Nitrogen mediates above-ground effects of ozone but not below-ground effects in a rhizomatous sedge

Ozone and atmospheric nitrogen are co-occurring pollutants with adverse effects on natural grassland vegetation. Plants of the rhizomatous sedge Carex arenaria were exposed to four ozone regimes representing increasing background concentrations (background-peak): 10-30, 35-55, 60-80 and 85-105 ppb ozone at two nitrogen levels: 12 and 100 kg N ha⁻¹ yr⁻¹. Ozone increased the number and proportion of senesced leaves, but not overall leaf number. There was a clear nitrogen × ozone interaction with high nitrogen reducing proportional senescence in each treatment and increasing the ozone dose (AOT40) at which enhanced senescence occurred. Ozone reduced total biomass due to significant effects on root biomass. There were no interactive effects on shoot:root ratio. Rhizome tissue N content was increased by both nitrogen and ozone. Results suggest that nitrogen mediates above-ground impacts of ozone but not impacts on below-ground resource translocation. This may lead to complex interactive effects between the two pollutants on natural vegetation.     

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

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

Persistent stimulation of CO2 assimilation and stomatal conductance by summer ozone fumigation in Norway spruce

CO(2) assimilation rate, stomatal conductance and chlorophyll content of current and previous years' needles of Norway spruce were measured in May 1988, 205 days after the cessation of ozone fumigation during the summer of 1987. Rates of assimilation were consistently higher for both needle year age classes for ozone fumigated trees in comparison to control trees, although only statistically significant for part of the day for current year's needles. A 26% and 48% stimulation, overall, in mean daily rates of assimilation for current and previous years' needles of ozone fumigated trees was observed. This was due to an enhanced apparent quantum yield and light saturated rate of assimilation of ozone fumigated trees. The temperature response regression of assimilation versus temperature was also greater, such that at any given temperature, assimilation was higher for ozone treated trees than control trees. Stomatal conductance was greater for ozone fumigated trees than the controls, but this was only marginally statistically significant. Moreover, there was a consistent increase in chlorophyll content in both year classes in ozone-treated trees. These results are discussed in relation to a possible long term effect of ozone fumigation upon the processes of conifer winter hardening and spring de-hardening.     

Ozone Injury to Pinus Strobus

In a study of the ozone-induced needle blight of eastern white pine in central New York, acute injuries naturally induced on field trees during a year of relatively low ozone concentrations (1 966) were compared with injuries induced during a year of higher concentrations (1967). Injuries were more frequent and severe and were associated with higher mean ozone concentrations in 1967 than in 1966. Characteristic symptoms were induced on foliage of pine branches exposed to controlled doses of ozone as low as 7 ± 1 pphm for four hours or 3 ± 1 pphm for 48 hours. Such doses were equalled or exceeded two and four times, respectively, in the field during the 1 967 season. Ozone sensitivity of pine needle tissue was increased by fumigation in atmospheres containing water mist. High concentrations of ozone (40-60 pphm) caused general injury of foliage of both ozone-susceptible and resistant trees; the symptoms were unlike those found in the field or caused by fumigation with low concentrations of ozone.     

Fine root dynamics of mature European beech (Fagus sylvatica L.) as influenced by elevated ozone concentrations

Fine root dynamics (diameter < 1 mm) in mature Fagus sylvatica, with the canopies exposed to ambient or twice-ambient ozone concentrations, were investigated throughout 2004. The focus was on the seasonal timing and extent of fine root dynamics (growth, mortality) in relation to the soil environment (water content, temperature). Under ambient ozone concentrations, a significant relationship was found between fine root turnover and soil environmental changes indicating accelerated fine root turnover under favourable soil conditions. In contrast, under elevated ozone, this relationship vanished as the result of an altered temporal pattern of fine root growth. Fine root survival and turnover rate did not differ significantly between the different ozone regimes, although a delay in current-year fine root shedding was found under the elevated ozone concentrations. The data indicate that increasing tropospheric ozone levels can alter the timing of fine root turnover in mature F. sylvatica but do not affect the turnover rate.     

