Ageing-related Anatomical and Ultrastructural Changes in Leaves of Birch (Betula pendula Roth.) Clones as Affected by Low Ozone Exposure

Effects of ozone on the leaf anatomy and ultrastructure of fivebirch (Betula pendula Roth.) clones were studied during onegrowing season in open-field conditions. Cumulative ozone exposurewas 1·5 times higher than ambient. Ozone exposure decreasedtotal leaf thickness in one, ozone sensitive, clone. The effecton palisade spongy mesophyll thickness was clone-specific, whilethe amount of palisade intercellular space was reduced in allclones. A second effect was a change in the relative amountsof adaxial and abaxial epidermis. In palisade and spongy parenchymacells of all clones, ozone increased the number of irregularand spherical shaped chloroplasts, the electron density of chloroplaststroma, swelling and curling of thylakoids, translucency ofthe mitochondrial matrix and also the amount of cytoplasmiclipids. In the sensitive clone shorter chloroplasts and reducedamount of starch were observed in ozone-exposed plants, whilst,in the tolerant clone, the size of chloroplasts and the amountof starch were unaffected. Ozone effects on number, size andelectron density of plastoglobuli and vacuolar tannin were clone-dependent.At the ultrastructural level, the normal leaf ageing processprogressed at different rates in the birch clones. Ozone acceleratedsenescence-related structural changes, in accordance with earlierobservations of deciduous species.Copyright 1995, 1999 AcademicPress Betula pendula Roth., birch, clones, ageing, ozone, leaf anatomy, ultrastructure     

The response of sensitive and tolerant clones of Populus tremuloides to dynamic ozone exposure under controlled environmental conditions

Both sensitive and tolerant clones of aspen ( Populus tremuloides ) were exposed to ozone using four different exposure regimes under controlled environmental conditions. Based on data on ambient ozone from 10 cities in the USA, three treatments of 4-wk exposure to the same SUM06 (an accumulation of hourly O₃ concentrations greater than 0.06 ml l⁻¹) were constructed. The regimes allowed us to investigate: (a) the importance of long (3 wk, treatment 1) versus short (1 wk, treatment 2) duration of regimes with high peaks; (b) the effect of treatments with variable peak occurrence (treatments 1 and 2) versus uniform peak occurrence (treatment 3) during the exposure period. Nonfumigated control plants were maintained at ozone concentrations <10 nl l⁻¹. Bifacial black necrosis, a typical symptom of ozone injury on aspen leaves, occurred on both clones after 2 wk exposure. Up to 60% of the leaves on the sensitive clone were injured, with an average of 6% of total leaf area injured. In the tolerant clone only 10% of the leaves were injured, with less than 1% of the total leaf area symptomatic. The severity of injury was consistently greatest in treatment 2, followed by treatments 1 and 3, respectively. The interval between peak exposures was less important than the occurrence of peaks versus a stable maximum concentration. Premature leaf abscission occurred in the sensitive clone. Measures of gas exchange demonstrated reduced photosynthesis under ozone fumigation, but exposure regime was not a significant factor. Concentrations of two antioxidants, ascorbic acid and glutathione, were almost always greater in the resistant than in the sensitive clone, but the differences were not statistically significant. The levels of these antioxidants in aspen leaves did not change with ozone fumigation or leaf age.     

Olfactory responses of the vine weevil, Otiorhynchus sulcatus, to tree odours

Abstract A Y-tube olfactometer and a still-air olfactometer were developed to determine the attractiveness of several host plants for the vine weevil ( Otiorhynchus sulcatus (F.); Coleoptera: Curculionidae). Odours of weevil-damaged yew ( Taxus baccata ) and spindle trees ( Euonymus fortunei ) are attractive to the vine weevil, but Rhododendron and strawberry ( Fragaria  ×  ananassa ) are not. Undamaged Euonymus is attractive to the weevils in springtime but not in late summer. When clean air or undamaged Euonymus is the alternative, weevils strongly prefer weevil-damaged Euonymus foliage, and this preference is retained throughout the year. Hence, plant damage plays a role in attraction of the vine weevil. In contrast to the permanent attractiveness of weevil-damaged Euonymus , mechanically damaged plants gradually lose the attractiveness that they have early in the growing season. This suggests that emission of volatiles, produced by the plants in response to weevil damage, is important for attraction of the weevils because the weevils may use these plant odours to find suitable food plants throughout the season. Apart from weevil-damage-related plant volatiles, green leaf volatiles must also play a significant role, as indicated by the fact that weevils prefer: early season, undamaged Euonymus over clean air; early season, mechanically damaged Euonymus over undamaged Euonymus ; and, throughout the season, had no preference when mechanically damaged Euonymus is tested against weevil-damaged Euonymus . Thus, monitoring traps may be developed by the use of green leaf volatiles and/or herbivore-induced volatiles, as attractants.     

