The effects of lead-resistant pseudomonads on the growth of Triticum Aestivum seedlings under lead stress

Five Pseudomonad strains, SPb-1, SPb-2, SPb-3, (from a water sample), SPb-4, and SPb-5 (from rhizosphere), which could tolerate lead acetate up to 1000 microm ml(-1), were isolated from an industrially polluted area around Kasoor, Pakistan. Only SPb-5 harbours a lead-resistant plasmid. Triticum aestivum seeds inoculated with strains SPb-4 and SPb-5 were germinated and grown under different concentrations (0, 1, 5, 10, 15 and 20 mM) of lead acetate for ten days. Germination and seedling growth were adversely affected. Poor growth was associated with increased lead content of seedlings. With bacterial inoculation, germination and seedling growth were improved, as compared with non-inoculated treatments. Stimulation in the growth of seedlings was accompanied by a decrease in lead content, as compared with non-inoculated treatments.     

Effects of ozone and simulated acid rain on birch seedling growth and formation of ectomycorrhizae

Four-week-old paper birch (Betula papyrifera Marsh.) seedlings, inoculated or non-inoculated with the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker & Couch and grown in steamed or non-steamed soil, were exposed to ozone (O(3)) and/or simulated acid rain (SAR). Plants were exposed to O(3) for 7 h per day on 5 days per week for 12 weeks. O(3) concentrations were maintained between 0.06 and 0.08 ppm. SAR was applied 10 min per day on 2 days per week. O(3), SAR, soil regime and mycorrhizal treatment did not significantly affect any of the measured variables. Interactions between O(3) and SAR, SAR and mycorrhizal treatment, soil regime and mycorrhizal treatment and ozone and soil regime had significant effects. Treatment of seedlings with pH 3.5 SAR caused increases in growth which were more apparent in birch exposed to O(3). Mucorrhizal treatment caused increased growth in non-steamed soil, while growth appeared to decrease in steamed soil. Birch seedlings grew much better in steamed soil. The implications of increased growth in steamed soil may demonstrate the importance of looking at the secondary effects of pollutants on soil-borne organisms.     

Effect of ectomycorrhizae and ammonium on 134Cs and 85Sr uptake into Picea abies seedlings

Microorganisms play an important role in the fixation of radionuclides in forest soils. In particular, fungi have the capacity to absorb and translocate radionuclides. The role of the ectomycorrhizal fungus Hebeloma crustuliniforme in the uptake of radiocaesium (134Cs) and radiostrontium (85Sr) into seedlings of Norway spruce (Picea abies) was investigated in a pouch test system. Inoculated and non-inoculated seedlings; seedlings inoculated during 8 and 15 weeks; seedlings exposed during 2 and 3 weeks to the radioactive solution; and seedlings grown under low and high ammonium conditions prior to the application of the radionuclides were compared. The final 134Cs and 85Sr activity was determined in fine-roots, main-roots, stems and needles. The results showed that ectomycorrhizae reduced the uptake of 134Cs and 85Sr. The degree of ectomycorrhization was of crucial importance and seemed to be governed by the period during which ectomycorrhizae were allowed to develop and by the ammonium concentration in the nutrient solution. The radionuclide uptake increased with increasing exposure time. Both radionuclides were predominantly accumulated in fine-roots. However, needles proved to describe best the result of net root uptake and translocation to the shoot. The uptake-and and translocation-rates of 85Sr were smaller than those of 134Cs. It is assumed that the translocation is coupled with the intensity of water fluxes through the xylem and that 85Sr is more readily adsorbed into mycelium or plant tissue relative to 134Cs. The effect of high ammonium growth conditions was overcome by the effect of ectomycorrhization, except in needles with a very large biomass which behaved as a strong sink and led to a high accumulation of 134Cs.     

