response model is based on lookup tables which are generated by a set of emission variation simulations performed with the global chemistry–climate model EMAC (ECHAM5 v5.3.02, MESSy v2.53.0). Evaluating TransClim against independent EMAC simulations reveals low deviations of all considered species (0.01 %–10 %). Hence, TransClim is able to reproduce the results of an EMAC simulation very well. Moreover, TransClim is about 6000 times faster in computing the climate effect of an emission scenario than the complex chemistry–climate model. This makes TransClim a suitable tool to efficiently assess the climate effect of a broad range of mitigation options for road traffic or to analyse uncertainty ranges by employing Monte Carlo simulations.

Short-term exposure to gaseous air pollutants and daily hospitalizations for acute upper and lower respiratory infections among children from 25 cities in China

To examine the short-term association between gaseous air pollutants (CO, NO2, SO2, and O3) and all-cause respiratory disease, acute upper respiratory infections (AURIs) as well as acute lower respiratory infections (ALRIs) among children, we conducted the study from 25 major cities in China. Hospitalization records of children aged 0–18 years due to all-cause respiratory diseases (889,926), AURIs (97,858), and ALRIs (642,154) from 2016 to 2019 were extracted. Concentrations of CO, NO2, SO2, and O3 were averaged across monitoring stations. Generalized additive models were used to estimate the associations between gaseous air pollutants and daily hospitalizations for all-cause respiratory disease, AURIs, and ALRIs. The meta-analysis was used to combine the city-specific estimates. A 10 mg/m3 increase in CO at lag01, and a 10 μg/m3 increase in NO2, SO2, and O3 at lag01 were associated with 1.65% (95%CI, 0.41–2.91), 0.54% (95%CI, 0.30–0.79), 0.60% (95%CI, 0.22–0.99), and 0.23% (95%CI, 0.06–0.39) increase of hospitalizations due to all-cause respiratory disease, respectively. For the disease subtype, O3 only had adverse effects on AURIs, CO and SO2 mainly on ALRIs, and NO2 on both AURIs and ALRIs. Children aged 4–6years were more vulnerable to the effects of CO and NO2, but those aged <1year were more susceptible to SO2 and O3. Besides, the O3 effect was stronger in the warm season than in the cold season. The study indicated that short-term exposure to CO, NO2, SO2, and O3 was associated with increased hospitalization for pediatric respiratory disease, and the association may vary by position of the respiratory tract, age, and season.

Experimental assessment of ozone risk on ecotypes of the tropical tree Moringa oleifera

Ozone (O3) is an oxidative air pollutant that affects plant growth. Moringa oleifera is a tree species distributed in the tropical and subtropical regions. This species presents high morphological plasticity, which increases its ability to tolerate stressful conditions, but with no O3 risk assessment calculated so far. The present study assessed the O3 risk to different M. oleifera ecotypes using exposure-based index (AOT40) or flux-based index (PODy - where y is a threshold of O3 uptake). PODy considers the O3 uptake through the stomata and the consequence of environmental climate conditions on stomatal conductance (gsto); thus, it is efficient in assessing O3 risk. Five M. oleifera ecotypes were subjected to ambient (Amb.); middle (Mid. X1.5), and High (x2.0) O3 concentrations for 77 days in a free-air controlled exposure facility (FACE). Leaf biomass (LB) was evaluated, and the biomass loss was projected assuming a clean atmosphere (10 ppb as 24 h O3 average). The gsto parameterization was calculated using the Jarvis-type multiplicative algorithm considering several climate factors, i.e., light intensity, air temperature, air vapor pressure deficit, and AOT40. Ozone exposure harmed the LB of all ecotypes. The high gsto (~559 mmol H2O m−2 s−1) can be considered the reason for the species' O3 sensitivity. M. oleifera is adapted to hot climate conditions, and gsto was restricted with air temperature (Tmin) below ~ 9 °C. As expected, the PODy index performed better than the AOT40 for estimating the O3 effect on biomass losses. We recommend a y threshold of 4 nmol m−2 s−1 to incorporate O3 effects on M. oleifera LB. To not exceed a 4% reduction of LB for any M. oleifera genotype, we recommend the critical levels of 1.1 mmol m−2 POD4.

