Research

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/COMAX, 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.

Some research results: 

• W. Gao, R.H. Grant, G.M. Heisler, and J.R. Slusser. A geometric UV-B radiation transfer model applied to agricultural vegetation canopies
• W. Gao, J. Slusser, J Gibson, G. Scott, D. Bigelow, J. Kerr, B Mc Arthur. Direct-sun column ozone retrievals by the UV multi-filter rotating shadow-band radiometer and comparison with those from brewer and dobson spectrophotometers
• R.H. Grant, G.M. Heisler, and W. Gao. Estimation of pedestrian level UV-B exposure under trees in suburban environmnets
• R.H. Grant, G.M. Heisler, W. Gao, and M. Jenks. Ultraviolet leaf reflectance of common urban trees and the prediction of reflectance from leaf surface characteristics