Effects Of Chronic Ozone Exposure Research Articles

Identifying and modelling key physiological traits that confer tolerance or sensitivity to ozone in winter wheat

Tropospheric ozone threatens crop production in many parts of the world, especially in highly populated countries in economic transition. Crop models suggest substantial global yield losses for wheat, but typically such models fail to address differences in ozone responses between tolerant and sensitive genotypes. Therefore, the purpose of this study was to identify physiological traits contributing to yield losses or yield stability under ozone stress in 18 contrasting wheat cultivars that had been pre-selected from a larger wheat population with known ozone tolerance. Plants were exposed to season-long ozone fumigation in open-top chambers at an average ozone concentration of 70 ppb with three additional acute ozone episodes of around 150 ppb. Compared to control conditions, average yield loss was 18.7 percent, but large genotypic variation was observed ranging from 2.7 to 44.6 percent. Foliar chlorophyll content represented by normalized difference vegetation index and net CO2 assimilation rate of young leaves during grain filling were the physiological traits most strongly correlated with grain yield losses or stability. Accumulative effects of chronic ozone exposure on photosynthesis were more detrimental for grain yield than instantaneous effects of acute ozone shocks, or accelerated senescence of older leaves represented by changes in the ratio of brown leaf area/green leaf area index. We used experimental data of two selected tolerant or sensitive varieties, respectively, to parametrize the LINTULCC2 crop model expanded with an ozone response routine. By specifying parameters representing the distinct physiological responses of contrasting genotypes, we simulated yield losses of 7 percent (tolerant) or 33 percent (sensitive). By considering genotypic differences in ozone response models, this study helps to improve the accuracy of simulation studies, estimate the effects of adaptive breeding, and identify physiological traits for the breeding of ozone tolerant wheat varieties that could deliver stable yields despite ozone exposure.

Hyperspectral Reflectance of Light-Adapted Leaves Can Predict Both Dark- and Light-Adapted Chl Fluorescence Parameters, and the Effects of Chronic Ozone Exposure on Date Palm (Phoenix dactylifera).

High-throughput and large-scale measurements of chlorophyll a fluorescence (ChlF) are of great interest to investigate the photosynthetic performance of plants in the field. Here, we tested the capability to rapidly, precisely, and simultaneously estimate the number of pulse-amplitude-modulation ChlF parameters commonly calculated from both dark- and light-adapted leaves (an operation which usually takes tens of minutes) from the reflectance of hyperspectral data collected on light-adapted leaves of date palm seedlings chronically exposed in a FACE facility to three ozone (O3) concentrations (ambient air, AA; target 1.5 × AA O3, named as moderate O3, MO; target 2 × AA O3, named as elevated O3, EO) for 75 consecutive days. Leaf spectral measurements were paired with reference measurements of ChlF, and predictive spectral models were constructed using partial least squares regression. Most of the ChlF parameters were well predicted by spectroscopic models (average model goodness-of-fit for validation, R2: 0.53–0.82). Furthermore, comparing the full-range spectral profiles (i.e., 400–2400 nm), it was possible to distinguish with high accuracy (81% of success) plants exposed to the different O3 concentrations, especially those exposed to EO from those exposed to MO and AA. This was possible even in the absence of visible foliar injury and using a moderately O3-susceptible species like the date palm. The latter view is confirmed by the few variations of the ChlF parameters, that occurred only under EO. The results of the current study could be applied in several scientific fields, such as precision agriculture and plant phenotyping.