Role of ethylene in the regulation of cell death and leaf loss in ozone-exposed European beech

To test the involvement of ethylene in mediating ozone-induced cell death and leaf loss in European beech ( Fagus sylvatica L.), tree seedlings were exposed to proportionally increased or decreased field ozone levels for up to 6 months. Ozone treatment caused cell death and accelerated leaf loss at higher than ambient levels, but had only minor effects at ambient and no effects at subambient ozone levels. The emission of ethylene, the levels of its precursor, 1-aminocyclopropane-1-carboxylate (ACC), and mRNA levels of specific ACC synthase ( FS-ACS2 ) and ACC oxidase ( FS-ACO1 ) isoforms showed a persistent increase and preceded cell death by approximately 2 weeks. Inhibition of ethylene biosynthesis led to reduced lesion formation whereas application of ACC accelerated ozone-induced cell death and leaf loss. Similar results were obtained when adult beech trees were exposed to 2 × ozone by a whole tree free-air canopy exposure system. The results suggest a role of ethylene in amplifying ozone effects under field conditions in this major European broad-leaved tree species.     

Diversity of an early successional plant community as influenced by ozone

An early successional plant community was exposed to various ozone concentrations for two growing seasons (1994–1995) in open-top chambers in Auburn, Alabama, USA. The ozone treatments were: AA, ambient air (open plots); CF, carbon-filtered air ( c . 0·5×ambient air), 1×, non-filtered air, and 2×, twice ambient air. Vegetative canopy cover exhibited a pattern of accumulation in the spring, with maximum canopy cover attained in summer, then senescence of foliage in the autumn 1994. This pattern was not observed in 1995 as a result of a drought during the spring and summer. Varying ozone exposures caused shifts in the competitive interactions between plants, thereby altering community structure. Higher canopy cover, vertical canopy density (layers of foliage), species richness, diversity, and evenness existed in the CF treatments than in the other treatments. In addition, winged sumac ( Rhus copallina L.) became a major component of the CF treatments only during 1995. Surprisingly, blackberry ( Rubus cuneifolius Pursh.), a species considered ozone-sensitive, based on visible injury, dominated canopy cover within the 2× treatments, 41 and 33% of total canopy cover in 1994 and 1995, respectively. From these results it is concluded that plant communities existing in areas where lower ozone concentrations are prevalent might be more complex and diverse than those existing in areas with higher ozone concentrations.     

Responses of Leaf Processes in a Sensitive Birch (Betula pendulaRoth) Clone to Ozone Combined with Drought

Saplings of an ozone sensitive clone of birch (Betula pendulaRoth,KL-5-M) were well-watered or exposed to mild drought-stresscombined with ambient or elevated (1.5xthe ambient) ozone for11 weeks in open-field conditions in central Finland. Stomatalresponse, visible injury, chlorophyll and nutrient content,and changes in cellular anatomy and plant growth were studied.Drought stress alone, in ambient ozone, reduced stomatal densityand stomatal conductance. Drought stress and ozone effects wereadditive, reducing total leaf number, foliage area and starchformation in mesophyll cells. Drought stress and ozone effectswere additive, increasing the N concentration in the leaves,the thickness of the upper epidermal cell wall, the number ofpectinaceous projections of mesophyll cell walls, and the vacuolartannin-like depositions and phenolic droplets, regarded as signsof activated stress defence mechanisms. The increase in specificfoliage mass, cytoplasmic lipids (younger leaves), and a condensedappearance of the upper epidermal mucilaginous layer were causedby both drought and ozone, but were not additive. The resultsshow that combined drought stress contributed to birch responsesto 1.5xcurrent ambient ozone concentrations, corresponding tocritical-level ozone exposure. The only beneficial effect ofdrought stress was the slight reduction of visible leaf symptomsinduced by ozone in autumnal leaves.Copyright 1998 Annals ofBotany Company Birch,Betula pendula, sensitive clone, ozone, drought, microscopy.     

