Physiological and biochemical responses of two cultivars of wheat to elevated levels of CO2 and SO2, singly and in combination

In view of the present increasing trends of anthropogenic emissions of carbon dioxide (CO2) and sulphur dioxide (SO2) throughout the world, the present study was aimed at investigating the long-term influence of elevated concentrations of CO2 and SO2, singly and in combination on the physiological and biochemical characteristics of two cultivars of wheat (Triticum aestivum L. cv. Malviya 234 and HP1209). For this purpose, the plants were grown in open top chambers under field conditions and were fumigated with 600 ppm CO2, 0.06 ppm SO2 and 600 ppm CO2 + 0.06 ppm SO2 separately for 8 h daily (0800-1600 h) from germination to grain maturity. The individual treatment of SO2 advers#ely affected both the cultivars of wheat by reducing protein and starch contents. The respiration rate, total soluble sugars and total phenolics, however, increased in response to SO2. Stimulation of photosynthesis rate and reduction in stomatal conductance and transpiration rate were observed under CO2 treatment. Concentrations of total soluble sugars, starch and total phenolics increased in response to CO2 and CO2 + SO2 treatments. In combined treatment, CO2 modified the plant response to SO2 in both the cultivars. Elevated CO2 increased the photosynthesis rate under combined treatment. Higher levels of starch and soluble sugars under combined treatment provided extra carbon for SO2 detoxification. The pattern of intraspecific response of wheat to different treatments was more or less similar, but the magnitude of response differed significantly.     

Interactive effects of CO2 and O3 on a ponderosa pine plant/litter/soil mesocosm.

To study individual and combined impacts of two important atmospheric trace gases, CO2 and O3, on C and N cycling in forest ecosystems; a multi-year experiment using a small-scale ponderosa pine (Pinus ponderosa Laws.) seedling/soil/litter system was initiated in April 1998. The experiment was conducted in outdoor, sun-lit chambers where aboveground and belowground ecological processes could be studied in detail. This paper describes the approach and methodology used, and presents preliminary data for the first two growing seasons. CO2 treatments were ambient and elevated (ambient + 280 ppm). O3 treatments were elevated (hourly averages to 159 ppb, cumulative exposure > 60 ppb O3, SUM 06 approximately 10.37 ppm h), and a low control level (nearly all hourly averages <40 ppb. SUM 06 approximately 0.07 ppm h). Significant (P < 0.05) individual and interactive effects occurred with elevated CO2 and elevated O3. Elevated CO2 increased needle-level net photosynthetic rates over both seasons. Following the first season, the highest photosynthetic rates were for trees which had previously received elevated O3 in addition to elevated CO2. Elevated CO2 increased seedling stem diameters, with the greatest increase at low O3. Elevated CO2 decreased current year needle % N in the summer. For 1-year-old needles measured in the fall there was a decrease in % N with elevated CO2 at low O3, but an increase in % N with elevated CO2 at elevated O3. Nitrogen fixation (measured by acetylene reduction) was low in ponderosa pine litter and there were no significant CO2 or O3 effects. Neither elevated CO2 nor elevated O3 affected standing root biomass or root length density. Elevated O3 decreased the % N in coarse-fine (1-2 mm diameter) but not in fine (< 1 mm diameter) roots. Both elevated CO2 and elevated O3 tended to increase the number of fungal colony forming units (CFUs) in the AC soil horizon, and elevated O3 tended to decrease bacterial CFUs in the C soil horizon. Thus, after two growing seasons we showed interactive effects of O3 and CO2 in combination, in addition to responses to CO2 or O3 alone for a ponderosa pine plant/litter/soil system.     