Coleus cultivars (Solenostemon scutellarioides (L.) Codd.) as potential bioindicators of chronic ozone exposure

Sensitivity of plant under ozone exposure can indicate its potency of being important bioindicator. Early studies have found that coleus plant (Solenostemon scutellarioides (L.) Codd.) has a potency to be ozone bio-indicator. This study aims to investigate the effect of chronic ozone exposure on root and leaf biomass and to quantify any change based on the plant appearance. Four different cultivars of coleus plant with different colour namely fully green (FG), green purple (GP), yellow purple (YP), and reddish (RD) had been selected. These four cultivars were fumigated with three different concentrations of ozone gas (≤ 10 ppb, 40 ppb, and 150 ppb) for 8 hours fumigation during 30-day period of experiment. All cultivars showed a stable leaf biomass after 30-day period of ozone exposure. Similarly, root biomass of all cultivars was not significant changed after fumigation period. Nonetheless, magnitude of ozone symptoms on leaf showed variation in certain cultivars. FG cultivar showed a significant number of chlorosis leaves under 40 and 150 ppb ozone exposure. The exposure of 150 ppb ozone also caused a noticeable percentage of curling leaves on RD cultivar. Moreover, the purple area in YP and GP showed a larger ratio under exposure of 150 ppb ozone. Consequently, coleus plants displayed resistance responds in terms of biomass. On the other hand, the plants also revealed variation in leaf symptom magnitudes and colour patterns under ozone exposure. However, these cultivars are potential to be bio-indicator due to their sensitivity in terms of appearance.

Simulating the effects of chronic ozone exposure on hydrometeorology and crop productivity using a fully coupled crop, meteorology and air quality modeling system

In this study, the Noah-Multiparameterization with Crop land surface model in the Weather Research and Forecasting (WRF) with Chemistry (WRF/Chem) model is modified to include the effects of chronic ozone exposure (COE) on plant conductance and photosynthesis (PCP) found from field experiments. Based on the modified WRF/Chem, the effects of COE on regional hydrometeorology and crop productivity have been investigated over the central United States. Our results indicate that the model in its current configuration can reproduce the rainfall and temperature patterns of the observations and reanalysis data, although it overestimates rainfall. The model underestimates daily maximum 8-hour average ozone concentrations by 4–7 ppb compared with ozone observations from the Clean Air Status and Trend Network. The experimental tests on the effects of COE include setting different thresholds of ambient ozone concentrations ([O3]) and using linear regressions to quantify PCP against the COE. Compared with the WRF/Chem control run (i.e., without considering the effects of COE), the modified model at different experimental setups consistently improves the simulated estimates of rainfall and temperatures. The simulations in June, July, August, and September of 2009–2014 show that, over crop lands, surface [O3] decrease latent heat fluxes (LH) by 9 to 11 W/m2, increase surface air temperatures (T2) by 0.6 to 0.7 °C with the daily maximum temperature increasing up to 1 °C, and decrease rainfall by 0.15 to 0.21 mm per day by mostly reducing convective rainfall. Additionally, surface [O3] decrease crop yields by 18–23%, decrease Gross Primary Productivity (GPP) by 30%–38% in a domain average and up to 50% in some areas, and decrease crop yields by 30–45%, all of which highly depends on the precise experimental setup, especially the [O3] threshold. The mechanism producing these results is also discussed. Employing this modified WRF/Chem model in any high [O3] region can more precisely elucidate the interactions of vegetation, meteorology, chemistry/emissions, and crop productivity.

Simulating the impacts of chronic ozone exposure on plant conductance and photosynthesis, and on the regional hydroclimate using WRF/Chem

The Noah-Multiparameterization land surface model in the Weather Research and Forecasting (WRF) with Chemistry (WRF/Chem) is modified to include the effects of chronic ozone exposure (COE) on plant conductance and photosynthesis (PCP) found from field experiments. Based on the modified WRF/Chem, the effects of COE on regional hydroclimate have been investigated over the continental United States. Our results indicate that the model with/without modification in its current configuration can reproduce the rainfall and temperature patterns of the observations and reanalysis data, although it underestimates rainfall in the central Great Plains and overestimates it in the eastern coast states. The experimental tests on the effects of COE include setting different thresholds of ambient ozone concentrations ([O3]) and using different linear regressions to quantify PCP against the COE. Compared with the WRF/Chem control run (i.e., without considering the effects of COE), the modified model at different experiment setups improves the simulated estimates of rainfall and temperatures in Texas and regions to the immediate north. The simulations in June, July and August of 2007–2012 show that surface [O3] decrease latent heat fluxes (LH) by 10–27 W m−2, increase surface air temperatures (T2) by 0.6 °C–2.0 °C, decrease rainfall by 0.9–1.4 mm d−1, and decrease runoff by 0.1–0.17 mm d−1 in Texas and surrounding areas, all of which highly depends on the precise experiment setup, especially the [O3] threshold. The mechanism producing these results is that COE decreases the LH and increases sensible heat fluxes, which in turn increases the Bowen ratios and air temperatures. This lowering of the LH also results in the decrease of convective potential and finally decreases convective rainfall. Employing this modified WRF/Chem model in any high [O3] region can improve the understanding of the interactions of vegetation, meteorology, chemistry/emissions, and crop productivity.

