Spectral balance and UV‐B sensitivity of soybean: a field experiment

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Abstract
Soybean [Glycine max (L.) Merr.] cultivar Essex was grown and tested for sensitivity to UV‐B radiation (280–320 nm) under different combinations of UV‐A (320–400 nm) and PFD (400–700 nm) radiation in four simultaneous field experiments. The radiation conditions were effected with combinations of filtered solar radiation and UV‐B and UV‐A lamps electronically modulated to track ambient radiation. Significant UV‐B‐caused decreases in total aboveground production and growth were seen only when PFD and UV‐A were reduced to less than half their flux in sunlight. When PFD was low, UV‐A appeared to be particularly effective in mitigating UV‐B damage. However, when PFD was high, substantial UV‐A did not appear to be required for UV‐B damage mitigation. Leaf chlorophyll fluorescence did not indicate photosynthetic damage under any radiation combination. With UV‐B, leaves in all experiments exhibited increased UV‐absorbing pigments and decreased whole‐leaf UV transmittance. Results of these field experiments indicate difficulties in extrapolating from UV‐B experiments conducted in glasshouse or growth cabinet conditions to plant UV‐B sensitivity in the field. Implications for UV radiation weighting functions in evaluating atmospheric ozone reduction are also raised.