Effects of ozone on managed pasture: II. Yield, species composition, canopy structure, and forage quality

Managed pasture composed of grasses, clover and weeds was exposed in open-top chambers to different levels of ozone (O(3)) during two consecutive seasons to study changes in yield, species composition, canopy structure, and forage quality. The pasture was established in 1990 and exposed in 1991 and 1992. Ozone treatments included charcoal-filtered air (CF), non-filtered air (NF), and two treatments with O(3) added to NF air during periods with global radiation >/= 400 W m(-2) (NF(+), NF(++)). The ratio between the 2-year cumulative, radiation-weighted O(3) concentration in ambient air (= 365 microl litre(-1) h) and in the different treatments was 0.50 (CF), 0.85 (NF), 1.11 (NF(+)), and 1.64 (NF(++)). Plots were harvested four times in 1991, and five times in 1992. The total forage yield for both seasons was modified little by O(3). The yield reduction in NF(++) was only 10% as compared to the CF treatment. Also, only marginal changes were observed in forage quality (Ca, crude protein, crude fibre), and in leaf area index and fractional light penetration. Ozone strongly reduced the yield of clover (Trifolium repens L. and Trifolium pratense L.). The O(3)-effect on clover growth was small after the first harvest and increased with each growth period. In NF, the 2-year cumulative clover yield was reduced by 24% relative to CF. In NF(++), clover growth almost ceased near the end of the second season. The reduction in clover yield with increasing O(3) was associated with a slight increase in the yield of grasses (mainly Dacytlis glomerata L). The increase in the proportion of invading species (weeds or herbs) (Taraxacum officinale L.) during the experiment was not significantly affected by O(3). A second order polynomial function was fitted to the data to establish an exposure-response model for the cumulative clover yield and the cumulative, radiation-weighted O(3) dose, and linear models were developed for total forage mass, grass yield and yield of weeds. Reducing O(3) from elevated levels (NF(+) and NF(++)) during the first season to near-ambient levels (NF) during the second season resulted in a significant recovery of clover yield after two re-growth periods. It is concluded that continuous exposure to ambient levels of O(3) negatively affects the yield of clover in frequently cut, managed pasture, but because of the relatively small proportion of clover, the shift in species composition only marginally affects total forage yield and forage quality. It is emphasised, however, that limitations of the experimental system must be taken into account before extrapolations to real field situations can be made.     

Influence of ozone stress on growth processes, yields and grain quality characteristics among soybean cultivars

Field studies were conducted at USDA Beltsville Agricultural Research Center, Beltsville, Maryland, in 1984 and 1985 using open-top chambers to acquire information on the responses of 12 soybean (Glycine max L. Merr.) cultivars to O3 stress and to examine the interactions between maturity groups and O3 stress. Cultivars representing Groups III, IV, and V were exposed for approximately 3 months to charcoal-filtered air (CF) and nonfiltered air plus 40 nl litre(-1) O3 (NF + O3). Ozone was added 6 h d(-1), 5 d week(-1) for 13 weeks. The CF effectively reduced the accumulative oxidant exposure (AOX) to less than 1.0 microl litre(-1) h and the NF + O3 treatment approximately doubled the ambient AOX (16.7 microl litre(-1) h) to about 30 microl litre(-1) h. The AOX estimates the total O3 exposure above 30 nl litre(-1) during an entire growing season. Plant growth rates and relative growth rates were reduced by 17.0 and 14.4%, respectively, when averaged over cultivars. Based on growth rates, the Group III cultivars were the most affected by O3 stress. Averaged over cultivars, leaf expansion rates, leaf conductance, and transpiration rates were lower in the NF + O3 treatment compared to the CF control; however, wide variation was found with the stomatal results from field observations. Combined over years and cultivars, grain yield was reduced by an average of 12.5% by O3 stress with 3 of 12 cultivars showing significant reductions. Grain protein content was increased by 0.7% by O3 stress, but cultivar differences were equal to the differences caused by the O3 treatments. Grain oil content was unchanged by the O3 treatments. Group IV cultivars showed the greatest decrease in grain yield due to O3 stress. Multiple regression analyses were calculated using the difference between the CF and NF + O3 treatment as a measure of O3 stress. Significant positive relationships were found among net assimilation rates, plant growth rates, relative growth rates, and leaf expansion rates, which suggest that growth analysis characteristics would be useful in addition to yield in air pollution tolerance improvement studies with soybeans.     