Effects of elevated ozone on CO2 uptake and leaf structure in sugar maple under two light environments

The interactive effects of ozone and light on leaf structure, carbon dioxide uptake and short-term carbon allocation of sugar maple ( Acer saccharum Marsh.) seedlings were examined using gas exchange measurements and ¹⁴C-macroautoradiographic techniques. Two-year-old sugar maple seedlings were fumigated from budbreak for 5 months with ambient or 3 × ambient ozone in open-top chambers, receiving either 35% (high light) or 15% (low light) of full sunlight. Ozone accelerated leaf senescence, and reduced net photosynthesis, ¹⁴CO₂ uptake and stomatal conductance, with the effects being most pronounced under low light. The proportion of intercellular space increased in leaves of seedlings grown under elevated ozone and low light, possibly enhancing the susceptibility of mesophyll cells to ozone by increasing the cumulative dose per mesophyll cell. Indeed, damage to spongy mesophyll cells in the elevated ozone × low light treatment was especially frequent. ¹⁴C macroautoradioraphy revealed heterogeneous uptake of ¹⁴CO₂ in well defined areole regions, suggesting patchy stomatal behaviour in all treatments. However, in seedlings grown under elevated ozone and low light, the highest ¹⁴CO₂ uptake occurred along larger veins, while interveinal regions exhibited little or no uptake. Although visible symptoms of ozone injury were not apparent in these seedlings, the cellular damage, reduced photosynthetic rates and reduced whole-leaf chlorophyll levels corroborate the visual scaling of whole-plant senescence, suggesting that the ozone × low light treatment accelerated senescence or senescence-like injury in sugar maple.     

Modelling the effects of elevated atmospheric CO2 on crown development, light interception and photosynthesis of poplar in open top chambers

An open-top chamber experiment was carried out to examine the likely effects of elevated atmospheric [CO₂] on architectural as well as on physiological characteristics of two poplar clones ( Populus trichocarpa × P. deltoides clone Beaupré and P. deltoides × P. nigra clone Robusta). Crown architectural parameters required as input parameters for a three-dimensional (3D) model of poplar structure, such as branching frequency and position, branch angle, internode length and its distribution pattern, leaf size and orientation, were measured following growth in ambient and elevated [CO₂ ] (ambient + 350 μmol mol^–1) treated open-top chambers. Based on this information, the light interception and photosynthesis of poplar canopies in different [CO₂] treatments were simulated using the 3D poplar tree model and a 3D radiative transfer model at various stages of the growing season. The first year experiments and modelling results showed that the [CO₂] enrichment had effects on light intercepting canopy structure as well as on leaf photosynthesis properties. The elevated [CO₂] treatment resulted in an increase of leaf area, canopy photosynthetic rate and above-ground biomass production of the two poplar clones studied. However, the structural components responded less than the process components to the [CO₂] enrichment. Among the structural components, the increase of LAI contributed the most to the canopy light interception and canopy photosynthesis; the change of other structural aspects as a whole caused by the [CO₂] enrichment had little effect on daily canopy light interception and photosynthesis.     

Efficacy of Beauveria bassiana (Bals.) Vuill. against the spruce bark beetle, Ips typographus L., in the laboratory under various conditions

