title: Light-energy processing and freezing-tolerance traits in red spruce and black spruce: species and seed-source variation.
abstract: Red spruce (Picea rubens Sarg.) and black spruce (Picea mariana (Mill.) B.S.P.) are genetically and morphologically similar but ecologically distinct species. We determined intraspecific seed-source and interspecific variation of red spruce and black spruce, from across the near-northern margins of their ranges, for several light-energy processing and freezing-tolerance adaptive traits. Before exposure to low temperature, red spruce had variable fluorescence (Fv) similar to black spruce, but higher photochemical efficiency (Fv/Fm), lower quantum yield, lower chlorophyll fluorescence (%), and higher thermal dissipation efficiency (qN), although the seed-source effect and the seed-source x species interaction were significant only for Fv/Fm. After low-temperature exposure (-40 degrees C), red spruce had significantly lower Fv/Fm, quantum yield and qN than black spruce, but higher chlorophyll fluorescence and relative fluorescence. Species, seed-source effect, and seed-source x species interaction were consistent with predictions based on genetic (e.g., geographic) origins. Multi-temperature exposures (5, -20 and -40 degrees C) often produced significant species and temperature effects, and species x temperature interactions as a result of species-specific responses to temperature exposures. The inherent physiological species-specific adaptations of red spruce and black spruce were largely consistent with a shade-tolerant, late-successional species and an early successional species, respectively. Species differences in physiological adaptations conform to a biological trade-off, probably as a result of natural selection pressure in response to light availability and prevailing temperature gradients.
authors.affiliation: Natural Resources Canada, Canadian Forest Service-Atlantic Forestry Centre, P.O. Box 4000, Fredericton, NB E3B 5P7, Canada.
authors.forename: John E
authors.initials: JE
authors.lastname: Major
authors.forename: Debby C
authors.initials: DC
authors.lastname: Barsi
authors.forename: Alex
authors.initials: A
authors.lastname: Mosseler
authors.forename: Moira
authors.initials: M
authors.lastname: Campbell
authors.forename: Om P
authors.initials: OP
authors.lastname: Rajora
mesh_terms: D002734:Chlorophyll / Q000502:physiology; D005615:Freezing; D014644:Genetic Variation / Q000502:physiology; D008027:Light; D028222:Picea / Q000502:physiology*; D012639:Seeds / Q000502:physiology; D013696:Temperature; D014197:Trees / Q000502:physiology*
chemical_list: D002734:Chlorophyll