Effects of chronic ozone exposure on growth, root respiration and nutrient uptake of rice plants

To clarify the response of growth and root functions to low concentrations of ozone (O(3)), rice plants (Oryza sativa L.) were exposed to O(3) at 0.0 (control), 0.05 and 0.10 ppm for 8 weeks from vegetative to early heading stages. Exposure to 0.05 ppm O(3) tended to slightly stimulate the dry weight of whole plants up to 5 weeks and then slightly decrease the dry weight of whole plants. However, these effects were statistically significant only at 6 weeks. Exposure to 0.10 ppm O(3) reduced the dry weight of whole plants by 50% at 5 and 6 weeks, and thereafter the reduction of the dry weight of whole plants was gradually alleviated. Those changes in dry weight can be accounted for by a decrease or increase in the relative growth rate (RGR). The changes in the RGR caused by 0.05 and 0.10 ppm O(3) could be mainly attributed to the effect of O(3) on the net assimilation rate. Root/shoot ratio was lowered by both 0.05 and 0.10 ppm O(3) throughout the exposure period. The root/shoot ratio which had severely decreased at 0.10 ppm O(3) in the first half period of exposure (1-4 weeks) became close to the control in the latter part of exposure (5-8 weeks). Time-course changes in NH(4)-N root uptake rate were similar to those in the root/shoot ratio especially for 0.10 ppm O(3). On the other hand, root respiration increased from the middle to later periods. Since it is to be supposed that plants grown under stressed conditions change the ratio of plant organ weight to achieve balance between the proportion of shoots to roots in the plant and their activity for maintaining plant growth, these changes in root/shoot ratio and nitrogen uptake rate under long-term exposure can be considered to be an adaptive response to maintain rice growth under O(3) stress.     

Screening loblolly pine seedling responses to SO2 and O3: analysis of families differing in resistance to fusiform rust disease

Open pollinated families of loblolly pine differing in resistance to fusiform rust disease were screened in laboratory studies for responses to gaseous air pollutants. Twenty families were given acute exposures (2 fumigations for 4 h each) to SO(2) (0.4-1.0 ppm), O(3) (0.25 ppm), SO(2) (0.4-1.0 ppm) + O(3) (0.25 ppm) and control. Analyses of variance were performed to evaluate the treatment effects of these air pollutants on percent foliar injury, and to determine whether the families responded differentially to the air pollution treatments. Treatment effects were significant, with the combination treatment of SO(2) + O(3) producing a higher percentage of foliar injury than the controls; however, injury levels were very low and may not be of biological significance. Subsequently, twelve families were grown in two soil types for exposure to chronic levels of SO(2) (0.06 ppm), O(3) (0.07 ppm), SO(2) (0.06 ppm) + O(3) (0.07 ppm) and control. The families were then ranked for decreased primary shoot growth, shoot dry weight, root dry weight, total plant dry weight and root/shoot ratio after exposure to air pollution treatments. Air pollution treatments as a main effect were significant for only one of five growth parameters measured, that of primary shoot growth. The main effect of family, and the interaction of family and air pollution treatments, were significant for most growth parameters measured. In general, O(3) alone and in combination with SO(2) reduced growth more than SO(2) alone. Fumigation with O(3) reduced growth of two families in comparison with control groups, whereas SO(2) alone produced decreased growth in one family and stimulated growth in three families. Treatment with O(3) alone produced higher root/shoot ratios than fumigation with charcoal-filtered air in two families. Overall, families which were fast growers under control conditions maintained their ranking after exposure to air pollution. Families producing less growth in charcoal-filtered air also produced less growth under various air pollution regimes. Results indicated that these families exhibited a high degree of resistance to air pollution injury. Growth responses of seedlings may not reflect family differences in long-term productivity. No relationship was apparent between fusiform rust resistance and growth reductions due to air pollutants.     

