Edward H. Lee’s research while affiliated with United States Department of Agriculture and other places

The current study confirmed earlier conclusions regarding differential ozone (O(3)) tolerances of two soybean cultivars, Essex and Forrest, and evaluated antioxidant enzyme activities of these two varieties based on their performance under environmentally relevant, elevated O(3) conditions. The experiment was conducted in open-top chambers in the field during the 1994 and 1995 growing seasons. Exposure of plants to moderately high O(3) levels (62.9 nl l(-1) air, 2-year seasonal average) caused chlorophyll loss and increased membrane permeability when compared to control plants grown in charcoal filtered air (24.2 nl l(-1) air). The other effects of O(3) treatment were decrease in seed yield, loss of total sulfhydryl groups, reduction of soluble protein content, and increase in guaiacol peroxidase activity in leaves of both cultivars. The O(3)-induced increase in guaiacol peroxidase activity was much smaller in cv. Essex leaflets. Cv. Essex had less leaf oxidative damage and smaller reduction in seed yield than cv. Forrest under elevated O(3) conditions. During ozonation, mature leaflets of the more O(3) tolerant cv. Essex had higher levels of glutathione reductase (30%), ascorbate peroxidase (13%), and superoxide dismutase (45%) activity than did mature leaflets of cv. Forrest. Cu,Zn-superoxide dismutase, which represented 95% of total superoxide dismutase activity in the two cultivars, appeared to be increased by O(3) exposure in the leaflets of O(3) tolerant cv. Essex but not in those of cv. Forrest. Cytosolic ascorbate peroxidase activity was also higher in leaflets of cv. Essex than in cv. Forrest regardless of O(3) level. Stromal ascorbate peroxidase and Mn-superoxide dismutase activity did not appear to be involved in the O(3) tolerance of the two soybean cultivars.

Plant growth simulation models designated to assess teh future impacts of such complete phenomenon as climate change on crop growth and productivity, have typically considered only the beneficial effects of rising atmospheric CO2 concentration on plants, especially C3 species. Such models largely neglect potential negative impacts of phytotoxic gases such as O3 on crops (Adams et al., 1990; Stockle et al., 1992). Tropospheric CO2 and O3 are commonly referred to as "greenhouse" gases because of their abilities to absorb infrared radiation being emitted by Earth resulting in the reemission of this energy into the troposphere (Krupa and Kickert, 1989). Other trace gases of increasing concern include methane (CH4), nitrous oxide N2O, methyl chloride CHCl and chlorofluorocarbons (CFC's), because of their potential for disrupting stratospheric O3 as well as tehir "greenhouse" properties (Worrest et al., 1989). Pages: 155-179

Experiments were performed to characterize the fluorescence emissions of leaves from four soybean (′Harosoy′) plants containing different concentrations of flavonols (kaempferol glycosides). The study used genetically mutated soybean flavonol isolines grown in a constant environment. Overall, the results indicate that green fluorescence emission due to kaempferol glycosides excited by the blue fluorescent compounds with UV excitation could become a factor in the fluorescence studies of in vivo plants.

Ethylenediurea (EDU), N- [2-(2-oxo-1-imidazolidinyl) ethyl]-N′-phenylurea is known to prevent ozone (O3) damage to leaf tissues. However, the mechanisms of protection are unclear. We tested the hypothesis that EDU protects against O3 damage by scavenging hydroxyl free radicals (OH). An in vitro study involving the use of high-performance liquid chromatography equipped with an electrochemical detector (HPLC-EC) showed that EDU does not serve as an antioxidant to remove OH free radicals. Effects of O3 and EDU (soil drench) on leaf antioxidant scavenger systems (AOSS) were also studied. The first fully expanded trifoliate leaves of O3-sensitive snap bean (Phaseolus vulgaris cv. Bush Blue Lake 290) was examined. Measurements were made before and after a single O3 exposure (0.30 μl 1−1 O3 for 3 h). Pretreatment with EDU 48 h before exposure protected against O3-induced necrosis and chlorosis. EDU pretreatments did not alter superoxide dismutase (SOD), guaiacol-peroxidase (GPX), ascorbate peroxidase (APX) and glutathione reductase (GR) activities. However, O3-fumigated plants (no EDU) showed elevated SOD activity with decreased GR activity. EDU-treated plants exposed to O3 stress showed no measurable loss of GR activity. These tissues maintained high levels of total glutathione [i.e. reduced glutathione (GSH) + oxidized glutathione (GSSG)] contents, and had higher GSH/GSSG ratios than the controls at the end of 3 h exposure to O3. These data suggest that EDU protection against O3 damage in plants do not necessarily involve the direct stimulation or induction of antioxidative enzyme defense mechanisms. Instead, protection may result from a more general retention of chlorophyll and maintenance of GR and GSH levels during O3 exposure.

