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.

Reproductive barriers and hybridity in two spruces, Picea rubens and Picea mariana, sympatric in eastern North America

“…They found no unique alleles in red spruce and suggested red spruce may have evolved from black spruce via allopatric speciation because of glaciation-induced isolation. Their conclusions may be logical given the limited number of loci they studied; however, red spruce has genetic traits that clearly distinguish it from black spruce, including partial sexual incompatibility (this study), seedling growth rate (this study), growth rate in the field (Johnsen et al 1998), cone, leaf, and stem morphology (Manley 1971;Johnsen et al 1998), and adaptive traits (Major et al 2003a(Major et al , 2003c. Again, we emphasize caution must be applied to interpretations based solely on molecular markers as, so far, they provide a limited (albeit still important) view of the spruce genome and that available molecular data do not reflect adaptive differences.…”

“…Ecological barriers would appear to be quite strong, given the very different ecological and adaptive traits (Major et al 2003a(Major et al , 2003c and successional roles of red and black spruce (i.e., early-vs. late-successional forest types) (Blum 1990;Viereck and Johnston 1990;Seymour 1992). However, in areas of sympatry (most of the red spruce range), particularly those dominated by human disturbances such as clearcutting, increased opportunities for natural hybridization might be expected.…”

“…As a long-lived, shade-adapted species, red spruce often responds poorly to clearcut harvesting (Major et al 2003b(Major et al , 2003c, whereas black spruce establishes and responds well. If the aim of forest management is to promote natural or artificial regeneration following forest harvesting, then it is important that species adaptation and hybridity be better understood to select the most appropriate silvicultural methods.…”

“…Interspecific hybridization with black spruce may also contribute to the decline of red spruce (Major et al 2003b). Hybridization can result in a species hybrid complex that combines the traits of both species in a way that may undermine the specific ecophysiological adaptations of both species (Major et al 2003a(Major et al , 2003c, and can cause identification and forest management problems for these otherwise ecologically distinct species (Manley 1975;Beylor 1999).…”

Comparative nutrient economy, stable isotopes, and related adaptive traits in Picea rubens, Picea mariana, and their hybrids

“…The westernmost extension of RS occurs as disjunct remnants in a highly fragmented metapopulation associated with the Algonquin Highlands of southern Ontario . Red spruce and BS occupy ecologically distinct niches with a suite of species-specific morphological allocation and light-energy processing traits (Major et al 2003a(Major et al , b, 2007a. Estimates of the extent of natural hybridization and introgression range from extensive (Morgenstern and Farrar 1964;Manley 1972;Bobola et al 1996) to minor (Gordon 1976;Manley and Ledig 1979;Mosseler et al 2000).…”