摘要:

A qualitative architectural analysis conducted on young beech (Fagus sylvaticaL.), benefiting from the protection of a leaf canopy or exposed to full sunlight, revealed architectural characteristics susceptible of influencing the arrangement of vertical lateral axes entering in direct competition with the trunk and contributing to the formation of forked axes. The distinct structures of the forked trees are dependent on the absence or the presence of a superior forest canopy. Forks are formed when the following events occur in nature: monocyclic growth (formation of a single growth unit per year) and polycyclic growth (formation of numerous growth units per year) of the terminal meristem originating from the main axis, destruction of this terminal meristem, and large increases or decreases in the annual growth rate. None of these characteristics alone will determine the arrangement of a forked branch. Nonetheless, the annual fluctuations in growth rate seem to have the strongest influence. A quantitative analysis conducted on two 18-year-old groups exposed to either full sunlight (no canopy) or shade (under dense high forest) revealed that the frequency in vertical lateral axes is greater in full sunlight (0.18 – 0.45) than in shade (0.03 – 0.1). Similarly, the percentage of polycyclic shoots is greater in full sunlight (51%) than in shade (14%). However, this polycyclic growth does not seem to have a direct influence on the formation of vertical lateral axes. On the other hand, there may be an intermediary influence on apical mortality since in full sunlight the percentage of seasonally traumatized stems is greater (31%) than in shade (21%). The apical mortalities seem to stimulate the organization of the vertical branches. However, this formation of vertical lateral axes seems mainly controlled by the fluctuations in annual growth rates and more specifically by the rate of growth reached by the plant. In full sunlight, the annual stems have an average size (40 – 75 cm) notably superior to 50 cm. It is beyond this threshold of development that the observed trees produced greater annual frequencies in the appearance of vertical lateral axes. In the shade, the average size of annual stems ranged from 20 to 55 cm, but seldomly surpassed 50 cm. The annual frequency in the appearance of vertical lateral axes is negligeable.Key words: beech,Fagus sylvatica, architecture, forked branch, growth, forest canopy. [Journal translation]

ISSN:0008-4026    

DOI:10.1139/b94-213

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Eleven species ofAchnanthesfrom Signy Island, South Orkney Islands are described including one new species. Benthic algal material from a range of shallow lakes of varying trophic status was examined by light microscopy and scanning electron microscopy. Detail of morphology is provided with an overview of the taxonomic literature for each species. In all cases source descriptions are cited, and where possible holotype and lectotype material was examined. The variation between populations inhabiting different lakes is considered. An examination of the geographical distributionof Achnanthesin southern latitudes from the literature confirms numerous records of widespread occurrence in freshwater environments in sub-antarctic regions but not from higher latitudes.Key words:Achnanthes, Antarctic, taxonomy, benthic, phytogeography.

ISSN:0008-4026    

DOI:10.1139/b94-214

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

To improve understanding of light – growth response relationships in western red cedar, seedlings were grown on three environmentally comparable sites representing nearly optimum growth conditions for the species in coastal British Columbia. On each site, the seedlings were planted on transects extending from a clearcut to the interior of an adjacent old-growth stand. After three growing seasons, seedling mortality, vigour, growth characters, and foliar nutrients were compared across five light classes and between study sites using analysis of variance and related to the percentage of above-canopy light available to each seedling using regression analysis. Three-year mortality was ≤ 27%, and most mortality (≥ 85%) occurred at ≤ 20% of above-canopy light. Seedling growth improved consistently with increasing light; however, the actual growth response at > 40% of above-canopy light varied with study site. The pattern of variation in the growth characters suggested that planted seedlings were able to acclimate morphologically to varying light conditions in three structural traits typically associated with shade adaptation: specific leaf area, height to caliper ratio, and aboveground to root biomass ratio. Specific leaf area and height to caliper ratio decreased and aboveground to root biomass ratio increased with increasing light. This study does not support the contention that under optimal moisture and nutrient conditions carbohydrate deficiency increases the allocation of net biomass production to aboveground structures. We consider western red cedar in the study area to be a. very shade-and exposure-tolerant species but not one that is specifically adapted to an understory environment.Key words:Thuja plicataseedlings, light – growth response relationships, specific leaf area, height to caliper ratio, aboveground to root biomass ratio, shade tolerance.

