摘要:

Seedlings ofAbies grandis(Dougl.) Lindl. (grand fir),Lithocarpus densiflora(Hook. & Arn.) Rehd. (tanoak),Pinus ponderosaDougl. ex Laws. (ponderosa pine),Pseudotsuga menziesii(Mirb.) Franco (Douglas-fir), andArbutus menziesiiPursh (madrone) were planted in mixture and monoculture in soil collected from three adjacent forest sites in southwestern Oregon (a clearcut area, a 25-year-old Douglas-fir plantation, and a mature 90- to 160-year-old Douglas-fir - pine forest) to determine the effect of host tree diversity on retrieval of ectomycorrhizal morphotypes. In this greenhouse bioassay, 18 morphotypes of mycorrhizae were recognized overall from all soils with a total of 55 host-fungus combinations: 14 types with ponderosa pine, 14 with Douglas-fir, 10 with tanoak, 10 with grand fir, and 7 for madrone. Four genus-specific morphotypes were retrieved (three on ponderosa pine and one on Douglas-fir), even in mixture situations, demonstrating selectivity of some fungal propagules by their respective host. Five types were detected on all hosts, but not necessarily in soils from all sites. The remaining nine types were associated with two, three, or four hosts, which indicates a wide potential for interspecific hyphal linkages between trees. More morphotypes were retrieved from the monoculture treatments compared with the mixture treatments, although the differences were not significant. Several examples of acropetal replacement of one fungus by another (interpreted as succession) were recorded on all hosts during the course of the experiment. These results illustrate the importance of different host species in maintaining ectomycorrhizal fungus diversity, especially fungi with restricted host range, and the strong potential for fungal linkages between trees in forest ecosystems.Key words: fungal succession, fungal communities, compatibility,Arbutus menziesii,Pseudotsuga menziesii,Pinus ponderosa,Abies grandis,Lithocarpus densiflora.

ISSN:0008-4026    

DOI:10.1139/b99-115

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Russian olive (Elaeagnus angustifoliaL.) is an exotic tree that is invasive in western North America where it may replace native riparian cottonwood forests. We mapped the occurrence of Russian olive and measured the size, density, and age of it and cottonwood in sandbar, low-terrace, and high-terrace habitats along the lower Marias River below Tiber Dam in Montana. Russian olive occurs along the entire study reach but is more abundant near domesticated plantings. It establishes in moist lower terrace habitat as well as under mature cottonwood on high terraces. Seventy-seven percent of cottonwood trees in all size classes were damaged by beavers in low terrace sites, while only 22% of Russian olives showed damage. Since construction of Tiber Dam, cottonwood establishment has been restricted to lower terrace sites. Beaver prevent cottonwood from developing a mature canopy close to the river while having little effect on the continued invasion of Russian olive. Riparian cottonwood forests will eventually be replaced by Russian olive as old cottonwoods die on upper terraces and young plants on low terraces are removed by beaver or shaded by the less palatable species.Key words: Russian olive, cottonwood, riparian, beaver, exotic, dam.

ISSN:0008-4026    

DOI:10.1139/b99-088

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In southwestern Alberta, the prairie cottonwood (Populus deltoidesBartr.), balsam poplar (Populus balsamiferaL.), narrowleaf cottonwood (Populus angustifoliaJames), and interspecific hybrids provide the foundation of the biologically rich riparian forests. In addition to seedling-based reproduction, these cottonwoods are capable of clonal propagation, the extent of which is poorly understood. To investigate clonality in mature cottonwoods, a method for clone recognition was investigated. Between 1995 and 1997, the morphology and phenology of each tree in a mature cottonwood grove along the Oldman River were characterized. In decreasing order of utility, the characteristics most effective in revealing clones were sex, leaf shape, floral (inflorescence) phenology, and leaf phenology: flushing, senescence, and abscission. Independent traits of poplar bud gall mite (Aceria parapopuliKeifer) susceptibility and trunk architecture were less useful in clone delineation but validated the clonal determinations. Based on the analysis, the grove's 391 trunks (>10 cm diameter) included 115 genotypes, 48 single-trunked individuals, and 67 multiple-trunked clones. The clones (genets) contained from 2 to 53 trunks (ramets). It was found that 88% of trunks belonged to clonal groups, a proportion that was higher than anticipated. The extensive capacity for clonal recruitment should thus be considered in analyses of cottonwood reproductive ecology and cottonwood conservation and restoration programs.Key words: asexual reproduction, clone delineation, cottonwoods, morphology, phenology,Populus.