The Effect of Chronic Ozone Exposure on the Activation of Endoplasmic Reticulum Stress and Apoptosis in Rat Hippocampus.

The chronic exposure to low doses of ozone, like in environmental pollution, leads to a state of oxidative stress, which has been proposed to contribute to neurodegenerative disorders, including Alzheimer’s disease (AD). It induces an increase of calcium in the endoplasmic reticulum (ER), which produces ER stress. On the other hand, different studies show that, in diseases such as Alzheimer’s, there exist disturbances in protein folding where ER plays an important role. The objective of this study was to evaluate the state of chronic oxidative stress on ER stress and its relationship with apoptotic death in the hippocampus of rats exposed to low doses of ozone. We used 108 male Wistar rats randomly divided into five groups. The groups received one of the following treatments: (1) Control (air); (2) Ozone (O3) 7 days; (3) O3 15 days; (4) O3 30 days; (5) O3 60 days; and (6) O3 90 days. Two hours after each treatment, the animals were sacrificed and the hippocampus was extracted. Afterwards, the tissue was processed for western blot and immunohistochemistry using the following antibodies: ATF6, 78 kDa glucose-regulated protein (GRP78) and caspase 12. It was also subjected to terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and electronic microscopy. Our results show an increase in ATF6, GRP78 and caspase 12 as well as ER ultrastructural alterations and an increase of TUNEL positive cells after 60 and 90 days of exposure to ozone. With the obtained results, we can conclude that oxidative stress induced by chronic exposure to low doses of ozone leads to ER stress. ER stress activates ATF6 inducing the increase of GRP78 in the cytoplasm, which leads to the increase in the nuclear translocation of ATF6. Finally, the translocation creates a vicious cycle that, together with the activation of the cascade for apoptotic cell death, contributes to the maintenance of ER stress. These events potentially contribute in the neurodegeneration processes in diseases like AD.

Activation of p38 mitogen‐activated protein kinase in ovalbumin and ozone‐induced mouse model of asthma

Ozone exposure worsens the development of allergen-induced asthma. The p38 mitogen-activated protein kinase (MAPK) pathway plays an important role in the development of the inflammatory response, airway hyperresponsiveness (AHR) and airway remodelling. In this study, the role of the p38 MAPK pathway on the effects of chronic ozone exposure in ovalbumin (OVA)-sensitized and -challenged mice was investigated. Mice were sensitized and challenged with OVA followed by ozone exposure. Dexamethasone (Dex) and SB239063, a p38 MAPK inhibitor, were used as preventive treatment. Compared with OVA-challenged mice, ozone exposure of OVA-challenged mice led to enhanced recruitment of inflammatory cells in bronchoalveolar lavage fluid, increases in inflammation scores, collagen accumulation, bronchial wall thickness and messenger RNA levels of inflammatory cytokines, along with activation of p38 MAPK/HSP27 and downregulation of MAPK phosphatase-1 (MKP-1) in the lung tissue. Dex treatment partially attenuated lung inflammation, while the cotreatment of Dex and SB239063 effectively reduced lung inflammation, inhibited airway remodelling, inactivated p38 MAPK/HSP27 and upregulated MKP-1 in the lung tissue. Ozone exposure aggravated airway inflammation, airway remodelling, activation of p38 MAPK and downregulation of MKP-1 in OVA-sensitized and -challenged mice, which was ineffectively controlled by corticosteroids. p38 MAPK activation is a likely pathway involved in corticosteroid insensitivity.