Assessment of the impact of rising carbon dioxide and other potential climate changes on vegetation

The projected doubling of current levels of atmospheric carbon dioxide concentration ([CO(2)]) during the next century along with increases in other radiatively active gases have led to predictions of increases in global air temperature and shifts in precipitation patterns. Additionally, stratospheric ozone depletion may result in increased ultraviolet-B (UV-B) radiation incident at the Earth's surface in some areas. Since these changes in the Earth's atmosphere may have profound effects on vegetation, the objectives of this paper are to summarize some of the recent research on plant responses to [CO(2)], temperature and UV-B radiation. Elevated [CO(2)] increases photosynthesis and usually results in increased biomass, and seed yield. The magnitude of these increases and the specific photosynthetic response depends on the plant species, and are strongly influenced by other environmental factors including temperature, light level, and the availability of water and nutrients. While elevated [CO(2)] reduces transpiration and increases photosynthetic water-use efficiency, increasing air temperature can result in greater water use, accelerated plant developmental rate, and shortened growth duration. Experiments on UV-B radiation exposure have demonstrated a wide range of photobiological responses among plants with decreases in photosynthesis and plant growth among more sensitive species. Although a few studies have addressed the interactive effects of [CO(2)] and temperature on plants, information on the effects of UV-B radiation at elevated [CO(2)] is scarce. Since [CO(2)], temperature and UV-B radiation may increase concurrently, more research is needed to determine plant responses to the interactive effects of these environmental variables.     

Growth and yield responses of spring wheat (Triticum aestivum L. cv. Minaret) to elevated CO2 and water limitation

Spring wheat (Triticum aestivum L. cv. Minaret) was grown at two different CO2 concentrations (367 and 650 micromol mol(-1)) in open-top-chambers from sowing until final harvest. Furthermore two different watering treatments (well watered and water stressed) and two soil types of different fertility were used. At final harvest, which took place at growth stage 92, plants were separated into different fractions. Elevated atmospheric CO2 caused an accelerated chlorophyll-a breakdown and increased growth and yield. Total shoot biomass was enhanced by 43%, grain yield by 46% and main stem yield by 19%. Water stress also accelerated chlorophyll-a breakdown but reduced total shoot biomass by 40%, grain yield by 45%, main stem yield by 30% and thousand grain weight by 6%. On average, soil fertility altered shoot biomass by 30%, grain yield by 39% and main stem yield by 25%.     

Mercury accumulation in grass and forb species as a function of atmospheric carbon dioxide concentrations and mercury exposures in air and soil

The goal of this study was to investigate the potential for atmospheric Hg degrees uptake by grassland species as a function of different air and soil Hg exposures, and to specifically test how increasing atmospheric CO(2) concentrations may influence foliar Hg concentrations. Four common tallgrass prairie species were germinated and grown for 7 months in environmentally controlled chambers using two different atmospheric elemental mercury (Hg major; 3.7+/-2.0 and 10.2+/-3.5 ng m(-3)), soil Hg (<0.01 and 0.15+/-0.08 micro g g(-1)), and atmospheric carbon dioxide (CO(2)) (390+/-18, 598+/-22 micro mol mol(-1)) exposures. Species used included two C4 grasses and two C3 forbs. Elevated CO(2) concentrations led to lower foliar Hg concentrations in plants exposed to low (i.e., ambient) air Hg degrees concentrations, but no CO(2) effect was apparent at higher air Hg degrees exposure. The observed CO(2) effect suggests that leaf Hg uptake might be controlled by leaf physiological processes such as stomatal conductance which is typically reduced under elevated CO(2). Foliar tissue exposed to elevated air Hg degrees concentrations had higher concentrations than those exposed to low air Hg degrees , but only when also exposed to elevated CO(2). The relationships for foliar Hg concentrations at different atmospheric CO(2) and Hg degrees exposures indicate that these species may have a limited capacity for Hg storage; at ambient CO(2) concentrations all Hg absorption sites in leaves may have been saturated while at elevated CO(2) when stomatal conductance was reduced saturation may have been reached only at higher concentrations of atmospheric Hg degrees . Foliar Hg concentrations were not correlated to soil Hg exposures, except for one of the four species (Rudbeckia hirta). Higher soil Hg concentrations resulted in high root Hg concentrations and considerably increased the percentage of total plant Hg allocated to roots. The large shifts in Hg allocation patterns-notably under soil conditions only slightly above natural background levels-indicate a potentially strong role of plants in belowground Hg transformation and cycling processes.     

