Donald T. Krizek

Photochemical reduction of iron. I. light reactions

Abstract The role of spectral quality in the photochemical reduction of Fe3+ in vitro was investigated under various lamps to determine the basis for severe chlorosis observed in certain species and cultivars under low pressure sodium (LPS) lamps when used as a sole source of artificial light in plant growth chambers. The comparative efficacy of LPS and cool white fluorescent (CWF) lamps was evaluated by means of an automated spectroradiometer with capability of measuring spectral irradiance every nanometer from 250 nm to 840 nm; by visible appearance of the plants (e.g., extent of greening and morphological development); by physiological measurements (e.g., of biomass and chlorophyll content); and by use of ferrozine as a chemical actinometer. Reduction of Fe3+ to Fe2+, measured as Fe2+ ferrozine (at 562 nm) was more than 4 times as great under CWF lamps, which emit appreciable amounts of UV and blue irradiance, as under LPS lamps, which are deficient in these wavelengths. By use of appropriate filters t...

A Four-Year Study of Biomass Production of Eastern Gamagrass Grown on an Acid Compact Soil

A field study was conducted from 1997 to 2000 to determine the biomass production of ‘Pete’ eastern gamagrass [Tripsacum dactyloides (L.) L.] grown on a restrictive (acid compact) soil on six unlimed sites located on the North Farm at the Beltsville Agricultural Research Center in Beltsville, MD. Total biomass from two cuttings in 1997, 1998, and 2000 averaged 4261, 4995, and 6611 kg ha−1, respectively, despite deficits in moisture during those years. A single cutting in July 1999 averaged 2288 kg ha−1. Overall biomass varied more than two-fold for the six sites. Significant differences in biomass were found among sites, years, and harvests. In general, biomass varied with position on the slope, bulk density, and depth of the topsoil, but not with pH. The average biomass was generally lowest at the top of the slope where the thickness of the Ap horizon was relatively thin and the soil was extremely acidic (pH 4.3–4.4) (1:1 soil–water). High silt content and low bulk density of the soil were associated with highest biomass; rainfall distribution also appeared to be important. Eastern gamagrass at Sites 4 to 6 at the top of the slope generally had a low pH (4.3–4.4), high penetrometer resistance, and high bulk density. Penetrometer readings were lower between rows than within rows at the 5 cm depth. There was no significant relationship between bulk density and penetrometer readings, but biomass appeared to be related to bulk density. Dry weight of roots was reduced by increasing bulk density (r2=0.57) and also reduced at depths below 15 cm. Despite adverse stress imposed by shallow top soil, low pH, high bulk density, and moisture deficits, eastern gamagrass produce relatively high biomass. These results demonstrate the resilience of eastern gamagrass to an acid compact soil and indicate that this species is suited for reclamation of acid compact soils and for producing high quality forage on marginal lands, when supplied with adequate NPK.

Fluorescence imaging system: application for the assessment of vegetation stresses

As a part of an ongoing laser induced fluorescence (LIF) project, out laboratories have developed a fluorescence imaging system (FIS) to acquire fluorescence images at wavelengths centered at 450 nm, 550 nm, 680 nm, and 740 nm. The system consists of ultraviolet (UV) fluorescent lamps as an exciting source, automated filter wheel, and charge coupled device (CCD) camera. The automated filter wheel and CD camera are controlled by a microcomputer via a computer interface,a nd digital images are captured. The FIS is capable of capturing steady state fluorescence and chlorophyll fluorescence induction images. Experimental studies were conducted to demonstrate the utility of the FIS. One such study included experiments to observe the effects of ethylenediurea (EDU) in soybean leaves with FIS. Five different concentrations of EDU were sued to establish a doe-response relationship. Although visual effects of EDU treatment were not apparent, the intensities of the fluorescence images of the plant leaves varied depending on the EDU concentration, the location on the leaf surface and the emission wavelength. EDU appeared mainly to affect the photosynthetic apparatus causing non-uniform increases in red and far-red fluorescence. Ratio images of red-green and blue/far-red were found to be sensitive indicators in detecting EDU effects. A ratio of fluorescence induction to steady state fluorescence had a curvilinear relationship with EDU-dosage. Such kinetic measurements can be used to assess photosynthetic activity in response to a range of chemical and environmental stresses. This study demonstrates that FIS is an excellent tool to detect stress symptoms before the onset of visible injury. It will enhance our understanding of the interactions among photosynthetic activity, vegetative stresses and fluorescence responses. Characterization of steady state fluorescence patterns in leaves is of significant value in our LIF research studies, and images taken with FIS greatly complement non-imaging fluorescence measurements by finding the spatial distribution of fluorescence in leaves.

Evaluating UV-B effects and EDU protection in soybean leaves using fluorescence.

Abstract A growth-chamber experiment was conducted to evaluate whether ethylenenediurea (EDU), a chemical shown to be protective against ozone pollution, could ameliorate foliar damage induced by ultraviolet-B (UV-B) radiation exposure in ‘Roanoke’ soybean (Glycine max L.), a UV-B–sensitive cultivar, and whether these effects could be discriminated using fluorescence (F) observations. The experiment had four treatment groups: control; biologically effective UV-B (18 kJ m−2 day−1); EDU (500 μmol mol−1); and both UV-B and EDU (UV/EDU). Measurements included photosynthetic pigments, F image system (FIS) images of adaxial surfaces in four spectral regions (blue, green, red and far-red) and F emission spectra of the pigment extracts produced at two excitation wavelengths, 280 nm (280EX) and 380 nm (380EX). Several F ratios from 280EX, 380EX and the FIS images successfully separated the low UV vs high EDU group responses based on means alone, with intermediate values for controls and the combined UV/EDU groups. A UV-B/blue emission ratio, F315/F420 (280EX), was correlated with chlorophyll content (μg cm−2)(R = 0.88, P < 0.001), as was a ratio of emissions at two UV-A wavelengths: F330/F385 (280EX) (R = 0.87). These two 280EX ratios were also linearly correlated with emission ratios produced by 380EX, such as the far-red/green ratio, F730/F525 (380EX) (R = 0.92, P < 0.001), and clearly distinguished the UV-B and EDU groups separately, and which bracketed the similar intermediate responses of the UV/EDU and control groups. The FIS images additionally captured the following anatomical spatial patterns across the leaf surfaces: (1) emissions of UV-B–irradiated leaves were more uniform but lower in intensity than those of other groups; and (2) emissions of EDU-treated leaves exhibited the greatest variation in spatial patterns because veins had elevated blue F and leaf edges had enhanced red and far-red F. This experiment supports the hypothesis that EDU substantially ameliorated UV-B damage to foliage, a result that relied on the combined use of FIS images and emission spectra.

INTRODUCTION - Ultraviolet Radiation and Terrestrial Ecosystems†

Symposium-in-Print Introduction Ultraviolet Radiation and Terrestrial Ecosystemsy Donald T. Krizek* and Wei Gao Sustainable Agricultural Systems Laboratory, Animal and Natural Resources Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, MD and USDA UV-B Monitoring and Research Program, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO