In vitro exposure of Ostrya carpinifolia and Carpinus betulus pollen to atmospheric levels of CO,O3 and SO2

Ostrya spp. and Carpinus spp. pollen was in vitro exposed to three atmospheric pollutants: CO, O₃ and SO₂. Two levels of each pollutant were used, and the first level corresponds to a concentration about the atmospheric hour-limit value acceptable for human health protection in Europe and the second level to about the triple of the first level. Experiments were done under artificial solar light with temperature and relative humidity controlled. The viability of the exposed pollen samples showed a significant decrease. Also, the germination percentage showed a significant decrease in both exposed pollens, and the effect was most pronounced for SO₂, followed by O₃ and CO. A general decreasing trend in the total soluble protein content of the exposed pollen samples when compared with the control was observed, but it was only statistically significant for the Ostrya spp pollen. The results showed marked effects were observed on the Ostrya spp. and Carpinus spp. pollen when exposed to air pollutant levels that can be considered safe for human health protection.     

Oxidative stress and arsenic toxicity: Role of NADPH oxidases

The effect of arsenic (25 and 50 μM As for 1 and 5 d) was analysed in wild type (WT) and Arabidopsis thaliana (L.) Heynh plants deficient in NADPH oxidase C (AtrbohC). The content of H₂O₂ and malondialdehyde (MDA) increased with the As concentration, while the opposite effect was found for NO in WT and AtrbohC plants. The As treatment reduced catalase and increased glutathione reductase activities to the same extent in WT and AtrbohC plants, although the induction of all SOD isoforms (mainly CuZn–SODs) was observed in WT plants, the opposite effects being found in AtrbohC plants. Glycolate oxidase (H₂O₂ producers) considerably increased with the concentration and time of treatment with As in WT and AtrbohC mutants. Arsenic induced the uptake and translocation of P, S, Cu, Zn, and Fe in WT plants, while in AtrbohC plants the opposite trend was noted and the uptake of As became considerably lower than in WT plants. These results suggest that As causes oxidative stress by inducing glycolate oxidase, while NADPH oxidase does not appear to participate in ROS overproduction but could be critical in regulating antioxidant defences as well as the transport and translocation of As and macro/micronutrients.     

Atmospheric deposition of macronutrients by pollen at a semi-remote site in northern Wisconsin

Pine pollen concentrations in air at a semi-remote site in northern Wisconsin attained levels of 18 and 25 μ m⁻³ in late May and early June of 1979 and 1981, respectively. The upper and lower limits for the deposition velocity of pine pollen at this site are approximately 30 and 1.3 cm s⁻¹, respectively. Consequently, the average annual pine pollen flux at this location for 1979 and 1981 was between 8.0 and 0.35 g m⁻². Deposition of total phosphorus and organic C by pollen dispersal are about 5–100% and 11–240%, respectively, of the measured bulk atmospheric loading rate in the region. Pine pollen fluxes of water-extractable K are about 10–230% of the average annual wet deposition, while the fluxes of waterextractable NO₃⁻ and SO₄⁻² by pollen appear to be negligible in comparison to the total atmospheric deposition (wet plus dry deposition) by other particles. The annual pine pollen flux to Crystal Lake, an oligotrophic seepage lake in the region, was estimated to be 6.5 g m⁻² during 1981. The deposition of total P by pollen to this lake was 5.8 kg a⁻¹, which is 45 % of the external input of total phosphorus. About 60% of the total P in samples of Pinus strobus and P. resinosa was dissolved reactive P, which is readily available for plant uptake. Because P is the limiting nutrient for many lacustrine systems and pine pollen dispersal coincides with the period of phytoplankton blooms in temperate-region lakes, this episodic input of P may represent an important source for seepage lakes whose external inputs are dominated by atmospheric deposition.     

Photosynthesis, chloroplast pigments, and antioxidants in Pinus canariensis under free-air ozone fumigation

High O₃ levels, driving uptake and challenging defense, prevail on the Canary Islands, being associated with the hot and dry summers of the Mediterranean-type climate. Pinus canariensis is an endemic conifer species that forms forests across these islands. We investigated the effects of ozone on photosynthesis and biochemical parameters of P. canariensis seedlings exposed to free-air O₃ fumigation at Kranzberg Forest, Germany, where ambient O₃ levels were similar to those at forest sites in the Canary Islands. The twice-ambient O₃ regime (2xO₃) neither caused visible injury-like chlorotic or necrotic spots in the needles nor significantly affected violaxanthin, antheraxanthin and zeaxanthin levels and the de-epoxidation state of the xanthophyll cycle. In parallel, stomatal conductance for water vapour, net photosynthesis, intercellular CO₂ concentration, chlorophyll fluorescence parameters, as well as antioxidant levels were hardly affected. It is concluded that presently prevailing O₃ levels do not impose severe stress on P. canariensis seedlings.     

