Two-yr-old Norway (Picea abies (L.) Karst.), red (P. rubens Sarg.), black (P. mariana (Mill.) B.S.P.) and white (P. glauca (Moench.) Voss) spruce seedlings were exposed from bud break for 35 or 63 d (4n5 h irradiance d −" ) to a gradient of biologically effective u.v.-B radiation (λ l 280-315 nm) ranging from 0n61 kJ m −# d −" to 5n99 kJ m −# d −" . No visible symptoms of u.v.-B injury were observed. Epicuticular wax production was not affected by needle exposure to increasing u.v.-B irradiance. Seven constituent classes were resolved by GC and confirmed by GC-MS in wax recovered from needles of the four species. Wax composition of Norway, black and red spruce was altered following needle exposure to increasing u.v.-B dose. White spruce wax composition was unaffected. Direction and magnitude of wax composition response was species-dependent. The proportion of nonacosane diols on Norway spruce needles increased (P 0n05) whereas that of alkyl esters decreased with increasing u.v.-B dose. The proportion of fatty acids in black spruce needle wax increased (P 0n05), and that of estolides (GC-identified) in red spruce needle wax increased (P 0n05) with increasing u.v.-B dose. Changes in wax chemical composition reported were induced following to daily, 4-h duration exposures of needles to u.v.-B centred on 1200 hours. Affected variables exhibited a continuum of response. The highest dose applied was within the range of measured or predicted increases in mid-northern latitudes. Such changes in conifer needle epicuticular wax chemical composition might result in increased seedling sensitivity to the changing atmospheric environment, especially from co-exposure to tropospheric ozone in mid-northern latitudes where much of Canada's productive forest is located.

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