Active carbon-pools in rhizosphere of wheat (Triticum aestivum L.) grown under elevated atmospheric carbon dioxide concentration in a Typic Haplustept in sub-tropical India

Study on active and labile carbon-pools can serve as a clue for soil organic carbon dynamics on exposure to elevated level of CO2. Therefore, an experimental study was conducted in a Typic Haplustept in sub-tropical semi-arid India with wheat grown in open top chambers at ambient (370 micromol mol-1) and elevated (600 micromol mol-1) concentrations of atmospheric CO2. Elevated atmospheric CO2 caused increase in yield and carbon uptake by all plant parts, and their preferential partitioning to root. Increases in fresh root weight, volume and length have also been observed. Relative contribution of medium-sized root to total root length increased at the expense of very fine roots at elevated CO2 level. All active carbon-fractions gained due to elevated atmospheric CO2 concentration, and the order followed their relative labilities. All the C-pools have recorded a significant increase over initial status, and are expected to impart short-to-medium-term effect on soil carbon sequestration.     

Influences of elevated ozone and carbon dioxide in growth responses of lowland hay meadow mesocosms

We studied the effects of relatively low levels of O(3) (40-50 ppb) and CO(2)-enrichment (+100 ppm) on a northern European lowland hay meadow during the summers 2002-2004 using open-top chambers (OTCs) and ground-planted mesocosms. Ozone reduced the aboveground biomass of the community (up to 40%), and four out of seven species (Campanula rotundifolia, Fragaria vesca, Trifolium medium, Vicia cracca) showed either significant growth reduction and/or visible injuries under elevated O(3). However, the reductions in aboveground biomass were not reflected as changes in the dominance of different functional groups or in the total community root biomass. Elevated CO(2) did not amend the detrimental effects of O(3) on aboveground biomass. Elevated CO(2) alone had only minor effects. An O(3)-induced reduction in the aboveground biomass and N pool of the community are likely to have important consequences in the nutrient cycling of the ecosystem.     

Consequences of elevated carbon dioxide and ozone for foliar chemical composition and dynamics in trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera).

Atmospheric chemical composition affects foliar chemical composition, which in turn influences the dynamics of both herbivory and decomposition in ecosystems. We assessed the independent and interactive effects of CO2 and O3 fumigation on foliar chemistry of quaking aspen (Populus tremuloides) and paper birch (Betula papyrifera) at a Free-Air CO2 Enrichment (FACE) facility in northern Wisconsin. Leaf samples were collected at five time periods during a single growing season, and analyzed for nitrogen. starch and condensed tannin concentrations, nitrogen resorption efficiencies (NREs), and C:N ratios. Enriched CO2 reduced foliar nitrogen concentrations in aspen and birch; O3 only marginally reduced nitrogen concentrations. NREs were unaffected by pollution treatment in aspen, declined with 03 exposure in birch, and this decline was ameliorated by enriched CO2. C:N ratios of abscised leaves increased in response to enriched CO2 in both tree species. O3 did not significantly alter C:N ratios in aspen, although values tended to be higher in + CO2 + O3 leaves. For birch, O3 decreased C:N ratios under ambient CO2 and increased C:N ratios under elevated CO2. Thus, under the combined pollutants, the C:N ratios of both aspen and birch leaves were elevated above the averaged responses to the individual and independent trace gas treatments. Starch concentrations were largely unresponsive to CO2 and O3 treatments in aspen. but increased in response to elevated CO2 in birch. Levels of condensed tannins were negligibly affected by CO2 and O3 treatments in aspen, but increased in response to enriched CO2 in birch. Results from this work suggest that changes in foliar chemical composition elicited by enriched CO2 are likely to impact herbivory and decomposition, whereas the effects of O3 are likely to be minor, except in cases where they influence plant response to CO2.     

