Edward H. Lee

Growth and physiological characteristics of soybean in open-top chambers in response to ozone and increased atmospheric CO2☆

Abstract Open-top chamber studies were conducted during 1989 at USDA-BARC to determine interactive effects of increased atmospheric CO2 and O3 air pollution on physiological and growth responses in soybeans. The plants were grown full-season in chambers supplied with charcoal-filtered air (CF), non-filtered (NF) air or NF+40 nl l−1 O3 having CO2 concentrations of ambient, +50 or +150 μl l−1 CO2. The resultant seasonal 7 h O3 concentrations for the three air quality regimes were 23.0 nl l−1, 40.3 nl l−1 and 66.4 nl l−1 O3, respectively. Photosynthesis rates (PS) and stomata conductance (SC) values were measured on fully expanded leaves on 11 dates throughout the growing season and vegetative samples were collected for carbohydrate analyses and for plant biomass determinations. Seed weights, grain yields and quality measurements were made following harvest at physiological maturity. Photosynthesis rates were stimulated by the +50 and +150 μl−1 CO2 treatments and reduced by the NF+40 nl l−1 O3 treatment. Reductions in PS rates observed for the NF+O3 treatment during preflowering were counteracted by the +150 μl l−1 CO2 treatment. Wide variation in stomata conductance was observed throughout the study; however, the combined effects of CO2 and O3 on stomata conductance appeared additive. Leaf glucose and fructose concentrations were lower for the high O3 exposures but were unchanged by CO2 concentrations. Sucrose and starch concentrations were significantly increased by + 150 μl l−1 CO2. Sucrose was unaffected by O3 treatments, but starch was significantly increased by the NF+O3 treatment at ambient and +50 μl l−1 CO2 thus suggesting that O3 injury reduced the flux of carbohydrates from leaves, especially at low CO2 levels. Leaf N concentrations were significantly reduced by the NF+O3 treatment. Significant changes in plant biomass, leaf area, specific leaf weight, pods and seeds per plant, and grains yield were observed among treatments. Maximum increases in plant growth and productivity were observed in response to CO2 increases in the absence of O3 air pollution. Changes observed in plant biomass, pods and seeds per plant and grain yields were consistent with the results for the PS and leaf carbohydrate data which suggest that the +50 μl l−1 CO2 treatment had a protective role against adverse effects of O3 exposure. Grain oil contents were increased and protein contents significantly reduced in response to CO2; however, both quality features were unaffected by the O3 treatments.

Differential ozone tolerance in soybean and snapbeans: Analysis of ascorbic acid in O3-susceptible and O3-resistant cultivars by high-performance liquid chromatography

The relationship between foliar ozone (O3) tolerance and leaf ascorbic acid (AA) concentrations in O3-susceptible (O3-S) and O3-resistant (O3-R) cultivars of soybean (Glycine max L.) cv. ‘Hark’ (O3-S) and ‘Hood’ (O3-R), and in snapbean (Phaseolus vulgaris L.) cv. ‘BBL-290’ (O3-S) and ‘Astro’ (O3-R) was examined by use of high-performance liquid chromatography (HPLC). Isocratic separation of AA for leaf tissues was accomplished in < 5 min on a μBondapak C-8 reverse phase column using 2% NH4H2PO4 (pH 2.8) as the solvent. Tissues were wxtracted with 6% metaphosphoric acid containing 1 × 10−6 M EDTA. Results showed that resistant genotypes contained more AA in their trifoliate leaves than did the correspnding susceptible genotypes. Young trifoliate leaves were highly tolerant to O3 and had proportionally higher AA concentrations than newly expanded leaves. A threshold concentration of approximately 1000 μg AA/g leaf fresh weight was required for good O3 protection. Ascorbic acid is an antioxidant and is a free radical scavenger which at physiological levels can protect against lipid peroxidation and leaf damage. Ozone stress was shown to induce the production and accumulation of AA in O3-treated leaves. Possible mechanisms for enhanced tolerance to O3 stress are discussed.

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.

Effects of enhanced O3 and CO2 enrichment on plant characteristics in wheat and corn.