Ozone and Survival in Four Cohorts with Potentially Predisposing Diseases

Time series studies have reported associations between ozone and daily deaths. Only one cohort study has reported the effect of long-term exposures on deaths, and little is known about effects of chronic ozone exposure on survival in susceptible populations. We investigated whether ozone was associated with survival in four cohorts of persons with specific diseases in 105 United States cities, treating ozone as a time varying exposure. We used Medicare data (1985–2006), and constructed cohorts of persons hospitalized with chronic conditions that might predispose to ozone effects: chronic obstructive pulmonary disease, diabetes, congestive heart failure, and myocardial infarction. Yearly warm-season average ozone was merged to the individual follow-up in each city. We applied Cox proportional hazard model for each cohort within each city, adjusting for individual risk factors, temperature, and city-specific long-term trends. We found significant associations with a hazard ratio for mortality of 1.06 (95% confidence interval [CI], 1.03–1.08) per 5-ppb increase in summer average ozone for persons with congestive heart failure; of 1.09 (95% CI, 1.06–1.12) with myocardial infarction; of 1.07 (95% CI, 1.04–1.09) with chronic obstructive pulmonary disease; and of 1.07 (95% CI, 1.05–1.10) for diabetics.We also found that the effect varied by region, but that this was mostly explained by mean temperature, which is likely a surrogate of air conditioning use, and hence exposure. This is the first study that follows persons with specific chronic conditions, and shows that long-term ozone exposure is associated with increased risk of death in these groups.

Role of Polyamines in Ozone Exposed Ischemic-Reperfused Hearts

The effect of chronic ozone exposure to ischemia reperfusion (I/R) injury in isolated perfused rat hearts was previously demonstrated. The present study tested our hypothesis that chronic ozone exposure led to attenuation of polyamines in the heart, which may limit sensitivity to I/R. Sprague Dawley rats were continuously exposed for 8 hrs/day for 28 days to filtered air or 0.8 ppm ozone. Isolated hearts were previously subjected to 0.5 hour of global ischemia followed by 1 hour of reperfusion after which global polyamine content was examined between the two groups. Spermidine production was significantly increased in the experimental group compared to control group (of I/R hearts). These results suggest that ozone-induced sensitivity to chronic I/R injury activates myocardial polyamine stress response characterized by increased enzymatic activities and accumulation of spermidine. Collectively, these results suggest that I/R possibly disturbs polyamine metabolism, and increased oxidative stress and concomitant reduced myocardial cell viability.

A DIGE analysis of developing poplar leaves subjected to ozone reveals major changes in carbon metabolism

Tropospheric ozone pollution is described as having major negative effects on plants, compromising plant survival. Carbon metabolism is especially affected. In the present work, the effects of chronic ozone exposure were evaluated at the proteomic level in developing leaves of young poplar plants exposed to 120 ppb of ozone for 35 days. Soluble proteins (excluding intrinsic membrane proteins) were extracted from leaves after 3, 14 and 35 days of ozone exposure, as well as 10 days after a recovery period. Proteins (pI 4 to 7) were analyzed by 2-D DIGE experiments, followed by MALDI-TOF-TOF identification. Additional observations were obtained on growth, lesion formation, and leaf pigments analysis. Although treated plants showed large necrotic spots and chlorosis in mature leaves, growth decreased only slightly and plant height was not affected. The number of abscised leaves was higher in treated plants, but new leaf formation was not affected. A decrease in chlorophylls and lutein contents was recorded. A large number of proteins involved in carbon metabolism were identified. In particular, proteins associated with the Calvin cycle and electron transport in the chloroplast were down-regulated. In contrast, proteins associated with glucose catabolism increased in response to ozone exposure. Other identified enzymes are associated with protein folding, nitrogen metabolism and oxidoreductase activity.

