Photochemical oxidants, sulphur dioxide and fluoride are the major air pollutants affecting agricultural crops in Ontario, but scientific documentation of their effects is limited, particularly for sulphur dioxide and fluoride. Airborne road salt, cement dust, soot, boron, nickel, cobalt and ammonia have also been implicated in a few localized instances of crop injury. The most widespread injury to agricultural crops is caused by photochemical oxidants, mainly in southern Ontario where tobacco, bean, potato, grape, cucumber, onion, tomato and other crops have been affected. Sulphur dioxide has had significant effects on forests and natural vegetation in Ontario, and may become important in agricultural areas due to the proliferation of coal-fired electric generating stations. The effects of sulphur dioxide in combination with other gaseous pollutants such as photochemical oxidants, and the long-term effects of acid precipitation are current concerns. In addition, there have been a few cases of fluoride injury to crops localized around fluoride-emitting industries. Very few estimates of economic losses to agricultural crops have been documented anywhere and to date no assessment of the economic value of air pollution damage to agricultural crops in Ontario has been attempted.

Patterns of environmental change in the biosphere include concurrent and sequential combinations of increasing ultraviolet (UV-B) and ozone (O(3)) at increasing carbon dioxide (CO(2)) levels; long-term changes are resulting mainly from stratospheric O(3) depletion, greater tropospheric O(3) photochemical synthesis, and increasing CO(2) emissions. Effects of selected combinations were evaluated in tomato (Lycopersicon esculentum cv. New Yorker) seedlings using sequential exposures to enhanced UV-B radiation and O(3) in differential CO(2) concentrations. Ambient (7.2 kJ m(-2 )day(-1)) or enhanced (13.1 kJ m(-2) day(-1)) UV-B fluences and ambient (380 microl l(-1)) or elevated (600 microl l(-1)) CO(2) were imposed for 19 days before exposure to 3-day simulated O(3) episodes with peak concentrations of 0.00, 0.08, 0.16 or 0.24 microl l(-1) O(3) in ambient or elevated CO(2). CO(2) enrichment increased dry mass, leaf area, specific leaf weight, chlorophyll concentration and UV-absorbing compounds per unit leaf area. Exposure to enhanced UV-B increased leaf chlorophyll and UV-absorbing compounds but decreased leaf area and root/shoot ratio. O(3) exposure generally inhibited growth and leaf photosynthesis and did not affect UV-absorbing compounds. The highest dose of O(3) eliminated the stimulating effect of CO(2) enrichment after ambient UV-B pre-exposure on leaf photosynthesis. Pre-exposure to enhanced UV-B mitigated O(3) damage to leaf photosynthesis at elevated CO(2).

It has been demonstrated, in both herbaceous and woody species, that tissue hydration resulting from exposure to drought is less pronounced if plants are concurrently exposed to ultraviolet-B radiation (UV-B). An explanation for the mechanisms underlying this phenomenon has been elusive. Arabidopsis thaliana (L.) Heynh. genotypes, defective in specific defences against UV-B exposure, may permit more insightful study of drought-UV-B interactions than is possible with genetically uniform plants. Arabidopsis has a rosette stature and has predominantly abaxial stomata. Thus, it is difficult to investigate its stomatal behaviour and gas exchange using conventional techniques and instrumentation. In this study, the relative abundance of C-13 and C-12 in leaf tissue (delta C-13) was used as a means of determining water use efficiency (WUE) and the relative balance, at the site of carbon fixation, between CO2 supply and demand. UV-B insensitive (Ler) and sensitive (fah1) Arabidopsis genotypes were raised in a growth chamber and exposed to 6 kJ m(-2) d(-1) UV-B irradiation and subjected to drought. In both genotypes, leaf desiccation was less pronounced than that of control plants that were subjected to drought but not exposed to UV-B. The relatively low (more negative) leaf delta C-13 values (indicating low WUE), but high dry matter production of the UV-B exposed plants suggest that their higher leaf water content was not primarily due to stomatal closure. We propose that the mechanisms underlying the maintenance of higher leaf water content involved UV-B and water stress induced biosynthesis of stress proteins and compatible osmolytes. (C) 2000 Annals of Botany Company.

