Effects of supplemental UV‐B radiation on growth and leaf photosynthetic reactions of soybean (Glycine max)

Experiments were conducted under greenhouse conditions to investigate the effects of enhanced UV‐B radiation (280 to 320 nm) on height, fresh and dry weights, leaf chlorophyll and carotenoids, CO 2 uptake rates, and Hill activity in soybean ( Glycine max L. cv. Bragg). Plants were exposed for 6 h continuously from midmorning to midafternoon each day to UV‐B radiation which was provided by Westinghouse FS‐40 sun lamps filtered with 0.127‐mm cellulose acetate film (UV‐B enhanced) or 0.127‐mm Mylar S film (UV‐B Mylar control). Three different UV‐B enhanced radiation levels were tested: 1.09 (treatment T 1 ), 1.36 (treatment T 2 ), and 1.83 (treatment T 3 ) UV‐B sun equivalent units (UV‐B sec ) where 1 UV‐B sec = 15.98 mW·m −2 of solar UV‐B obtained by applying EXP ‐[(α‐265)/21] 2 , a weighting function that simulates the DNA absorption spectrum, to the UV‐B lamp systems. These UV‐B levels correspond to a calculated decrease in stratospheric ozone content of 6%, 21%, and 36% for treatment T 1 , T 2 , and T 3 , respectively. Daily exposure of soybean plants to UV‐B radiation significantly decreased height, fresh and dry weights, leaf chlorophyll and carotenoid contents, and CO 2 uptake rates. Leaf pigment extracted in 80% acetone from UV‐B‐treated soybean plants showed considerable increase in absorption in the wavelength region of 330 to 400 nm with increased UV‐B radiation levels. Chloroplast preparations from leaves of T 2 and T 3 plants showed significant reductions in Hill reaction measurements.