ISSN:0008-4026    

DOI:10.1139/b94-215

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Substrates influenced germination of conidia of the mycoherbicide,Colletotrichum truncatum. Very few (< 10%) conidia germinated when incubated while suspended in water or when incubated on or in partially liquefied agar. Many (> 70%) were induced to germinate when incubated on firm agar. The percentage of germinated conidia increased as agar firmness increased. Not all solid substrates equally influenced germination. Over 50% of the conidia germinated on chromatography paper, cellulose acetate filter, or on hard (plastic cover slip) substrates. In contrast, germination was relatively poor on cellulose nitrate filter and glass cover slips. Some natural substrates of dissimilar texture (wood, live plant leaf) produced good germination. Lower O2levels or limited gas exchange for submerged conidia did not prevent germination because many conidia germinated while submerged on or between firm substrates. Subjecting conidia to motion during incubation between glass cover slips favored germ tube production rather than appressoria formation. Evidence suggests a positive germination response ofC.truncatumconidia to solid substrates that occurs prior to the well-documented thigmotropic response of germ tubes of germinated conidia.Key words:Colletotrichum truncatum, conidia germination, thigmotropism, substrate.

ISSN:0008-4026    

DOI:10.1139/b94-216

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

From 1990 to 1993, 690 small cottonwood saplings were excavated along four rivers in the Oldman River Basin to determine their method of origin. Overall, 52% began as seedlings while 48% originated through clonal mechanisms, of which 30% (of the total) were root suckers, i.e., adventitious shoots from preexisting roots, and 18% were shoot suckers, i.e., new shoots originating from buried shoots. The shoot suckers arose primarily through (i) flood training, i.e., new shoot emergence from young shoots that had been toppled and buried during flood events, and (ii) shoot regrowth following decapitation by ice scouring or animal browsing. Only two saplings originated through cladoptosis, propagation from excised shoot fragments. The proportion of seedlings versus clonally established shoots varied somewhat across years and sites. Within a site, saplings near the river's edge were more commonly seedlings, whereas saplings further from the river were more commonly root suckers. Three cottonwood species occurred in the forests studied and their reproductive strategies varied somewhat. Unlike the balsam poplar (Populus balsamifera), narrowleaf cottonwood (Populus angustifolia), and interspecific hybrids, the prairie cottonwood (Populus deltoides) did not propagate through root suckers; all species produced seedlings and shoot suckers. This study demonstrates that clonal reproduction has the potential to contribute to the regeneration of riparian cottonwood forests in southern Alberta. The contribution through clonal propagation complicates the forest population structure and should be considered in programs to conserve the remaining riparian cottonwood forests in southern Alberta and elsewhere in North America.Key words:Populus, cottonwoods, hybrid poplar, reproduction, clones, suckering, seedlings.

ISSN:0008-4026    

DOI:10.1139/b94-217

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Classificatory discriminant analysis was used as an analytical technique not only to classify specimens ofAntennaria gaspensis,Antennaria isolepis,Antennaria media,Antennaria pulvinata,Antennaria rosea, andAntennaria umbrinellabut also to define and to evaluate the classification criterion. The classification criterion was subsequently used to identify collections ofAntennaria bayardi,Antennaria brunnescens, andAntennaria foggiiwith one of the previously defined species. The latter species were consistently classified to the western Rocky Mountain speciesA.pulvinata. The disjunct Newfoundland populations ofA.pulvinatarepresent in part the polyploid, apomictic component of this typically western species. The eastward migration ofA.pulvinataprobably occurred during the Wisconsonian glacial period. Population numbers ofA.pulvinatain Newfoundland support the recognition of the species as threatened. Habitat destruction is the single most important factor threatening the survival of this species in Newfoundland.Key words:Antennaria pulvinata, Asteraceae, Newfoundland, disjuncts, limestone.

ISSN:0008-4026    

DOI:10.1139/b94-218

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Allozyme variation at 36 loci was estimated for 19 populations of red spruce (Picea rubensSarg.) from throughout its natural range. Average estimates of polymorphic loci (95% criterion), effective number of alleles per locus, and observed and expected heterozygosities are 23%, 1.13, 7.47%, and 7.89%, respectively. Mean genetic distance among populations is 0.007, and 93% of the genetic diversity resides within red spruce populations. Comparisons with other species indicate that red spruce is less genetically variable than most other north-temperate woody plant species. Observed heterozygosity varied significantly among geographic regions, with northern cool-temperate populations having the highest mean observed heterozygosity, followed by central montane populations, then southern isolated populations with the lowest observed heterozygosity. Regional differences in genetic variability could be due to several factors, including migration from different glacial refugia, introgression of red spruce with more genetically variable black spruce in areas of sympatry in the north, and genetic drift followed by higher than expected levels of inbreeding in small isolated southern red spruce populations. Based on genetic distance, northern cool-temperate red spruce are more closely related to nonintrogressed red spruce than to nonintrogressed black spruce, suggesting that introgression is not a major factor contributing to greater genetic variability in the northern portion of the red spruce range. Relatively high genetic differentiation among populations, higher than expected levels of inbreeding, and evidence of reduced gene flow among populations suggest that low genetic variability evident in southern red spruce populations may be a result of genetic drift followed by inbreeding.Key words:Picea rubens, genetic diversity, isozymes, population genetic structure.