Abstract:  In laboratory bioassays, the efficacy of the entomopathogenic fungus Beauveria bassiana against the spruce bark beetle, Ips typographus , was tested under various conditions. Four of the tested isolates and the commercial product Boverol^® caused 99–100% mortality when tested at a concentration of 1.0 × 10⁷ conidia/ml at 25°C. Using B. bassiana isolate 138 at a concentration of 1.0 × 10⁶, the median survival time (MST) was 6.1 d and significantly longer compared with the MST of 4.2 and 4.0 d at 1.0 × 10⁷ and 1.0 × 10⁸ conidia/ml, respectively. In the next experiment, the beetles were maintained on spruce bark, filter paper or artificial diet during the bioassay with Boverol^®, and significant differences in the MST of 3.6, 2.5 and 5.3 d, respectively, were noticed. The experiment with Boverol^® at different temperatures showed that the beetles lived significantly longer at 15°C (MST 8.7 d) than at 20, 25, 30 and 35°C. At 25°C, the beetles died most rapidly (MST 3.5 d). At different relative humidities (RH) of 40, 70 and 100%, nearly all beetles were dead after treatment with a suspension of Boverol^® at 1.0 × 10⁷ conidia/ml. At 40% RH, 49% of the untreated beetles died after 7 d. The best effects were achieved with the following bioassay: beetles were fed for three days on artificial diet, then dipped into a solution of 1.0 × 10⁷ conidia/ml and transferred on a piece of spruce bark in Petri dishes at 25°C and 70% RH.     

Evolutionary conservatism of geographic variation in host preference in Callosobruchus maculatus

Abstract.  1. A study of host preference of four pairs of populations of the cowpea weevil Callosobruchus maculates was carried out. The pairs had different geographical origins.
2. One population of each pair had been maintained for about 110 generations on cowpea Vigna unguiculata , the other population had been maintained on mung bean V. radiata . Half of the tested females from each population were raised on cowpea and exposed to this host prior to the assay; the other half was raised on mung bean. This design permitted assessment of the relative contributions of geographical origin, recent host use in the laboratory, and individual experience, to variation in host preference.
3. Host preference was assayed by letting the females oviposit on an equal-weight mixture of cowpea and mung seeds; two experiments were performed six generations apart.
4. Both experiments revealed a strong effect of geographical origin: populations originating from Nigeria laid a much greater proportion (68–86%) of their eggs on cowpea than those originating from Uganda and Yemen (30–42%); those from Cameroon were intermediate (56–60%). These preferences were not affected consistently by about 110 generations of laboratory evolution on one or the other host, or by experience of individual females.
5. These results indicate considerable geographical variation in host preference, and suggest that host preference is behaviourally inflexible and evolutionarily conserved.     

Survival and recovery of perennial forage grasses under prolonged Mediterranean drought: II. Water status, solute accumulation, abscisic acid concentration and accumulation of dehydrin transcripts in bases of immature leaves

Effects of ozone on spring wheat ( Triticum aestivum L. cv. Satu) were studied in an open-top chamber experiment during two growing seasons (1992–1993) at Jokioinen in south-west Finland. The wheat was exposed to filtered air (CF), non-filtered air (NF), non-filtered air+35 nl l⁻¹ ozone for 8 h d⁻¹ (NF⁺) and ambient air (AA). Each treatment was replicated five times. Two wk after anthesis, after 4 wk of ozone treatment (NF⁺, 45 nl l⁻¹ 1000–1800 hours, seasonal mean) the net CO₂ uptake of wheat flag leaves was decreased by c . 40% relative to CF and NF treatments, both initial and total activity of Rubisco and the quantity of protein-bound SH groups were decreased significantly. Added ozone also significantly accelerated flag leaf senescence recorded as a decrease in chloroplast size. The effect was significant 2 wk after anthesis, and senescence was complete after 4 wk. In the CF and NF treatments senescence was complete 5 wk after anthesis. The significant effect of ozone on the chloroplasts and net CO₂ uptake 2 wk after anthesis did not affect the grain filling rate. However, since the grain filling period was shorter for ozone fumigated plants, kernels were smaller. The decrease in 1000-grain weight explained most of the yield reduction in the plants under NF⁺ treatment. The results indicate that wheat plants are well buffered against substantial decrease in source activity, and that shortened flag leaf duration is the major factor causing ozone-induced yield loss.     