The relationship between foliar injury, nitrogen metabolism, and growth parameters in ozonated soybeans

A single 12 h ozone exposure peaking at 0.20 ppm proved phytotoxic to greenhouse-grown 'Cutler 71' soybeans at each growth stage tested from V5 to R6. Visible injury occurred within 40 h on the unifoliodate leaves and middle-aged and older trifoliolates while the younger leaves were free from toxicity symptoms. In some instances visible injury was accompanied by a decrease in chlorophyll and an increase in leaf diffusive resistance. Although nitrogen fixation was not significantly altered except at early pod formation (R3), and nitrate reductase activity was significantly reduced only if the ozone exposure occurred at the time of maximal enzyme activity (V5), nitrogen content of the leaves was reduced by ozone treatment. Shoot dry weight was not affected 40 h after ozone treatment, but root dry weight was significantly reduced. Plants grown with supplemental NO(3)(-) were more sensitive to ozone than those dependent on fixed nitrogen. At plant maturity, there was no evidence of an ozone effect on shoot, root, or seed dry weight, NO(3)(-) -grown plants showed a significant increase in growth and yield over N(2)(-) plants; but no ozone effect was observed, despite the increased foliar sensitivity. Multiple ozone exposures at growth stages V3, R1 and R3 exacerbated the effects noted with a single episode and also reduced nitrogenase activity (reflected in specific and total nodule activity) and shoot and root dry weight. At plant maturity, there was again no evidence of a significant effect of multiple ozone treatment on shoot dry weight or seed yield although root weight remained low. The results would tend to support the hypothesis that older leaves of soybean do not make a significant contribution to seed yield. Although they may be injured by ozone during the reproductive phases of growth, seed yield may not be affected if the younger O(3)-tolerant leaves remain functional.     

Effects of nitrogen dioxide on biochemical and physiological characteristics of soybean

One month old soybean (Glycine max (L.) Merrill) cv. 'Williams' plants were exposed to nitrogen dioxide (NO2 at 0.1, 0.2, 0.3, and 0.5 microl liter(-1) and carbon filtered air (control), 7 h per day for five days, under controlled environment. Data were collected on net photosynthetic rate (PN), stomatal resistance (SR), and dark respiration rate (DR), immediately following the fifth day of exposure and 24 h after termination of exposure. Chlorophyll a (Ch a), chlorophyll b (Ch b), total chlorophyll (tot Ch) and foliar nitrogen (N) were measured before and after exposures. Growth characteristics--relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), and root shoot ratio (RSR) -- were computed for treated plants using standard growth equations. Increases of 18% and 23% in PN were observed immediately following exposure to 0.2 microl liter(-1) NO2 and after 24 h recovery period, respectively. With 0.5 microl liter(-1) NO2 treatment, reductions in PN of 23% and 50% were observed, immediately after exposure and following 24 h recovery, respectively. DR rates with 0.2 l liter(-1) treatment were higher than the control. Chlorophyll a and tot Ch showed significant reduction with 0.5 microl liter(-1) NO2 treatment. The percent reduction in Ch a and tot Ch with 0.5 microl liter(-1) NO2 were 45% and 47%, respectively. Increases in foliar nitrogen content after 0.2 and 0.3 microl liter(-1) NO2 treatments were 46% and 69%, respectively. Nitrogen dioxide at 0.5 microl liter(-1) reduced RGR and NAR by 47% and 51%, respectively. Leaf area ratio was 42% higher in 0.5 microl liter(-)1 NO2 treated plants, compared with the control; this increase was insufficient to compensate for the decrease in NAR resulting in a net decline in RGR. Nitrogen dioxide up to 0.2 microl liter(-1) increased PN and foliar-N content of soybean. With 0.5 microl liter(-1) NO2, significant decreases were observed in PN, leaf chlorophyll, foliar-N, NAR and RGR. Nitrogen dioxide up to 0.2 microl liter(-)1 has a favorable influence on overall growth characteristics of soybean; however, inhibitory effects were seen with NO2 treatment at 0.5 microl liter(-1).     

Growth and crown architecture of two aspen genotypes exposed to interacting ozone and carbon dioxide.

To study the impact of ozone (O3) and O3 plus CO2 on aspen growth, we planted two trembling aspen clones, differing in sensitivity to O3 in the ground in open-top chambers and exposed them to different concentrations of O3 and O3 plus CO, for 98 days. Ozone exposure (58 to 97 microl l(-1)-h. total exposure) decreased growth and modified crown architecture of both aspen clones. Ozone exposure decreased leaf, stem, branch, and root dry weight particularly in the O3 sensitive clone (clone 259). The addition of CO2 (150 microl l(-1) over ambient) to the O3 exposure counteracted the negative impact of O3 only in the O3 tolerant clone (clone 216). Ozone had relatively little effect on allometric ratios such as, shoot/root ratio, leaf weight ratio, or root weight ratio. In both clones, however, O3 decreased the shoot dry weight, shoot length ratio and shoot diameter. This decrease in wood strength caused both current terminals and long shoots to droop and increased the branch angle of termination. These results show that aspen growth is highly sensitive to O3 and that O3 can also significantly affect crown architecture. Aspen plants with drooping terminals and lateral branches would be at a competitive disadvantage in dense stands with limited light.     