Competing effects of nitrogen deposition and ozone exposure on northern hemispheric terrestrial carbon uptake and storage, 1850–2099

Abstract. Tropospheric ozone (O3) and nitrogen deposition affect vegetation growth and, thereby, the ability of the land biosphere to take up and store carbon. However, the magnitude of these effects on the contemporary and future terrestrial carbon balance is insufficiently understood. Here, we apply an extended version of the O–CN terrestrial biosphere model that simulates the atmosphere to canopy transport of O3, its surface and stomatal uptake, the O3-induced leaf injury, and the coupled terrestrial carbon and nitrogen cycles. We use this model to simulate past and future impacts of air pollution against a background of concurrent changes in climate and carbon dioxide concentrations (CO2) for two contrasting representative concentration pathway (RCP) scenarios (RCP2.6 and RCP8.5). The simulations show that O3-related damage considerably reduced northern hemispheric gross primary production (GPP) and long-term carbon storage between 1850 and the 2010s. The simulated O3 effect on GPP in the Northern Hemisphere peaked towards the end of the 20th century, with reductions of 4 %, causing a reduction in the northern hemispheric carbon sink of 0.4 Pg C yr−1. During the 21st century, O3-induced reductions in GPP and carbon storage are projected to decline, through a combination of direct air pollution control methods that reduce near-surface O3 and the indirect effects of rising atmospheric CO2, which reduces stomatal uptake of O3 concurrent with increases of leaf-level water use efficiency. However, in hot spot regions such as East Asia, the model simulations suggest a sustained decrease in GPP by more than 8 % throughout the 21st century. O3 exposure reduces projected carbon storage at the end of the 21st century by up to 15 % in parts of Europe, the US, and East Asia. Our simulations suggest that the stimulating effect of nitrogen deposition on regional GPP and carbon storage is lower in magnitude compared to the detrimental effect of O3 during most of the simulation period for both RCPs. In the second half of the 21st century, the detrimental effect of O3 on GPP is outweighed by nitrogen deposition, but the effect of nitrogen deposition on land carbon storage remains lower than the effect of O3. Accounting for the stimulating effects of nitrogen deposition but omitting the detrimental effect of O3 may lead to an overestimation of projected carbon uptake and storage.

Effect of ozone stress on yield characteristics of indica-japonica hybrid rice Yongyou 538 in two consecutive growing seasons

The hybrid rice cultivar Yongyou 538 (Y538) was exposed to 100 ppb ozone (O3) and control conditions throughout the cropping seasons in 2016–2017 in Yangzhou, China. The average daily maximum temperature during reproductive the growth stage (mid-August) of Y538 in 2016 was 3.6 °C higher than that in 2017. The heading stage of Y538 was reached 6.5 days earlier in the control than in the high-O3 treatments. Ozone stress decreased plant height and tiller number at all growth stages, and the O3–induced reductions in these two parameters were gradually increased with plant development. Compared to the control, O3 stress significantly decreased yield by an average of 29.9 %, and by 35.2 and 24.0 % in 2016 and 2017, respectively. Averaged across 2 years, O3 stress caused slight reductions in both panicle number (PN) and filled grain weight (FGW). However, spikelet number per panicle (-9.6 %, SNP) and filled grain percentage (-17.5 %, FGP) showed significant reductions due to O3 exposure, while O3 stress increased empty grain percentage (EGP) and incompletely-filled grain percentage (IGP) by 72.9 and 80.0 %, respectively, when averaged across 2 years. A significant interaction of O3 by year or grain position in a panicle was observed on yield, FGP, EGP, and IGP, as the changes in 2016 were more significantly affected than those in 2017; grains at lower parts of the panicle were more affected than those at upper parts. Ozone stress significantly reduced the above ground dry weight of rice at maturity in 2 years by an average of 18.3 %, which was mainly related to the decrease in stem (-19.3 %) and panicle weight (-22.9 %), while no O3 effect was detected for leaf weight. Ozone stress significantly increased the ratio of leaf to aboveground dry weight by 23.4 % when averaged across 2 years, while the ratio of stem or panicle showed a declining trend. Correlation and path analysis showed that yield loss due to O3 exposure was closely related to the decreases in FGP (especially the middle and lower parts of the panicle) and SNP. Ozone treatment of 100 ppb significantly decreased the productivity of Y538, and the high temperature in the reproductive growth period would further exacerbate the damage caused by O3, leading to substantial yield losses.

High nitrogen addition decreases the ozone flux by reducing the maximum stomatal conductance in poplar saplings.