Effect of 3 years' free-air exposure to elevated ozone on mature Norway spruce (Picea abies (L.) Karst.) needle epicuticular wax physicochemical characteristics

We examined the effect of ozone (O₃) on Norway spruce (Picea abies) needle epicuticular wax over three seasons at the Kranzberg Ozone Fumigation Experiment. Exposure to 2× ambient O₃ ranged from 64.5 to 74.2 μl O₃ l⁻¹ h AOT40, and 117.1 to 123.2 nl O₃ l⁻¹ 4th highest daily maximum 8-h average O₃ concentration. The proportion of current-year needle surface covered by wax tubes, tube aggregates, and plates decreased (P = 0.011) under 2× O₃. Epistomatal chambers had increased deposits of amorphous wax. Proportion of secondary alcohols varied due to year (P = 0.004) and O₃ treatment (P = 0.029). Secondary alcohols were reduced by 9.1% under 2× O₃. Exposure to 2× O₃ increased (P = 0.037) proportions of fatty acids by 29%. Opposing trends in secondary alcohols and fatty acids indicate a direct action of O₃ on wax biosynthesis. These results demonstrate O₃-induced changes in biologically important needle surface characteristics of 50-year-old field-grown trees.     

Light-induced heterogeneous ozone processing on organic coated particles: Kinetics and condensed-phase products

For the first time we investigated the effect of solar irradiation upon the heterogeneous ozonation of adsorbed 3,4,5-trimethoxybenzaldehyde on solid surface. Light-induced heterogeneous reactions between gas-phase ozone and 3,4,5-trimethoxybenzaldehyde adsorbed on silica particles were performed and the consecutive reaction products were identified. At an ozone mixing ratio of 250 ppb, the loss of 3,4,5-trimethoxybenzaldehyde ranged from 1.0 · 10^?6 s^?1 in the dark to 2.9 · 10^?5 s^?1 under light irradiation. Such large enhancement of 29 times clearly shows the importance of light (λ > 300 nm) during the heterogeneous ozonolysis on organic coated particles.The reaction products identified in this study (3,4,5-trimethoxybenzoic acid, syringic acid, methyl 3,4,5-trimethoxybenzoate) absorb light in the spectral window (λ > 300 nm) which implies that light-induced heterogeneous ozone processing can have an influence on the aerosol surfaces by changing their physico-chemical properties.The main identified product of the heterogeneous reactions between gas-phase ozone and 3,4,5-trimethoxybenzaldehyde under dark conditions and in presence of light was 3,4,5-trimethoxybenzoic acid. For this reason we estimated the carbon yield of 3,4,5-trimethoxybenzoic acid. Carbon yields of 3,4,5-trimethoxybenzoic acid decreased with increasing ozone mixing ratio; from 40% at 250 ppb to 15% at ≥2.5 ppm under dark conditions. At ozone mixing ratio (250 ppb–1 ppm), carbon yields of 3,4,5-trimethoxybenzaldehyde are relatively higher in the experiment under dark condition than under simulated solar light.     

Ozone uptake by citrus trees exposed to a range of ozone concentrations

The Citrus genus includes a large number of species and varieties widely cultivated in the Central Valley of California and in many other countries having similar Mediterranean climates. In the summer, orchards in California experience high levels of tropospheric ozone, formed by reactions of volatile organic compounds (VOC) with oxides of nitrogen (NO_x). Citrus trees may improve air quality in the orchard environment by taking up ozone through stomatal and non-stomatal mechanisms, but they may ultimately be detrimental to regional air quality by emitting biogenic VOC (BVOC) that oxidize to form ozone and secondary organic aerosol downwind of the site of emission. BVOC also play a key role in removing ozone through gas-phase chemical reactions in the intercellular spaces of the leaves and in ambient air outside the plants. Ozone is known to oxidize leaf tissues after entering stomata, resulting in decreased carbon assimilation and crop yield. To characterize ozone deposition and BVOC emissions for lemon (Citrus limon), mandarin (Citrus reticulata), and orange (Citrus sinensis), we designed branch enclosures that allowed direct measurement of fluxes under different physiological conditions in a controlled greenhouse environment. Average ozone uptake was up to 11 nmol s^?1 m^?2 of leaf. At low concentrations of ozone (40 ppb), measured ozone deposition was higher than expected ozone deposition modeled on the basis of stomatal aperture and ozone concentration. Our results were in better agreement with modeled values when we included non-stomatal ozone loss by reaction with gas-phase BVOC emitted from the citrus plants. At high ozone concentrations (160 ppb), the measured ozone deposition was lower than modeled, and we speculate that this indicates ozone accumulation in the leaf mesophyll.     