The individual and combined effects of ozone and simulated acid rain on growth, gas exchange rate and water-use efficiency of Pinus armandi Franch

The seedlings of Pinus armandi Franch. were exposed to ozone (O(3)) at 300 ppb for 8 h a day, 6 days a week, and simulated acid rain of pH 3.0 or 2.3, 6 times a week, alone or in combination, for 14 weeks from 15 June to 20 September 1993. The control seedlings were exposed to charcoal-filtered air and simulated rain of pH 6.8 during the same period. Significant interactive effects of O(3) and simulated acid rain on whole plant net photosynthetic rate were observed, but not on other determined parameters. The exposure of the seedlings to O(3) caused the reductions in the dry weight growth, root dry weight relative to the whole plant dry weight, net photosynthetic rate, transpiration rate in light, water-use efficiency and root respiration activity, and increases in shoot/root ratio, and leaf dry weight relative to the whole plant dry weight without an appearance of acute visible foliar injury, but did not affect the dark respiration rate and transpiration rate in the darkness. The decreased net photosynthetic rate was considered to be the major cause for the growth reduction of the seedlings exposed to O(3). On the other hand, the exposure of the seedlings to simulated acid rain reduced the net photosynthetic rate per unit chlorophyll a + b content, but did not induce the significant change in other determined parameters.     

Effect of imazaquin applications on the growth, leaf chlorophyll and yield of soybean in the Guinea savanna of Nigeria

Field trials were conducted during the wet seasons of 1989, 1991, 1994 and 1995 to evaluate the effects of pre-emergence and post-emergence applications of four rates of imazaquin (0.00; 0.15; 0.30 and 0.45kg a.i/ha) on the growth, leaf chlorophyll types and grain yield of soybean c.v. SAMSOY 2. Imazaquin applications had no significant effect on the growth of soybean roots on most of the sampling dates, but pre-and post-emergence applications of imazaquin at 0.30 and 0.45kg a.i/ha reduced soybean root nodules at 5 and 7 weeks after planting (WAP). Soybean shoot growth was generally reduced at 5WAP by the pre-emergence and at 7WAP by the higher rates (0.30 & 0.45kg a.i/ha) of post-emergence application of imazaquin. Pre-and post-emergence applications of imazaquin showed a strong tendency to reduce the concentration of chlorophyll a and total chlorophyll at 3 and 5WAP respectively. The concentrations of chlorophyll types in soybean leaves at 9WAP was generally comparable among most treatments especially in 1991. Whole plant fresh weight of soybean at 7WAP was reduced by all rates of post-emergence application of imazaquin. However, there was no significant difference in the whole plant dry weight of soybean at 3 to 7 WAP in 1989 and at 3, 5 and 9WAP in 1991. In each trial, pre-and post-emergence applications of soybean significantly increased the grain yield of soybean compared with the control treatment. This study showed that, inhibition of soybean shoot growth and leaf chlorophyll concentration was transient and that soybean plants require about 6 weeks for complete recovery from imazaquin phytotoxicity.     

Effects of nitrogen dioxide on growth and yield of black turtle bean (Phaseolus vulgaris L.) cv. 'Domino'