Inorganic nanoparticles enhance the production of reactive oxygen species (ROS) during the autoxidation of L-3,4-dihydroxyphenylalanine (L-dopa)

Public concerns over the toxicity of nanoparticles (NPs) are growing due to the rapid development of nanotechnology. An important mechanism of nanotoxicity is oxidative stress resulting from reactive oxygen species (ROS). In this study, the chemical production of ROS by inorganic NPs oxidizing the mammalian phenolic compound, l-3,4-dihydroxyphenylalanine (l-dopa) was evaluated using a ROS sensitive dye, 2′,7′-diclorodihydrofluorescin (DCFH). CeO₂, Fe₂O₃ and Fe⁰ NPs enhanced ROS production during the autoxidation of l-dopa by more than four-fold in reactions that were dependent on O₂. This is the first report of chemical ROS production due to interaction of phenolic compounds with NPs. Mn₂O₃ oxidized DCFH in a reaction that did not require O₂ or l-dopa, suggesting a direct redox reaction between the Mn₂O₃ and the dye. CeO₂, Mn₂O₃ and to a lesser extent Fe⁰ formed clear electron paramagnetic resonance (EPR) signature for hydroxyl radicals when incubated in aerobic aqueous suspensions with spin traps. The results indicate that NPs can generate ROS via chemical reactions with medium components and biomolecules susceptible to oxidation, such as l-dopa. NPs were reactive whereas micron-sized particles were not. The combined assay with l-dopa and DCFH is a method proposed to screen for chemical ROS production by NPs.     

Spring leaf flush in aspen (Populus tremuloides) clones is altered by long-term growth at elevated carbon dioxide and elevated ozone concentration

Early spring leaf out is important to the success of deciduous trees competing for light and space in dense forest plantation canopies. In this study, we investigated spring leaf flush and how long-term growth at elevated carbon dioxide concentration ([CO₂]) and elevated ozone concentration ([O₃]) altered leaf area index development in a closed Populus tremuloides (aspen) canopy. This work was done at the Aspen FACE experiment where aspen clones have been grown since 1997 in conditions simulating the [CO₂] and [O₃] predicted for ∼2050. The responses of two clones were compared during the first month of spring leaf out when CO₂ fumigation had begun, but O₃ fumigation had not. Trees in elevated [CO₂] plots showed a stimulation of leaf area index (36%), while trees in elevated [O₃] plots had lower leaf area index (−20%). While individual leaf area was not significantly affected by elevated [CO₂], the photosynthetic operating efficiency of aspen leaves was significantly improved (51%). There were no significant differences in the way that the two aspen clones responded to elevated [CO₂]; however, the two clones responded differently to long-term growth at elevated [O₃]. The O₃-sensitive clone, 42E, had reduced individual leaf area when grown at elevated [O₃] (−32%), while the tolerant clone, 216, had larger mature leaf area at elevated [O₃] (46%). These results indicate a clear difference between the two clones in their long-term response to elevated [O₃], which could affect competition between the clones, and result in altered genotypic composition in future atmospheric conditions.     

Sensitivity of tropospheric oxidants to global chemical and climate change

A photochemical model has been used to quantify the sensitivity of the tropospheric oxidants O₃ and OH to changes in CH₄, CO and NO emissions and to perturbations in climate and stratospheric chemistry. Coefficients of the form ∂1n[O₃]/∂1n[X] and ∂1n[OH]/∂1n[X], where [X] = flux of CH₄, CO, NO; stratospheric O₃ and H₂O have been calculated for a number of “chemically coherent” regions (e.g. nonpolluted continental, nonpolluted marine, urban) at low and middle latitudes. Sensitivities in O₃ and OH vary with regional emissions patterns and are nonlinear within a given region as [X] changes. In most cases increasing CH₄ and CO emissions will suppress OH (negative coefficients) and increase O₃ (positive coefficients) except in areas where NO and O₃ influenced by pollution are sufficient to increase OH. Stratospheric O₃ depletion will tend to decrease O₃ (except in high NO_x areas) and increase OH through enhanced u.v. photolysis. Increased levels of water vapor (one possible outcome of a global warming) will also decrease O₃ and increase OH. We conclude that in most regions, NO, CO and CH₄ emission increases will suppress OH and increase O₃, but these trends may be opposed by stratospheric O₃ depletion and climate change. A regional survey of OH and O₃ levels suggests that the tropics have a pivotal role in determining the earth's future oxidizing capacity.     