Soybean root distribution, top growth and yield responses to ambient ozone and soil moisture stress when grown in soil columns in greenhouses

Soybeans (Glycine max. cv. Williams) were grown to maturity in soil columns within polyvinyl pipe and placed in greenhouses with charcoal filtered (CF) and nonfiltered (NF) air. In each greenhouse plants were grown with and without soil moisture stress (SMS). Targeted soil water potentials at 0.25 m for no SMS and between 0.45 and 0.60 m for the SMS regime were -0.05 and -0.45 M Pa, respectively. The 7 h (1000-1700 h EDT) mean O(3) concentrations (June-October) were 0.039 and 0.009 ppm in NF and CF air, respectively. Ozone and SMS in combination were less than additive in their effects on growth of the plant top and bean yields. Plants in CF air had 70% greater top weight, 58% more bean yield and 43% more root dry weight than in NF air. Both the plant and the seed weight from plants without SMS weighed 35% more than with SMS. Total root length in CF air for plants with and without SMS averaged 1.84 and 1.98 km, respectively, as compared to 1.59 and 1.66 km for plants with and without SMS in NF air. The resultsare different, so far as the combined effects of O(3) and SMS on yield and root growth are concerned, than in a similar field study by Heggestad and co-workers primarily because of the presence of a water table in the field but absence of it in the columns, as planned, in this experiment. It is unique to use large soil columns to study root distribution and length as related to the effects of ambient O(3) alone, and its combination with SMS.     

Tibouchina pulchra (Cham.) Cogn., a native Atlantic Forest species, as a bio-indicator of ozone: visible injury

Tibouchina pulchra saplings were exposed to carbon filtered air (CF), ambient non-filtered air (NF) and ambient non-filtered air+40 ppb ozone (NF+O3) 8 h per day during two months. The AOT40 values at the end of the experiment were 48, 910 and 12,895 ppb h(-1), respectively, for the three treatments. After 25 days of exposure (AOT40=3871 ppb h(-1)), interveinal red stippling appeared in plants in the NF+O3 chamber. In the NF chamber, symptoms were observed only after 60 days of exposure (AOT40=910 ppb h(-1)). After 60 days, injured leaves per plant corresponded to 19% in NF+O3 and 1% in the NF treatment; and the average leaf area injured was 7% within the NF+O3 and 0.2% within the NF treatment. The extent of leaf area injured (leaf injury index) was mostly explained by the accumulated exposure of ozone (r2=0.89; p<0.05).     

Photoinduced toxicity of fluoranthene on germination and early development of plant seedling

The influence of light on phytotoxicity of increased concentration (2, 5, 10 mg/l) of intact fluoranthene (FLT) and photomodified fluoranthene (phFLT) diluted in experimental solutions was investigated. The germination rate of lettuce (Lactuca sativa L.), onion (Allium cepa L.) and tomato (Lycopersicum esculentum L.) seeds and some parameters of seedlings primary growth of these plant species were used as laboratory indicators of phytotoxicity. Among them a length of root and shoot, their dry weight and a content of photosynthetic pigments in shoot were measured. The results demonstrated that the higher concentration (5 and 10 mg/l) of FLT and especially of phFLT significantly inhibited the germination rate of seeds and the length of root and shoot seedlings of all plant species. Decreased production of biomass expressed by dry weight of root and shoot was found in lettuce seedlings under the inhibitory effect of FLT and phFLT. An increased concentration of FLT and phFLT did not exhibit an unambiguous effect on the content of photosynthetic pigments in shoot of experimental plants. Only the highest concentration (10 mg/l) of FLT significantly increased content of chlorophylls a and b in lettuce, onion and tomato plants and content of carotenoids in lettuce and onion. Light intensified a significant inhibitory effect of phFLT in the most testified parameters of germination and seedling growth.     