Twenty-six-day-old black turtle bean cv. 'Domino' plants were exposed to nitrogen dioxide (0.0, 0.025, 0.05 and 0.10 microl liter(-1)), 7 h per day for 5 days per week for 3 weeks, under controlled environment. Data were collected on net photosynthesis rate (PN), stomatal resistance (SR), and dark respiration rate (DR), immediately after exposure, 24 h after the termination of exposure and at maturity (when the leaves had just started turning yellow), using a LICOR 6000 Portable Photosynthesis System. Chlorophyll-a (Ch-a), chlorophyll-b (Ch-b), total chlorophyll (tot-Ch) and leaf nitrogen were measured immediately after exposure and at maturity. Growth characteristics-relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR) and root: shoot ratio (RSR)-were computed for treated plants. Net photosynthesis rate increased by 53% in 0.10 microl liter(-1) NO2 treated plants immediately after exposure compared to control plants. Dark respiration rates were also higher in treated plants. Ch-a, Ch-b and tot-Ch showed significant increases with 0.1 microl liter(-1) NO2 treatment immediately after exposure. Foliar nitrogen content showed an increase in treated plants both immediately after exposure and at maturity. Increases were also seen in RGR and NAR. Plant yield increased by 86% (number of pods), 29% (number of seeds) and 46% (weight of seeds), respectively. Nitrogen dioxide stimulated the overall plant growth and crop yield.     

Effect of carbon dioxide concentration on biomass production and partitioning in Betula pubescens Ehrh. seedlings at different ozone and temperature regimes

Seedlings of Betula pubescens were grown at two CO(2) concentrations, in combination with either two O(3) concentrations or two air temperatures, during 34-35 days at 24 h day(-1) photoperiod in growth chambers placed in a greenhouse. Increasing the CO(2) concentration from 350 to 560 micromol mol(-1) at 17 degrees C air temperature increased the dry weight of the main leaves, main stem, branches and root. The mean relative growth rate (RGR) was increased 10% by CO(2) enrichment, while increasing the O(3) concentration from 7 to 62 nmol mol(-1) decreased the RGR by 9%. The relative biomass distribution between the different plant components was not significantly affected by the CO(2) concentration irrespective of the O(3) concentration. No significant interactions between CO(2) and O(3) concentration were found except on leaf size, which was stimulated more by elevated CO(2) concentration at high, compared to low, O(3) levels. In another experiment, elevated CO(2) (700 micromol mol(-1)) significantly increased the dry weight of the different plant components, and more at 20 degrees C than at 15 degrees C. Raising the CO(2) concentration increased the RGR by 5 and 10% at 15 and 20 degrees C, respectively. CO(2) enrichment increased the branch dry weight relatively more than the dry weight of the other plant parts. Increasing the CO(2) concentration or temperature increased the plant height and stem diameter, however, no interactions between CO(2) and temperature were found.     

Effect of imazaquin applications on the growth,leaf chlorophyll and yield of soybean in the Guinea Savanna of Nigeria

Abstract

Field trials were conducted during the wet seasons of 1989, 1991, 1994 and 1995 to evaluate the effects of pre‐emergence and post‐emergence applications of four rates of imazaquin (0.00; 0.15; 0.30 and 0.45kg a.i/ha) on the growth, leaf chlorophyll types and grain yield of soybean c.v. SAMSOY 2. Imazaquin applications had no significant effect on the growth of soybean roots on most of the sampling dates, but pre‐and post‐emergence applications of imazaquin at 0.30 and 0.45kg a.i/ha reduced soybean root nodules at 5 and 7 weeks after planting (WAP). Soybean shoot growth was generally reduced at 5WAP by the pre‐emergence and at 7WAP by the higher rates (0.30 & 0.45kg a.i/ha) of post‐emergence application of imazaquin. Pre‐and post‐emergence applications of imazaquin showed a strong tendency to reduce the concentration of chlorophyll a and total chlorophyll at at 3 and 5WAP respectively. The concentrations of chlorophyll types in soybean leaves at 9WAP was generally comparable among most treatments especially in 1991. Whole plant fresh weight of soybean at 7WAP was reduced by all rates of post‐emergence application of imazaquin. However, there was no significant difference in the whole plant dry weight of soybean at 3 to 7 WAP in 1989 and at 3, 5 and 9WAP in 1991. In each trial, pre‐and post‐emergence applications of soybean significantly increased the grain yield of soybean compared with the control treatment. This study showed that, inhibition of soybean shoot growth and leaf chlorophyll concentration was transient and that soybean plants require about 6 weeks for complete recovery from imazaquin phytotoxicity.     

Additive and antagonistic effects of ozone and salinity on the growth, ion contents and gas exchange of five varieties of rice (Oryza sativa L.)