Variation in ozone sensitivity among clones of Betula pendula and Betula pubescens

Forty clones of Betula pendula and 6 clones of Betula pubescens, originating from southern and central Finland, were ranked in order of ozone sensitivity according to visible injuries, growth and leaf senescense under low ozone exposure. The plants were fumigated in natural climatic conditions using an open-air exposure system during two growing seasons. Control plants were grown under ambient air, and the elevated-ozone exposures were 1.6x the ambient in 1994 and 1.7x the ambient in 1995. The differences in ozone sensitivity among clones were large. Ozone tolerance was related to thicker leaves and higher stomatal density as compared to sensitive clones. Ultrastructural ozone-induced symptoms were found in chloroplasts of sensitive clones. Increased number of visibly injured leaves on fumigated plants was correlated with reduced leaf formation, foliage area, shoot dry wt and number of stomata, and increased yellowing of leaves. The results suggest that a considerable proportion of birch trees, showing high sensitivity to ozone, are at risk if ambient ozone exposures increase.     

Ozone response to precursor controls: comparison of data analysis methods with the predictions of photochemical air quality simulation models

Comparisons were made between the predictions of six photochemical air quality simulation models (PAQSMs) and three indicators of ozone response to emission reductions: the ratios of O₃/NO_z and O₃/NO_y and the extent of reaction. The values of the two indicator ratios and the extent of reaction were computed from the model-predicted mixing ratios of ozone and oxidized nitrogen species and were compared to the changes in peak 1 and 8 h ozone mixing ratios predicted by the PAQSMs. The ozone changes were determined from the ozone levels predicted for base-case emission levels and for reduced emissions of volatile organic compounds (VOCs) and oxides of nitrogen (NO_x). For all simulations, the model-predicted responses of peak 1 and 8 h ozone mixing ratios to VOC or NO_x emission reductions were correlated with the base-case extent of reaction and ratios of O₃/NO_z and O₃/NO_y. Peak ozone values increased following NO_x control in 95% (median over all simulations) of the high-ozone (>80 ppbv hourly mixing ratio in the base-case) grid cells having mean afternoon O₃/NO_z ratios less than 5 : 1, O₃/NO_y less than 4 : 1, or extent less than 0.6. Peak ozone levels decreased in response to NO_x reductions in 95% (median over all simulations) of the grid cells having peak hourly ozone mixing ratios greater than 80 ppbv and where mean afternoon O₃/NO_z exceeded 10 : 1, O₃/NO_y was greater than 8 : 1, or extent exceeded 0.8. Ozone responses varied in grid cells where O₃/NO_z was between 5 : 1 and 10 : 1, O₃/NO_y was between 4 : 1 and 8 : 1, or extent was between 0.6 and 0.8. The responses in such grid cells were affected by ozone responses in upwind grid cells and by the changes in ozone levels along the upwind boundaries of the modeling domains.     

