Alan H. Teramura
University of Maryland, College Park
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Photochemistry and Photobiology | 1989
Manfred Tevini; Alan H. Teramura
The potential impacts of an increase in solar UV‐B radiation reaching the Earths surface due to stratospheric ozone depletion have been investigated by several research groups during the last 15 years. Much of this research has centered on the effects of plant growth and physiology under artificial UV‐B irradiation supplied to plants in growth chambers or greenhouses. Since these artificial sources do not precisely match the solar spectrum and due to the wavelength dependency of photobiol‐ogical processes, weighting functions, based on action spectra for specific responses, have been developed to assess the biological effectiveness of the irradiation sources and of predicted ozone depletion. Recent experiments have also utilized artificially produced ozone cuvettes to filter natural solar radiation and simulate an environment of reduced UV‐B for comparative purposes.
Journal of Photochemistry and Photobiology B-biology | 1998
Martyn M. Caldwell; Lars Olof Björn; Janet F. Bornman; Stephan D. Flint; G. Kulandaivelu; Alan H. Teramura; Manfred Tevini
Elevated solar UV-B radiation associated with stratospheric ozone reduction may exert effects on terrestrial ecosystems through actions on plants, microbes, and perhaps on some animals. At the ecosystem level, the effects are less well understood than at the molecular and organismal levels. Many of the most important, yet less predictable, consequences will be indirect effects of elevated UV-B acting through changes in the chemical composition and form of plants and through changes in the abiotic environment. These indirect effects include changes in the susceptibility of plants to attack by insects and pathogens in both agricultural and natural ecosystems; the direction of these changes can result in either a decrease or an increase in susceptibility. Other indirect effects of elevated UV-B include changes in competitive balance of plants and nutrient cycling. The direct UV-B action on plants that results in changes in form or function of plants appears to occur more often through altered gene activity rather than damage. The yield of some crop varieties can be decreased by elevated UV-B, but other varieties are not affected. Plant breeding and genetic engineering efforts should be able to cope with the potential threats to crop productivity due to elevated UV-B. For forest trees, this may be more difficult if effects of elevated UV-B accumulate over several years. All effects of elevated UV-B radiation must be considered in the context of other climate changes such as increased temperature and levels of carbon dioxide, which may alter the UV-B responses, especially for plants. The actions of elevated carbon dioxide and UV-B appear to be largely independent, but interactions occur between changes in UV-B and other factors. Other ecosystem-level consequences of elevated UV-B radiation are emerging and their magnitude and direction will not be easily predicted.
Photosynthesis Research | 1994
Alan H. Teramura; Joe H. Sullivan
The photosynthetic apparatus of some plant species appears to be well-protected from direct damage from UV-B radiation. Leaf optical properties of these species apparently minimizes exposure of sensitive targets to UV-B radiation. However, damage by UV-B radiation to Photosystem II and Rubisco has also been reported. Secondary effects of this damage may include reductions in photosynthetic capacity, RuBP regeneration and quantum yield. Furthermore, UV-B radiation may decrease the penetration of PAR, reduce photosynthetic and accessory pigments, impair stomatal function and alter canopy morphology, and thus indirectly retard photosynthetic carbon assimilation. Subsequently, UV-B radiation may limit productivity in many plant species. In addition to variability in sensitivity to UV-B radiation, the effects of UV-B radiation are further confounded by other environmental factors such as CO2, temperature, light and water or nutrient availability. Therefore, we need a better understanding of the mechanisms of tolerance to UV-B radiation and of the interaction between UV-B and other environmental factors in order to adequately assess the probable consequences of a change in solar radiation.
Trends in Ecology and Evolution | 1989
Martyn M. Caldwell; Alan H. Teramura; Manfred Tevini
There is compelling evidence that a general erosion of the global ozone layer is occurring. Since ozone in the stratosphere absorbs much of the shortwave solar ultraviolet radiation (UV-B), diminished ozone means that more UV-B of a very specific wavelength composition will be received at the earths surface. Evaluating the implications for vegetation involves consideration of the wavelength specificity of biological photochemical reactions and their sensitivity to the extant and future solar spectrum. Recent research suggests the occurrence of direct damaging reactions and of indirect morphological and chemical responses with implications at the community and ecosystem levels.
Plant Physiology | 1993
Elizabeth M. Middleton; Alan H. Teramura
The increase in ultraviolet-B (UV-B; 0.290–0.320 [mu]m) radiation received by plants due to stratospheric ozone depletion heightens the importance of understanding UV-B tolerance. Photosynthetic tissue is believed to be protected from UV-B radiation by UV-B-absorbing compounds (e.g. flavonoids). Although synthesis of flavonoids is induced by UV-B radiation, its protective role on photosynthetic pigments has not been clearly demonstrated. This results in part from the design of UV-B experiments in which experimental UV-A irradiance has not been carefully controlled, since blue/UV-A radiation is involved in the biosynthesis of the photosynthetic pigments. The relationship of flavonoids to photosynthetic performance, photosynthetic pigments, and growth measures was examined in an experiment where UV-A control groups were included at two biologically effective daily UV-B irradiances, 14.1 and 10.7 kJ m-2. Normal, chlorophyll-deficient, and flavonoid-deficient pigment isolines of two soybean (Glycine max) cultivars that produced different flavonol glycosides (Harosoy produced kaempferol, Clark produced quercetin and kaempferol) were examined. Plants with higher levels of total flavonoids, not specific flavonol glycosides, were more UV-B tolerant as determined by growth, pigment, and gas-exchange variables. Regression analyses indicated no direct relationship between photosynthesis and leaf levels of UV-B-absorbing compounds. UV-B radiation increased photosynthetic pigment content, along with UV-B-absorbing compounds, but only the former (especially carotenoids) was related to total biomass (r2 = 0.61, linear) and to photosynthetic efficiency (negative, exponential relationship, r2 = 0.82). A reduction in photosynthesis was associated primarily with a stomatal limitation rather than photosystem II damage. This study suggests that both carotenoids and flavonoids may be involved in plant UV-B photoprotection, but only carotenoids are directly linked to photoprotection of photosynthetic function. These results additionally show the importance of UV-A control in UV-B experiments conducted using artificial lamps and filters.