Five varieties of rice (Oryza sativa L.) of varying salinity resistance were grown in non-saline and in saline conditions, with and without a repeated exposure to ozone at a concentration of 83 nmol mol(-1) giving an AOT40 (cumulative exposure above 40 nmol mol(-1)) of 3600 nmol mol(-1) h. Salinity caused a substantial reduction in shoot and root dry weight in all varieties, but the effect on root growth was proportionately less than on shoot growth. Ozone reduced root dry weight but the treatment used did not significantly affect shoot dry weight. Both salinity and ozone reduced plant height. The potassium concentration in the leaves of all five varieties was reduced by salinity, and by ozone in both saline and non-saline treatments. Ozone reduced the sodium concentration in plants grown at 50 mM NaCl but had no effect upon the chloride concentration. Carbon dioxide assimilation, transpiration and stomatal conductance were all reduced by salinity and by ozone and there was close quantitative similarity between the effects of ozone and/or salinity upon assimilation, stomatal conductance and transpiration. There were some antagonistic effects but there were additive effects of salinity and of ozone on root dry weight, plant height, shoot potassium concentration, photosynthesis, transpiration and stomatal conductance. The possible basis of the additive effects of salinity and ozone on gas exchange and mineral uptake are discussed.     

Effects of lead and chelators on growth, photosynthetic activity and Pb uptake in Sesbania drummondii grown in soil

Effects of lead (Pb) and chelators, such as EDTA, HEDTA, DTPA, NTA and citric acid, were studied to evaluate the growth potential of Sesbania drummondii in soils contaminated with high concentrations of Pb. S. drummondii seedlings were grown in soil containing 7.5 g Pb(NO(3))(2) and 0-10 mmol chelators/kg soil for a period of 2 and 4 weeks and assessed for growth profile (length of root and shoot), chlorophyll a fluorescence kinetics (F(v)/F(m) and F(v)/F(o)) and Pb accumulations in root and shoot. Growth of plants in the presence of Pb+chelators was significantly higher (P<0.05) than the controls grown in the presence of Pb alone. F(v)/F(m) and F(v)/F(o) values of treated seedlings remained unaffected, indicating normal photosynthetic efficiency and strength of plants in the presence of chelators. On application of chelators, while root uptake of Pb increased four-five folds, shoot accumulations increased up to 40-folds as compared to controls (Pb only) depending on the type of chelator used. Shoot accumulations of Pb varied from 0.1 to 0.42% (dry weight) depending on the concentration of chelators used.     

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.     

Performance of some growth variables

European beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Silver fir (Abies alba Mill.) were exposed to low concentrations of ozone (O(3)) and sulfur dioxide (SO(2)), alone and combined, and simulated acid rain (pH 4.0) in sheltered open-top chambers in Hohenheim (Southwest Germany) for almost five years. The concentrations of O(3) and SO(2) used were related to annual ambient average found in southern West Germany. Two control chambers were ventilated with charcoal filtered air and rainfall was simulated at pH 4.0 and 5.0. Because of large dense plant growth in the chambers it was only possible to measure uncompleted growth of shoots in the upper canopy. Therefore, growth analysis was restricted to this area. The treatment with acidic precipitation decreased the annual shoot growth of beech and reduced leaf surface area of those trees. Exposure to SO(2), O(3) alone and in combination resulted in further reduction of shoot length and leaf surface area. Fumigation with SO(2) and O(3) + SO(2) caused insignificant decreases of shoot length, total dry weight and needle surface area of spruce. The lateral leader shoot growth of spruce exposed to O(3) was significantly reduced only in the last year of the experiment. Growth rates of the spruce exposed to charcoal filtered air and non-acidic precipitation were reduced more than those of beech and fir. Growth variables determined for fir reflected different rates of incremental change. Exposure to O(3) resulted in the largest dry matter production of all fir groups but those exposed to charcoal filtered air and non-acidic precipitation responded with the best lateral leader shoot growth, lowest specific leaf area (SLA) and leaf area ratio (LAR) respectively indicating best metabolic efficiency. At the conclusion of this study a classification of sensitivity was developed for the tree species.     