Psidium guajava 'Paluma' (the guava plant) as a new bio-indicator of ozone in the tropics

Psidium guajava 'Paluma' saplings were exposed to carbon filtered air (CF), ambient non-filtered air (NF), and ambient non-filtered air+40ppb ozone (NF+O(3)) 8h per day during two months. The AOT40 values at the end of the experiment were 48, 910 and 12 895ppbh(-1), respectively for the three treatments. After 5 days of exposure (AOT40=1497ppbh(-1)), interveinal red stippling appeared in plants in the NF+O(3) chamber. In the NF chamber, symptoms were observed only after 40 days of exposure (AOT40=880ppbh(-1)). After 60 days, injured leaves per plant corresponded to 86% in NF+O(3) and 25% in the NF treatment, and the average leaf area injured was 45% in NF+O(3) and 5% in the NF treatment. The extent of leaf area injured (leaf injury index) was explained mainly by the accumulated exposure of ozone (r(2)=0.91; p<0.05).     

Wheat-kernel growth characteristics during exposure to chronic ozone pollution

Chronic exposure to ozone (O(3)) air pollution can reduce yield in wheat; however, little is known concerning the effects of O(3) stress on kernel development. A field study was conducted to investigate the effects of chronic O(3) exposure on kernel-growth components of two soft red winter-wheat genotypes (Seven and MD5518308). Five air-quality treatments, including charcoal-filtered air (CF), non-filtered air (NF), NF + 20, and NF + 40 and NF + 80 nl O(3) liter(-1) air were applied 4 h d(-1), 5 d wk(-1) through maturity. In the case of the NF + treatments, O(3) was added to existing ambient O(3) levels. Spike samples were collected 16, 20, 24, 28, and 32 days after anthesis (DAA). Linear and quadratic equations were fitted to kernel-weight data to estimate kernel-growth rate (KGR) and kernel-fill duration (KFD). Effective filling period (EFP) and assimilate utilization (AU) were also determined. Rates of growth for individual kernels were 0.74 mg d(-1) and 1.07 mg d(-1) for the NF + 80 and CF treatments, respectively. The NF + 80 nL litter(-1) O(3) treatment significantly reduced KGR and AU compared with the CF treatment. Severn had a significantly loger KFD than MD5518308, but O(3) had no significant effect on KFD of either genotype. Each genotype had similar EFP values, and O(3) had no significant effect on EFP. Linear relationships between O(3) exposure and kernel weight suggests that O(3) effects on kernel weight begin soon after anthesis in MD5518308, but, in Severn, O(3) has a greater effect on kernel weight during the later stages of kernel development. These data suggest that decreased economic yield associated with chronic O(3) exposure is primarily the result of decreased KGR.     

Responses of sensitive and tolerant bush beans (Phaseolus vulgaris L.) to ozone in open-top chambers are influenced by phenotypic differences, morphological characteristics, and the chamber environment

Responses of bush bean (Phaseolus vulgaris L.) lines 'S156' (O(3)-sensitive) and 'R123' (O(3)-tolerant), and cultivars 'BBL 290' (O(3)-sensitive) and 'BBL 274' (O(3)-tolerant) to ambient ozone (O(3)) were investigated during the 2001 and 2002 growing seasons. Seedlings were grown in pots inside open-top chambers (OTCs), with charcoal filtered (CF) and non-filtered (NF) ambient air, and in non-chambered ambient air (AA) plots. Growth parameters from individual plants were evaluated after harvests at the end of vegetative (V(4)) and reproductive (R(10)) growth phases. Results at V(4) indicated that CF did not provide additional benefits over NF in 'S156' in 2001 and 2002. In contrast, exposure to CF significantly impaired the growth of 'R123'. At the end of R(10), 'S156' produced more pods, most of which remained immature, and contained fewer seeds or were more frequently aborted, whereas pods produced in 'R123' reached pod maturation and senescence more consistently. Despite increased seed weights inside the OTCs, as observed in 'S156', differences between the two lines were insignificant when grown outside OTCs. Results from the 'BBL 290'/'BBL 274' pair, especially at V(4) phase, remained inconclusive. Plant morphological characteristics, variabilities in environmental conditions, and 'chamber effects' inside OTCs were influential in determining plant response to ambient O(3).     