ISSN:0008-4026    

DOI:10.1139/b99-123

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The conservation of the remaining riparian woodlands of western North America will benefit from a better understanding of cottonwood (poplar) regeneration. Following our discrimination of the 67 cottonwood clones present in an island population of 391 trunks, the present investigation characterized the grove's clonal architecture in terms of species, sex, spatial patterns, and beaver impacts. Large clones containing up to 53 trunks occurred near the river channel in areas prone to flooding, scouring, deposition, and beaver damage.PopulussectionTacamahacaSpach. speciesPopulus angustifoliaJames andPopulus balsamiferaL. produced larger (mean diameter = 9.2 m) clones with more ramets (mean = 6.7) than the sectionAigeirosDuby speciesPopulus deltoidesBartr. (7.3 m diameter, 2.7 ramets). The increased clonal nature of theTacamahacaspecies is probably adaptive along steeper gradient streams in foothill regions where increased physical disturbance encourages clonal sprouting. Conversely,P. deltoidesoccurs along more gradually sloped reaches with finer substrates and smoother stage patterns that would favor seedling recruitment. The grove's clonal structure accounted for the female-biased sex ratio among trunks (204 females : 116 males) since the sex ratio was even among genets (49 females : 51 males). Clonality has contributed substantially to regeneration and grove composition, favoring certain genotypes and influencing woodland structural diversity and spatial distributions. Clonal characteristics differ across Alberta's cottonwood species and would influence the distribution of these native trees.Key words: asexual reproduction, beavers, clonality, cottonwoods,Populus, sex.

ISSN:0008-4026    

DOI:10.1139/b99-152

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Plants ofAtriplex sagittataBorkh. were grown under different density and (or) nutrient conditions, and the effect of stress on plant allometry and variation in particular biometrical parameters was studied. Increasing density significantly reduced total weight, basal diameter, stem length, and number of branches. Nutrient deficiency had a negative effect on the total weight and basal diameter only, and the density × nutrients interactions were all nonsignificant. Basal diameter was the best predictor of the total weight, explaining 93.6% of the variation in the whole data set. The relationship between total plant weight and basal diameter was unaffected by growth conditions, indicating that competition determined the position of a plant along the line describing the allometric relationship between both variables but did not seem to alter the relationship. However, the allometric relationships between total weight and stem height and between total weight and number of branches found at low density were significantly different from those at high density, indicating a faster increase in total weight at low densities. Branching, and consequently plant form, were affected by competition. Branch length consistently increased with total plant weight in plants grown under high density, but for low density plants, such an increase was recorded only in branches of the middle section of the stem. In each fruit type, the total weight of fruits produced was more closely predicted by branch weight than by branch length. Allometric relationships between fruit production and branch weight differed among particular fruit types, with a faster increase in the production of type A than in that of types B or C. Competition had less effect on the mean size of type B fruits compared with that of types A or C. Fruits of types C and A had higher variation in mean weight, than type B fruit. Variation in total weight of fruits per plant was of a higher order of magnitude than that in the mean fruit weight. The results show that plants ofA. sagittatagrown under contrasting conditions change both their allometry and the number of particular fruit types produced. Nevertheless, the question of whether the shift in the fruit ratio is a function of allometric constraints or the result of a basic shift in allometry needs further study.Key words: allometry,Atriplex sagittata, Chenopodiaceae, density stress, nutrient stress, heterocarpy

ISSN:0008-4026    

DOI:10.1139/b99-087

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Evolutionary relationships among 48 genera of Apiaceae (Umbelliferae) were inferred using maximum parsimony, maximum-likelihood, and neighbor-joining analyses of chloroplast DNArps16 intron and adjacentrps16 3prime exon sequences. Emphasis was placed on woody members of Apiaceae subfamily Apioideae endemic to southern Africa, a region hypothesized to be the place of origin of this largely herbaceous subfamily. The resultant phylogenies were highly concordant and indicate that the apioid generaPolemanniopsisandSteganotaeniaform a clade sister to Apiaceae subfamily Saniculoideae. The African generaAnginon,Dracosciadium,Glia,Heteromorpha, andPolemanniaalso comprise a clade and likely represent the most basal elements within Apioideae.Heteromorpha, however, is not monophyletic, withHeteromorpha arborescens(Spreng.) Cham. & Schltdl. var.abyssinica(A. Rich.) H. Wolff andHeteromorpha arborescens(Spreng.) Cham. & Schltdl. var.arborescensarising in separate subclades. Progressing up the trees,AnnesorhizathenBupleurumfall as successive sister taxa to all remaining Apioideae. The major clades recognized within subfamily Apioideae are largely congruent with those inferred using other types of molecular evidence. Sequence divergence is similar to that of other chloroplast introns, including being generally low among congeners and woody taxa. While therps16 intron has seen very little use in molecular systematic studies to date, this study demonstrates its ability to discern high-level relationships within Apiaceae.Key words: Apiaceae, Apioideae, chloroplastrps16 intron, phylogeny, southern Africa, Umbelliferae.