Ultraviolet-B (UV-B) radiation (280–320 nm) is increasing in the biosphere because anthropogenic ozone scavengers diffusing to the stratosphere are depleting the protective stratospheric ozone layer (Kerr and McElroy, 1993). For every 1% decrease in stratospheric 142ozone there is a 2% increase in UV-B reaching the earth’s surface (Caldwell, 1979). This study describes morphological and anatomical changes in needles of ecologically and economically important conifers exposed to differential UV-B doses.

Tomato (Lycopersicon esculentum Mill.) plants were exposed, in controlled environments with 2.7 kJ/(m2 ∙ day) background ultraviolet-B (UV-B) radiation from fluorescent and incandescent lamps, to ambient (380 μL ∙ L−1) or elevated (600 μL−1) CO2 combined with a total of 7.2 or 13.1 kJ/(m2 ∙ day) UV-B radiation to determine effects on growth and photosynthesis. Ten consecutive days of exposure to the higher level of UV-B significantly reduced total and stem dry weight, leaf area, and plant height compared with the lower level. Only leaf area and plant height were significantly reduced after 19 consecutive days of exposure. To investigate whether plants recover from UV-B damage, the UV-B exposures were halted for 3 days after 19 days of UV-B exposure and then restarted for a further 2 days. The largest reduction in plant growth was found after 3 days with no UV-B followed by 2 days of the higher level of UV-B. Plants did not recover from UV-B damage during the 3 days with background UV-B. Significant CO2xUV-B interactions were detected on stem dry weight after 10 consecutive days of the higher level of UV-B and on total dry weight, leaf dry weight, stem dry weight, and plant height after 3 days with no UV-B followed by 2 days of the higher level of UV-B. The higher dose of enhanced UV-B resulted in more severe damage at 600 μL ∙ L−1 CO2, than at ambient CO2. The higher level of UV-B did not affect the leaf net photosynthesis rate on a leaf area basis, although this UV-B level may have inhibited tomato growth through reducing the photosynthetic area. UV-absorbing compounds in leaves in the highest UV-B radiation level for 19 days were greater than for leaves with the lower dose. These UV-absorbing compounds in the higher UV-B dose diminished more than in the lower dose plants during the 3 days without UV-B. The UV-absorbing compounds maintained by plants exposed to the highest level of UV-B radiation may have protected plants from UV-B damage, particularly between 10 and 19 consecutive days of exposure. Key words: CO2, growth, Lycopersicon esculentum Mill., photosynthesis, tomato, ultraviolet-B radiation (UV-B), UV-absorbing compounds.

An application of stable carbon isotope analysis to the mechanistic interpretation of ultraviolet‐B (UV‐B) effects on growth inhibition is described that is particularly useful for small plants such as Arabidopsis thaliana that are not well suited for gas exchange studies. Many investigators use tissue δ13C, relative abundance of 13C and 12C, as a proxy for water use efficiency and as an indicator of environmental effects on stomatal behaviour and on photosynthesis during growth. Discrimination against 13C is enhanced by both high stomatal conductance and damage to photosynthetic machinery. Because the thinning of the stratospheric ozone layer is permitting more UV‐B to enter the biosphere, the mechanisms of action of UV‐B radiation on plants are of particular current interest. Arabidopsis thaliana wild‐type Landsberg erecta (Ler) and the UV‐B‐sensitive mutant fah I, deficient in UV‐absorbing sinapate esters, were grown in a controlled environment and exposed to UV‐BBE doses of 0 or 6–7 kJ m−2 day−1. UV‐B exposure decreased dry matter production and δ13C in both genotypes, but growth inhibition was generally greater in fah I than in Ler. The fah I mutant also had less leaf greenness than Ler. Changes in leaf tissue δ13C were detected before growth inhibition and were evident in treatments of both genotypes that did not cause marked growth effects. This suggests that the effects of UV‐B contributing to increased carbon isotope discrimination in Ler may have been primarily associated with high stomatal conductance, and in fah I with both high stomatal conductance and damage to photosynthetic machinery.

