Effects of Enhanced UV-B Radiation on Agricultural Crops

Methodology for the assessment of UV-B effects on plants

experiment in a growth chamber The measurements and physical simulation of UV-B radiation in the growth chamber, greenhouse or under ambient field conditions is not straightforward. Table 1 gives a summery of methods used for the examining the effects of UV-B on plants. The general principle in the experiments to determine the effects of UV-B on plants involves the use of a UV source (a lamp) coupled with different types of filters to exclude bands of UV wavelength not desired in the experiment. The intensity of UV is varied by changing the height between the lamp source and the plant canopy. Because different biological processes exhibit different degrees of sensitivity to different wavelengths of UV-B, a mathematical response function, the action spectrum, must be used as a weighting factor to adjust the measured UV-B flux. The various sources of uncertainties in calculating biologically effective UV-B flux should be considered.

Table 1 Summery of methods used to determine the effects of UV-B on plants

Methods

Reference

Greenhouse: UV lamps and selective wavelength filters, Westinghouse FS-40 sun lamp frames with cellulose acetate or Mylar type S filters		Dumpert & Knacker (1985) Mirecki & Teramura (1984)
Growth chamber: UV-B lamps, simulated PAR (photosynthetic active radiation) and selective wavelength cut-off filters		Tevini & Iwanzik (1986)
Field exposure: FS-40 sun lamps coupled with Aclar, Mylar and cellulose acetate filters, Modulated fluorescent lamp system for supplementing natural UV-B		Becwar et al. (1982) Lydon et al. (1986) Caldwell et al. (1983a)

UV-B effects on plants

Photosynthetic Responses of Cotton to UV Agricultural scientists have responded with a series of pioneering investigations on the effect of artificial and solar UV radiation upon plant growth and development. A great variety of physiological and morphological plant responses to UV radiation have been subsequently demonstrated over the past years. Most of these experiments, however, have employed UV lamps which usually emit radiation quite unlike the radiation present in the normal terrestrial solar spectrum. The importance of solar angle, atmospheric turbidity, elevation above the sea level, cloud cover, total atmospheric ozone column, and the UV albedo of the earth's surface with respect to the total UV irradiation intensity and wavelength composition should be considered in UV radiation of natural environments. Though not all the plant responses demonstrated as the result of UV radiation are considered as damaging or disadvantageous for the plant; the majority of evidence indicates that UV irradiation is usually detrimental, particularly UV-B irradiation (Caldwell, 1971). In this section a summery of the UV-B effects on crops from the literature will be presented. The growth of many plant species is reduced by enhanced levels of UV-B radiation (Teramura et al., 1989). Sunburn cotton leaf The enhanced UV-B radiation generally has negative impacts on growth, yield and quality of some crop plants such as soybean, winter wheat, rice, sorghum, cotton and corn. The response varies with different plant species. Some are very sensitive and some are least sensitive. With enhanced UV-B radiation photosynthesis decreases, plant height and leaf area decrease, dry matter production, yield and quality reduces in many crops. In the study conducted by Tevini et al. (1991b) plant height, leaf area, and the dry weight of sunflower, corn, and rye seedlings were significantly reduced with enhanced UV-B radiation. Rice is among the most important crop plants in the world. Sixteen rice cultivars from several different geographical regions were grown in greenhouses with supplemental levels of UV-B radiation (Teramura et al., 1991). Alterations in biomass, morphology, and maximum photosynthesis were determined. Approximately one-third of all cultivars tested showed a statistically significant decrease in total biomass with increased UV-B radiation. For these sensitive cultivars, leaf area and tiller number were also significantly reduced. Photosynthetic capacity, as determined by oxygen evolution, declined for some cultivars. In a six year field study of a UV-sensitive soybean, Teramura et al. (1990) presented a statistically significant 19%-25% reduction in seed yield in five of the six years under a 25% ozone reduction level.

Interests

A wide range of UV impact research problems have been addressed by the center coordinated by Dr. Wei Gao. We have developed extensive collaboration and interaction with researchers in agricultural, natural resources, and science communities. Many Application studies on UV are ongoing:

Measurement and modeling of UV-B and UV-A irradiance in and under canopies of vegetation
A 3-Dimensional model was developed to predict the UV-B and UV-A irradiance for horizontal surfaces in open canopies. Tests of the model accuracy were made using field measurements in an open canopy apple orchard and in a closed canopy of maize for cloudless sky conditions. Measured and predicted values generally agreed well. The model can serve as a much-needed tool to examine UV loading of people and other life in and below tree and other vegetation canopies. Research conducted in cooperation with Dr. Richard Grant at Purdue University and Dr. Gordon Heisler at USDA Forest Service.