The effects of elevated CO2 on clonal growth and nutrient content of submerge plant Vallisneria spinulosa

An approximately four months long glasshouse experiment was conducted to examine the effects of elevated carbon dioxide (CO(2)) concentration (1,000 +/- 50 micromol mol(-1)) in the atmosphere on biomass accumulation and allocation pattern, clonal growth and nitrogen (N), phosphorus (P) accumulation by the submerged plant Vallisneria spinulosa Yan. Elevated CO(2) significantly increased V. spinulosa total fresh biomass ( approximately 130%) after 120 days, due to more biomass accumulation in all morphological organs than in those at ambient CO(2) (390 +/- 20 micromol mol(-1)). About 75% of the additional total biomass at elevated CO(2) was accounted for by leaf and rhizome (above ground) biomass and only 25% of it belonged to root and turion (below ground). However, the turions biomass exhibited a greater increase rate than that of organ above ground, which caused reduction in the above/below ground biomass ratio. The clonal growth of V. spinulosa responded positively to elevated CO(2). The number of primary ramets increased up to 1.4-folds at elevated CO(2) and induced a dense growth pattern. For nutrients absorption, concentration of N in leaf and in turion was significantly (p 相似文献   

Effects of elevated CO2 concentration on the polyamine levels of field-grown soybean at three O3 regimes

Effects of increased ozone (O3) and carbon dioxide (CO2) on polyamine levels were determined in soybean (Glycine max L. Merr. cv. Clark) grown in open-top field chambers. The chamber treatments consisted of three O3 regimes equal to charcoal filtered (CF), non-filtered (NF), and non-filtered plus 40 nl litre(-1) O3 and CO2 treatments equal to 350, 400 and 500 microl litre(-1) for a total of nine treatments. Leaf samples were taken at three different times during the growing season. Examination of growth and physiological characteristics, such as photosynthesis, stomatal resistance, and shoot weight, revealed that increasing CO2 ameliorated the deleterious effects of increased O3. Results from the initial harvest, at the pre-flowering growth stage (23 days of treatment), showed that increasing O3 at ambient CO2 caused increases in putrescine (Put) and spermidine (Spd) of up to six-fold. These effects were lessened with increased CO2. Elevated CO2 increased polyamines in plants treated with CF air, but had no effect in the presence of ambient or enhanced O3 levels. Leaves harvested during peak flowering (37 days of treatment) showed O3-induced increases in Put and Spd at ambient CO2 concentrations. However, increased CO2 levels inhibited this response by blocking the O3-induced polyamine increase. Leaves harvested during the pod fill stage (57 days of treatment) showed no significant O3 or CO2 effects on polyamine levels. Our results demonstrate that current ambient O3 levels induce the accumulation of Put and Spd early in the growing season and that further increases in O3 could result in even greater polyamine increases. These results are consistent with a possible antiozonant function for polyamines. The ability of increased CO2 to protect soybeans from O3 damage, however, does not appear to involve polyamine accumulation.     

Scots pine responses to CO2 enrichment--I. Ectomycorrhizal fungi and soil fauna

Ectomycorrhizal Scots pine seedlings were grown in unfertilized forest soil at ambient and double (ca 700 ppm) atmospheric concentrations of CO2. The biomass of seedlings and fungal biomass both in the roots and in the soil and the numbers of certain groups of soil animals were measured under summer conditions and after an artificial winter acclimation period. No biomass parameter showed any significant change due to CO2 elevation. Increases were found during the winter acclimation period in total and fine root biomasses, fungal biomass in the soil and total fungal biomass both in the roots and in the soil, while the ratio of needle biomass: fungal biomass and the shoot: root ratio decreased. The N concentration in previous-year needles was lower in the double CO2 environment than with ambient CO2. Enchytraeids almost disappeared in the double CO2 environment during winter acclimation, while the numbers of nematodes increased at the same time in both treatments.     