Physiological and growth responses of differentially irrigated cotton to ozone

This study was conducted to determine the physiological and growth responses of cotton (Gossypium hirsutum L.) to the interaction of ozonee (O3) and drought stress. Cotton (cv SJ-2) was grown in open-top chambers in the field at three levels of soil water and exposed to charcoal-filtered air (CF), nonfiltered air (NF), and NF x 1.25, and NF x 1.5 ambient O3 concentrations in Riverside, CA, from June to October 1986. Ozone reduced carbon fixation an average of 74.6% in optimally watered (OW) plots, 63.4% in suboptimal (SO) plots, but only 19.3% in severely water-stressed (SS) plots. Leaf and stem biomass in OW and SO plots showed similar linear reductions in mass response to increased O3 concentrations, but SS plots showed no response to O3 except at the highest O3 treatment (seasonal 12-h O3 mean of 0.111 ppm 218 microm(-3)). These results showed that moderately water-stressed cotton had similar physiological and growth responses to O3 as well-watered plants, but severely water-stressed cotton showed little response to O3 at ambient O3 concentrations.     

Yield and nutritive quality of sericea lespedeza (Lespedeza cuneata) and little bluestem (Schizachyrium scoparium) exposed to ground-level ozone

Sericea lespedeza (Lespedeza cuneata cv. Interstate 76) and little bluestem (Schizachyrium scoparium cv. Aldous) were raised from seed in a glasshouse, transplanted into 5.7-l pots and placed into open-top chambers (OTC) on 6 June 1999. Following a 7-day adjustment period, each of six OTCs (duplicate OTCs per treatment) was ventilated with either air that had been carbon-filtered (CF) to remove ambient ozone (O3); non-filtered (NF), representative of ambient air; or enriched to twice-ambient O3 concentration (2X). Primary-growth forage was harvested on days 7, 32, 46, 59 and 72 following the start of fumigation, and regrowth forage from the first primary-growth harvest was harvested on days 36, 54 and 72 following the start of fumigation. Dry matter (DM) yield of either forage species did not differ among treatments except in the final regrowth period when yield of sericea lespedeza was greater for the NF than 2X O3 treatment. In vitro DM digestibility (IVDMD) and concentrations of crude protein (CP), soluble phenolics (SP) and condensed tannins (CT) in primary-growth sericea lespedeza did not differ between treatments, but NF primary-growth forage had higher concentration of protein-precipitating tannins (PPT) than did 2X primary-growth forage. Concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were higher in NF and 2X than in CF primary-growth sericea lespedeza. Similarly, concentrations of NDF and ADL were higher, and IVDMD was lower for NF and 2X than for CF regrowth sericea lespedeza. Concentrations of ADF and ADL were lower, whereas IVDMD, in vitro NDF digestibility (IVNDFD) and concentrations of CP and SP were greater, in CF than in NF and 2X primary-growth little bluestem. Percentages IVDMD and IVNDFD and concentrations of CP and SP in NF primary-growth little bluestem were greater than those in forage exposed to 2X O3 treatment. No significant differences were observed among treatments in percentages IVDMD and IVNDFD, or concentrations of cell wall constituents or SP in little bluestem regrowth. Nutritive quality of little bluestem was decreased by < 2%, and that of sericea lespedeza by approximately 7% as a result of increased concentrations of cell wall constituents and decreased in vitro digestibility of NF and 2X compared with CF forages. Results indicate that existing and projected O3 levels can drive alterations in forage quality of select warm-season forages sufficient to have nutritional and economic implications for their utilization by ruminant herbivores.     

Determination of disulfoton and permethrin residues in an organic soil and their translocation into lettuce, onion and carrot.