Physiological and foliar injury responses of Prunus serotina,Fraxinus americana,and Acer rubrum seedlings to varying soil moisture and ozone

Sixteen black cherry (Prunus serotina, Ehrh.), 10 white ash (Fraxinus americana, L.) and 10 red maple (Acer rubrum, L.) 1-year old seedlings were planted per plot in 1997 on a former nursery bed within 12 open-top chambers and six open plots. Seedlings were exposed to three different ozone scenarios (ambient air: 100% O3; non-filtered air: 98% ambient O3; charcoal-filtered air: 50% ambient O3) within each of two different water regimes (nine plots irrigated, nine plots non-irrigated) during three growing seasons.During the 1998 and 1999 growing season, leaf gas exchange, plant water relations, and foliar injury were measured. Climatic data,ambient- and chamber-ozone-concentrations were monitored. We found that seedlings grown under irrigated conditions had similar (in 1998) but significantly higher gas exchange rates (in 1999) than seedlings grown within non-irrigated plots among similar ozone exposures. Cherry and ash had similar ozone uptake but cherry developed more ozone-induced injury (< 34% affected leaf area, LAA) than ash (<5% LAA), while maple rarely showed foliar injury, indicating the species differed in ozone sensitivity. Significantly more severe injury on seedlings grown under irrigated conditions than seedlings grown under non-irrigated conditions demonstrated that soil moisture altered seedling responses to ambient ozone exposures.     

Growth, ectomycorrhizae and nonstructural carbohydrates of loblolly pine seedlings exposed to ozone and soil water deficit

Loblolly pine (Pinus taeda) seedlings from three full-sib families were exposed to 0, 50, 100 or 150 ppb ozone (O(3)) (5 h/d, 5 d/week for 6 or 12 weeks). Soil water potential was maintained near pot capacity (-0.03 MPa) or soil was allowed to dry to approximately -1.0 MPa and resaturated. Chlorotic mottling and flecking of needles due to O(3) injury were observed for seedlings from all pine families. Soil water deficit lessened the intensity of O(3) symptoms, possibly due to stomatal closure. Exposure to O(3) and soil water deficit each resulted in less seedling volume growth and dry weight, and changed the nonstructural carbohydrate content of seedlings compared with controls. Increasing O(3) concentrations resulted in a linear reduction in foliar starch content but did and affect hexose or sucrose content. Soil water deficit resulted in less starch and soluble sugar contents in above- and below-ground plant parts compared with controls. Soil water deficit did not affect numbers or percentages of roots that formed ectomycorrhizal tips. A linear dose-response relationship between O(3) and ectomycorrhizae was observed. The number of ectomycorrhizal tips/cm long root and the percentage of feeder roots that formed ectomycorrhizae were lower as O(3) concentration increased. Overall, each stress alone caused less seedling growth and carbohydrate content compared with controls, but only O(3) was responsible for suppression of ectomycorrhizae.     

A cumulative ozone uptake-response relationship for the growth of Norway spruce saplings

Norway spruce saplings [Picea abies (L.) Karst.] were exposed during four growing seasons to different ozone treatments in open-top chambers: charcoal filtered air (CF), non-filtered air (NF) and non-filtered air with extra ozone (NF+, 1.4xambient concentrations). The CF and NF+ ozone treatments were combined with phosphorous deficiency and drought stress treatments. The total biomass of the trees was harvested at different intervals during the experimental period. The ozone uptake to current-year needles of the Norway spruce saplings was estimated using a multiplicative stomatal conductance simulation model. There was a highly significant correlation between the reduction of total biomass and the estimated cumulative ozone uptake, which did not vary when different thresholds were applied for the rate of ozone uptake. The reduction of the total biomass was estimated to 1% per 10 mmol m(-2) cumulated ozone uptake, on a projected needle area basis.     

Effects of long-term ozone fumigations on growth and gas exchange of Fraser fir seedlings

Fraser fir seedlings from two seed sources in the Southern Appalachians (Mt Mitchell, North Carolina, a declining population; and Mt Rogers, Virginia, a relatively healthy population) were subjected to long-term (2.5 years) intermittent ozone fumigations (0.025, 0.070, and 0.150 ppm) while being grown through five growth cycles in an accelerated-growing regime. Fumigations took place during bud break, stem elongation and bud set. Following each growing cycle, gas exchange parameters and dry weights were determined. The ozone fumigations did not produce any effect on seedling growth. The ozone fumigation effects on gas exchange parameters were inconsistent, and generally not statistically different, with no differences occurring between seed sources. There was no correlation between photosynthetic rates and seedling growth. These results provide no evidence that ozone may be contributing to the differences in decline noted between the Mt Rogers and Mt Mitchell populations of Fraser fir.     