Interactive effects of ozone and elevated carbon dioxide on the growth and physiology of black cherry, green ash, and yellow-poplar seedlings

Potted seedlings of black cherry (Prunus serotina Ehrh.) (BC), green ash (Fraxinus pennsylvanica Marsh.) (GA), and yellow-poplar (Liriodendron tulipifera L.) (YP) were exposed to one of the four treatments: (1) charcoal-filtered air (CF) at ambient CO(2) (control); (2) twice ambient O(3) (2 x O(3)); (3) twice ambient CO(2) (650 microl l(-1)) plus CF air (2 x CO(2)); or (4) twice ambient CO(2) (650 microl l(-1)) plus twice ambient O(3) (2 x CO(2) + 2 x O(3)). The treatments were duplicated in eight continuously stirred tank reactors for 10 weeks. Gas exchange was measured during the last 3 weeks of treatment and all seedlings were destructively harvested after 10 weeks. Significant interactive effects of O(3) and CO(2) on the gas exchange of all three species were limited. The effects of elevated CO(2) and O(3), singly and combined, on light-saturated net photosynthesis (A(max)) and stomatal conductance (g(s)) were inconsistent across species. In all three species, elevated O(3) had no effect on g(s). Elevated CO(2) significantly increased A(max) in GA and YP foliage, and decreased g(s) in YP foliage. Maximum carbon exchange rates and quantum efficiencies derived from light-response curves increased, while compensation irradiance and dark respiration decreased in all three species when exposed to 2 x CO(2). Elevated O(3) affected few of these parameters but any change that was observed was opposite to that from exposure to 2 x CO(2)-air. Interactive effects of CO(2) and O(3) on light-response parameters were limited. Carboxylation efficiencies, derived from CO(2)-response curves (A/C(i) curves) decreased only in YP foliage exposed to 2 x CO(2)-air. In general, growth was significantly stimulated by 2 x CO(2) in all three species; though there were few significant growth responses following exposure to 2 x O(3) or the combination of 2 x CO(2) plus 2 x O(3). Results indicate that responses to interacting stressors such as O(3) and CO(2) are species specific.     

Comparison of photosynthetic responses to manganese toxicity of deciduous broad-leaved trees in northern Japan

The effects of manganese (Mn) toxicity on photosynthesis of four tree species in northern Japan representing different successional traits were examined. The four species are: Betula ermanii (Be) and Alnus hirsuta (Ah) representing two early successional species, Ulmus davidiana var. japonica (Ud) as the mid-successional species, and Acer mono (Am) as the late successional species. Seedlings were grown hydroponically in a solution containing nutrients and Mn of four concentrations (1, 10, 50, 100 mg litre(-1)) for 50 days. Gas exchange measurements indicate that in all species, Mn accumulation in leaves resulted in the decline of light-saturated net photosynthetic rate ai ambient CO(2) pressure (35 Pa, Pn(amb)) and at saturating (5%) CO(2) pressure (Pn(sat)), and of carboxylation efficiency but has little effect on the maximum efficiency of photochemistry. Sensitivity to elevated levels of Mn differed among species where the decline of Pn(amb) was much more modest in the two early successional species of Be and Ah than the mid- and late successional species of Ud and Am. The same trends were observed in both Pn(sat) and carboxylation efficiency. Based on these results, we suggest that early successional species (Betula ermanii and Alnus hirsuta) have greater tolerance for excess Mn in leaves than mid- and late successional species.     

Does living in elevated CO2 ameliorate tree response to ozone? A review on stomatal responses

Short-term elevated O3 reduces photosynthesis, which reduces stomatal conductance (g(s)) in response to increased substomatal CO2 concentration (Ci). Further exposure causes stomata to become sluggish in response to environmental stimuli. Exposure to elevated CO2 stimulates rapid stomata closure in response to increased Ci. This reduction in g(s) may not be sustained over time as photosynthesis down-regulates and with it, g(s). The relationship between g(s) and photosynthesis may not be constant because stomata respond more slowly to environmental changes than photosynthesis, and because elevated CO2 may alter guard cell sensitivity to other signals. Also, reduced stomatal density (and g(s)) in response to long-term CO2 enrichment suggests sustained reduction in g(s). Elevated CO2 is believed to ameliorate the deleterious O3 effects by reducing g(s) and thus the potential O3 flux into leaves. Confirmation that g(s) acclimation to CO2 enrichment does not lessen over time is critical for developing meaningful O3 flux scenarios.     