The residues of disulfoton and permethrin in an organic soil and in vegetables grown in soil treated with a granular formulation of the pesticides were determined by gas chromatography. The residues were removed from soil or plant samples by successive extractions with acetone and hexane. Permethrin persisted in the soil for the initial 28 days and declined slowly during the rest of the season but disulfoton after persisting for one week at the applied concentration was degraded in the next two weeks. The insecticides did not translocate into the edible parts of the vegetables but were present in the root system of onion and lettuce. Carrot and lettuce yields were not singificantly different from those of the controls but onion yields were substantially decreased by the use of permethrin.     

Ambient ozone and crop loss: establishing a cause-effect relationship

This paper provides the results of a retrospective mathematical analysis of the US NCLAN (National Crop Loss Assessment Network) open-top chamber data. Some 77% of the 73 crop harvests examined, showed no statistically significant yield differences between NF (non-filtered open-top chamber) and AA (chamberless, ambient air) treatments (no easily discernable chamber effects on yield). However, among these cases only seven acceptable examples showed statistically significant yield reductions in NF compared to the CF (charcoal filtered open-top chamber) treatment. An examination of the combined or cumulative hourly ambient O3 frequency distribution for cases with yield loss in NF compared to a similar match of cases without yield loss showed that the mean, median and the various percentiles were all higher (>/= 3 X) in the former in contrast to the latter scenario. The combined frequency distribution of hourly O3 concentrations for the cases with yield loss in NF were clearly separated from the corresponding distribution with no yield loss, at O3 concentrations > 49 ppb. Univariate linear regressions between various O3 exposure parameters and per cent yield losses in NF showed that the cumulative frequency of occurrence of O3 concentrations between 50 and 87 ppb was the best predictor (adjusted R2 = 0.712 and p = 0.011). This analysis also showed that the frequency distribution of hourly concentrations up to 87 ppb O3 represented a critical point, since the addition of the frequency distributions of > 87 ppb O3 did not improve the R2 values. In fact as the frequency of hourly O3 concentrations included in the regression approached 50-100 ppb, the R2 value decreased substantially and the p value increased inversely. Further, univariate linear regressions between the frequencies of occurrence of various O3 concentrations between 50 and 90 ppb and: (a) cases with no yield difference in NF and (b) cases with yield increase in NF compared to the CF treatment (positive effect) provided no meaningful statistical relationship (adjusted R2 = 0.000) in either category. These results support the basis that additional evaluation of the frequency of occurrence of hourly O3] concentrations between 50 and 87 ppb for cases with the yield reductions could provide a meaningful ambient O3 standard, objective or guideline for vegetation.     

Crop loss assessment for California: modeling losses with different ozone standard scenarios

Crop yield losses were estimated for ambient O3 concentrations and for a series of potential O3 air quality standards for California, including the current statewide 1-h oxidant (O3) standard of 0.10 ppm (196 microg m(-3)), 12-h growing season averages, and other models. A model for statewide losses was developed using hourly O3 data for all sites in the State, county crop productivity data, and available O3 concentration-yield loss equations to determine potential yield losses for each crop in each county in California for 1984. Losses were based on comparison to an estimated background filtered air concentration of 0.025 or 0.027 ppm, for 12 or 7 h, respectively. Potential losses due to ambient air in 1984 were estimated at 19% to 25% for dry beans, cotton, grapes, lemons, onions, and oranges. Losses of 5% to 9% were estimated for alfalfa and sweet corn. Losses of 4% or less were estimated for barley, field corn, lettuce, grain sorghum, rice, corn silage, spinach, strawberries, sugar beets, fresh tomatoes, processing tomatoes, and wheat. Implementation of either a modified rollback to meet the current 1 h California O3 standard (0.10 ppm) or a three-month, 12-h growing season average of 0.045 ppm was necessary to produce large reductions in potential crop losses.     