Chronic ozone exposure increases the susceptibility of hybrid Populus to disease caused by Septoria Musiva

Rooted cuttings of hybrid Populus (DN34, Populus deltoides X nigra) were grown outdoors in pots in open-top chambers at Ithaca, NY (74.5 degrees W, 42.5 degrees N), during 1988 and 1989 (Experiment 1) and during 1989 and 1990 (Experiment 2). Ambient air was passed through charcoal filters to produce a 0.5 times ambient ozone treatment, and ozone generated from oxygen was added to produce one and two times ambient ozone treatments. In Experiment 1, treatments were applied for 8-12 h each day for 112 days of the 1988 growing season; then the plants were grown outdoors with ambient ozone in 1989. In Experiment 2, treatments were applied for 9 h each day for 98 days of the 1989 growing season; then the plants were grown outdoors with ambient ozone in 1990. Shallow wounds were made into the bark tissue and inoculated with either an aqueous suspension of conidia of Mycosphaerella populorum or sterile water on 1 and 2 September 1988 (Experiment 1) or 16 and 17 August 1989 (Experiment 2). In Experiment 1, wounds were inoculated either 0, 7, or 14 days after wounding. In Experiment 2, wounds were inoculated either 0, 3, or 6 days after wounding. Canker development was measured after harvest on 16 and 17 July 1989 (Experiment 1) and 28 May 1990 (Experiment 2). In both experiments, chronic exposure to ozone significantly increased the incidence of canker formation in inoculated wounds, and no cankers formed in wounds that received only sterile water. In Experiment 1, cankers formed only on plants inoculated the same day as wounding. No cankers formed on plants inoculated either 7 or 14 days after wounding. In Experiment 2, cankers formed on plants inoculated on the same day as wounding, and on a few plants inoculated 3 days after wounding. No cankers formed on plants inoculated 6 days after wounding. Additionally, in Experiment 2, exposure to increased concentrations of ozone caused a significantly higher number of plants to die during the subsequent winter. Analysis of partial correlation coefficients among plant growth and plant disease variables suggested that the observed ozone-induced increase in the susceptibility of the plants to disease was not mediated by alterations in plant growth.     

Does interspecific competition alter effects of early season ozone exposure on plants from wet grasslands? Results of a three-year experiment in open-top chambers

Chronic effects of ozone on wet grassland species early in the growing season might be altered by interspecific competition. Individual plants of Holcus lanatus, Lychnis flos-cuculi, Molinia caerulea and Plantago lanceolata were grown in monocultures and in mixed cultures with Agrostis capillaris. Mesocosms were exposed to charcoal-filtered air plus 25 nl l(-1) ozone (CF+25), non-filtered air (NF), non-filtered air plus 25 nl l(-1) ozone (NF+25) and non-filtered air plus 50 nl l(-1) ozone (NF+50) early in the growing seasons of 2000 through 2002. Ozone-enhanced senescence and visible foliar injury were recorded on some of the target plants in the first year only. Ozone effects on biomass production were minimal and plant response to ozone did not differ between monocultures and mixed cultures. After three years, above-ground biomass of the plants in mixed culture compared to monocultures was three times greater for H. lanatus and two to four times smaller for the other species.     

The effects of ozone-exposed sugar maple seedlings on the biological performance and the feeding preference of the forest tent caterpillar (Malacosoma disstria Hbn.)