High NOx levels and lack of ozone in downtown Caracas

An evaluation of the NO, NO₂ and O₃ concentrations in downtown Caracas atmosphere at two different heights (1.5 and 56 m ) during the dry and wet season was performed.The qualitative variation of NO and NO₂ concentrations throughout the day was the same for all conditions. The profiles are explained considering the automobile emissions and the fates by photochemical reactions and dispersion. The daily mean averages for NO_x exceed all available air quality standards, making the downtown Caracas air polluted with these compounds at harmful levels.The O₃ concentrations are lower than the natural background levels practically all day long for all conditions. This lack of O₃ is explained mainly by the very high continuous NO emissions occuring in Caracas. NO reacts very fast with O₃ consuming all the O₃ produced by photochemical reactions. Possible health implications of the low O₃ levels are pointed out.     

Consistency of Ozone and Nitrogen Oxides Standards at Tropospherically Relevant Mixing Ratios

Abstract

The absolute accuracy and long‐term precision of atmospheric measurements hinge on the quality of the instrumentation and calibration standards. To assess the consistency of the ozone (O₃) and nitrogen oxides (NO_x) standards maintained at the National Institute of Standards and Technology (NIST), these standards were compared through the gas‐phase titration of O3 with nitric oxide (NO). NO and O₃ were monitored using chemiluminescence and UV absorption, respectively. Nitrogen dioxide (NO₂) was monitored directly by laser‐induced fluorescence and indirectly by catalytic conversion to NO, followed by chemiluminescence. The observed equivalent loss of both NO and O₃ and the formation of NO₂ in these experiments was within 1% on average over the range of 40–200 nmol mol^?1 of NO in excess O3, indicating that these instruments, when calibrated with the NIST O₃ and NO standards and the NO₂ permeation calibration system, are consistent to within 1% at tropospherically relevant mixing ratios of O₃. Experiments conducted at higher initial NO mixing ratios or in excess NO are not in as good agreement. The largest discrepancies are associated with the chemiluminescence measurements. These results indicate the presence of systematic biases under these specific conditions. Prospects for improving these experiments are discussed.     

Using optical remote sensing techniques to track the development of ozone-induced stress

In this paper, a literature review about optical remote sensing (RS) of O₃ stress is presented. Studies on O₃-induced effects on vegetation reflectance have been conducted since late ‘70s based on the analysis of optical RS data. Literature review reveals that traditional RS techniques were able to detect changes in leaf and canopy reflectance related to O₃-induced stress when visible symptoms already occurred. Only recently, advanced RS techniques using hyperspectral sensors, demonstrated the feasibility of detecting the stress in its early phase by monitoring excess energy dissipation pathways such as chlorophyll fluorescence and non-photochemical quenching (NPQ). Steady-state fluorescence (Fs), measured by exploiting the Fraunhofer line depth principle and NPQ related xanthophyll-cycle, estimated through the photochemical reflectance index (PRI) responded to O₃ fumigation before visible symptoms occurred. This opens up new possibilities for the early detection of vegetation O₃ stress by means of hyperspectral RS.     

Physiological and biochemical responses of <Emphasis Type="Italic">Machilus ichangensis</Emphasis> Rehd. et Wils and <Emphasis Type="Italic">Taxus chinensis</Emphasis> (Pilger) Rehd. to elevated O<Subscript>3</Subscript> in subtropical China

Considerable researches have documented the negative effects of ozone on woody species in North America and Europe; however, little is known about how woody tree species respond to elevated O₃ in subtropical China, and most of the previous studies were conducted using pot experiment. In the present study, Machilus ichangensis Rehd. et Wils (M. ichangensis) and Taxus chinensis (Pilger) Rehd. (T. chinensis), evergreen tree species in subtropical China, were exposed to non-filtered air (NF), 100 nmol mol^?1 O₃ (E1) and 150 nmol mol^?1 O₃ (E2), in open-top chambers under field conditions from 21st March to 2nd November 2015. In this study, O₃ fumigation significantly reduced net photosynthesis rate (Pn) in M. ichangensis in the three measurements and in T. chinensis in the last measurement. Also, non-stomatal factors should be primarily responsible for the decreased Pn. O₃ fumigation-induced increase in malondialdehyde, superoxide dismutase, and reduced ascorbic acid levels indicated that antioxidant defense mechanism had been stimulated to prevent O₃ stress and repair the oxidative damage. Yet, the increase of antioxidant ability was not enough to counteract the harm of O₃ fumigation. Because of the decrease in CO₂ assimilation, the growth of the two tree species was restrained ultimately. The sensitivity of the two tree species to O₃ can be determined: M. ichangensis > T. chinensis. It suggests a close link between the rising O₃ concentrations and the health risk of some tree species in subtropics in the near future.     