Earlier studies with Arabidopsis thaliana exposed to ultraviolet B (UV-B) and ozone (O3) have indicated the differential responses of superoxide dismutase and glutathione reductase. In this study, we have investigated whether A. thaliana genotype Landsberg erecta and its flavonoid-deficient mutant transparent testa (tt5) is capable of metabolizing UV-B- and O3-induced activated oxygen species by invoking similar antioxidant enzymes. UV-B exposure preferentially enhanced guaiacol-peroxidases, ascorbate peroxidase, and peroxidases specific to coniferyl alcohol and modified the substrate affinity of ascorbate peroxidase. O3 exposure enhanced superoxide dismutase, peroxidases, glutathione reductase, and ascorbate peroxidase to a similar degree and modified the substrate affinity of both glutathione reductase and ascorbate peroxidase. Both UV-B and O3 exposure enhanced similar Cu,Zn-superoxide dismutase isoforms. New isoforms of peroxidases and ascorbate peroxidase were synthesized in tt5 plants irradiated with UV-B. UV-B radiation, in contrast to O3, enhanced the activated oxygen species by increasing membrane-localized NADPH-oxidase activity and decreasing catalase activities. These results collectively suggest that (a) UV-B exposure preferentially induces peroxidase-related enzymes, whereas O3 exposure invokes the enzymes of superoxide dismutase/ascorbate-glutathione cycle, and (b) in contrast to O3, UV-B exposure generated activated oxygen species by increasing NADPH-oxidase activity.

Atmospheric carbon dioxide (CO2) and photochemical ozone (O-3) have been increasing in the biosphere and will continue to do so with further industrialization and burning of fossil fuels, The purpose of this study was to examine the interaction of CO2 and O-3 on plant growth and aboveground competition using a forage mixture of alfalfa (Medicago sativa L.) and timothy (Phleum pratense L.). Mixtures were grown at two CO2 levels (350 and 700 mu L/L) in controlled environment chambers and exposed to four weekly O-3 episodes of 8-h duration with peak daily concentrations of 0.03, 0.08, 0.13, or 0.18 mu L/L on Days (d) 21, 28, 35, and 42 after seeding. Roots of individual plants were in separate containers, The plants were harvested 2 d after the fmal O-3 exposure. Total dry biomass of alfalfa and timothy was 50 and 40%, respectively, greater at 700 than at 350 mu L CO2/L with low O-3. Increasing peak O-3 concentration decreased alfalfa shoot dry biomass at 700 mu L CO2/L but not at 350 mu L/L and decreased root dry biomass at both CO2 levels. In timothy, intermediate O-3 levels reduced shoot growth but the highest level of O-3 resulted in more shoot growth in the mixture at both CO2 levels. Partitioning of dry matter to alfalfa roots was strongly retarded by increasing O-3, particularly in the CO2-enriched environment, while timothy root growth vias unaffected by O-3. The enhancement of timothy shoot biomass is, the mixture by exposure to the highest level of O-3 at either CO2 level could not be fully explained by changes in competition between timothy and alfalfa in relation to differential O-3 tolerance.

This study of exogenous polyamine effects on NO2 sensitivity of bean was designed to elucidate relationships between spermine and spermidine, NO2 exposure and nitrogen nutrition, and their effects on leaves at different physiological stages. Green bean (Phaseolus vulgaris L. cv. Kinghorn Wax) seedlings were raised on nutrient solution without nitrogen either in the dark for 7 d or in a 14-h photoperiod for 14 d. The plants were then treated with nutrient solution containign 0 or 5 mM nitrate as nitrogen source and 100 mu M spermine or spermidine with our without nitrate, and exposed to 0.3 mu L L(-1) NO2 for 3 d in a 14 h photoperiod. Protective effects against NO2-induced loss of leaf dry mass were demonstrated in greening leaves on plants treated with a combination of nitrate and spermidine, in secondary leaves on plants given either polyamine with or without nitrate, and in senescing primary leaves on plants treated with nitrate and spermine or nitrate and spermidine. These protective effects could not be consistently related to differential levels of total chlorophyll or total organic nitrogen induced by the treatments. It is suggested that polyamines applied to plants supplied with nitrate are able to ameliorate the injurious effects of NO2 on growth by restricting NO2 conversion to injurious products, and/or protecting tissues from injurious products.