The objective of this research was to determine the effects of elevated concentrations of carbon dioxide (CO2) and sulfur dioxide (SO2) on field-grown soybean. Soybeans (Glycine max L. Merr. cv. ‘Essex’) were grown a full-season in open-top field chambers exposed to either ambient (350 μl L−1) or elevated CO2 (500 μl L−1) levels under two levels of SO2 (0.00 and 0.12 μl L−1). Enriched CO2, with or without SO2 treatments, significantly increased net photosynthesis rates, leaf area index (LAI; in R4 growth stage) and leaf dry weight, but did not significantly affect stomatal resistance, transpiration rates, leaf area, plant height, total biomass or grain yield. Elevated SO2 treatments significantly decreased photosynthesis and LAI during pod fill stages, but did not significantly affect stomatal resistance, transpiration, total biomass, plant height or grain yield. Sulfur dioxide inhibited growth and development (i.e., LAI) during canopy coverage before any effects on photosynthesis were detected. The interactive effects of CO2 and SO2 treatments on the gas exchange parameters were significant during pod fill, where high SO2 reduced photosynthesis at ambient CO2 but not under elevated CO2. Leaf area index values were likewise reduced by SO2 exposure under ambient CO2 during late flowering and pod fill stages. Thus, enriched CO2 under high SO2 exposure partially compensated for the negative impact of SO2 stress on PS and LAI during the pod fill stages.

Short- and long-term N uptake/partitioning dynamics were studied using stable isotope techniques to investigate the uncertain mechanism(s) of O3 action on plant yield and photosynthate partitioning.Glycine max [L.] Merr.(soybean) plants were grown in 15N enriched soil within open-top chambers and exposed to one of three O3 regimes: half-ambient, ambient, or 2 × ambient. The seasonal 7 h average O3 concentrations (nl l−1) were 25, 43, and 76 nl l−1, respectively. Nitrogen fixation was estimated using the 15N isotope dilution method utilizing a non-nodulating soybean isoline as the control. Macro-kjeldahl technique was used for determining N concentration. Short-term plant responses were investigated by evaluating the following parameters: % N, total N, total N fixed, total N fixed per organ dry weight, the proportion of N-fixed/soil N, and the fraction of N derived through rhizobial N-fixation on an individual organ (leaves, stems, roots, pods, and nodules) and whole plant basis at two reproductive growth stages. Long-term plant responses were investigated by characterizing the same N parameters of the mature grain.Ozone significantly affected both short- and long-term N uptake/partitioning dynamics. Ozone exposure reduced the amount of N derived from N-fixation, but did not significantly affect total N or % N for organs and whole plants. For mature grain, O3 significantly decreased seed yield and all N parameters except N-fixed/soil N, but the responses were dependent upon year.Our results suggest that total nodule activity was affected rather than specific activity. Total N uptake was maintained despite significant decreases in % N-fixed and N-fixed/soil N. We conclude that N-fixation was inhibited by reduced photosynthate translocation to nodules. The photosynthate translocated was sufficient to maintain moderate rates of soil N uptake, but not adequate to maintain high rates of N-fixation, the latter costing more energy. Thus, soybeans damaged by the exposures imposed here, relied more heavily on soil N to meet their total N requirements when photosynthate translocation was inhibited. The long-term negative effects for mature seed also indicate a significant reduction in photosynthate and total N translocated to nodules, and an increased reliance on soil N. In summation, these findings and those of our companion carbon study, support the hypothesis that the mechanism of chronic O3 action involves an inhibition of carbon translocation from leaves to other organs.