Effects of ozone exposure in open-top chambers on poplar (Populus nigra) and beech (Fagus sylvatica): a comparison

Rooted cuttings of poplar (Populus nigra) and seedlings of beech (Fagus sylvatica) were exposed to ozone in open-top chambers for one growing season. Three treatments were applied: charcoal-filtered (CF), non-filtered (NF) and non-filtered air plus 30 ppb (nl l(-1)) ozone (NF+). Extra ozone was only added on clear days, from 09:00 until 17:00-20:00. The AOT40s (accumulated exposure over a threshold of 40 ppb), calculated from April to September were 4055 ppb.h for the NF and 8880 ppb.h for the NF+ treatments. For poplar ozone exposure caused highly significant reductions in growth rate, light-saturated net CO(2) assimilation rate, stomatal conductance, F(v)/F(m) and chlorophyll content. The largest effects were observed in August at which time ozone concentrations were elevated. A reduction was noticed in new leaf production, while accelerated ageing and visible damage to leaves caused high leaf losses. For beech the responses were similar but less pronounced: ozone exposure resulted in non-significant growth reductions, slight changes in light-saturated photosynthesis and accelerated leaf abscission. The chlorophyll content of beech leaves was not affected by the ozone treatments. The results confirmed previous observations that fast-growing tree species, such as most poplar species and hybrids, are more sensitive and responsive to tropospheric ozone than slower-growing species, such as beech. The growth reductions observed and reported here for beech were within the range of those reported in relationship to the AOT40 (accumulated exposure over a threshold of 40 ppb) critical level for ozone.     

Effects of Sphagnum moss and urban runoff on bioavailability of lead and zinc from acidic wetlands of the New Jersey pinelands

The effects of Sphagnum and urban runoff on the bioavailability of metals were tested by adding PbCl2 and ZnCl2 to laboratory microcosms constructed of peat substrate with or without live Sphagnum spp. and planted with Acer rubrum L. seedlings or Vaccinium macrocarpon Ait. shoots. We hypothesized that Sphagnum would increase bioavailability through its acidifying action, while urban runoff would decrease availability through increases in alkalinity. Metals were more available to the test plants treated with acidic swampwater than with alkaline runoff. Sphagnum moss caused increases in tissue concentrations in V. macrocarpon, but not in A. rubrum. The latter species took up more metals when grown on substrate from sites receiving runoff, whereas the former took up more metals from substrate from undisturbed sites, despite the lower substrate metal concentrations. Differences in uptake by the two species may reflect differences in their ability to root in the Sphagnum mat. The results demonstrate that Sphagnum spp. exerts strong species-specific effects on the uptake of metals by vascular plants, and that plant species native to acidic wetlands vary widely in their response to metals in the substrate.     

Lead,zinc and copper accumulation and tolerance in populations of Paspalum distichum and Cynodon dactylon

Both Fankou and Lechang lead/zinc (Pb/Zn) mine tailings located at Guangdong Province contained high levels of total and DTPA-extractable Pb, Zn and Cu. Paspalum distichum and Cynodon dactylon were dominant species colonized naturally on the tailings. Lead, zinc and copper accumulation and tolerance of different populations of the two grasses growing on the tailings were investigated. Tillers of these populations including those from an uncontaminated area were subjected to the following concentrations: 5, 10, 20, 30 and 40 mg l(-1) Pb, 2.5, 5, 10, 20 and 30 mg (l-1) Zn, or 0.25, 0.50, 1 and 2 mg l(-1) Cu for 14 days, respectively, then tolerance index (TI) and EC50 (the concentrations of metals in solutions which reduce 50% of normal root growth) were calculated. The results indicated that both Lechang and Fankou populations of the two grasses showed a greater tolerance to the three metals than those growing on the uncontaminated area, which suggested that co-tolerant ecotypes have evolved in the two grasses. P. distichum collected from Fankou tailings had the highest tolerance to Cu while Lechang population the highest tolerance to Pb and Zn among the tested populations, and tolerance levels in P. distichum were related to metal concentrations in the plants. P. distichum had a better growth performance than C. dactylon when both of them were grown on the tailings sites. Tolerant populations of these species would serve as potential candidates for re-vegetation of wastelands contaminated with Pb, Zn and Cu.     