Application of phosphate-solubilizing bacteria for enhancing bioavailability and phytoextraction of cadmium (Cd) from polluted soil

In this study, phosphate-solubilizing bacteria (PSB), Bacillus megaterium, were used to enhance Cd bioavailability and phytoextractability of Cd from contaminated soils. This strain showed a potential for directly solubilizing phosphorous from soils more than 10 folds greater than the control without inoculation. The results of pot experiments revealed that inoculation with B. megaterium significantly increased the extent of Cd accumulation in Brassica juncea and Abutilon theophrasti by two folds relative to the uninoculated control. The maximum Cd concentrations due to inoculation were 1.6 and 1.8 mg Cd g⁻¹ plant for B. juncea and A. theophrasti after 10 wk, respectively. The total biomass of A. theophrasti was not significantly promoted by the inoculation treatment, yet the total biomass of B. juncea increased from 0.087 to 0.448 g. It is also worth to mention that B. juncea predominantly accumulates Cd in its stems (39%) whereas A. theophrasti accumulates it in its leaves (68%) after 10 wk. The change of the Cd speciation indicated that inoculation of B. megaterium as PSB increased the bioavailabilty of Cd and consequently enhanced its uptake by plants. The present study may provide a new insight for improving phytoremediation using PSB in the Cd-contaminated soils.     

Seabird feathers as monitors of the levels and persistence of heavy metal pollution after the Prestige oil spill

We measured heavy metal concentrations in yellow-legged gulls (n = 196) and European shags (n = 189) in order to assess the temporal pattern of contaminant exposure following the Prestige oil spill in November 2002. We analysed Pb, Cu, Zn, Cr, Ni and V levels in chick feathers sampled at four colonies during seven post-spill years (2003-2009), and compared results with pre-spill levels obtained from feathers of juvenile shag corpses (grown in spring/summer 2002). Following the Prestige wreck, Cu (4.3-10 μg g⁻¹) and Pb concentrations (1.0-1.4 μg g⁻¹) were, respectively, between two and five times higher than pre-spill levels (1.5-3.6 and 0.1-0.4 μg g⁻¹), but returned to previous background concentrations after three years. Our study highlights the suitability of chick feathers of seabirds for assessing the impact of oil spills on heavy metal contamination, and provides the best evidence to date on the persistence of oil pollution after the Prestige incident.     

Effects of reactive hydrocarbons and hydrogen peroxide on antioxidant activity in cherry leaves

One-year-old cherry trees were fumigated with propene and gas-phase hydrogen peroxide, singly and in combination, in controlled-environment chambers for an 8-week period during the summer season. A UV light source was included with the combined propene and hydrogen peroxide regime to provide a source of hydroxyl radicals and ozone, and thus all the constituents of a photochemical smog. Measurements were made of soluble protein concentration and of glutathione reductase activity in leaf extracts from two or three leaf classes in plants from each treatment regime at the end of each fumigation period. Significant increases in soluble protein concentration with respect to the controls were found in plants fumigated with propene and hydrogen peroxide. The occurrence and extent of these differences depended on the leaf class and on the timing of the fumigation period over the summer with respect to bud break. The activity of glutathione reductase was found to be significantly increased in mature lower leaves of plants which had been fumigated with hydrogen peroxide. This effect was independent of the timing of fumigation with respect to bud break. Enzyme activity was also increased in propene and in propene plus hydrogen peroxide treatments, but only when plants were fumigated early in the growth season.     

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

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

Behavior of decabromodiphenyl ether (BDE-209) in soil: effects of rhizosphere and mycorrhizal colonization of ryegrass roots

A rhizobox experiment was conducted to investigate degradation of decabromodiphenyl ether (BDE-209) in the rhizosphere of ryegrass and the influence of root colonization with an arbuscular mycorrhizal (AM) fungus. BDE-209 dissipation in soil varied with its proximity to the roots and was enhanced by AM inoculation. A negative correlation (P < 0.001, R² = 0.66) was found between the residual BDE-209 concentration in soil and soil microbial biomass estimated as the total phospholipid fatty acids, suggesting a contribution of microbial degradation to BDE-209 dissipation. Twelve and twenty-four lower brominated PBDEs were detected in soil and plant samples, respectively, with a higher proportion of di- through hepta-BDE congeners in the plant tissues than in the soils, indicating the occurrence of BDE-209 debromination in the soil-plant system. AM inoculation increased the levels of lower brominated PBDEs in ryegrass. These results provide important information about the behavior of BDE-209 in the soil-plant system.     

