Old-growth red spruce forests as reservoirs of genetic diversity and reproductive fitness.

Old-growth forests are assumed to be potential reservoirs of genetic diversity for the dominant tree species, yet there is little empirical evidence for this assumption. Our aim was to characterize the relationship of stand traits, such as age, height and stem diameter, with the genetic and reproductive status of old-growth and older second-growth stands of red spruce (Picea rubens Sarg.) in eastern Canada. We found strong relationships between height growth (a fitness trait) and measures of genetic diversity based on allozyme analyses in red spruce. The negative relationship between height and the proportion of rare alleles suggests that high proportions of these rare alleles may be deleterious to growth performance. Latent genetic potential, however, showed a significant and positive relationship with height. Stand age was not correlated to height, but was correlated to seedling progeny height. In late-successional species such as red spruce, age and size (e.g., height and stem diameter) relationships may be strongly influenced by local stand disturbance dynamics that determine availability of light, growing space, moisture and nutrients. In larger and older stands, age appeared to provide a good surrogate measure or indicator for genetic diversity and progeny height growth. However, in smaller and more isolated populations, these age and fitness relationships may be strongly influenced by the effects of inbreeding and genetic drift. Therefore, older populations or old-growth forests may represent superior seed sources, but only if they are also of sufficient size and structure (e.g., stem density and spatial family structure) to avoid the effects of inbreeding and genetic drift. Thus, larger and older forests appear to have an important evolutionary role as reservoirs of both genetic diversity and reproductive fitness. Given the rapid environmental changes anticipated (as a result of climate change, increasing population isolation through fragmentation, or following the introduction of exotic pests and diseases) these older populations of trees may have a valuable function in maintaining the adaptive potential of tree species.

Shoot water relations of mature black spruce families displaying a genotype x environment interaction in growth rate. III. Diurnal patterns as influenced by vapor pressure deficit and internal water status.

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 (r(2) = 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 x environmental interaction in growth.

Increasing the sink:source balance enhances photosynthetic rate of 1-year-old balsam fir foliage by increasing allocation of mineral nutrients.

To determine the impact of altering the sink:source balance on gas exchange rates in 1-year-old foliage of balsam fir (Abies balsamea (L.) Mill.), seedlings were either debudded before the growing season began or left intact. To assess alternative explanations for the observed photosynthetic response, additional seedlings were variously root pruned, shaded, drought stressed or deprived of fertilizer in combination with debudding. Foliar gas exchange rates and carbohydrate concentrations, xylem water potential and current-year growth were measured on three occasions spanning the shoot extension period. In addition, growth, foliar concentrations of chlorophyll, nitrogen, phosphorus and potassium, chlorophyll fluorescence and photosynthetic rate at different CO2 concentrations were determined 1 month after shoot extension ceased. Debudded seedlings had higher photosynthetic rates than budded seedlings, and the difference increased as the growing season progressed. We observed no evidence that debudding increased photosynthetic rate by improving water relations or by reducing foliar carbohydrate concentrations. Debudding increased foliar concentrations of nitrogen, phosphorus, potassium and chlorophyll, as well as quantum yield and photochemical quenching as determined by chlorophyll fluorescence measurements. Therefore, we conclude that debudding increased the photosynthetic rate by increasing the allocation of nutrients to 1-year-old foliage, thereby enhancing the amount or activity, or both, of photosynthetic enzymes, as well as increasing chlorophyll concentration.

Growth, shoot phenology and physiology of diverse seed sources of black spruce: II. 23-year-old field trees.

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 degrees N, 77 degrees 30' W) were assessed for height growth, shoot phenology and seasonal gas exchange. The provenances were designated 7000 (Yukon, 63 degrees 34' N, 135 degrees 55' W), 6979 (Alberta 52 degrees 22' N, 115 degrees 15' W), 6908 (Ontario, 48 degrees 59' N, 80 degrees 38' W) and 6901 (Ontario, 45 degrees 10' N, 77 degrees 10' W). Trees of southern provenances (6901 and 6908) were considerably taller, and broke bud and ceased growth later than trees of northern provenances (6979 and 7000). In early spring, trees of northern provenances had higher net photosynthetic rates (P(n)) than trees of southern provenances (6908 and 6901). During midsummer, trees of Provenance 7000 generally had the highest P(n) as a result of low rates of shoot dark respiration (R(d)). Trees of northern provenances displayed an earlier autumn decline in P(n) than trees of southern provenances. Provenance differences in growth, shoot phenology and physiology agreed well with results from a greenhouse study of seedlings from the same provenances. We conclude that the poor growth performance of trees of northern provenances in Ontario was associated with: (1) a short period of shoot growth, (2) a high rate of dry matter partitioning to roots, (3) low rates of late-season P(n) in response to decreasing photoperiod, and possibly, (4) a high rate of root R(d).

Vascular compression of the duodenum.

A successfully treated case of vascular compression of the duodenum is presented. The associated factors that might have been involved in predisposing this patient to the development of an acute intermittent, yet worsening clinical picture, are discussed, as well as the possible precipitating factor. Diagnosis and management of this disease entity are discussed.