Temporal and Fluence Responses of Tree Foliage to UV-B Radiation

Needle ontogeny of mature Scots pines under enhanced UV-B radiation

“…The present study supported the suggestion that UV-B accelerates needle development (Sullivan 1994). The microscopic observations showed that, in both treatments, 1-day-old needles were still covered by several layers of fascicular sheaths and the needles in each pair remained attached to each other (Fig.…”

“…The lower enhanced UV-B level applied in the field with natural sunlight was probably not sufficient to produce growth reduction (Allen et al 1998), because the high levels of photosynthetically active radiation (PAR) minimize UV-B-induced damage (Mirecki and Teramura 1984;Flint et al 1985;Cen and Bornman 1990;Fernbach and Mohr 1992;Jordan et al 1992;Mackerness et al 1996). In greenhouse and growth chamber experiments, it is almost impossible to achieve a natural solar spectrum and PAR levels, which is why the earlier studies showing UV-B-induced biomass losses in conifers (Kossuth and Biggs 1981;Sullivan andTeramura 1988, 1989;Fernbach and Mohr 1992;Yakimchuk and Hoddinott 1994) are not comparable to field experiments. In the field, growth reductions have only been observed in loblolly pine (P. taeda) (Sullivan and Teramura 1992;Naidu et al 1993;Sullivan et al 1996).…”

Effect of low doses of UV-A and UV-B radiation on photosynthetic activities inPhaseolus mungo L.

“…The UV-A treatment had no observable effect-on photosynthesis or productivity. Many field studies have predicted that increasing exposure to UV-B will reduce plant produtivity and photosynthesis (Teramura et al, 1990;Naidu et al, 1993;Sullivan, 1994;Nikolopoulos et al, 1995;Drilias et al, 1997). Many reports exist on the target site of UV-B radiation in PS 2 activity of the photosynthetic system of higher plants.…”

Ultraviolet-B Radiation and Photosynthesis

“…This indicates a direct inhibition to photosynthesis not related to stomatal limitation. Additional evidence for a direct effect of UV-B radiation is given by Naidu et al (1993) and Sullivan (1994), who demonstrated through carbon isotope discrimination a higher internal concentration within UV-B irradiated loblolly pine (Pinus taeda) needles. This suggests that in the absence of direct changes in stomatal conductance, UV-B radiation induces a chronic reduction in photosynthetic capacity.…”

“…However, selective filtration is imperfect as evidenced by the wide range of studies showing photosynthetic inhibition with increased UV-B radiation . Even in conifers where UV-B attenuation is high, UV-B radiation may reduce photosynthesis during the period shortly following needle elongation and emergence past the highly UV-B protective bud scales Sullivan, 1994). In addition, it is also possible that despite protective mechanisms, microsites of relatively high levels of UV-B radiation occur because of uneven distribution of screening pigments.…”