Photosynthetic parameters of birch (Betula pendula Roth) leaves growing in normal and in CO2- and O3- enriched atmospheres

Two silver birch (Betula pendula Roth) clones K1659 and V5952 were grown in open‐top chambers over 3 years (age 7–9 years). The treatments were increased CO₂ concentration (+CO₂, 72 Pa), increased O₃ concentration (+O₃, 2 × ambient O₃ with seasonal AOT40 up to 28 p.p.m. h) and in combination (+CO₂ + O₃). Thirty‐seven photosynthetic parameters were measured in the laboratory immediately after excising leaves using a computer‐operated routine of gas exchange and optical measurements. In control leaves the photosynthetic parameters were close to the values widely used in a model (Farquhar, von Caemmerer and Berry, Planta 149, 78–90, 1980). The distribution of chlorophyll between photosystem II and photosystem I, intrinsic quantum yield of electron transport, uncoupled turnover rate of Cyt b₆f, Rubisco specificity and K_m (CO₂) were not influenced by treatments. Net photosynthetic rate responded to +CO₂ with a mean increase of 17% in both clones. Dry weight of leaves increased, whereas protein, especially Rubisco content and the related photosynthetic parameters decreased. Averaged over 3 years, eight and 17 mechanistically independent parameters were significantly influenced by the elevated CO₂ in clones K1659 and V5952, respectively. The elevated O₃ caused a significant decrease in the average photosynthetic rate of clone V5952, but not of clone K1659. The treatment caused changes in one parameter of clone K1659 and in 11 parameters of clone V5952. Results of the combined treatment indicated that +O₃ had less effect in the presence of +CO₂ than alone. Interestingly, changes in the same photosynthetic parameters were observed in chamberless grown trees of clone V5952 as under +O₃ treatment in chambers, but this was not observed for clone K1659. These results suggest that during chronic fumigation, at concentrations below the threshold of visible leaf injuries, ozone influenced the photosynthetic parameters as a general stress factor, in a similar manner to weather conditions that were more stressful outside the chambers. According to this hypothesis, the sensitivity of a species or a clone to ozone is expected to depend on the growth conditions: the plant is less sensitive to ozone if the conditions are close to optimal and it is more sensitive to ozone under conditions of stress.     

Unikaryon polygraphi sp.n. (Protista, Microspora): a new pathogen of the four-eyed spruce bark beetle Polygraphus poligraphus (Col., Scolytidae)

The microsporidium Unikaryon polygraphi sp.n., a pathogen of Polygraphus poligraphus in Austria is described based on light microscopic and ultrastructural characteristics. All life stages have isolated nuclei. Sporogony ends with uninucleate single sporoblasts and spores. Mature oval spores measure 2.5–3.0 μm × 1.0–1.5 μm. The larger spores (3 × 1.5 μm) belong to the `early spore type' with a polar filament coiled in five turns and the smaller spores (2.5 × 1 μm) with polar filament coiled in 6/7 turns belong to the `environmental spore type'. Columnar cells of the midgut, longitudinal and circular muscles and the secretory part of Malpighian tubules of adult beetles are infected. Mature spores are excreted together with the faeces.     

Salicylic acid - a potential biomarker of tobacco Bel-W3 cell death developed as a response to ground level ozone under ambient conditions

Salicylic acid content and benzoic acid 2-hydroxylase (BA2H) activity were investigated in tobacco Bel-W3 and Bel-B leaves after exposure to tropospheric ozone in the conditions of ambient air. Plants were exposed in accordance with a standard methodology for ozone biomonitoring, in a three-year experiment. Free salicylic acid (SA), conjugated with glucose (SAG), and as a product of the BA2H activity was quantified with HPLC. In order to evaluate ozone injuries of leaves, an open source image analysis software was employed. Plants exposure to ambient ozone resulted in enhanced BA2H activity and intensified salicylic acid biosynthesis in leaves of Bel-W3 cultivar showing visible ozone injuries. The BA2H activity significantly correlated with SAG for ozone-exposed Bel-W3 plants. Both injuries and salicylic acid biosynthesis rate depended on the growth phase of leaves and nearly linear correlation between SA content and injuries was found for particular leaves of Bel-W3.     