Ground-level ozone (O3) and nitrogen (N) deposition are major environmental pollutants, often occurring concurrently. Ozone exposure- and flux-response relationships for tree biomass are used for regional O3 risk assessment. In order to investigate whether soil N addition affects stomatal O3 uptake of poplar, poplar saplings were exposed to treatment combinations of five O3 levels and four N addition levels. High N addition treatment reduced the accumulated stomatal O3 uptake in the leaf due to reduced maximum stomatal conductance (gs). Nitrogen addition also significantly reduced the steady-state light-saturated gs in August and September. Elevated O3 significantly reduced and N addition increased total plant biomass; however, there were no significant O3×N interactions. The slopes of biomass-based O3 exposure- and flux-response relationships did not differ significantly among N treatments. The critical levels for a 5% biomass reduction were estimated at 15.4ppmh and 17.1mmol O3 m-2 projected leaf area (PLA) for Accumulated O3 exposure Over an hourly Threshold of 40ppb (AOT40) and Phytotoxic Ozone Dose above a threshold 1nmol O3 m-2 PLA s-1 (POD1). These results can facilitate the evaluations of O3 effect on the carbon-sink capacity and productivity of forest.

How do forest landscapes respond to elevated CO2 and ozone? Scaling Aspen‐FACE plot‐scale experimental results

AbstractThe Aspen‐FACE (Free‐Air Carbon Enrichment) experiment was an 11‐yr study of the effect of elevated CO2 and ozone (alone and in combination) on the growth productivity of model aspen communities (pure aspen, aspen‐birch, and aspen‐maple) in the field in northern Wisconsin, USA. Uncertainty remains about how these short‐term plot‐level responses might play out at landscape scales where climate change, competition, succession, and disturbances interact with tree‐level responses. In this study, we used a recent physiology‐based approach (PnET‐Succession v3.1) within the forest landscape model LANDIS‐II to scale the site‐scale FACE results to landscape extents by mechanistically accounting for the globally changing drivers of CO2, ozone, temperature, and precipitation. We conducted a factorial simulation experiment to test five hypotheses about the effects of three treatments (CO2 concentration, cumulative ozone exposure, and disturbance). CO2 was clearly the dominant driver of landscape response, with disturbance also having a large effect. Ozone was not a dominant driver of landscape dynamics or total landscape biomass, but its negative effect on mean landscape biomass was nevertheless significant. We found that CO2 mitigation of water stress may not have a major effect on species composition or biomass accumulation. We found that species diversity was somewhat decreased by elevated CO2 as expected, but somewhat increased by O3, contrary to expectations. The spatial pattern of the landscape was minimally affected by the treatments. While rising CO2 concentrations have some mitigating effect on the negative O3 effect on the species studied, additional research is needed to confirm whether researchers and managers can be justified in disregarding O3 as a primary driver of forest dynamics in other ecosystems. Our results also add more support to the growing consensus that projections of climate change effects must include robust, direct links between CO2 and tree growth and competition; temperature effects (as demonstrated elsewhere) appear to be less by comparison.

Early Detection of Sage (Salvia officinalis L.) Responses to Ozone Using Reflectance Spectroscopy.

Advancements in techniques to rapidly and non-destructively detect the impact of tropospheric ozone (O3) on crops are required. This study demonstrates the capability of full-range (350–2500 nm) reflectance spectroscopy to characterize responses of asymptomatic sage leaves under an acute O3 exposure (200 ppb for 5 h). Using partial least squares regression, spectral models were developed for the estimation of several traits related to photosynthesis, the oxidative pressure induced by O3, and the antioxidant mechanisms adopted by plants to cope with the pollutant. Physiological traits were well predicted by spectroscopic models (average model goodness-of-fit for validation (R2): 0.65–0.90), whereas lower prediction performances were found for biochemical traits (R2: 0.42–0.71). Furthermore, even in the absence of visible symptoms, comparing the full-range spectral profiles, it was possible to distinguish with accuracy plants exposed to charcoal-filtered air from those exposed to O3. An O3 effect on sage spectra was detectable from 1 to 5 h from the beginning of the exposure, but ozonated plants quickly recovered after the fumigation. This O3-tolerance was confirmed by trends of vegetation indices and leaf traits derived from spectra, further highlighting the capability of reflectance spectroscopy to early detect the responses of crops to O3.