Abstract— The impact of sequential exposure to ozone (O3) and UVB (290–320 nm) was studied using two genotypes of Arabidopsis thaliana differing in UVB sensitivity. The negative impact of UVB on dry matter production and photosynthetic pigments was absent in the ecotype Landsberg erecta (LER), while the negative impact of UVB was more pronounced when LER plants preexposed to O3 were irradiated with UVB. However, the growth of tt5 plants (a mutant virtually incapable of synthesizing flavonoids) was significantly affected by the UVB exposures, while the impact of UVB was significantly counteracted when tt5 plants pre‐exposed to O3 were irradiated with UVB. These results suggest that pre‐exposure to O3 decreased sensitivity of tt5 but increased sensitivity of LER to UVB. Concentrations of UV‐absorptive compounds were almost the same in plants exposed to UVB alone or sequentially to O3 and UVB. Exposures of LER and tt5 to UVB enhanced both ascorbic acid and glutathione as well as their redox state compared to control plants. Pre‐exposure to O3 enhanced the total ascorbic acid and glutathione as well as the redox state of ascorbate and glutathione in tt5 but decreased the redox state in LER. Irradiation of plants pre‐exposed to O3 with UVB enhanced the redox state of ascorbate and glutathione slightly in tt5 but decreased it further in LER. The high redox state of ascorbate and glutathione in tt5 pre‐exposed to O3 would have protected plants from UVB and decreased their sensitivity to UVB in spite of their inability to synthesize flavonoids. The decreased redox state in O3‐exposed LER plants would have enhanced their sensitivity to UVB. These results suggest that O3 influences plant response to UVB in environments enriched with both O3 and UVB.

O3-induced changes in growth, oxidative damage to protein, and specific activities of certain antioxidant enzymes were investigated in wheat plants (Triticum aestivum L. cv Roblin) grown under ambient or high CO2. High CO2 enhanced shoot biomass of wheat plants, whereas O3 exposure decreased shoot biomass. The shoot biomass was relatively unaffected in plants grown under a combination of high CO2 and O3. O3 exposure under ambient CO2 decreased photosynthetic pigments, soluble proteins, and ribulose-1,5-bisphosphate carboxylase/oxygenase protein and enhanced oxidative damage to proteins, but these effects were not observed in plants exposed to O3 under high CO2. O3 exposure initially enhanced the specific activities of superoxide dismutase, peroxidase, glutathione reductase, and ascorbate peroxidase irrespective of growth in ambient or high CO2. However, the specific activities decreased in plants with prolonged exposure to O3 under ambient CO2 but not in plants exposed to O3 under high CO2. Native gels revealed preferential changes in the isoform composition of superoxide dismutase, peroxidases, and ascorbate peroxidase of plants grown under a combination of high CO2 and O3. Furthermore, growth under high CO2 and O3 led to the synthesis of one new isoform of glutathione reductase. This could explain why plants grown under a combination of high CO2 and O3 are capable of resisting O3-induced damage to growth and proteins compared to plants exposed to O3 under ambient CO2.

The effect of UVB and ozone (O-3) on growth and ascorbate-glutathione cycle were investigated in Arabidopsis thaliana wild-type Landsberg erecta (LER) and its transparent testa (tt5) mutant differing in UVB sensitivity. Ultraviolet-B radiation decreased dry matter production of tt5, while the dry weight of LER remained unaltered. Ozone exposure decreased dry weight of both genotypes. Ultraviolet-B radiation decreased the F-v/F-m ratio in tt5 but not in LER plants, while O-3 exposure decreased the F-v/F-m ratio in both genotypes. Ultraviolet-B radiation enhanced total ascorbic acid, total glutathione and their redox state and superoxide dismutase and glutathione reductase activities in both genotypes and the increases were greater in tt5 compared to UVB-irradiated LER. Although O, exposure enhanced total ascorbic acid and total glutathione in both genotypes, the redox state was significantly higher in tt5. Ozone exposure enhanced superoxide dismutase and glutathione reductase activities in tt5 while there were no major changes in LER. These results suggested that (1) plants blocked in flavonoid biosynthesis are sensitive to UVB in spite of their ability to maintain efficient oxygen free radical scavenging systems and (2) plants sensitive to UVB are comparatively tolerant of O, compared to UVB-insensitive plants. The differential responses of plants are discussed with reference to their ability to maintain high redox states of ascorbate and glutathione.