Impact of four years exposure to different levels of ozone, phosphorus and drought on chlorophyll, mineral nutrients, and stem volume of Norway spruce, Picea abies

Saplings of one clone of Norway spruce, Picea abies (L.) Karst, were planted in 120 l pots in 1991 and exposed to three levels of ozone, two levels of phosphorus and two levels of water supply in 42 open-top chambers (OTCs), during 1992–1996. The effects of pots and OTCs were also tested. Nutrient concentrations of the needles were not affected by ozone, while the low phosphorus supply (LP) and drought stress (D) treatments had significant effects on several mineral nutrients, e.g. phosphorus, calcium, magnesium, manganese, sulphur and boron. Ozone reduced the chlorophyll concentration in the 2- and 3-year-old needles in 1994 and 1995. The highest ozone concentration reduced the stem volumes (− 8%), as well as the stem lengths (− 5%), of the saplings in 1993 and 1994, after two and three years of exposure. After the fourth growing season this ozone-induced reduction in stem volume disappeared which might be caused by pot limitation. LP supply and D both caused large decreases in the stem volume and length. The needles from LP treatment had as high P concentration as 1.2–1.5 mg g⁻¹, implying a need for increasing the critical value for phosphorus. The OTC enclosure stimulated the stem volume growth significantly compared to saplings growing in ambient plots. This was suggested to be attributed to the slightly higher temperature in the OTCs. The overall result is that ozone in southern Sweden is likely to have negative effects on Norway spruce trees, although much less than other environmental factors, e.g. water and phosphorus.     

Effects of elevated CO2 and temperature on development and consumption rates of Octotoma championi and O. scabripennis feeding on Lantana camara

We carried out a factorial experiment to explore the effect of doubled CO₂ concentration and a 3 °C temperature increase on the development of a complete generation of the beetles Octotoma championi Baly and O. scabripennis Guérin‐Méneville (Coleoptera: Chrysomelidae). These species are biological control agents of Lantana camara L. (Verbenaceae), with a leaf‐mining larval phase and free‐living, leaf‐chewing adults. Plants grown at elevated CO₂ had enhanced above‐ground biomass, thicker leaves, reduced nitrogen concentration, and increased C:N ratios. Under the high temperature treatment, plants grown at ambient CO₂ suffered wilting and premature leaf loss, despite daily watering; this effect was ameliorated at elevated CO₂. The wilting of plants in the ambient CO₂/high temperature treatment reduced the emergence success of the beetles, particularly O. championi. Development time was accelerated by approximately 10–13 days at the higher temperature, but was not affected by CO₂. Neither CO₂ nor temperature affected adult beetle weight. Consumption rates of free‐living beetles were not affected by either CO₂ or temperature. By contrast, in the short‐term trials using excised foliage, beetles given no choice between ambient and elevated CO₂‐grown foliage, consumed more from ambient plants. When beetles were offered a choice between foliage grown at the two CO₂ levels, O. championi did not display a significant preference but O. scabripennis consumed more ambient CO₂‐grown foliage when feeding at the lower temperature. This study indicates that under future conditions of higher temperatures, amelioration of water stress in host plants growing in elevated CO₂ may benefit some endophagous insects by reducing premature leaf loss. Under some circumstances, this benefit may outweigh the deleterious effects of lower leaf nitrogen. Our results also indicate that foliage consumption under elevated CO₂ by mobile, adult insects on whole plants may not be significantly increased, as was previously indicated by short‐term experiments using excised foliage.     

Inactivation of Salmonella enterica serovar enteritidis in shell eggs by sequential application of heat and ozone

Aims:  To assess the contribution of ozone to lethality of Salmonella enterica serovar Enteritidis in experimentally inoculated whole shell eggs that are sequentially treated with heat and gaseous ozone in pilot-scale equipment.
Methods and Results:  Whole shell eggs were inoculated with small populations of Salmonella Enteritidis (8·5 × 10⁴–2·4 × 10⁵ CFU per egg) near the egg vitelline membrane. Eggs were subjected to immersion heating (57°C for 21 min), ozone treatment (vacuum at 67·5 kPa, followed by ozonation at a maximum concentration of approx. 140 g ozone m⁻³ and 184–198 kPa for 40 min) or a combination of both treatments. Survivors were detected after an enrichment process or enumerated using modified most probable number technique. Ozone, heat and combination treatments inactivated 0·11, 3·1 and 4·2 log Salmonella Enteritidis per egg, respectively.
Conclusions:  Sequential application of heat and gaseous ozone was significantly more effective than either heat or ozone alone. The demonstrated synergy between these treatment steps should produce safer shell eggs than the heat treatment alone.
Significance and Impact of the Study:  Shell eggs are the most common vehicle for human infection by Salmonella Enteritidis. Many cases of egg-related salmonellosis are reported annually despite efforts to reduce contamination, including thermal pasteurization of shell eggs and egg products. Treatment with ozone-based combination should produce shell eggs safer than those treated with heat alone.     