Ozone will remain a threat for plants independently of nitrogen load

Abstract Elevated concentrations of ground‐level ozone (O3) and atmospheric nitrogen (N) deposition occur concurrently. The negative effects of elevated O3 on plants have been widely studied and are well understood nowadays. However, how the effects of elevated O3 on plants may be driven by N deposition remains an unsolved puzzle. We conducted a meta‐analysis and showed that the negative effects of elevated O3 on photosynthesis, stomatal conductance, growth and biomass production of semi‐natural and natural vegetation may remain unchanged by N deposition in the coming future under realistic increases in O3 concentrations (+20 to 40 ppb) and N deposition (up to 60 kg ha−1 year−1). The negative effect of elevated O3 on chlorophyll content is offset by soil N addition; however, the negative effect on biomasses is not offset by soil N addition. Across functional groups and O3 levels, N addition exacerbated O3 effects on root when N increased from 0–10 kg N ha−1 year−1 to 11–30 kg N ha−1 year−1. However, an analysis as per the plant functional group revealed that such a N‐dependent O3 effect was significant only in perennial non‐woody plants, and was non‐significant when only realistic increases in O3 concentrations were considered. Likewise, N addition appeared to exacerbate O3‐negative effects on photosynthesis of trees when N increased from 0–30 kg N ha−1 year−1 to &gt;60 kg N ha−1 year−1; however, this effect was significant only when realistic increases in O3 concentrations were considered. The results suggest potential error in the current estimates of the overall O3 impacts on plants due to no consideration of soil N availability, and encourage further studies on the interaction of O3 and N availability that will permit more robust analyses in the future. Elevated O3 will likely remain a persistent agricultural and ecological issue independently of N deposition. A free Plain Language Summary can be found within the Supporting Information of this article.

New Insights into Leaf Physiological Responses to Ozone for Use in Crop Modelling.

Estimating food production under future air pollution and climate conditions in scenario analysis depends on accurately modelling ozone (O3) effects on yield. This study tests several assumptions that form part of published approaches for modelling O3 effects on photosynthesis and leaf duration against experimental data. In 2015 and 2016, two wheat cultivars were exposed in eight hemispherical glasshouses to O3 ranging from 22 to 57 ppb (24 h mean), with profiles ranging from raised background to high peak treatments. The stomatal O3 flux (Phytotoxic Ozone Dose, POD) to leaves was simulated using a multiplicative stomatal conductance model. Leaf senescence occurred earlier as average POD increased according to a linear relationship, and the two cultivars showed very different senescence responses. Negative effects of O3 on photosynthesis were only observed alongside O3-induced leaf senescence, suggesting that O3 does not impair photosynthesis in un-senesced flag leaves at the realistic O3 concentrations applied here. Accelerated senescence is therefore likely to be the dominant O3 effect influencing yield in most agricultural environments. POD was better than 24 h mean concentration and AOT40 (accumulated O3 exceeding 40 ppb, daylight hours) at predicting physiological response to O3, and flux also accounted for the difference in exposure resulting from peak and high background treatments.

Interaction of Diet and Ozone Exposure on Oxidative Stress Parameters within Specific Brain Regions of Male Brown Norway Rats

Oxidative stress (OS) contributes to the neurological and cardio/pulmonary effects caused by adverse metabolic states and air pollutants such as ozone (O3). This study explores the interactive effects of O3 and diet (high-fructose (FRUC) or high–fat (FAT)) on OS in different rat brain regions. In acute exposure, there was a decrease in markers of reactive oxygen species (ROS) production in some brain regions by diet and not by O3. Total antioxidant substances (TAS) were increased in the cerebellum (CER) and frontal cortex (FC) and decreased in the striatum (STR) by both diets irrespective of O3 exposure. Protein carbonyls (PC) and total aconitase decreased in some brain regions irrespective of exposure. Following subacute exposure, an increase in markers of ROS was observed in both diet groups. TAS was increased in the FC (FAT only) and there was a clear O3 effect where TAS was increased in the FC and STR. Diet increased PC formation within the CER in the FAT group, while the hippocampus showed a decrease in PC after O3 exposure in controls. In general, these results indicate that diet/O3 did not have a global effect on brain OS parameters, but showed some brain region- and OS parameter-specific effects by diets.

The weekday/weekend ozone differences induced by the emissions change during summer and autumn in Guangzhou, China