Abstract— The effect of UVB (280–320 nm radiation) and ozone (O3) on growth, photosynthetic pigments, ribulose bisphosphate carboxylase/oxygenase (rubisco) activity and rubisco protein were investigated in Arabidopsis thaliana genotypes wild type Landsberg erecta (LER) and tt5, a flavonoid‐deficient mutant. The UVB exposure for 5 days decreased whole plant dry weight of only tt5 plants, while O3 exposure decreased the whole plant dry weight of both genotypes. The UVB exposure enhanced chlorophylls and carotenoids in both genotypes while O3 exposure decreased photosynthetic pigments in both genotypes. Both UVB and 03 exposure enhanced UV‐absorbing compounds in LER but not in tt5. Ultraviolet‐B exposure decreased initial and total rubisco activities only in tt5 plants, which contained smaller amounts of UV‐absorbing pigments. The effect of UVB was greater on initial rubisco activity resulting in decreased percent activatible rubisco. Ozone exposure decreased initial and total rubisco activities in both genotypes, and the magnitudes of decrease were greater on total rubisco activity, resulting in enhanced levels of percent activatible rubisco. Immunoblot analysis performed with antibodies raised against rubisco large subunit (LSU) and rubisco small subunit (SSU) showed no major changes in the levels of rubisco protein of either genotype irradiated with UVB. However, both rubisco LSU and SSU decreased in tt5 plants exposed to UVB for 7 days (70% of total leaf area necrotic). In contrast, O3 exposure of both the genotypes decreased the levels of rubisco LSU and SSU before the appearance of visible symptoms of injury. These results suggested that UVB‐induced limitations of growth are independent of changes in rubisco protein while O3‐induced growth limitations appeared to be due to a significant reduction in rubisco protein.

Phaseolus vulgaris cv. Kinghorn Wax seedlings grown in darkness at 25 degrees C for 7 days with half strength Hoagland's nutrient solution containing no nitrogen, were transferred to lit continuous stirred tank reactors (CSTRs) in atmospheres containing 0 or 0.3 ppm NO(2) and irrigated with a nutrient solution containing 0 or 5 mm nitrate as sole nitrogen source and allowed to grow for a period of up to 5 days in a 14 h photoperiod. Exposure to NO(2) increased total Kjeldahl nitrogen in the leaves. Further, the exposure to NO(2) increased chlorophyll content from day 3 onwards and inhibited the leaf dry weight substantially on days 4 and 5. The primary leaves of the seedlings exposed to 0.3 ppm NO(2) and supplied with nitrate accumulated some nitrite after 5 days of exposure. Some of the seedlings were returned from CSTRs to growth chambers and allowed to grow for a further period of 5 days in a 14 h photoperiod without NO(2). The growth which developed after the NO(2) exposure growth period, as measured by fresh and dry weights of the leaves, was significantly less in NO(2)-exposed plants than in nitrate-grown plants. The experiments demonstrate that the leaves of greening seedlings are able to assimilate NO(2) and that a reduction in leaf dry weight by prolonged NO(2) exposure in the presence of nutrient nitrate can be associated with nitrite accumulation, and that NO(2) has a carry-over effect beyond the duration of NO(2) exposure. It is apparent that NO(2) induces some durable biochemical or cytological aberration in the presence of nutrient nitrate, which adversely affects subsequent leaf growth.

Green bean (Phaseolus vulgaris L. cv. Kinghorn Wax) seedlings grown with or without 5 mM nitrate as the nutrient nitrogen source were exposed to 0.3 μL L−1 NO2. The cytokinins BAP or kinetin were foliar applied at 10 μM concentration to 7-d old greening or 14-d old green plants to determine whether they would modify physiological responses to NO2. Exposure to NO2 increased chlorophyll content of senescing primary leaves of green plants in the absence of nutrient nitrate. Increases in tissue organic nitrogen veere induced by NO2 in the presence and absence of nutrient nitrate in greening leaves, young secondary leaves, and senescing primary leaves. When BAP or kinetin was applied, any stimulatory effect of NO2 on chlorophyll content was masked by the effects of cytokinin. Higher total nitrogen induced by NO2 was greatly enhanced by cytokinin application. Cytokinins appear to accelerate NO2 assimilation into some critical regulator substance in senescing leaves; this regulator in turn negates some of the injurious effects of NO2 and stimulates tissue nitrogen accumulation.

