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Hybridization between red spruce (Picea rubens Sarg.) and black spruce (Picea mariana (Mill.) BSP), late- and early-successional species, respectively, has resulted in identification and management problems. We investigated the nature and magnitude of reproductive and life-cycle success barriers in controlled intra- and inter-specific crosses of red and black spruce. We quantified a number of reproductive, germination, phenological, and performance traits, and examined traits by parental pedigree and hybrid index. Species' pollen had no effect on number of aborted or nonpollinated ovules. Controlled intraspecific crosses had, on average, 6.6 times more filled seeds than interspecific crosses. Cone and seed morphometric traits were species specific, with seed traits showing negative hybridization effects on both species. Germination, cotyledon number, and seedling height had significant species-specific traits, with hybrids showing an additive or slightly negative heterosis. Severe, negative heterosis appears to be of limited importance as an isolating barrier between red and black spruce. Reproductive phenology was remarkably similar among species and hybrid progenies when grown in common garden experiments. Crossability barriers are clearly paramount in maintaining the separation of the species. Ecological separation based on ecophysiological differences (e.g., shade tolerance) also represents an important prezygotic barrier for minimizing the negative effects of hybridization (e.g., postzygotic inviability) on reproductive fitness. [ABSTRACT FROM AUTHOR]

Pressure–volume curves were constructed and shoot water potentials measured for +20-year-old black spruce (Picea mariana (Mill.) BSP) trees from four full-sib families growing on a moist site and a dry site at the Petawawa Research Forest, Ontario, to determine whether differences in diurnal water relations traits were related to productivity. To assess the basis for the observed diurnal patterns, we analyzed effects of environmental and internal water stress variables on diurnal water relations traits. Among the water relations traits examined, turgor pressure was the most sensitive, responding to site, family and environmental variables and displaying the strongest diurnal responses to varying soil water availability and atmospheric vapor pressure deficit (VPD). Overall, there was an 84% drop in turgor pressure with increasing VPD: turgor pressure fell 46% in response to the first 0.75 kPa increase in VPD, and 9.7% in response to a second 0.75 kPa increase in VPD. The families differed in water relations responses to moderate water stress, but not in responses to minor or more extreme water stresses. Thus, at a VPD of 0.5 kPa, there was an estimated 83% greater family difference in turgor pressure on the dry site compared with the moist site. Soil and atmospheric water stress appeared to exert effects in tandem to elicit these responses (r2 = 0.728). A comparison of the mechanisms of response to water deficit indicated that osmotic adjustment was more important than change in cell wall elasticity. We used a conceptual water relations model to illustrate the differences between tolerant and intolerant families in their mechanisms of water stress response. We conclude that, because genetic responses to site factors are dynamic, the integrated response over time contributes to the observed genetic × environmental interaction in growth. [ABSTRACT FROM PUBLISHER]

Pressure–volume curves and shoot water potentials were determined for black spruce (Picea mariana (Mill.) BSP) trees from four full-sib families at the Petawawa Research Forest, Ontario, Canada. Trees were sampled from a dry site in 1992 and from the dry site and a wet site in 1993. Modulus of elasticity (μ), osmotic potential at turgor loss point (Ψtlp) and relative water at turgor loss point (RWCtlp) all decreased during the growing season. Osmotic potential at saturation (Ψsat) and turgor displayed no general temporal trend. Across a range of environmental conditions, Female 59 progeny had equal or lower Ψsat, and higher or similar μ, mean turgor pressure (Px) and predawn turgor pressure (Ppd) compared with Female 63 progeny. Osmotic potential at saturation decreased as water stress increased from mild to moderate and increased as water stress increased from moderate to severe. Stable genetic differences in Ψsat were maintained by the same rate of osmotic adjustment from low to moderate water stress. Modulus of elasticity and RWCtlp decreased with decreasing water availability, whereas Ψtlp showed no response. The combined effects of Ψsat and μ resulted in no change in Ppd as water stress increased from low to moderate values, but turgor declined sharply as water stress increased from moderate to high values. We conclude that drought tolerance traits strongly influence the growth of these black spruce families across sites of varying water availability. [ABSTRACT FROM PUBLISHER]

Pressure–volume curves were determined for black spruce (Picea mariana (Mill.) BSP) trees from four full-sib families. During the first two years, trees were measured from a plantation on a dry site. In the third year, trees were sampled from the dry site and a wet site. Diurnal measurements of shoot water potential allowed in situ shoot turgor to be estimated in addition to standard water relations traits. Over all years, Female 59 progeny displayed lower osmotic potentials at saturation (Ψsat) than Female 63 progeny. Genetic differences in Ψsat were similar on both the dry and wet sites. Modulus of elasticity (μ) was greater for Female 59 progeny than for Female 63 progeny, producing a compensatory effect resulting in no genetic or site differences in osmotic potential at turgor loss point (Ψtlp) or relative water content at turgor loss point (RWCtlp). Mean and predawn shoot turgor pressures (Px and Ppd) were higher for Female 59 progeny than for Female 63 progeny and higher at the wet site than the dry site. Genotype × environment trends were observed; compared to Female 63 progeny, Female 59 progeny displayed 9.8 and 5.1% higher Ppd on the dry and wet sites, respectively, and 3.4 and 9.8% greater Ppd values in wet and dry years, respectively. Tree volume growth showed no relationship to Ψtlp or RWCtlp, but was correlated with Ψsat and Px; however, the strongest correlation was with Ppd (r = 0.90). [ABSTRACT FROM PUBLISHER]

Four sources of 23-year-old black spruce (Picea mariana (Mill.) B.S.P.) from a provenance test at the Petawawa National Forestry Institute (46° N, 77°30′ W) were assessed for height growth, shoot phenology and seasonal gas exchange. The provenances were designated 7000 (Yukon, 63°34′ N, 135°55′ W), 6979 (Alberta 52°22′ N, 115°15′ W), 6908 (Ontario, 48°59′ N, 80°38′ W) and 6901 (Ontario, 45°10′ N, 77°10′ W). [ABSTRACT FROM PUBLISHER]

We performed genetic analyses of growth, carbon isotope discrimination (delta13C), and foliar N concentration using a half-diallel subset of a 7 x 7 complete diallel planted on three sites ranging in water availability. Trees were 22 years old. Heritabilities; general and specific combining abilities; as well as phenotypic, genetic, and environmental correlations were calculated using the best linear unbiased prediction and restricted maximum-likelihood methods. Thefour traits measured showed variable levels of genetic control. The calculated heritablilities for the traits were as follows: height, 0.39 +/- 0.22 (estimate +/- SD); diameter, 0.14 +/- 0.10; delta13C value, 0.54 +/- 0.26; and foliar N, 0.00. Phenotypic correlations were moderate (r = -0.35), genetic correlations were strong (r = -0.97), and environmental correlations were weak (r = -0.18) between height growth and delta13C. The strong negative genetic correlation between delta13C and growth supports earlier work with a subset of families indicating photosynthetic differences caused genetic variation in delta13C. Inbreeding greatly decreased growth while not impacting delta13C. High heritability, lack of inbreeding depression, and low environmental correlationsindicate that a major proportion of delta13C genetic control may be relatively simple. Because delta13C is highly heritable, highly genetically correlated to growth, less environmentally sensitive than growth, and has the possibility of early selection,the trait is a good candidate trait for indirect selection for growth. [ABSTRACT FROM AUTHOR]