Effects of UV-B radiation on cotton growth, development and physiology experimentation and model development
This work addresses our long-term goal of understanding the interactive effects of environmental factors including UV-B radiation on cotton growth, development and yield. The objectives of this study are to test the hypothesis that elevated UV-B radiation will modify the response of transpiration, respiration, carbon acquisition, development, reproduction and yield of cotton, and to understand the physiological, anatomical and phenological basis of these effects. This study will use an internationally unique system of daylight chambers that allow the growth of row crops under complete control of microclimate and atmosphere, with simultaneous precise monitoring of water, carbon, and nitrogen balance throughout the experimental period of the crop. We intend to incorporate the effects of UV-B radiation effects into a physiologically-based crop model, GOSSYM, to be used for impact analysis in the fourteen Southern contiguous states cotton cropping regions of the U.S. This research effort is ongoing in cooperation with the research group of Dr. K. Raja Reddy at Mississippi State University.

Evaluation of the influence of epicuticular waxes on the optical properties of leaves, stalks, and canopies of a range of Sorghum cultivars
This work will provide understanding as to the leaf characteristics that cause UV-B leaf reflectance, give useful information in the estimation of the UV-B reflectance of any plant leaf given the characteristics of the leaf surface, and assist in the understanding of how Sorghum thrives in low latitude areas where UV-B irradiance is high. This research activity is ongoing in cooperation with the research group of Dr. Richard Grant at Purdue University.

Evaluation of the impact of heliotropism on the reported susceptibility of various soybean cultivars
This work will provide greater understanding of the risk of soybean to enhanced UV-B effects, and can also lead to a means of providing potential impact maps across the soybean growing region for various cultivars based on current and historic USDA UVB monitoring measurements. This research activity is ongoing in cooperation with the research group of Dr. Richard Grant at Purdue University.

Integrating plant biochemical and phytochemical responses to incident levels of solar UV-B radiation
This work will provide evaluation of short-term plant responses to UV-B such as leaf development, foliar chemistry (photosynthetic and putative UV-screening phenolics) and level of DNA dimmers produced in plants developing under contrasting UV-B environments. These responses will be linked with ambient UV-B fluxes obtained from the USDA UV-B monitoring network. The research results could also lead to further understanding about the mechanisms of UV-B responses. Tested plants include soybean, cucumber, and melons. This research activity is ongoing in cooperation with the research group of Dr. Joseph Sullivan at the University of Maryland.

UV, abiotic and biotic components of production and decomposition in shortgrass steppe: interactions with CO₂ enrichment
This work will investigate the effects of UV and moisture on decomposition and address an important UV plus CO₂ interaction. We intend to assess UV effects on decomposition of plant tissues and fibre qualities, and assess the effects of UV in very wet, average, and very dry years on the decomposition of shortgrass steppe vegetation. This research activity is ongoing in cooperation with the research group of Dr. Daniel Milchunas at Colorado State University.

References

Becwar, M.R., F.D. Morre III, and M.J. Bureke. 1982. Effects of depletion and enhancement of ultraviolet-B (280-315nm) radiation on plants grown at 3000 m elevation. J. Amer. Soc. Hort. Sci., 107: 771-779.
Biggs, R.H., S.V. Kossuth, and A.H. Teramura. 1981. Response of 19 cultivars of soybeans to ultraviolet-B irradiance. Physiol. Plant., 53: 19-26.
Bornman, J.F. 1989. Target sites of UV-B radiation in photosynthesis of higher plants. J. Photochem. Photobiol. B: Biol. 4: 145-158.
Caldwell, M.M. 1971. Solar UV irradiation and growth and development of higher plants. p. 131-177. In A.C. Giese (ed.) Photophysiology, Volume 4.
Caldwell, M.M., L.O. Bjorn, J.F. Bornman, S.D. Flint, G. Kulandaivelu, A.H. Teramura, and M. Tevini. 1998. Effects of increased solar ultraviolet radiation on terestrial ecosystems. J. Photochem. Photobiol. B: Biol., 46(1-3): 40-52.
Krupa, S.V., R.N. Kickert. 1989. The greenhouse effect impacts of ultraviolet-B (UV- B) radiation, carbon dioxide (CO₂), and ozone (O₃) on vegetation. Environmental Pollution, 61: 263-393.
Madronich, S., R.L. McKenzie, L.O. Bjorn, and M.M. Caldwell. 1998. Changes in biologically active ultraviolet radiation reaching the Earth's surface. J. Photochem. Photobiol. B: Biol., 46(1-3): 5-19.
Teramura, A.H., M. Tevini and W. Iwanzik. 1983. Effects of ultraviolet-B irradiance on plants during mild water stress. I. Effects on diurnal stomatal resistance. Physiol Plant., 57: 175-180.
Teramura, A.H., and N.S. Murali. 1986. Intraspecific differences in growth and yield of soybean exposed to ultraviolet-B radiation under greenhouse and field conditions. Environ. and Experi. Botany. 26: 89-95.
Teramura, A.H., J.H.Sullivan, and J.Lydon. 1990. Effects of solar UV-B radiation on Soybean yield and seed quality: a six-year field study. Physiologia Plantarum. 80: 5-11.
Teramura, A.H., and J.H. Sullivan. 1991. Potential effects of increased solar UV-B on global plant productivity. p. 625-634. In E. Riklis (ed.) Photobiology, Plenum Press, New York.
Tevini. M., and A.H. Teramura. 1989. UV-B effects on terrestrial plants. Photochem. Photobiol. 50:479-487.