Plant Responses to Current Solar Ultraviolet‐B Radiation and to Supplemented Solar Ultraviolet‐B Radiation Simulating Ozone Depletion: An Experimental Comparison^¶

Abstract

Field experiments assessing UV‐B effects on plants have been conducted using two contrasting techniques: supplementation of solar UV‐B with radiation from fluorescent UV lamps and the exclusion of solar UV‐B with filters. We compared these two approaches by growing lettuce and oat simultaneously under three conditions: UV‐B exclusion, near‐ambient UV‐B (control) and UV‐B supplementation (simulating a 30% ozone depletion). This permitted computation of “solar UV‐B” and “supplemental UV‐B” effects. Microclimate and photosynthetically active radiation were the same under the two treatments and the control. Excluding UV‐B changed total UV‐B radiation more than did supplementing UV‐B, but the UV‐B supplementation contained more “biologically effective” shortwave radiation. For oat, solar UV‐B had a greater effect than supplemental UV‐B on main shoot leaf area and main shoot mass, but supplemental UV‐B had a greater effect on leaf and tiller number and UV‐B‐absorbing compounds. For lettuce, growth and stomatal density generally responded similarly to both solar UV‐B and supplemented UV‐B radiation, but UV‐absorbing compounds responded more to supplemental UV‐B, as in oat. Because of the marked spectral differences between the techniques, experiments using UV‐B exclusion are most suited to assessing effects of present‐day UV‐B radiation, whereas UV‐B supplementation experiments are most appropriate for addressing the ozone depletion issue.

Ambient UV‐B radiation decreases photosynthesis in high arctic Vaccinium uliginosum

“…This is different from earlier findings of UV-B promoted senescence in beech (Zeuthen et al 1997). Although difficulties in results comparisons because of different methodologies, supplemental UV-B vs UV-B exclusion, have been pointed to , Rousseaux et al 2004), several mechanisms have been suggested to be responsible for UV-B-induced stress on photosynthesis. Effects on gene expression in field conditions have been shown (Keiller et al 2003), while indoor supplementation studies have identified changes in stomatal conductance (Negash andBjörn 1986, Teramura et al 1983), Rubisco content, reductions in capacity for photosynthetic electron transport (J max ) and maximum carboxylase activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (V c,max ) , He et al 1993, Jordan et al 1992 as possible limitations on photosynthesis.…”

Unravelling the neglected role of ultraviolet radiation on stomata: A meta‐analysis with implications for modelling ecosystem–climate interactions

“…Indeed, when analysing results as a function of experimental design, UV‐effects on stomatal size are strongly linked with supplementation experiments, that is, exposure to above aUV doses. Thus, supplementation experiments yield different results than exclusion experiments, consistent with earlier observations (i.e., Rousseaux et al, 2004). Further, the analysis showed that the effect of supplemental UV doses was clearly notable in environmentally relevant UV field studies.…”

Integration and scaling of UV‐B radiation effects on plants: from DNA to leaf

“…The leaf growth process is driven initially by active cell division, followed by cell expansion and differentiation, and leaf maturity (Beemster et al 2005). Ultraviolet radiation may inhibit cell division (Gonz alez et al 1998;Rousseaux et al 2004), cell expansion (Wargent et al 2009b;Hectors et al 2010), or both (Hopkins et al 2002;Hofmann et al 2003;Wargent et al 2009b). While the connection between UV-B radiation, induction of DNA damage, and cell cycle arrest or apoptosis seems clear (Britt 1996;Lo et al 2005;Weber 2005;De Lima-Bessa et al 2008), the mechanisms of UV-B radiation-induced reduced cell expansion rates are less understood (Hectors et al 2010).…”