No abstract

No abstract

No abstract

Genetic variability in three jack pine (Pinus banksiana) populations, spaced 10 km apart in southern Manitoba, was analyzed electrophoretically for 15 enzymes encoded by 20 structural loci. These populations were studied as spatial and temporal controls in an investigation of the effects of long-term gamma irradiation on boreal tree species. Individual populations were, on average, polymorphic at 53.3% of the loci and had 2.0 alleles per locus. Individual trees were heterozygous at 20.7% of their loci. An F-statistic analysis revealed an overall 10% excess of heterozygotes over Hardy–Weinberg expectations. Only 2% of the genetic variation occurred among populations. Consequently Nei's genetic distance between populations was small [Formula: see text]. The amount and disposition of the genetic variation in neighbouring populations resembled that observed by others among widely spaced populations. The similarity of the genetic structure of jack pine populations at the meso- and macro-geographic levels might result from the antagonistic effects of long distance gene flow via pollen transport (increasing homogeneity) and adaptation to fire or other patchily distributed environmental factors (reducing homogeneity).Key words: Jack pine, Pinus banksiana, allozymic variation, genetic structure.

Soil air normally contains elevated levels of CO2 relative to the atmosphere. The primary source of soil C is plant‐root and microbial respiration. The exchange of soil and atmospheric CO2 is important to many environmental concerns, such as acid rain, global warming and waste management. Proposed disposal of high‐level nuclear wastes containing primarily inorganic 14C may provide a source of 14CO2 to the atmosphere. Field and laboratory experiments show that 14CO2 soil degassing rate constants, the flux density (Bq·m2·s−1) divided by soil inventory (Bq·m−2), range from −10−7 to −10−2 s−1, and that the loss of inorganic 14C is driven primarily by gaseous diffusion. These constants are affected by soil pH and porosity, with smaller influences of soil temperature, moisture and organic matter content. Degassing rate constants derived through mass balance calculations to estimate loss differ only by 20% from direct trapping methods. Frozen soil degassing rate constants were up to 25 times smaller than lab values, indicating that annual 14C loss rates in northern climates would be lower because of reduced gaseous diffusion during the winter months. Using our field data, we recommend an annual 14C soil degassing rate constant of −1 × 10−6 s−1 for acidic soils and a value of −5 × 10−7 s−1 for calcareous soils. For probabilistic assessment modelling, we recommend a geometric mean degassing constant of −4.3 × 10−7 s−1 with a geometric standard deviation of 3.26 for three different soils. This indicates the median half‐life of 14C in surface soils is 18 d, with a 99% confidence interval of 13 h and 640 d.