The effects of exposure of sugar maple (Acer saccharum Marsh.) to ozone on the entire larval stage of a native insect have not been previously investigated. This study reports the effects of sugar maple seedlings exposed to different ozone concentrations on the relative performance and the feeding preference of the forest tent caterpillar (Malacosoma disstria Hbn.). Three-year-old seedlings were set in nine open-top field chambers in the spring of 1992 and 1993. Three ozone concentrations were generated: charcoal-filtered ambient air (0x), ambient air (1x) and three times ambient air (3x). In 1992, female and male larval development time did not differ among ozone treatments. In 1993, female larvae reared on 3x developed faster than those on 0x and 1x, while male larvae were not affected. Ozone treatments did not influence pupal weights except for males in 1993 where pupae reared on 0x were heavier than 1x but did not differ from 3x. Larval and pupal survival rates were not affected by ozone in either year. Finally, 4th and 5th instar larvae showed a significant feeding preference for 3x foliage in 1993 but not in 1992. The response of the forest tent caterpillar to ozone exposed seedlings varied between years and could be more sensitive to annual climatic variations than ozone.     

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.     

Yield and grain quality of spring wheat (Triticum aestivum L., cv. Drabant) exposed to different concentrations of ozone in open-top chambers

Spring wheat (Triticum aestivum L., cv. Drabant) was exposed to different concentrations of ozone in open-top chambers for two growing seasons, 1987 and 1988, at a site located in south-west Sweden. The chambers were placed in a field of commercially grown spring wheat. The treatments were charcoal-filtered air (CF), non-filtered air (NF) and non-filtered air plus extra ozone (NF(+)). In 1988, one additional ozone concentration (NF(++)) was used. Grain yield was affected by the ozone concentration of the air. Air filtration resulted in an increase in grain yield of about 7% in both years, compared to NF. The addition of ozone (NF(+), NF(++)) reduced grain yield and increased the content of crude protein of the grain in both years. Filtration of the air had no significant effect on the content of crude protein, compared to NF. The results showed a strong positive chamber effect on grain yield in the cold and wet summer of 1987. In 1988, there was no net chamber effect on grain yield. The relative differences between the CF, NF and NF(+) treatments with respect to grain yield were of the same magnitude in the two years, despite the very different weather conditions.     

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.     

Impact of ozone on the growth of birch (Betula pendula) saplings

Saplings of one half-sib family of birch, Betula pendula, were exposed to three levels of ozone in open-top chambers (OTCs) during two growing seasons 1997-1998. The ozone treatments were non-filtered air (NF, accumulated daylight AOT40 over the two growing seasons of 3.0 l l-1 h), non-filtered air with extra ozone (NF+, accumulated daylight AOT40 of 27.3 l l-1 h) and non-filtered air with additional extra ozone (NF++, accumulated daylight AOT40 of 120 l l-1 h). The birch saplings, including the roots, were harvested after the first and second growing seasons. After the first growing season, the NF++ treatment reduced the total wood biomass by 22%, relative to the NF treatment. There was no further reduction of the total wood biomass in the NF++ treatment after the second growing season. The root biomass was reduced by 30% after the first growing season. The shoot/root ratio, as well as the proportional biomass of leaves, were increased by ozone during both years. The ozone impact on the relative growth rate was estimated to -2% per 10 l l-1 h daylight AOT40 per growing season.     

Foliar injury, leaf gas exchange and biomass responses of black cherry (Prunus serotina Ehrh.) half-sibling families to ozone exposure