ISSN:0008-4026    

DOI:10.1139/b94-219

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Fossil remains of aChamaecyparis-likemember of the Cupressaceae occur in the Upper Cretaceous Comox Formation of Vancouver Island, British Columbia. The cedar bore both flattened, opposite-branching foliage of theCupressinocladus interruptustype, as well as alternate-branching foliage more similar to that of extantThuja. Seed cones attached to the foliage are minute, about 3.0 mm in diameter, and consist of four cone scales with abaxial, leaflike umbos. Despite their small size, the structure of the cones and their disposition on axes resembles those of extant species ofChamaecyparis. It is apparent that the Comox cedar is closely related to extantChamaecyparisand appears to represent an early member of the clade. These data challenge the hypothesis thatChamaecyparisevolved from aCupressus-likeancestor with large, many-scaled seed cones and terete branches.Key words: Cupressaceae,Chamaecyparis, Late Cretaceous, fossil, seed cones, evolution.

ISSN:0008-4026    

DOI:10.1139/b94-220

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Patterns in α diversity (species richness) of submersed and floating-leafed aquatic plants were investigated for 45 lakes in the Adirondack region of northern New York State. Multiple linear regressions were used to build predictive models of species richness; the independent variables included lake surface area, approximate littoral zone area, pH, and measures of isolation and connectedness. The regression models that explained the most variance in species richness incorporated pH, a connectedness predictor, and either lake surface area or littoral zone area (r2 = 0.74). The two area measures accounted for a majority of the variance in species richness (about 57%), but neither was a superior predictor to the other. When acidic lakes were systematically removed from the multiple regression model,r2tended to increase. The coefficient of determination was maximized (atr2 = 0.822) when we limited the data set to lakes with pH > 5.6. As there was no significant correlation between pH and any of the isolation or connectedness measures we used (maximumr = 0.18), acidic lakes are not more isolated than circumneutral lakes. Point β diversity (the heterogeneity of species composition among sites) was measured for each pair of lakes. It was not strongly correlated to either the difference in surface area or the difference in pH between pairs of lakes. Standardized nestedness was calculated following Wright and Reeves (1992, Oecologia 92 : 416 – 428). Adirondack lakes are moderately nested. An implication of this is that species that are found in less diverse lakes have a 44% probability of being found in more diverse lakes.Key words: Adirondacks, aquatic plant, β diversity, biogeography, lake, nestedness, pH, species richness.

ISSN:0008-4026    

DOI:10.1139/b94-221

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Water was sprayed on the adaxial surfaces of hairy and nonhairy leaves to study the possible significance of trichomes in dew or rainwater absorption. Plant species adapted to Mediterranean climate, experiencing periodic water shortage, were used. Water retention was higher and its duration significantly longer on hairy leaves, confirming visual observations in the field. Gravimetric measurements and fluorescence microscopy with the apoplasmic indicator Calcofluor showed that surface water quickly penetrated into the mesophyll of hairy but not nonhairy leaves. The trichome did not participate in the entrance pathway. Direct absorption of water increased the water potential of water-stressed cut leaves, improving their photosynthetic performance through decreased abaxial stomatal resistance. No such effects were found in nonhairy leaves. In a long-term experiment with whole seedlings of the hairyPhlomis fruticosaL., growth rate and photosynthetic pigment content in plants receiving water only through the leaves were intermediate between those of well-watered and water-stressed plants. We conclude that leaf hairs, besides other functions, may also improve leaf water status by entrapping and retaining surface water, thus assisting in its final absorption into the mesophyll. Their contribution to drought avoidance may be critical under some circumstances.Key words: dew, drought,Phlomis fruticosaL., trichome.

ISSN:0008-4026    

DOI:10.1139/b94-222

出版商:NRC Research Press    

年代:1994

数据来源: NRC