Detoxification and repair process of ozone injury: from O3 uptake to gene expression adjustment

Plants react to O₃ threat by setting up a variety of defensive strategies involving the co-ordinated modulation of stress perception, signalling and metabolic responses. Although stomata largely controls O₃ uptake, differences in O₃ tolerance cannot always be ascribed to changes in stomatal conductance but cell protective and repair processes should be taken into account. O₃-driven ROS production in the apoplast induces a secondary, active, self-propagating generation of ROS, whose levels must be finely tuned, by many enzymatic and non-enzymatic antioxidant systems, to induce gene activation without determining uncontrolled cell death. Additional signalling molecules, as ethylene, jasmonic and salicylic acid are also crucial to determine the spreading and the containment of leaf lesions. The main recent results obtained on O₃ sensing, signal transduction, ROS formation and detoxification mechanisms are here discussed.     

Exposure to elevated ozone levels differentially affects the antioxidant capacity and the redox homeostasis of two subtropical Phaseolus vulgaris L. varieties

Ozone (O₃) has become one of the most toxic air pollutants to plants worldwide. However, investigations on O₃ impacts on crops health and productivity in South America countries are still scarce. The present study analyzed the differences on the enzymatic and non-enzymatic antioxidant system in foliar tissue of two subtropical Phaseolus vulgaris varieties exposed to high O₃ concentration. Both varieties were negatively impacted by the pollutant, but the responses between each variety were quite distinct. Results revealed that Irai has higher constitutive levels of reactive oxygen species (ROS) and ascorbate (AsA) concentration, but lower total thiol levels and catalase immunocontent. In this variety catalase protein concentration was increased after O₃ exposure, indicating a better cellular capacity to reduce hydrogen peroxide. On the opposite, Fepagro 26-exposed plants increased ROS generation and AsA concentration, but had the levels of total thiol content and catalase protein unchanged. Furthermore, O₃ treatment reduced the levels of chlorophylls a and b, and the relationship analysis between the chlorophyll ratio (a/b) and protein concentration were positively correlated indicating that photosynthetic apparatus is compromised, and thus probably is the biomass acquisition on Fepagro 26. Differently, O₃ treatment of Irai did not affect chlorophylls a and b content, and loss on the protein content was lower. Altogether, these data suggest that early accumulation of ROS on Fepagro 26 are associated with an insufficient leaf antioxidant capacity, which leads to cell structure disruption and impairs the photosynthesis. Irai seems to be more tolerant to O₃ toxic effects than Fepagro 26, and the observed differences on O₃ sensitivity between the two varieties are apparently based on constitutive differences involved in the maintenance of intracellular redox homeostasis.     

The uptake of O3 by poplar leaves: the impact of a long-term exposure to low O3-concentrations

Poplar shoots were exposed for 3–4 weeks to filtered air, ambient (maximum values 50–60 nl ℓ^-1) or two times ambient O₃-concentrations under controlled environmental conditions in fumigation chambers. A sensitive (Populus nigra ‘Brandaris’) and a tolerant (P. euramericana ‘Robusta’) cultivar were used. At regular intervals the uptake of O₃, transpiration and CO₂ assimilation rate (P_n) of full-grown leaves were measured with leaf cuvettes. For unaffected leaves, the measured flux of O₃ into the leaves appeared to be larger than can be calculated using the stomatal conductance for O₃ (g_s,o) estimated from the transpiration rates of the same leaves. Resistance analysis revealed that the difference was partly a result of a reaction with the external leaf surface. However, when the O₃ flux into the leaf was corrected for this reaction, it was still larger than can be estimated using g_s,o. As a consequence, negative residual or internal resistances (r_i) for O₃ transport into the leaves were assessed. It is postulated that O₃ molecules moving into the leaf follow a shorter pathway than effluxing H₂O-molecules. P. ‘Brandaris’ leaves showed a reduction in P_n after 12 days of exposure to ambient O₃-concentrations, whereas for P. ‘Robusta’ a reduction in P_n was only observed at two times ambient concentrations. A simultaneous decline in the O₃-flux was found in both cases. The decline occurred before a decrease in g_s,o was observed suggesting that the O₃ flux into the affected leaves was first hindered by internal factors. The measured flux of the affected leaves became smaller than the flux estimated using g_s,o and, consequently, positive r_i-values were estimated. The change in r_i suggests that O₃ molecules not only penetrated deeper into the leaf, but also were accumulating at a prolonged exposure. Our results indicate that r_i may be a potentially important component of the overall resistance for O₃-uptake, which may have important consequences for estimating O₃ uptake from water vapour flux data.     