The effects of CO(2) enrichment and O(3) induced stress on wheat (Triticum aestivum L.) and corn (Zea mays L.) were studied in field experiments using open-top chambers to simulate the atmospheric concentrations of these two gases that are predicted to occur during the coming century. The experiments were conducted at Beltsville, MD, during 1991 (wheat and corn) and 1992 (wheat). Crops were grown under charcoal filtered (CF) air or ambient air + 40 nl liter(-1) O(3) (7 h per day, 5 days per week) having ambient CO(2) concentration (350 microl liter(-1) CO(2)) or + 150 microl liter(-1) CO(2) (12 h per day.). Averaged over O(3) treatments, the CO(2)-enriched environment had a positive effect on wheat grain yield (26% in 1991 and 15% in 1992) and dry biomass (15% in 1991 and 9% in 1992). Averaged over CO(2) treatments, high O(3) exposure had a negative impact on wheat grain yield (-15% in 1991 and -11% in 1992) and dry biomass (-11% in 1991 and -9% in 1992). Averaged over CO(2) treatments, high O(3) exposure decreased corn grain yield by 9%. No significant interactive effects were observed for either crop. The results indicated that CO(2) enrichment had a beneficial effect in wheat (C(3) crop) but not in corn (C(4) crop). It is likely that the O(3)-induced stress will be diminished under increased atmospheric CO(2) concentrations; however, maximal benefits in crop production in wheat in response to CO(2) enrichment will not be materialized under concomitant increases in tropospheric O(3) concentration.

Differential aluminum tolerances of two barley cultivars related to organic acids in their roots

Abstract ‘Dayton’ barley is significantly more tolerant to excess Al in acid soils and nutrient solutions than is ‘Kearney’ barley; however, the physiological or biochemical mechanisms of such differential tolerance have not been clearly established. One hypothesis is that Al‐tolerant plants contain and exude organic acids or other ligands that form stable chelates with Al and thereby reduce its chemical activity and toxicity. The objective of our study was to determine the effects of Al on concentrations of organic acids in the roots of Al‐tolerant Dayton and Al‐sensitive Kearney barley cultivars. Plants were grown for 17 days in nutrient solutions containing 0, 55 and 110 μM Al (initial pH 4.5), and their roots were analyzed for organic acids by high performance liquid chromatography. Aluminum stress significantly reduced concentrations of citric, succinic and total organic acids in the roots of Al‐sensitive Kearney barley but not in those of Al‐tolerant Dayton. Aluminum decreased concentrations of levu...

Aluminum tolerances of two snapbean cultivars related to organic acid content evaluated by high‐performance liquid chromatography

Abstract High‐performance liquid chromatography (HPLC) was used to determine aluminum (Al)‐induced changes in organic acid (OA) concentrations of Al‐tolerant ‘Dade’ and Al‐sensitive ‘Romano’ snapbean cultivars. Two week old ‘Dade’ and ‘Romano’ snapbean were grown in 1/5‐strength Steinberg nutrient solution for 10 days and then subjected to 0, 2, 4, 6, and 8 mg L‐1 Al treatments at pH 4.5 for an additional 3–15 days. Current studies confirmed earlier findings that the Dade cultivar was significantly more tolerant to Al than the Romano variety. Organic acid analyses were performed on extracts of root and leaf, and on stem exudates. The organic acids were separated on an ion exclusion column using a mobile phase of 0.01 N H3PO4. Individual OA were quantified with a variable wavelength detector operating at 210 nm. Aluminum stress tended to reduce the concentrations of citric, malonlc, malic, glycolic, fumaric, and acetic acids in the roots and increased the OA concentrations in stem exudates. In the presence...

Photochemical reduction of iron. II. Plant related factors

Abstract Photochemical reduction of ferric iron induced by ultraviolet (UV) and blue radiation is enhanced by certain di‐ and tri‐carboxylic acids. Iron photoreduction proceeds according to the following relative rates in Fe3+‐organic acid solutions containing the major plant acids listed: tartaric >oxalic>citric> malic>aconitic > fumaric ≥succinic≥FeCl3 (control). Any sensitized ferric to ferrous photoreduction occurring in plant foliage exposed to sunlight or artificial light would make iron more available to the tissues for metabolism. Iron is translocated within plants primarily complexed with citric acid (Tiffin, 1972). Citric acid is decarboxylated during Fe‐citrate photoreduction‐oxidation. Ferric iron photoreduction is thus accompanied by citrate degradation. In plant foliage, the fate of ferric citrate taken up the stem depends upon many plant‐related factors. Chelated iron is translocated predominately to actively growing regions where enzymatic reactions largely determine the immediate fate. In...

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.

A new gibberellin biosynthesis inhibitor, paclobutrazol (PP333), confers increased SO2 tolerance on snap bean plants

Abstract A sulfur dioxide (SO 2 )-sensitive cultivar of snap bean ( Phaseolus vulgaris L. ‘Bush Blue Lake 290’) was treated with a new experimental plant growth regulator, paclobutrazol (PP 333 , a gibberellin biosynthesis inhibitor, which has been found to be a highly potent protectant against SO 4 -induced injury to plants. The SO 2 tolerance induced by paclobutrazol was reversed by subsequent applications of gibberellic acid (GA 3 ). The degree of reversibility was related to the duration of treatment and concentration of the respective GA 3 and paclobutrazol. The data show that the susceptibility or tolerance of sensitive plants to SO 2 stress can be manipulated by treatment with this growth regulator and the plant hormone, GA 3 .

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.