Archive | 1993
Janet F. Bornman; Alan H. Teramura
Determination of spectral radiation within plant tissues is normally complicated by the intricate path taken by photons of light through the tissue as a result of scattering, internal reflection, and absorption, none of which occurs in a uniform way. Methods which have been employed to estimate the penetration of radiation into plant tissues have included theoretical calculations, measurements of whole leaf or epidermal reflectance and absorptance, and the direct measurement of the internal spectral regime using fiber optics.
Environmental and Experimental Botany | 1986
Alan H. Teramura; N. S. Murali
Abstract Twenty-three soybean [ Glycine max (L.) Merr.] cultivars were grown in a greenhouse under a daily dose of either 0 or 10.1 kJ/m 2 biologically effective ultraviolet-B (UV-B BE ) radiation until reproductive maturity. Of these, six selected cultivars were also grown in the field with similar enhanced levels of UV-B. UV-B radiation substantially affected vegetative growth and seed yield in both environments. The magnitude of response varied intraspecifically and was character specific. Under both greenhouse and field conditions, Forrest was the most tolerant to UV-B radiation based upon a combination of responses including plant height, leaf area, total dry weight and seed yield. Using the same criteria, Shore and York were the most susceptible under greenhouse and field conditions, respectively. Additional comparisons revealed that UV-B sensitivity based on vegetative parameters was similar between greenhouse and field observations but based on seed yield differed markedly. This discrepancy might be related to environmental differences, particularly in the level of visible radiation between the two growth regimes.
Trees-structure and Function | 1992
Joe H. Sullivan; Alan H. Teramura
SummaryDepletion of stratospheric ozone and the resulting increase in ultraviolet-B (UV-B) radiation may negatively impact the productivity of terrestrial ecosystems. This concern has led to a number of studies that report the influence of supplementing UV-B radiation on plant growth and development. However, only two of these field studies have included tree species and both were singleseason experiments. In this study, loblolly pine (Pinus taeda L.) from seven seed sources was grown under natural and supplemental levels of UV-B radiation. Irradiation treatments were continued for three seasons on plants from four of the seven groups and for 1 year only for three groups. The supplemental irradiances simulated those that would be anticipated with stratospheric ozone reductions of 16% and 25% over Beltsville, Md. The effects of UV-B radiation during the 1st year on plant growth varied among the seed sources. The growth of plants from two of the seven seed sources tested showed significant reductions following a single irradiation season and plants from one group tended to be larger under increased UV-B radiation. However, after 3 years of supplemental irradiation, plant biomass was reduced in all four groups by 12–20% at the highest simulated ozone depletion. These results suggest that the effects of UV-B radiation may accumulate in trees and that increased UV-B radiation could significantly reduce the growth of loblolly pine over its lifetime. However, they also point to a need for multiple season research in any analysis of potential consequences of global change on the long-term growth of trees.
Photochemistry and Photobiology | 1986
N. S. Murali; Alan H. Teramura
Abstract— Soybeans [Glycine max (L) Merr. cv Essex] were grown in field plots during May‐October 1985 under ambient and an enhanced level of ultraviolet‐B (UV‐B) radiation (supplemental daily dose: 5.1 effective kJ m‐2). They were either subjected to water stress or supplementally irrigated, resulting in a 2.0 MPa lower soil water potential in stressed plots. Increased levels of UV‐B radiation reduced leaf area, total plant dry weight and net photosynthesis under well‐watered conditions, but no significant UV‐B effects were detected in plants concurrently subjected to water stress. The insensitivity of growth and net photosynthesis to UV‐B radiation in water‐stressed plants may be related to anatomical and biochemical changes induced by water stress. These include an increase in the concentration of UV absorbing compounds in leaf tissues and leaf thickening.
Photochemistry and Photobiology | 1988
N. S. Murali; Alan H. Teramura; Stephen Randall
Abstract— Soybeans (Glycine max [L.] Men. cvs. Essex and Williams) were grown in an unshaded greenhouse under two levels of biologically effective ultraviolet‐B (UV‐BBE) radiation (effective daily dose: 0 and 11.5 kJ m‐2) for 34 days. Ultraviolet‐B radiation reduced leaf area and total plant mass in Essex but these parameters were unaffected in Williams. Differences in both anatomical and biochemical characteristics were found between cultivars. Some of these differences were inherently distinct between cultivars while others were variably induced by UV treatment. Specific leaf weight. an estimate of leaf thickness, was unchanged in Essex but increased in Williams with UV‐B irradiation. The relative increase in concentration of UV‐absorbing compounds in leaf tissues after UV‐B irradiation was greater in Williams. The composition of UV‐absorbing compounds in leaf tissues differed between the two cultivars but was unaffected by UV‐B radiation. Although total soluble proteins and total peroxidase activity were similar between cultivars, several electrophoretically distinct peroxidase activities were detected. Therefore, the intraspecific variation in UV‐B sensitivity found in soybean appears to be correlated with a suite of anatomical and biochemical differences, including leaf thickness, composition and concentration of UV‐absorbing compounds in leaf tissues, and possibly differences in peroxidase activities.