Physiological responses of glyphosate-resistant and glyphosate-sensitive soybean to aminomethylphosphonic acid, a metabolite of glyphosate

Aminomethylphosphonic acid (AMPA) is formed in glyphosate-treated glyphosate-resistant (GR) and glyphosate-sensitive (GS) soybean [Glycine max (L.) Merr.] plants and is known to cause yellowing in soybean. Although, AMPA is less phytotoxic than glyphosate, its mode of action is different from that of glyphosate and is still unknown. Greenhouse studies were conducted at Stoneville, MS to determine the effects of AMPA on plant growth, chlorophyll content, photosynthesis, nodulation, nitrogenase activity, nitrate reductase activity, and shoot nitrogen content in GR and GS soybeans. AMPA was applied to one- to two-trifoliolate leaf stage soybeans at 0.1 and 1.0 kg ha(-1), representing a scenario of 10% and 100% degradation of glyphosate (1.0 kg ae ha(-1) use rate) to AMPA, respectively. Overall, AMPA effects were more pronounced at 1.0 kg ha(-1) than at 0.1 kg ha(-1) rate. Visual plant injury (18-27%) was observed on young leaves within 3d after treatment (DAT) with AMPA at the higher rate regardless of soybean type. AMPA injury peaked to 46-49% at 14 DAT and decreased to 17-18% by 28 DAT, in both soybean types. AMPA reduced the chlorophyll content by 37%, 48%, 66%, and 23% in GR soybean, and 17%, 48%, 57%, and 22% in GS soybean at 3, 7, 14, and 28 DAT, respectively. AMPA reduced the photosynthesis rate by 65%, 85%, and 77% in GR soybean and 59%, 88%, and 69% in GS soybean at 3, 7, and 14 DAT, respectively, compared to non-treated plants. Similarly, AMPA reduced stomatal conductance to water vapor and transpiration rates at 3, 7, and 14 DAT compared to non-treated plants in both soybean types. Photosynthesis rate, stomatal conductance, and transpiration rate recovered to the levels of non-treated plants by 28 DAT. Plant height and shoot dry weight at 28 DAT; nodulation, nitrogenase activity at 10 DAT, and nitrate reductase activity at 3 and 14 DAT were unaffected by AMPA. AMPA reduced root respiration and shoot nitrogen content at 10 DAT. These results suggest that a foliar application of AMPA could indirectly reduce photosynthesis through decreased chlorophyll content in GR and GS soybean up to 14 DAT, but affected plants can recover to normal growth by 28 DAT.     

Dynamics of biomass partitioning in field-grown radish varieties, treated with ethylenediurea

During the growing season of 1990, five staggered crops of radish (Raphanus sativus L.) were grown in the field, using the cultivars 'Cherry Belle', 'Red Prince', and 'Red Devil B'. Half of the plants received a soil drench (100 ml plant(-1); 100 mg litre(-1) of ethylenediurea (EDU) once, early in plant development. Destructive harvests were carried out at 2-day intervals during vegetative development. Non-linear growth kinetics, derived from Richards' function, were fitted to the dry weight data of the total plant, main organs (shoot and hypocotyl) and to the dry weight ratio between below-ground and above-ground organs. Estimating the parameters of these non-linear functions and testing their differences between EDU-treated and untreated plants unveiled biologically meaningful information on the impact of different levels of ambient ozone (O(3)) during the growth periods. The modified function which was applied to the data of biomass partitioning between the major plant parts was more powerful in detecting transient alterations in assimilate allocation compared to the growth dynamics of individual plant organs. At low levels of O(3), biomass partitioning towards the below-ground sink organs was slightly delayed and finally restricted in EDU-treated plants. When ambient O(3) reached moderate levels, which did not cause visible foliar injury, assimilate partitioning between organs was only insignificantly altered during early growth when EDU-treatments were compared. As growth progressed, however, less assimilates were allocated towards the hypocotyl and roots in the plants not protected by EDU. This pattern was similar in all cultivars tested, but was smallest in 'Cherry Belle', which is known to be sensitive to O(3) with respect to foliar injury. During the 15- to 19-day periods of rapid growth, the O(3)-exposure >80 nl litre(-1) ranged from 0.015 to 0.209 microl litre(-1) O(3) h, which corresponds to 7 h d(-1) mean values between 40 and 50 nl litre(-1) O(3), confirming that ambient ozone did not exceed a moderate level in this study.     

The Influence of Mycorrhiza on Uranium and Phosphorus Uptake by Barley Plants from a Field-contaminated Soil (7 pp)

Background Recent studies indicated that arbuscular mycorrhizal fungi (AMF) play important roles in plant accumulation of uranium (U) from contaminated environments, but the impacts of fertilization practices on functioning of the symbiotic associations, which are crucial factors influencing plant nutrition and growth responses to mycorrhiza, have rarely been considered. Materials and Methods In a greenhouse experiment, a bald root barley mutant (brb) together with the wild type (wt) were used to test the role of root hairs and AMF in uranium (U) uptake by host plants from a U contaminated soil. Nil, 20 and 60 mg KH2PO4-P kg–1 soil were included to investigate the influences of phosphorus (P) fertilization on plant growth and accumulation of U. Results Dry matter yield of barley plants increased with increasing P additions and wt produced significantly higher dry weight than brb. Mycorrhiza markedly improved dry matter yield of both genotypes grown at nil P, whereas only brb responded positively to mycorrhiza at 20 mg P kg-1. At the highest P level, mycorrhiza resulted in growth depressions in both genotypes, except for the roots of wt. In general, plant P concentrations increased markedly with increasing P additions and in response to mycorrhiza. Mycorrhiza and P additions had no significant effects on shoot U concentrations. However, root U concentrations in both genotypes were significantly increased by mycorrhiza. On the other hand, shoot U contents increased with increasing P levels, while 20 mg P kg-1 stimulated, but 60 mg P kg-1 marginally affected the U accumulation in roots. Root length specific U uptake was moderately enhanced both by root hairs and strongly enhanced by mycorrhiza. Moreover, non-inoculated plants generally had higher shoot-root ratios of U content than the corresponding inoculated controls. Conclusion Our study shows that AMF and root hairs improves not only P acquisition but also the root uptake of U, and mycorrhiza generally decreases U translocation from plant root to shoot. Hence, mycorrhiza is of potential use in the phytostabilization of U contaminated environments. Perspectives The complex impacts of P on U accumulation by barley plants suggested that U behavior in mycorrhizosphere and translocation along the soil-fungi-plant continuum as affected by fertilization practices deserve extensive studies for optimizing the function of mycorrhizal associations for phytoremediation purposes.     

Effect of gamma-irradiated sludge on the growth and yield of rice (Oryza sativa L. var. GR-3)

The effects of gamma-irradiated sludge on the growth and yield of rice (Oryza sativa L. var. GR-3) in pot cultures have been studied. Compared to plants grown only in soil, shoot length, root length, fresh weight, dry weight, total proteins, total soluble sugars, starch and chlorophyll content of plants grown in soil supplemented with unirradiated or gamma-irradiated sludge were found to be significantly increased. Irradiation of sludge significantly stimulated the linear growth of shoot and root systems as well as fresh and dry weights of plants, compared to those grown in soil containing unirradiated sludge. There was also an improvement in the grain yield (weight of seed) when plants were grown in soil supplemented with irradiated sludge. The results obtained suggest that the gamma-irradiated sewage sludge can be beneficially recycled for agricultural uses.     

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.     

Effects of ozone on three open-pollinated families of Pinus taeda L. grown in two substrates

Seedlings from three open-pollinated loblolly pine (Pinus taeda L.) families grown in a mixture of commercial peat moss and grade 3 vermiculite (1:3 by volume) or a mixture of mineral soil and peat (1:1 by volume) were exposed to 0, 160 or 320 ppb ozone (O3) for 6h/day, 4 days/week for 8 weeks beginning 12 weeks after transplanting. Before exposures began, seedlings grown in the vermiculite-peat substrate were taller but smaller in diameter than those grown in the mineral soil-peat substrate. After 8 weeks of exposure, seedlings grown in the mineral soil-peat substrate were significantly larger in diameter and total biomass than those grown in the vermiculite-peat substrate. Primary needle and secondary needle injury increased with increasing O3 concentrations. Suppression of diameter growth, shoot weight and root weight was linear as O3 concentration increased. The effect of O3 on height or diameter growth or shoot biomass was not influenced by substrate type; but the suppression of root biomass due to O3 was dependent on substrate, with greater suppression in biomass occurring in the vermiculite-peat substrate. Foliar injury due to O3 was slightly greater in family 8-103, but growth suppression due to O3 was not significantly different among the families. Based on root biomass, response of seedlings to O3 was substrate-dependent.