Response of Brazilian native trees to acute ozone dose

Ozone (O₃) is a toxic secondary pollutant able to cause an intense oxidative stress that induces visual symptoms on sensitive plant species. Controlled fumigation experiment was conducted with the aim to verify the O₃ sensibility of three tropical species: Piptadenia gonoachanta (Mart.) Macbr. (Fabaceae), Astronium graveolens Jacq. (Anacardiaceae), and Croton floribundus Spreng. (Euphorbiaceae). The microscopical features involved in the oxidative stress were recognized based on specific histochemical analysis. The three species showed visual symptoms, characterized as necrosis and stippling between the veins, mostly visible on the adaxial leaf surface. All the studied species presented hypersensitive-like response (HR-like), and peroxide hydrogen accumulation (H₂O₂) followed by cell death and proanthocyanidin oxidation in P. gonoachanta and A. graveolens. In P. gonoachanta, a decrease in chlorophyll autofluorescence occurred on symptomatic tissues, and in A. graveolens and C. floribundus, a polyphenol compound accumulation occurred. The responses of Brazilian native species were similar to those described for sensitive species from temperate climate, and microscopical markers may be useful for the detection of ozone symptoms in future studies in the field.     

Advances in understanding ozone impact on forest trees: Messages from novel phytotron and free-air fumigation studies

Recent evidence from novel phytotron and free-air ozone (O₃) fumigation experiments in Europe and America on forest tree species is highlighted in relation to previous chamber studies. Differences in O₃ sensitivity between pioneer and climax species are examined and viewed for trees growing at the harsh alpine timberline ecotone. As O₃ apparently counteracts positive effects of elevated CO₂ and mitigates productivity increases, response is governed by genotype, competitors, and ontogeny rather than species per se. Complexity in O₃ responsiveness increased under the influence of pathogens and herbivores. The new evidence does not conflict in principle with previous findings that, however, pointed to a low ecological significance. This new knowledge on trees' O₃ responsiveness beyond the juvenile stage in plantations and forests nevertheless implies limited predictability due to complexity in biotic and abiotic interactions. Unravelling underlying mechanisms is mandatory for assessing O₃ risks as an important component of climate change scenarios.     

Defining the Photochemical Contribution to Particulate Matter in Urban Areas Using Time-Series Analysis

Abstract

The objective of this project is to demonstrate how the ambient air measurement record can be used to define the relationship between O₃ (as a surrogate for photochemistry) and secondary particulate matter (PM) in urban air. The approach used is to develop a time-series transfer-function model describing the daily PM₁₀ (PM with less than 10 μm aerodynamic diameter) concentration as a function of lagged PM and current and lagged O₃, NO or NO₂, CO, and SO₂. Approximately 3 years of daily average PM₁₀, daily maximum 8-hr average O₃ and CO, daily 24-hr average SO₂ and NO₂, and daily 6:00 a.m.-9:00 a.m. average NO from the Aerometric Information Retrieval System (AIRS) air quality subsystem are used for this analysis. Urban areas modeled are Chicago, IL; Los Angeles, CA; Phoenix, AZ; Philadelphia, PA; Sacramento, CA; and Detroit, MI. Time-series analysis identified significant autocorrelation in the O₃, PM₁₀, NO, NO₂,CO, and SO₂ series. Cross correlations between PM₁₀ (dependent variable) and gaseous pollutants (independent variables) show that all of the gases are significantly correlated with PM₁₀ and that O₃ is also significantly correlated lagged up to two previous days. Once a transfer-function model of current PM₁₀ is defined for an urban location, the effect of an O₃-control strategy on PM concentrations is estimated by calculating daily PM₁₀ concentrations with reduced O₃ concentrations. Forecasted summertime PM₁₀ reductions resulting from a 5 percent decrease in ambient O₃ range from 1.2 μg/m³ (3.03%) in Chicago to 3.9 μg/m³ (7.65%) in Phoenix.