DIURNAL PATTERNS OF SOYBEAN LEAF INCLINATION ANGLES AND AZIMUTHAL ORIENTATION UNDER DIFFERENT LEVELS OF ULTRAVIOLET-B RADIATION

This paper documents the diurnal pattern of heliotropic leaf movements for four different soybean (Glycine max) cultivars and its relationsh ip to increased ambient levels of ultraviolet-B radiation. Considerabl e variation in diurnal patterns of leaf movement within and among cult ivars was found, but no effect of the level of UV-B radiation was obse rved. The ranking of the four cultivars in order of decreasing sensiti vity to UV-B radiation was the same as a ranking based on midday leaf inclination, with tolerant cultivars displaying steeper leaf angles, P lants that have the ability to reduce light interception at midday, th ereby reducing light and temperature stress effects, may be better pre pared to cope with the additional effects of UV-B radiation on photosy nthesis, stomatal conductance, plant morphology, and growth.