Corrigendum

Plant, Cell & EnvironmentVolume 29, Issue 7 p. 1460-1461 Free Access Corrigendum This article corrects the following: Effects of chronic ozone exposure on gene expression in Arabidopsis thaliana ecotypes and in Thellungiella halophila PINGHUA LI, SHRINIVASRAO P. MANE, ALLAN A. SIOSON, CECILIA VASQUEZ ROBINET, LENWOOD S. HEATH, HANS J. BOHNERT, RUTH. GRENE, Volume 29Issue 5Plant, Cell & Environment pages: 854-868 First Published online: December 22, 2005 First published: 06 June 2006 https://doi.org/10.1111/j.1365-3040.2006.01547.xAboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat The authors of ‘Effects of chronic ozone exposure on gene expression in Arabidopsis thaliana ecotypes and in Thellungiella halophila’, Li et al. (2005), wish it to be known that Fig. 1 was printed incorrectly in their paper. Figure 1Open in figure viewerPowerPoint Effect of ozone exposure on gene expression of metabolism in different ecotypes. Gene expression changes are depicted in MapMan format (Thimm et al. 2004). The complete data set used for MapMan analysis is listed in Supplementary Data S3. (a) Panel A: effect of ozone exposure on Wassilewskija (WS). (b) Panel B: effect of ozone exposure on Thellungiella halophila (Th). (c) Panel C: a comparison of the core metabolism gene expression in Cape Verde Islands (Cvi-0) and WS. MapMan is a user-driven tool that paints gene expression data sets onto diagrams of metabolic pathways or other processes (Thimm et al. 2004). Each square represents a gene. Red, blue and white meant up-expression, down-expression and no change in expression, respectively. Gradient of the colours depict the strength of gene expression. Supplementary Table 4a–c contain the annotation of the genes highlighted in panels A, B and C, respectively. The correct figure is reproduced below: REFERENCE Li P., Mane S.P., Sioson A.A., Vasquez Robinet C., Heath L.S., Bohnert H.J. & Grene R. (2005) Effects of chronic ozone exposure on gene expression in Arabidopsis thaliana ecotypes and in Thellungiella halophila. Plant, Cell & Environment 29, 854– 868. Wiley Online LibraryPubMedWeb of Science®Google Scholar Volume29, Issue7July 2006Pages 1460-1461 FiguresReferencesRelatedInformation

Effects of chronic ozone exposure on gene expression in Arabidopsis thaliana ecotypes and in Thellungiella halophila

Arabidopsis thaliana (At) ecotypes Columbia-0 (Col-0), Wassilewskija (WS), Cape Verde Islands (Cvi-0) and a relative, Thellungiella halophila (Th), were exposed to 20-25% over ambient ozone [O3] in a free air concentration enrichment (FACE) experiment (http://www.soyFACE. uiuc.edu), mirroring increases expected in the near future. Col-0 and WS accelerated development and developed lesions within 10 d under increased ozone, while Cvi-0 and Th grew slowly. RNAs were used in microarray hybridizations (Col-0-based 26 000 elements, 70-mer oligonucleotides). A two-step analysis of variance (ANOVA) model, including comparison with values obtained under [O3], was used for analyses. WS showed the greatest number of changes in gene expression in response to ozone. Th showed the least changes, suggesting that its expression state at [O3] was sufficient for resistance at increased ozone. Patterns observed in ambient air controls for Cvi-0 and Col-0 were most similar, while Th showed the greatest number of differences compared with the other controls. Compared with Col-0, however, Cvi-0 showed higher levels of expression of chaperones, receptor kinase-like and photosynthesis-related genes in ambient air. Cvi-0 exhibited ozone-mediated changes in a pathway involving AtSR, a homologue of the mammalian NF kappa B family of redox-sensitive transcription factors, changes in chaperones, WRKY and C2H2 proteins and antioxidants. WS displayed ozone-mediated decreases in the expression of two AtSR/NF kappa B family members, C2-domain proteins and genes associated with cell wall growth and changes in the expression of marker genes for programmed cell death (PCD), among them RCD1, a key regulator in this pathway. Microarray data were verified by reverse transcriptase (RT)-PCR. We relate O3-response diversity across the four lines to different responses among signaling and transcriptional response networks and differences in gene expression at [O3] levels.