Effects of ozone and soil water deficit on roots and shoots of field-grown soybeans

Water-stressed and well-watered soybean (Glycine max cvs. Williams and Corsoy) plants were exposed to increasing seasonal doses of ozone (O(3)) using open-top field chambers and ambient air plots. Chamber O(3) treatments included charcoal filtered (CF) air, non-filtered (NF) air, NF + 0.03, NF + 0.06 and NF + 0.09 microl litre(-1) O(3). Soil water potentials measured at 25 and 45 cm averaged -0.40 MPa and -0.05 MPa, respectively, for the plots in the water-stressed and well-watered series. Total root length/core, root length densities, and biomasses (dry weights) were determined. With Williams, a very popular cultivar in recent years, total root length for all O(3) treatments averaged 58% more under water-stress conditions than in well-watered plots, but the range was from 136% to 11% more for NF air and NF + 0.09 microl litre(-1) O(3), respectively. Increasing the O(3) exposure dose did not affect root lengths or weights in the well-watered series. With Corsoy, water stress did not significantly increase root development. In both soil moisture regimes, with both cultivars, there was a linear decrease in seed yield and top dry weight as the O(3) exposure dose increased.     

Determination of disulfoton and permethrin residues in an organic soil and their translocation into lettuce,onion and carrot 1

Abstract

The residues of disulfoton and permethrin in an organic soil and in vegetables grown in soil treated with a granular formulation of the pesticides were determined by gas chromatography. The residues were removed from soil or plant samples by successive extractions with acetone and hexane. Permethrin persisted in the soil for the initial 28 days and declined slowly during the rest of the season but disulfoton after persisting for one week at the applied concentration was degraded in the next two weeks. The insecticides did not translocate into the edible parts of the vegetables but were present in the root system of onion and lettuce. Carrot and lettuce yields were not significantly different from those of the controls but onion yields were substantially decreased by the use of per‐methrin.     

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.     

Growth and yield responses of spring wheat (Triticum aestivum L. CV. Turbo) grown in open-top chambers to ozone and water stress

Spring wheat (Triticum aestivum L.) cv. Turbo was exposed to different levels of ozone and water supply in open-top chambers in 1991. The plants were grown either in charcoal filtered air (CF), not filtered air (NF), in charcoal filtered air with proportional addition of ambient ozone (CF1), or in charcoal filtered air with twice proportional addition of ambient ozone (CF2). The mean seasonal ozone concentrations (24 h mean) were 2.3, 20.6, 17.3, and 24.5 nl litre(-1) for CF, NF, CF1, and CF2 treatments, respectively. Ozone enhanced senescence and reduced growth and yield of the wheat plants. At final harvest, dry weight reductions were mainly due to reductions in ear weight. Grain yield loss by ozone mainly resulted from depressions of 1000 grain weight, whereas numbers of ears per plant and of grains per ear remained unchanged. Pollutants other than ozone did not alter the response to ozone, as was obvious from comparisons between CF1 and NF responses. Water stress alone did not enhance senescence, but also reduced growth and yield. However, yield loss mainly resulted from reductions in the number of ears per plant; 1000 grain weight was not influenced by water stress. No water supply by ozone treatment interactions were detected for any of the estimated parameters.     

Influence of ozone and ethylenediurea (EDU) on growth and yield of bean (Phaseolus vulgaris L.) in open-top field chambers

Greenhouse and ambient air experiments have shown ethylene diurea (EDU) to be a strong and specific protective suppressant of ozone injury in plants. To examine how EDU affects plant responses to various ozone (O(3)) levels under controlled field conditions, Phaseolus vulgaris L. cv. Lit was treated with 150 ppm EDU every 14 days and exposed in open-top chambers to charcoal-filtered air (CF), nonfiltered air (NF) or two cf treatments with ozone added. The ozone treatments were proportional additions of one (CF1) and two (CF2) times ambient ozone levels. The mean ozone concentrations in the CF, NF, CF1 and CF2 treatments were 0.98, 14.1, 14.98 and 31.56 nl litre(-1). A two-way split plot ANOVA revealed that shoot dry weight was significantly reduced by ozone. EDU treatment was highly significant for leaf dry weight, root dry weight and shoot dry weight, but not for pod dry weight; leading to a higher biomass of EDU-treated plants. Ozone/EDU interactions were significant for root weight only, indicating that EDU reduced growth suppression by ozone. These results show that EDU action on plant biomass could be interpreted as a delay in senescence since EDU-treated plants showed a significant decreased biomass loss even in the CF treatment.     

