Effects of Ultraviolet-B Irradiance on Soybean

TLDR

Soybeans were grown in a greenhouse and their first trifoliate leaf was allowed to expand under either high or low photosynthetic photon flux density. The study employed a factorial design varying UV‑B radiation (0 or 80 mW m⁻²) and PPFD (0.8 or 1.4 mmol m⁻² s⁻¹) and measured photosynthetic parameters, enzyme activity, pigment and flavonoid levels, and leaf anatomy. Leaves grown under high PPFD were resistant to UV‑B damage, whereas those grown under low PPFD were sensitive, indicating that anatomical, morphological, physiological, and biochemical factors influence UV‑B sensitivity.

Abstract

Soybeans (Glycine max [L.] Merr. cv Essex) were grown in a green-house, and the first trifoliate leaf was either allowed to expand under a high photosynthetic photon flux density (PPFD) (1.4 millimoles per square meter per second) or a low PPFD (0.8 millimoles per square meter per second). After full leaf expansion, plants from each treatment were placed into a factorial design experiment with two levels of ultraviolet-B (UV-B) radiation (0 and 80 milliwatts per square meter biologically effective UV-B) and two levels of concomitant PPFD (0.8 and 1.4 millimoles per square meter per second) resulting in a total of eight treatments. Measurements of net photosynthesis and the associated diffusion conductances, ribulose-1,5-bisphosphate carboxylase activity, chlorophyll and flavonoid concentrations, and leaf anatomy were examined for all treatments. Leaves expanded in the high PPFD were unaffected by UV-B radiation while those expanded in the low PPFD were sensitive to UV-B-induced damage. Likewise, plants which were UV-B irradiated concomitantly with the high PPFD were resistant to UV-B damage, while plants irradiated under the low PPFD were sensitive. The results of this study indicate that both anatomical/morphological and physiological/biochemical factors contribute toward plant sensitivity to UV-B radiation.