Effects of decadal exposure to interacting elevated CO2 and/or O3 on paper birch (Betula papyrifera) reproduction

We studied the effects of long-term exposure (nine years) of birch (Betula papyrifera) trees to elevated CO(2) and/or O(3) on reproduction and seedling development at the Aspen FACE (Free-Air Carbon Dioxide Enrichment) site in Rhinelander, WI. We found that elevated CO(2) increased both the number of trees that flowered and the quantity of flowers (260% increase in male flower production), increased seed weight, germination rate, and seedling vigor. Elevated O(3) also increased flowering but decreased seed weight and germination rate. In the combination treatment (elevated CO(2)+O(3)) seed weight is decreased (20% reduction) while germination rate was unaffected. The evidence from this study indicates that elevated CO(2) may have a largely positive impact on forest tree reproduction and regeneration while elevated O(3) will likely have a negative impact.     

Interactive effects of elevated ozone and carbon dioxide on growth and yield of leaf rust-infected versus non-infected wheat

Spring wheat (Triticum aestivum L. cv. Turbo) was grown from seedling emergence to maturity (129 days) in chambers simulating the physical climate and ozone pollution of a field site in Northern Germany from 1 April to 31 July with a mean 1-h daily maximum of 61.5-62.4 nl l(-1) ozone compared to a constant low level of 21.5-22.8 nl l(-1) ozone. The two ozone levels were combined with either a current (374.1-380.2 microl l(-1)) or enriched (610.6-615.0 microl l(-1)) CO(2) atmosphere. Additionally, a leaf rust epidemic (Puccinia recondita f. sp. tritici) was induced at tillering stage by repeated re-inoculations with the inoculum formed on the plants. Leaf rust disease was strongly inhibited by ozone, but largely unaffected by elevated CO(2). Ozone damage on leaves was strongly affected by CO(2) and infection. On infected plants, ozone lesions appeared 2-4 weeks earlier and were up to fourfold more severe compared to non-infected plants. Elevated CO(2) did not delay the onset of ozone lesions but it significantly reduced the severity of leaf damage. It also enhanced the photosynthetic rate of flag leaves and increased the water use efficiency, biomass formation and grain yield. The relative increases in growth and yield induced by CO(2) were much larger on ozone-stressed than on non-stressed plants. Both ozone and fungal infection reduced biomass formation, number of grains per plant, thousand grain weight and grain yield; however, adverse effects of leaf rust infection were more severe. Elevated CO(2) largely equalized the negative effects of ozone on the photosynthetic rate, growth and yield parameters, but was not capable of compensating for the detrimental effects of fungal infection. The data imply that the impact of ozone in the field cannot be estimated without considering the predisposing effects deriving from fungal infections and the compensating effects deriving from elevated CO(2).     

Effects of elevated CO2 nitrogen supply and tropospheric ozone on spring wheat. I. Growth and yield

Spring wheat (Triticum aestivum L. cv. Minaret) was exposed to three CO(2) levels, in combination with two nitrogen fertilizer levels and two levels of tropospheric ozone, from sowing to ripening in open-top chambers. Three additional nitrogen fertilizer treatments were carried out at the lowest and the highest CO(2) level, respectively. Plants were harvested at growth stages 31, 65 and 93 and separated into up to eight fractions to gain information about biomass partitioning. CO(2) enrichment (263 microl litre(-1) above ambient levels) drastically increased biomass of organs serving as long-term carbohydrate pools. Peduncle weight increased by 92%, stem weight by 73% and flag leaf sheath weight by 59% at growth stage 65. Average increase in shoot biomass due to CO(2) enrichment amounted to 51% at growth stage 65 and 36% at final harvest. Average yield increase was 34%. Elevated nitrogen application was most effective on biomass of green tissues. Yield was increased by 30% when nitrogen application was increased from 150 to 270 kg N ha(-1). Significant interactions were observed between CO(2) enrichment and nitrogen application. Yield increase due to CO(2) ranged from 23% at 120 kg N to 47% at 330 kg N. Triticum aestivum cv. Minaret was not very responsive to ozone at 1.5 times ambient levels. 1000 grain weight was slightly decreased, which was compensated by an increased number of grains.