Factorial experiments in two growing seasons in open-top field chambers with two or three O 3 concentrations and two primocane-fruiting raspberry ( Rubus idaeus L.) cultivars were used to obtain dose-response relationships describing the effects of seasonal O 3 exposure on raspberry plant vegetative and reproductive growth. At the lower concentration (0.12 μl·liter -1 ), the response to O 3 was nonsignificant. However, at 0.24 μl·liter -1 , `Heritage' showed a significant decline relative to the control in cane height, node count, cane diameter, and dry weight. These changes were accompanied by a 52% decrease in yield, caused mainly by a reduction in fruit count. In contrast, vegetative and yield characters of the `Redwing' were not affected by O 3 .

HALE B., RYAN D., ORMROD D. P. and ALLEN O. B. An integrated statistical approach to estimating plant responses to sequential and concurrent gaseous pollutants. BIOTRONICS 22, 35-46, 1993. Controlled environment studies of plant response to multiple environmental stresses frequently have physical (such as chamber space) and analytical (such as experimental design and data summary) limitations. This study demonstrates the use of an efficient, integrated statistical approach in evaluating rutabaga (Brassica napus L. ssp. rapifera (Metzg.) Sinsk cv. Laurentian) and cabbage (Brassica oleracea L. var. capitata cv. Market Prize) shoot growth responses to sulphur dioxide (S02) followed by ozone (03) at acute doses. The approach combines analysis of covariance, an incomplete factorial experimental design, polynomial dose response functions and a reduced-rank regression procedure to the comparison of functions. Young plants were exposed to S02 on one day followed by 0 3 on the next day. Growth responses to sequential exposure were compared with previously reported growth responses to concurrent exposure to the same doses. Rutabaga growth was sensitive to both gases in both exposure regimes, whereas cabbage growth was sensitive to only S02 in the sequential exposure. Rutabaga leaf area and shoot fresh weight responses to sequential exposures followed the same pattern as concurrent responses, and their magnitudes following sequential exposures were approximately 60% of the concurrent responses. Rutabaga shoot dry weight and cabbage shoot fresh and dry weight, and leaf area responses to the sequential exposures were different in both magnitude and pattern from responses to the concurrent exposures. The importance of this work lies in the method for quantification and comparison of plant response to pollutant mixtures, in different exposure patterns. Using a suite of off-the-shelf statistical techniques, plant response to sequential versus concurrent exposure has been mathematically generalized over a broad range of pollutant mixture concentrations. Particularly for the purpose of environmental risk assessment, this integrated statistical technique has broad application to controlled environment studies of plant response to multiple stresses.

Bean seedlings (Phaseolus vulgaris cv. Kinghorn Wax) were grown in nutrient solutions containing three different N sources or no added N and exposed to NO2 and a cytokinin, benzyladenine (BA). Cytokinins are known effectors of nitrate reductase activity (NRA) and could stimulate the assimilation of nitrate derived from nutrient N sources or from NO2, decreasing NO2 injury to plant tissue. There was no consistent effect of BA on any of the response variables. Exposure to NO2 at 0.3 ppm retarded shoot growth but not root growth. The N source greatly affected plant growth with NH4NO3 providing the greatest growth followed by KNO3, NH4Cl and no added N. Shoot and root tissue N were greater with N salts supplied than without and generally higher in shoots but not roots after exposure to 0.3 ppm NO2. Visible NO2 injury occurred at the highest NO2 concentration only in NH4Cl-grown plants. NRA was generally increased by NO2 and was also highest in the NH4Cl-grown plants. While there were many significant interactions of treatment factors, including BA, the expected effect of BA in increasing NRA did not occur. This study demonstrated that BA treatment does not markedly affect NO2 assimilation or growth retardation by NO2.