Weekday/weekend mixing ratios of ozone (O3) and the O3 precursors of non-methane hydrocarbons (NMHCs) and nitrogen oxides (NOx) were recorded at the Guangzhou Panyu Atmospheric Composition Station (GPACS), a suburban site in Guangzhou, during the summer (June, July, and August) and autumn (September, October, and November) of 2011. In both summer and autumn, weekday/weekend O3 differences in the morning and at midday largely depend on how much the O3 precursors are affected by anthropogenic emissions. In the mornings (6:00–9:00 LT), pollutants (i.e. NOx and NMHCs) were more strongly influenced by vehicular emissions in autumn than in summer. In autumn, O3 titration and lower NOx on weekends in NMHCs-limited regimes lead to more rapid O3 production, which resulted in the O3 weekend effect during autumn morning. No O3 weekend effect occurred on summer mornings because O3 formation was in a NOx-limited regime, although O3 titration still existed. At midday (10:00–16:00 LT), the increase of biogenic NMHCs emissions reversed the sensitivity of O3 production from NMHCs-to NOx-sensitive. The weekday/weekend diurnal pattern of vehicular sources was the same at midday, more intense other human industrial activities in autumn not only gave rise to the higher mixing ratios of high-reactive anthropogenic NMHCs (e.g. aromatics) on weekdays, but also could affected the temperature in the city, leading to higher isoprene mixing ratio on weekdays. All these factors are likely to contribute to the O3 weekday effect in autumn. Meanwhile no weekday O3 effect occurred in summer due to the low-intensity industrial anthropogenic activities. Our results show that high-reactive NMHCs and NOx control can be effective for reducing peak O3 mixing ratios in Guangzhou. Further investigation based on numerical models is required to reach more robust conclusions.

Role of Nrf2 in preventing oxidative stress induced chloride current alteration in human lung cells.

The lung tissue is one of the main targets of oxidative stress due to external sources and respiratory activity. In our previous work, we have demonstrated in that O3 exposure alters the Cl- current-voltage relationship, with the appearance of a large outward rectifier component mainly sustained by outward rectifier chloride channels (ORCCs) in human lung epithelial cells (A549 line). In the present study, we have performed patch clamp experiments, in order to identify which one of the O3 byproducts (4hydroxynonenal (HNE) and/or H2 O2 ) was responsible for chloride current change. While 4HNE exposition (up to 25 μM for 30' before electrophysiological analysis) did not reproduce O3 effect, H2 O2 produced by glucose oxidase 10 mU for 24 hr before electrophysiological analysis mimicked O3 response. This result was confirmed treating the cell with catalase (CAT) before O3 exposure (1,000 U/ml for 2 hr): CAT was able to rescue Cl- current alteration. Since CAT is regulated by Nrf2 transcription factor, we pre-treated the cells with the Nrf2 activators, resveratrol and tBHQ. Immunochemical and immunocytochemical results showed Nrf2 activation with both substances that lead to prevent OS effect on Cl- current. These data bring new insights into the mechanisms involved in OS-induced lung tissue damage, pointing out the role of H2 O2 in chloride current alteration and the ability of Nfr2 activation in preventing this effect.

Exposure- and flux-based assessment of ozone risk to sugarcane plants

Ozone (O3) is a toxic oxidative air pollutant, with significant detrimental effects on crops. Sugarcane (Saccharum spp.) is an important crop with no O3 risk assessment performed so far. This study aimed to assess O3 risk to sugarcane plants by using exposure-based indices (AOT40 and W126) based on O3 concentrations in the air, and the flux-based index (PODy, where y is a threshold of uptake) that considers leaf O3 uptake and the influence of environmental conditions on stomatal conductance (gsto). Two sugarcane genotypes (IACSP94-2094 and IACSP95-5000) were subjected to a 90-day Free-Air Controlled Experiment (FACE) exposure at three levels of O3 concentrations: ambient (Amb); Amb x1.2; and Amb x1.4. Total above-ground biomass (AGB), stalk biomass (SB) and leaf biomass (LB) were evaluated and the potential biomass production in a clean air was estimated by assuming a theoretical clean atmosphere at 10 ppb as 24 h O3 average. The Jarvis-type multiplicative algorithm was used to parametrize gsto including environmental factors i.e. air temperature, light intensity, air vapor pressure deficit, and minimum night-time temperature. Ozone exposure caused a negative impact on AGB, SB and LB. The O3 sensitivity of sugarcane may be related to its high gsto (∼535 mmol H2O m−2 s−1). As sugarcane is adapted to hot climate conditions, gsto was restricted when the current minimum air temperature (Tmin) was below ∼14 °C and the minimum night-time air temperature of the previous day (Tnmin) was below ∼7.5 °C. The flux-based index (PODy) performed better than the exposure-based indices in estimating O3 effect on biomass losses. We recommend a y threshold of 2 nmol m−2 s−1 to incorporate O3 effects on both AGB and SB and 1 nmol m−2 s−1 on LB. In order not to exceed 4% reduction in the growth of these two sugarcane genotypes, we recommend the following critical levels: 1.09 and 1.04 mmol m−2 POD2 for AGB, 0.91 and 0.96 mmol m−2 POD2 for SB, and 3.00 and 2.36 mmol m−2 POD1 for LB of IACSP95-5000 and IACSP94-2094, respectively.