Open pollinated families of black cherry seedlings were studied to determine genotypic differences in foliar ozone injury and leaf gas exchange in 1994 and growth response following three growing seasons. An O(3)-sensitive half-sibling family (R-12) and an O(3)-tolerant half-sibling family (MO-7) planted in natural soil were studied along with generic nursery stock (NS) seedlings. Ozone exposure treatments were provided through open top chambers and consisted of 50, 75, and 97% of ambient ozone, and open plots from May 9 to August 26, 1994. Ambient ozone concentrations reached an hourly peak of 88 ppb with 7-hour averages ranging from 39 to 46 ppb. Seedlings in the 50 and 75% of ambient chambers were never exposed to greater than 80 ppb O(3). Visible foliar ozone injury (stipple) was significantly higher for R-12 seedlings than MO-7 seedlings and increased with increasing ozone exposures. For the chamber treatments averaged over all families, there was no significant difference in stomatal conductance and net photosynthetic rates, but there was a significant decrease in root biomass, and a significant decrease in root/shoot ratio between the 50 and 97% of ambient chambers. Stomatal conductance and net photosynthetic rates were significantly different between families with R-12 seedlings generally greater than MO-7 seedlings. The R-12 seedlings had a 7.5 mmol m(-2) increase in ozone uptake compared to MO-7, and at the same cumulative O(3) exposure R-12 exhibited 40.9% stippled leaf area, whereas MO-7 had 9.2% stippled leaf area. Significant differences were observed in stem volume growth and total final biomass between the open-top chambers and open plots. Although R-12 had the most severe foliar ozone injury, this family had significantly greater stem volume growth and total final biomass than MO-7 and NS seedlings. Root:shoot ratio was not significantly different between MO-7 and R-12 seedlings.     

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 photochemical smog and mineral nutrition on ponderosa pine seedlings

Two-year-old seedlings of ponderosa pine (Pinus ponderosa Dougl. ex Laws) were exposed to ambient concentrations of photochemical smog (AA) and clean air (CA) during a single field season at Tanbark Flat of the San Gabriel Mountains in the Los Angeles Basin. The seedlings were grown in a perlite-vermiculite medium with full supply of nutrients (based on modified Hoagland solution); reduced to 50% supply of N; reduced to 50% supply of Mg; and reduced to 50% supply of N+Mg. No significant effects of air pollution exposures on injury development, stem growth and concentrations of plant pigments were determined. The seedlings in the AA treatment had decreased N concentration in current year needles compared with CA seedlings; however, the needle concentrations of other elements did not change. Reduction of N supply in the growing medium caused decreased N, P, Ca, K and chlorophyll a concentrations in needles. Stem growth of the seedlings with reduced N supply was significantly decreased as well. No changes in stem growth or chemical composition of plants with reduced Mg supply were noted. Reduction of supply of nutrients did not change responses of trees to the air pollution exposures.     

Impact of ozone and reduced water supply on the biomass accumulation of Norway spruce saplings

Norway spruce saplings [Picea abies (L.) Karst.] were exposed during four growing seasons to two different ozone treatments in open-top chambers: charcoal filtered air (CF), and non-filtered air with extra ozone (NF+, 1.4xambient concentrations). Within each ozone treatment the saplings were either kept well watered or treated with a 7-8 week period with reduced water supply each growing season. The total biomass of the trees was measured in April and September during each of the last three growing seasons. NF+ significantly reduced the total biomass accumulation of Norway spruce saplings during the fourth growing season. No interaction between ozone and reduced water supply could be detected. The magnitude of the ozone impact after 4 years of exposure was an 8% reduction of the total plant biomass and a 1.5% reduction of the RGR. The reduced water supply reduced the total biomass 29% and the RGR 12%.     

Growth response of loblolly pine (Pinus taeda L.) seedlings to ozone fumigation

Twenty-two week-old Pinus taeda L. (loblolly pine) seedlings of 30 open-pollinated and five full-sib families, representing a wide range in geographic origin, were grown in charcoal-filtered (CF) air or CF-air supplemented with 160 or 320 nl liter(-1) ozone for 8 h day(-1), 4 days week(-1), for 9 weeks. Visible foliar injury (banded chlorosis, tip burn and premature senescence) was apparent in many families after 3 weeks in 320 nl liter(-1) and 6 weeks in 160 nl liter(-1) ozone. Decreases in relative height and root collar diameter growth rates, total dry weight, root dry weight, shoot dry weight, and root/shoot ratios were evident after 9 weeks of treatment with both 160 and 320 nl liter(-1) ozone. For relative height growth rates, family differences in response to ozone were observed. By the study's end, net photosynthesis rates were 15% less for the 320 nl liter(-1) ozone treatment as compared to the CF-air treatment. Total soluble sugar and total starch content of roots were not changed after 9 weeks of ozone exposure.     

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.