Cultivar-specific impairment of strawberry growth,photosynthesis, carbohydrate and nitrogen accumulation by ozone

In a 2-year study, fruiting plants of strawberry (Fragaria × ananassa Duch.) cv. ‘Korona’ and ‘Elsanta’ were exposed for 2 months to 78 ppb ozone on average or filtered air without ozone in controlled environment chambers. Plant growth, photosynthesis, carbohydrate accumulation, and macronutrient concentrations were investigated in order to demonstrate cultivar-specific differences in the ozone sensitivity of ‘Korona’ and ‘Elsanta’ on the whole plant level. Moreover, the hypothesis was tested whether properties of the root system in strawberry were involved in ozone tolerance, for example, the roots’ ability to store or make available carbohydrates and their capacity to secure plants’ supply with nitrogen during a stress situation. In strawberry, ozone reduced leaf area by reducing leaf number. Moreover, specific leaf area (SLA) and relative leaf water content were reduced. Net photosynthesis was only slightly impaired, but activity of Rubisco and chlorophyll content in older leaves of cv. ‘Elsanta’ were significantly reduced. The most important, indirect impairment of photosynthesis was the reduction of plants’ total leaf area, which resulted in a decrease in plant biomass. The reduction of root biomass, the root/shoot ratio, and also the distribution of carbohydrates indicated a partitioning priority of the shoot at expense of the root system. Cultivar ‘Elsanta’ was characterized by significantly lower carbohydrate levels in ozone-exposed leaves, whereas levels remained fairly stable in ‘Korona’ leaves. In addition, nitrogen concentrations in leaves and roots decreased significantly in ‘Elsanta’, not in ‘Korona’. The reduced nitrogen concentration in leaves may be related with the more distinct reduction in Rubisco activity and chlorophyll content in older leaves of ‘Elsanta’.     

Factors that affect leaf extracellular ascorbic acid content and redox status

Leaf ascorbic acid content and redox status were compared in ozone-tolerant (Provider) and ozone-sensitive (S156) genotypes of snap bean ( Phaseolus vulgaris L.). Plants were grown in pots for 24 days under charcoal-filtered air (CF) conditions in open-top field chambers and then maintained as CF controls (29 nmol mol⁻¹ ozone) or exposed to elevated ozone (71 nmol mol⁻¹ ozone). Following a 10-day treatment, mature leaves of the same age were harvested early in the morning (06:00–08:00 h) or in the afternoon (13:00–15:00 h) for analysis of ascorbic acid (AA) and dehydroascorbic acid (DHA). Vacuum infiltration methods were used to separate leaf AA into apoplast and symplast fractions. The total ascorbate content [AA + DHA] of leaf tissue averaged 28% higher in Provider relative to S156, and Provider exhibited a greater capacity to maintain [AA + DHA] content under ozone stress. Apoplast [AA + DHA] content was 2-fold higher in tolerant Provider (360 nmol g⁻¹ FW maximum) relative to sensitive S156 (160 nmol g⁻¹ FW maximum) regardless of sampling period or treatment, supporting the hypothesis that extracellular AA is a factor in ozone tolerance. Apoplast [AA + DHA] levels were significantly higher in the afternoon than early morning for both genotypes, evidence for short-term regulation of extracellular ascorbate content. Total leaf ascorbate was primarily reduced with AA/[AA + DHA] ratios of 0.81–0.90. In contrast, apoplast AA/[AA + DHA] ratios were 0.01–0.60 and depended on genotype and ozone treatment. Provider exhibited a greater capacity to maintain extracellular AA/[AA + DHA] ratios under ozone stress, suggesting that ozone tolerance is associated with apoplast ascorbate redox status.