Extended Abstract (500K)5.1
Soybean heliotropism and UVB dose estimation
Cheryl I. Bawhey, Purdue Univ., West Lafayette, IN; and R. H. Grant and W. Gao
The sensitivity of soybean cultivars to enhanced ultraviolet-B (UVB) irradiance varies widely with many studies producing contradictory conclusions. These results may in part be due to differences in the radiative environment between field and greenhouse used in the sensitivity studies. Prior work has suggested that at least some of the variability seen in the sensitivity of soybean cultivars corresponds to the heliotropic response of the cultivars. Measurements of leaf orientation using a coordinate digitizing system were made on three cultivars of soybean in the field, under ambient conditions, and in the greenhouse, under both enhanced-UV lighting and incident light, in the summer of 2001. The measured heliotropic response was complex and varied widely between cultivars. The center leaflet appeared to function like a solar "rudder" while the side leaflets moved like "solar collectors". The solar incidence angles of the field plant leaves were on average smaller by 30 degrees for the central leaflet and 10-15 degrees smaller for the two side leaflets than those in the greenhouse. Measurements indicated a greater heliotropism by the UV plants due to lower light levels in the greenhouse UV area, resulting in different radiation amplification factors between the UV-treated plants and those in the field. Results of the measurements were used to predict the UVB loading on the upper leaflet of the plants to determine if significantly different doses are received by different cultivars due to their heliotropic response. This work provides greater understanding of the risk of soybeans to enhanced UVB effects.
Session 5, Radiation
Tuesday, 21 May 2002, 11:15 AM-1:30 PM
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