Robust two-stage approach to repeated measurements analysis of chronic ozone exposure in rats

A robust two-stage approach is used to reanalyze the repeated measurements from an experiment of airway responsiveness in rats randomized to long-term exposure at four ozone doses. The concentration-response data generated for each rat may be represented as a hierarchical nonlinear model encompasing the sources of variation within and between individual profile for each rat, the conditional modeling approach can assess the adequacy of an assumed mean model, a fundamental advantage not intrinsic to marginal techniques. The two-stage population inference is based on the estimated individual parameters, thus maintaining an intuitive appeal to the toxicologists who traditionally have fitted a separate curve for each animal and then applied ANOVA to the summary statistics. However, we formally adjust the standard errors for the extra variability due to the initial estimation of the individual parameters and also allow for their within-rat correlation. The robust two-stage method appropriately down weights the a berrant responses arising sporadically within individualsand, more importantly, the rats which may be outlying relative to the usual population variation. The true effect of chronic ozone exposure, including a significant gender interaction, may be masked by a few rats which exert undue influence on the population estimates in a nonrobust analysis.

Inhibition of flowering and reproductive success in spreading dogbane ( Apocynum androsaemifolium) by exposure to ambient ozone

Ground-level ozone continues to be a cause for concern in terrestrial ecosystems in the northeastern United States and Canada. Spreading dogbane ( Apocynum androsaemifolium L.) is one of many indigenous herbaceous plant species exhibiting foliar injury that are commonly monitored in ecosystem assessment programs. Details about possible effects of ambient ozone on reproductive components of these species are lacking. For 103 days, from 31 May to 10 September, A. androsaemifolium plants were grown in open-top chambers in either carbon-filtered air (CF), non-filtered air (NF) (approximately 1×ambient), or chamberless ambient air plots (AA). Aspects of sexual reproduction were measured to determine whether impairment occurs in polluted air. Additionally, the ozone protectant chemical ethylenediurea (EDU) was applied to foliage to determine its effect on foliar injury. By the end of the experiment visible foliar injury was absent in CF air and nominal in the NF and AA treatments. Plants grown in CF-chamber air produced significantly more flowers and fruits than those grown in either NF-chamber air or AA plots. Flowers produced by plants grown in CF air also survived to mature fruits at a rate 1.7× greater than plants in NF air and 1.5× greater than plants in AA plots. We were unable to conclude whether EDU protected plants from foliar ozone injury due to the general lack of foliar injury in ozone-exposed plants. The results demonstrate that foliar injury is not necessarily required to elicit negative effects on sexual reproduction in A. androsaemifolium. Implications for the population biology of A. androsaemifolium related to adverse effects of chronic ozone exposure on sexual reproduction are discussed.

Long-lasting effects of chronic ozone exposure on rat nasal epithelium.

Ozone, the principal oxidant pollutant in photochemical smog, causes airway epithelial injury in the upper and lower respiratory tract of laboratory animals. We have recently reported that long-term inhalation exposure to ozone causes mucous-cell metaplasia (MCM) in the surface epithelium lining the nasal airways of F344 rats. The principal objective of the present study was to determine the persistence of ozone-induced MCM in the nasal epithelium after the end of a chronic exposure. Male F344/N rats were exposed to 0, 0.25, or 0.5 ppm ozone, for 8 h/d, 7 d/wk for 13 wk. Animals were killed 8 h, 4 wk, or 13 wk after the end of the chronic exposure. Ozone-related alterations in the nasal epithelium were qualitatively and quantitatively characterized through histochemistry, image analysis, and morphometric techniques. Some rats were exposed for an additional 8 h to 0.5 ppm ozone at 13 wk after the end of the chronic exposure to determine whether previous ozone exposure results in persistent changes in the sensitivity of nasal epithelium to acute injury. At the end of the chronic exposure, hyperplasia was present in the nasal epithelium of rats exposed to 0.25 and 0.5 ppm ozone. By 13 wk postexposure, this proliferative alteration was still evident only in the rats exposed to 0.5 ppm ozone. Ozone-induced MCM with associated intraepithelial mucosubstances was evident only in the nasal tissues of rats exposed to 0.5 ppm ozone. Though attenuated, these alterations in the nasal mucous apparatus were still detectable at 13 wk after the end of the exposure. At this same time after the chronic exposure, an acute (8 h) exposure to 0.5 ppm ozone induced an additional increase of mucosubstances in the nasal epithelium of rats previously exposed to 0.5 ppm ozone, but not in rats chronically exposed to 0 or 2.5 ppm ozone. The persistent nature of the ozone-induced MCM in rats documented in this report suggests that ozone exposure may have the potential to induce similar long-lasting alterations in the airways of humans.