Short- and long-term C uptake/transaction dynamics were studied using stable isotope techniques and leaf gas exchange to investigate the mechanism(s) of O3 action on plant yield and C partitioning.Glycine max (L.) Merr. (soybean) plants were grown in open-top chambers and exposed to one of three O3 regimes: half-ambient, ambient, or 2 × ambient for nearly the entire growing season. The seasonal 7 h average O3 concentrations (nl l−1) were 25, 43, and 76 nl l−1, respectively. Whole plant C translocation was measured using pulse-labeled 13CO2 (99 atom %13C) at two distant growth stages (R2 and R5). Translocation parameters were as follows: %13C (sink strength), % 13C/g dry weight (sink intensity), and % 13C/% organ dry weight (relative specific uptake). Single leaf photosynthesis (Pn) was measured at four growth stages (V7, R2, R3, and R4).Ozone significantly affected translocation, but the effect was dependent upon growth stage and the time following the 13C pulse. At the stage of rapid seed fill within the pods (R5), and at 42 h post-labeling, all three leaf translocation parameters had a significant positive linear relationship with O3 exposure. Conversely, root nodule values were all inversely related to O3 exposure. Generally, at 0.5 h post-labeling, no significant effects were observed for leaves and nodule translocation patterns, with the exception of an inverse relationship between sink strength and O3 exposure. No significant differences were observed for single leaf Pn among treatments.Our results indicate that the mechanism of chronic O3 action involves inhibition of translocation, implying reduced phloem loading and the inhibition may be occurring without a concomitant reduction in the amount of C fixed. In addition, 13C pulse labeling appears to be a very useful technique for investigating integrated long-term C translocation dynamics which might not otherwise be evident using instantaneous methods such as short-term labeling or limited leaf gas exchange measurements.

Estimates of increases in future agricultural production in response to increases in carbon dioxide (CO2) concentrations in the atmosphere are often based on the beneficial physiological effect of CO2 enrichment on plant growth, especially in C3 plants. However, these estimates fail to consider the negative impact of ozone (O3) air pollution on crop production. Increases in tropospheric concentrations of both gases, CO2 and O3, have been observed over the past century, and both are predicted to continue to increase at even higher rates in the near future to levels when they may have a significant impact on agricultural production. Field studies with wheat and corn were conducted using open-top chambers to mimic atmospheric concentations of CO2 that are predicted to occur at the Earth's surface during the first half of the 21st century. Wheat and corn produced clearly different responses to CO2 enrichment, but similar responses to O3 exposure. -from Authors

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.

The effects of two air pollutant gases (SO2 and O3) on leaf photosynthesis (PS), leaf chlorophyll (Chl), chlorophyll fluorescence transients (CFTs), leaf reflectance (LR) and canopy reflectance (CR) in soybeans (Glycine max L. Merr.) were studied under both ambient- and elevated-atmospheric (CO2) using open-top chambers. In the CO2 vs. O3 experiment, soybeans 'Clark' were exposed to charcoal filtered air (low-O3) or ambient air + 40 nL L-1(O3) (high O3) during 7 h day-1, 5 days week-1 having (CO2) of 350 (mu) L L-1 CO2 (ambient-CO2) or 500 (mu) L L-1 (enriched-CO2) for 12 h day-1. In the CO2 vs. SO2 experiment, soybeans 'Essex' were exposed to charcoal filtered air (low-SO2) or + 120 nL L-1 SO2 (high-SO2) during 5 hr day-1, 5 days week-1 having the same (CO2) as for the CO2 vs. O3 experiment. Plants were exposed to treatment gases from early growth until maturity. In the CO2 vs. O3 experiment, leaf PS, leaf Chl, and CR showed trends of reduced values under high-O3, while LR was largely unchanged. Leaf PS and CR had increased values under enriched CO2. Leaf Chl and LR were not affected by CO2 enrichment. In the CO2 vs. SO2 experiment, CFTs values indicated that the gases has no impact on the light reactions of photosynthesis. Reduction in leaf PS, leaf Chl, and CR were observed under high-SO2 while LR was unchanged. The enriched CO2 environment increased leaf PS rates but had no effect on LR and leaf Chl.