ISSN:0008-4026    

DOI:10.1139/b99-086

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The fate of mineral nitrogen (N) in an oligotrophic fen, located in Monts de Forez (Puy-de-Dôme department), was studied by15N tracking of 0.5 g (nitrogen)·m-2·year-1ammonitrate labelled on both ions (30% excess). Simulating atmospheric deposits, an important nutrient source in mires, N additions were made at two periods of the year, June and August, 1986, and the fate of the nitrogen was measured in October of the same year. Nitrogen recovery was measured in the living parts ofSphagnum fallaxKlinggr., aerial and hypogeous parts ofCarex rostrataStokes, and in peat. Vegetation preferably absorbed nitrogen in June, as compared to August, the period during which nitrogen allocation to hypogeous phytomasses ofCarexwas the highest. As compared toCarex,Sphagnumhas strong nitrogen assimilation and holding potentials. A nitrogen competition potential index or "nitrogen sink power" (PCN), calculated from recovery and stock data, showed thatSphagnumwas more efficient at intercepting nitrogen in August, when rainfall is the lowest in the studied area. In peat, nitrogen recovery was strongest in August. Most of the microbial processes seem to occur in the first 10 cm. Gross nitrogen mineralization and immobilization, calculated from organic matter degradation, were estimated as 11.4 and 6.9 g·m-2·year-1, respectively. The gross mineralization estimation according to the method of Fried and Dean was 17.2 g·m-2·year-1. This overestimation might be attributed to an underestimation of the nitrogen derived from input in plants and an overestimation of nitrogen from peat.Key words:15N, nitrogen balance, nitrogen uptake, competition, retention, turfigenous process

ISSN:0008-4026    

DOI:10.1139/b99-100

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

To evaluate the putative hybrid origin of fringed-orchids from York County, Ontario, morphological attributes of hybrid flowers were evaluated with respect to both a random sample of herbarium specimens and populations from the hybrid location. The putative hybrids were intermediate in spur length, petal width, and vertical distance across opening to the spur as well as in eight other quantitative characters. The hybrid is namedPlatanthera×hollandiaeCatling & Brownell (=Platanthera lacera(Michx.) G. Don ×Platanthera leucophaea(Nutt.) Lindl.). With pale greenish-white flowers, partly reflexed lateral sepals, and a horizontally linear spur opening, the putative hybrid plants resembleP. lacerabut can be readily distinguished by their relatively long spurs, relatively broad lateral petals, and ovoid instead of strap-shaped viscidium. A key including characteristics of the column is included that allows the separation of all northeastern North American fringed-orchids and their known natural hybrids.Key words: orchid, hybrid,Platanthera lacera,Platanthera leucophaea, Canada, Ontari

ISSN:0008-4026    

DOI:10.1139/b99-122

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Intrapopulational variability in the response to nutrient addition was studied in plants of the widespread annual weedChenopodium albumL. Five seed "families" (each the progeny of a single individual) were selected at random from a natural population, and the germinated seeds were grown for two generations with either a high or a low nutrient supply. Sequential harvests were performed in which we measured plant height, total biomass, leaf area, root/shoot ratios, and reproductive characteristics for each plant. The data were analysed with two- or three-way analysis of variance. The response to nutrient treatments varied among families and depended on both the particular trait considered and the stage of development. Maternal environment affected plant growth especially when the offspring was grown at low nutrient levels. Seed germination varied significantly according to both the maternal and the grand-maternal nutrient environment. The results show a high plasticity in the response to nutrient levels and the persistence of environmental effects for more than one generation.Key words:Chenopodium album, nutrients, maternal effects, phenotypic plasticity.

ISSN:0008-4026    

DOI:10.1139/b99-124

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

First-order lateral roots ofAsparagus officinalisL. have a dimorphic exodermis consisting of short and long cells. Short cells have a thickened outer tangential wall, retain their cytoplasm, appear to have high levels of Ca2+, and undergo suberization later than contiguous long cells. In regions of the root in which the dimorphic nature of the exodermis is clearly evident, short cells have numerous cortical microtubules arranged predominantly in the transverse plane in reference to the long axis of the root. Arbuscular mycorrhizal fungi (either indigenous unidentified species in field-grown plants orGlomus intraradicesSchenck & Smith in colonized plants in a growth chamber) form appressoria on epidermal cells located above exodermal short cells and infection hyphae then penetrate the outer tangential wall of short cells. A hyphal coil forms in short cells, and microtubules become closely associated with the coil; some cortical microtubules are retained in colonized short cells. A typicalArumtype of arbuscular mycorrhizal association forms in the cortex, and concomitant with this, a rearrangement of microtubules occurs. During arbuscule formation, microtubules are associated with the large trunk hypha and with the fine arbuscule branches; cortical microtubules, although reduced in number, are present. As the arbuscule degenerates, a few microtubules are still associated with the hyphal clump and many cortical microtubules, oriented primarily in a transverse plane, are present. This study shows that arbuscular mycorrhizal fungi interact closely with the microtubular component of the cytoskeleton from the earliest stages of entry through arbuscule degeneration. These results support the concept that biotrophic fungal species have evolved intimate associations with plant cells.Key words: asparagus, roots, mycorrhizas, exodermis, microtubules.

ISSN:0008-4026    

DOI:10.1139/b99-119

出版商:NRC Research Press    

年代:1999

数据来源: NRC