The Ntp/Hei Collaborative Ozone Project on the Health Effects of Chronic Ozone Inhalation

AbstractAlthough many people are exposed to ozone, the effects of chronic exposure to this ubiquitous pollutant, especially low-level chronic exposure, are not well understood. The U.S. Environmental Protection Agency (EPA) current national ambient air quality standard for ozone is exceeded in many communities, especially during the summer. The standard is attained when the number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is equal to or less than 1. The U.S. EPA estimates that 67 million people in the United States, or slightly more than a quarter of the residents, live in areas that were out of compliance with the current National Ambient Air Quality Standard (NAAQS) for ozone in 1989. Although there have been some studies of long-term exposure to ozone, many important questions remain about the health effects of chronic ozone exposure. The Health Effects Institute (HEI), in conjunction with the National Toxicology Program (NTP) carcinogenesis studies, has comple...

Diurnal water relations and gas exchange of two slash pine (Pinus elliottii) families exposed to chronic ozone levels and acidic rain *

summarySeedlings from two half‐sib families of Pinus elliottii var. elliottii Engelm. differing in sensitivity to ozone were grown in open‐top chambers for 22 months under simulated acidic rain (pH 3‐3) and four concentrations of ozone. The ozone concentrations were: charcoal‐filtered air (CF); non‐filtered ambient air (NF); twice the NF level (2X), thrice the NF level (3X). Ozone exposures were computer controlled to follow diurnal and seasonal fluctuations in ambient ozone concentrations.On two days, 24 April and 29 May, in the spring of 1990, trees were sampled repeatedly for xylem water potential, needle conductance and photosynthesis from sunrise to sunset on the oldest needle age class attached to the main stem (first needle cohort produced in 1989, and therefore, exposed the longest to ozone). On 30 May, three needle age classes (first age class of 1989, the last age class of 1989 and first ape class of 1990) were sampled over the day for needle conductance in trees exposed to CF and 3X ozone.Soil moisture measurements indicated that the 3X trees used significantly more water from the 75–l00 cm soil depth even though leaf area on these trees was about 30% less. Tree response showed very consistent xylem water potential among sample days, families and ozone treatments. By contrast, needle conductance and photosynthetic rate showed significant ozone and family differences. In addition, the response of needle conductance to vapour pressure deficit lessened as ozone exposure increased. The putative ozone‐sensitive family (106‐56) exhibited less needle conductance in the 2X and 3X treatments as well as reduced photosynthesis on both sample days, suggesting prior ozone injury. The youngest needle age class of this same family when exposed to 3X ozone showed higher needle conductance in the afternoon which could lead to both excessive water loss and uptake of ozone.The interactive effects of chronic ozone exposure, limited soil moisture and genetics altered the water relations and gas exchange of slash pine growing in north Florida. Changes in sromatal conductance along with possible adjustments in the hydraulic properties of the roots and stems appeared to be responsible for the control of water potentials in trees of differing sizes and leaf area. The importance of the contribution of different needle age classes to the water and carbon economy of slash pine, and their modification by cumulative ozone exposure, cannot he overlooked in interpreting air pollution effects on evergreen trees.