Effects of ozone on managed pasture: I. Effects of open-top chambers on microclimate, ozone flux, and plant growth

Open-top chambers (OTC) were established in a field of managed pasture, and environmental parameters were recorded inside and outside to study the influence of OTCs on radiation, air temperature (T(air)), saturation vapour pressure deficit (svpd), and soil water content in relationship to plant growth and yield. Canopy development in OTCs supplied with non-filtered air (NF) and in ambient (AA) plots was followed by measuring leaf area index (LAI). The dry matter yield was determined after three growth periods in each of two consecutive seasons. Boundary layer conductance (g(bw)) and wind speed (u) were measured along a vertical profile, and day-time flux were measured along a vertical profile, and day-time flux of O(3) was estimated throughout the experiment on the basis of a mass balance. The vertical profile of u showed values in the range 1-1.2 m s(-1) at the top of the canopy, and maximum g(bw) was 20-25 mm s(-1). Average reduction in global radiation in OTCs was 25%, and volumetric soil water content was reduced by about 5%. Daily mean T(air) was increased by 1.3 degrees C, mean daily maximum svpd by 0.08 kPa, and the temperature sum (degree days with base temperature of +5 degrees C) by 12%. Fluctuations in the difference in daily mean T(air) and svpd during the daytime between OTCs and ambient air were related to canopy structure. Differences were largest after each cut and declined with increasing LAI. A small effect of changes in LAI on T(air) and svpd occurred during periods with low soil water content. The flux of O(3) in OTCs was largest (>100 microg m(-2) min(-1)) before and smallest (<20 microg m(-2) min(-1)) after each cut. Calculated deposition velocities for O(3) (nu(d)) in the range 0-3 cm s(-1) were generally higher than those measured under most field conditions. Overall, in OTCs the deficit in soil and atmospheric moisture was larger than in the open field, and the increase in daily mean T(air) was strongly influenced by the stage of canopy development. Changes in microclimate and incoming radiation affected pasture development. LAI was slightly reduced in OTCs as compared to AA plots. The total accumulated dry matter yield for all six growth periods was only about 7% lower in OTCs, but the contribution of clover to total forage mass declined during the experiment. OTCs had no significant effect on weeds. The results indicate that OTCs reduced the competitiveness of clover, and that the increase in growth of grasses compensates for the loss in clover yield. The shift in species composition caused by OTCs must be considered when studying the effect of pollutants on pasture.     

Effects of ozone on the grain composition of spring wheat grown in open-top field chambers

In a three-year study carried out at a rural site in Switzerland, spring wheat (Triticum aestivum L. cv. Albis) was exposed to different levels of ozone (O(3)) in open-top-field chambers from the two-leaf stage until harvest. Field plots in ambient air (AA) were used for comparison. Grain recovered from the different treatments was analyzed for minerals (Ca, Mg, K, P), starch, protein, amino acids and alpha-tocopherol, in order to investigate the effect of O(3) on grain composition. Chamber-enclosure had small effects on some parameters (K, protein), but not on others (starch), as shown by the comparison of data from the AA and non-filtered-air treatment (NF). Differences between NF and charcoal-filtered air (CF) were very small. At O(3) concentrations higher than in the NF treatment (O(3)-1 = 1.5xNF and O(3)-2 = 2.5xNF), mineral contents were higher than in the NF and CF treatments. Protein content was increased only in the O(3)-2 treatment. Starch contents decreased from about 63% in the CF treatment to 54% in the O(3)-2 tratment. No effect of O(3) on the content of alpha-tocopherol and on the essential amino acid index of the protein was observed. It is concluded that compositional changes in wheat grain in response to O(3) are minor, and that ambient O(3) is not likely to cause important changes.