Growth of soybean at future tropospheric ozone concentrations decreases canopy evapotranspiration and soil water depletion

Tropospheric ozone is increasing in many agricultural regions resulting in decreased stomatal conductance and overall biomass of sensitive crop species. These physiological effects of ozone forecast changes in evapotranspiration and thus in the terrestrial hydrological cycle, particularly in intercontinental interiors. Soybean plots were fumigated with ozone to achieve concentrations above ambient levels over five growing seasons in open-air field conditions. Mean season increases in ozone concentrations ([O₃]) varied between growing seasons from 22 to 37% above background concentrations. The objective of this experiment was to examine the effects of future [O₃] on crop ecosystem energy fluxes and water use. Elevated [O₃] caused decreases in canopy evapotranspiration resulting in decreased water use by as much as 15% in high ozone years and decreased soil water removal. In addition, ozone treatment resulted in increased sensible heat flux in all years indicative of day-time increase in canopy temperature of up to 0.7 °C.     

The efficiency of tobacco Bel-W3 and native species for ozone biomonitoring in subtropical climate, as revealed by histo-cytochemical techniques

We aimed to verify whether hydrogen peroxide (H₂O₂) accumulation and cell death are detected early in three bioindicators of ozone (O₃), Nicotiana tabacum ‘Bel-W3’, Ipomoea nil ‘Scarlet O’Hara’ and Psidium guajava ‘Paluma’, and whether environmental factors also affect those microscopic markers. The three species were exposed to chronic levels of O₃ in a subtropical area and a histo-cytochemical technique that combines 3,3′-diaminobenzidine (DAB) with Evans blue staining was used in the assessments. The three species accumulated H₂O₂, but a positive correlation with O₃ concentration was only observed in N. tabacum. A positive correlation between O₃ and cellular death was also observed in N. tabacum. In I. nil and P. guajava, environmental factors were responsible for symptoms at the microscopic level, especially in P. guajava. We conclude that the most appropriate and least appropriate bioindicator plant for O₃ monitoring in the subtropics are N. tabacum ‘Bel-W3’ and P. guajava ‘Paluma’, respectively.     

Geostatistics as a validation tool for setting ozone standards for durum wheat

Which is the best standard for protecting plants from ozone? To answer this question, we must validate the standards by testing biological responses vs. ambient data in the field. A validation is missing for European and USA standards, because the networks for ozone, meteorology and plant responses are spatially independent. We proposed geostatistics as validation tool, and used durum wheat in central Italy as a test. The standards summarized ozone impact on yield better than hourly averages. Although USA criteria explained ozone-induced yield losses better than European criteria, USA legal level (75 ppb) protected only 39% of sites. European exposure-based standards protected ≥90%. Reducing the USA level to the Canadian 65 ppb or using W126 protected 91% and 97%, respectively. For a no-threshold accumulated stomatal flux, 22 mmol m⁻² was suggested to protect 97% of sites. In a multiple regression, precipitation explained 22% and ozone explained <0.9% of yield variability.     

Species-specific effects of elevated ozone on wetland plants and decomposition processes

Seven species from two contrasting wetlands, an upland bog and a lowland rich fen in North Wales, UK, were exposed to elevated ozone (150 ppb for 5 days and 20 ppb for 2 days per week) or low ozone (20 ppb) for four weeks in solardomes. The rich fen species were: Molinia caerulea, Juncus subnodulosus, Potentilla erecta and Hydrocotyle vulgaris and the bog species were: Carex echinata, Potentilla erecta and Festuca rubra. Senescence significantly increased under elevated ozone in all seven species but only Molinia caerulea showed a reduction in biomass under elevated ozone. Decomposition rates of plants exposed to elevated ozone, as measured by carbon dioxide efflux from dried plant material inoculated with peat slurry, increased for Potentilla erecta with higher hydrolytic enzyme activities. In contrast, a decrease in enzyme activities and a non-significant decrease in carbon dioxide efflux occurred in the grasses, sedge and rush species.