Sensitivity of frost resistance and growth in citrus and avocado to chronic ozone exposure

summaryThe effects of elevated levels of ozone on growth and frost resistance were studied using broadleaf‐evergreen citrus and avocado trees. ‘Ruby Red’ grapefruit (Citrus parodist L.) trees on either Volkamer lemon (Citrus volkanieriana Ten. & Pasq.) or sour orange (Citrus aurantium L.) rootstocks and ‘Simmonds’ or ‘Pancho’ avocado trees (Persea americana Mill.) on the rootstock ‘Waldin’ were exposed to ozone in open‐top chambers for 4 months in 1988 and for 8 months in a second experiment in 1989. The ambient ozone concentration, averaged over a 12 h day, was 30‐1 nl 1−1 in 1988 and 39‐1 nl 1−1 in 1989 during the exposure period. Citrus tree growth, estimated by total leaf mass, was unaffected by ozone concentrations of 3 × ambient in either year but the growth of avocado in 1989 was reduced 20 and 61 % by ozone concentrations at 2 × and 3 × ambient, respectively. Frost resistance, estimated by electrolyte leakage from leaf disks and from survival of leaves, stems and whole plants following exposure to freezing temperatures, was often diminished in avocado and citrus at 3 × ambient ozone, but occasionally was increased at 2 × ambient. The effects of chronic ozone exposure on frost resistance were generally subtle; 3 x ambient ozone exposure in 1989 compared to 0.3 × only caused the temperature for 50% electrolyte leakage (LT30) to increase less than 1 °C (− 5.3 to −4.8 °C) in citrus and about 2 °C (− 8.0 to −5.8 °C) in avocado. Nevertheless, the tests for frost resistance on whole plants indicated that these differences could have a substantial impact on stem and plant survival if the frost was at a critical temperature. The likelihood that chronic ozone exposure currently affects citrus frost resistance in Florida appears slight.

Effects of chronic ozone exposure on growth, root respiration and nutrient uptake of rice plants

To clarify the response of growth and root functions to low concentrations of ozone (O 3), rice plants ( Oryza sativa L.) were exposed to O 3 at 0·0 (control), 0·05 and 0·10 ppm for 8 weeks from vegetative to early heading stages. Exposure to 0·05 ppm O 3 tended to slightly stimulate the dry weight of whole plants up to 5 weeks and then slightly decrease the dry weight of whole plants. However, these effects were statistically significant only at 6 weeks. Exposure to 0·10 ppm O 3 reduced the dry weight of whole plants by 50% at 5 and 6 weeks, and thereafter the reduction of the dry weight of whole plants was gradually alleviated. Those changes in dry weight can be accounted for by a decrease or increase in the relative growth rate (RGR). The changes in the RGR caused by 0.05 and 0.10 ppm O 3 could be mainly attributed to the effect of O 3 on the net assimilation rate. Root/shoot ratio was lowered by both 0.05 and 0.10 ppm O 3 throughout the exposure period. The root/shoot ratio which had severely decreased at 0.10 ppm O 3 in the first half period of exposure (1–4 weeks) became close to the control in the latter part of exposure (5–8 weeks). Time-course changes in NH 4N root uptake rate were similar to those in the root/shoot ratio especially for 0.10 ppm O 3. On the other hand, root respiration increased from the middle to later periods. Since it is to be supposed that plants grown under stressed conditions change the ratio of plant organ weight to achieve balance between the proportion of shoots to roots in the plant and their activity for maintaining plant growth, these changes in root/shoot ratio and nitrogen uptake rate under long-term exposure can be considered to be an adaptive response to maintain rice growth under O 3 stress.

The effects of chronic ozone exposure on pulmonary collagen content and collagen synthesis in rats.

Male rats were exposed to 0.125, 0.25 or 0.5 ppm of ozone or clean air for up to 1 year. During this exposure period there was little evidence for collagen accumulation in the lungs. However, the rate of incorporation of tritiated proline into both lung collagen and total lung protein was accelerated. These data suggest that exposure to ozone under these conditions results in an increase in the turnover of collagen as well as other lung proteins.