摘要:

There are three primary types of graminoid-dominated communities in or near Wood Buffalo National Park, Canada: freshwater meadows and marshes composed ofCalamagrostis canadensis(Michx.) Beauv.,Carex atherodesSpreng.,Carex aquatilisWahlenb.,Scolochloa festucacea(Willd.) Link, andPoaL.; saline meadows composed ofHordeum jubatumL.,Puccinellia nuttalliana(Schult.) A.S. Hitchc.,Agropyron trachycaulum(Link) Malte,Calamagrostis stricta(Timm) Koeler, andCalamagrostis inexpansaA. Gray; and dry grasslands composed ofAgropyron trachycaulum,StipaL.,Carex siccataDewey,Carex obtusataLilj., andKoeleria macrantha(Ledeb.) J.A. Schultes f. Except for the Peace Point area, it is not known whether dry grasslands have declined in areal extent. Including various wetlands under "dry grasslands", and concluding that these areas no longer support dry grassland is misleading. Dry grasslands exist in Wood Buffalo National Park, but most graminoid-dominated communities in the park are, and have been, freshwater and saline meadows and marshes. A clear understanding of the ecological factors operating in these different ecosystems is critical to informed management.Key words: fire, grassland, prairie, vegetation, wetland, Wood Buffalo National Park.

ISSN:0008-4026    

DOI:10.1139/b99-120

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In examining dry grassland areas of Wood Buffalo National Park (WBNP), we used vascular plant indicators commonly found in the grassland landscapes in the southern and central parts of the Prairie Provinces. With distance northward the landscapes become increasingly tree-dominated and the dry grasslands have fewer dry grassland indicator species (about 40 in the area of WBNP) and become smaller in size (about 1 ha in WBNP). Key species areStipa comataTrin & Rupr.,Stipa curtiseta(A.S. Hitchc.) Barkworth, andStipa columbianaMacoun on the drier sites. Paleontological records and historical documents suggest that these remnant dry grasslands must expand during decades of drought and must contract during decades of higher summer rainfall. We hypothesize that fires might enhance dry grassland expansion by stressing and killing trees and shrubs. Southern dry grassland vascular plant species represent over 7% of the total in WBNP. It is reasonable to hypothesize that these represent special ecotypes that deserve special protection through prescribed burning.Key words: remnant grasslands,Stipaspp., climate change.

ISSN:0008-4026    

DOI:10.1139/b99-121

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

During early stand development, coniferous forests of the coastal Pacific Northwest commonly pass through a period of dense shade and intense competition during which the abundance and diversity of understory plants decline dramatically. In young, managed forests, silvicultural thinning has been proposed to enhance the structural and floristic diversity of the understory. Although germination of buried seeds is likely to be stimulated by thinning, we know little about the composition of the soil seed bank in these forests. We used the greenhouse emergence method to assess the potential contribution of the seed bank to understory reinitiation in 40- to 60-year-old, closed-canopy forests on the Olympic Peninsula, Washington. Seed banks were well developed (610-7009 germinants/m2), containing 46 native and exotic species representing a diversity of life forms. However, many common forest understory species were absent; only 11 species were typical understory plants and these comprised <10% of all germinants. In contrast, 30% of all species and 50% of all germinants were exotic, ruderal forbs. Wind-dispersed annuals and perennials dominated litter samples, whereas ruderal forbs and graminoids with limited dispersal dominated soil samples. Our results suggest that silvicultural thinning will enhance the establishment of ruderal, exotic species but will contribute little to the regeneration from buried seed of the vast majority of forest understory plants.Key words: canopy closure, forest understory, seed germination, soil seed bank, succession, understory reinitiation.

ISSN:0008-4026    

DOI:10.1139/b99-085

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Variation in belowground traits of herbaceous species may influence their ability to persist and spread during and after the closed-canopy period of forest development. In 40- to 60-year-old closed-canopy, coniferous forests of the Olympic Peninsula, Washington, we excavated root and rhizome systems of 11 herbaceous species to compare morphology, vegetative spread, and proportion of biomass in belowground structures. All species were perennial and most were rhizomatous; four species were nonclonal. Of the seven clonal species, only two (Maianthemum dilatatumandOxalis oregana) spread extensively (mean lateral spread >50 cm) by belowground perennating structures. The proportion of total biomass in belowground structures varied considerably among species (21-85%) and was higher for deciduous than for evergreen species. High variability in belowground traits suggests that multiple strategies may contribute to survival during closed-canopy conditions. For species with a high proportion of belowground biomass, we suggest that the ability to store resources or to acquire new resources through lateral spread may contribute to persistence in dense coniferous forests.Key words: biomass allocation, canopy closure, forest understory plants, rhizomes, root systems, succession.

ISSN:0008-4026    

DOI:10.1139/b99-056

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The gibberellin-deficient mutant,ga1-1(NG5) ofArabidopsis thaliana, when induced by 16-h-long days, will form floral buds. However, the flower stalk is very short and floral organs within the flowers remain undeveloped; petal growth is arrested, with the petals being scaly and translucent, the stamens are abortive, the filaments do not elongate, and the pollen does not mature. Sepals and pistils are also underdeveloped. All of the above defects of this mutant can be completely eliminated if certain gibberellins (GAs) are applied to the young floral buds. That is, the applied GA acts to normalize not only plant height but also development of floral organs, thereby yielding good seed set from self-pollination. There were appreciable differences in the efficacy of different GA structures in normalizing the various floral organs. For seed production, the order of efficacy was 2,2-dimethyl GA4> GA7> GA3= GA4> GA1> GA5= GA9. When 2,2-dimethyl GA4was used to determine an optimal GA dose, the following pattern emerged: filament elongation and pollen development, 1-10 ng; petal and pistil growth, 1 ng; sepal growth, 0.1 ng; papilla elongation, 0.01 ng. However, one application at these doses was insufficient to normalize the flowers, which were formed one after another, and a continuing supply of GA at the optimal dose was required for normal flower development and seed set. We conclude from this work that GAs play an essential role in the development of floral organs ofArabidopsisand that petals and stamens (filaments and pollen) in particular develop normally only when GAs are present at the optimal level.Key words:Arabidopsis thaliana, floral organ development, gibberellin, gibberellin-deficient mutant, petal and pollen development, reproductive function.

ISSN:0008-4026    

DOI:10.1139/b99-090

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Silica deposition in two upland rice cultivars, IRAT 109 and Moroberekan, and one lowland rice cultivar, Koshihikari, were compared. X-ray microanalysis coupled with environmental scanning electron microscopy was used to examine fresh, unfixed, hydrated samples for analyses. The results showed silica deposition in seminal roots exclusively in endodermal cells. A clear basipetal increase in Si content was found in the endodermis of all cultivars. Comparison of silicification intensity between the three cultivars showed higher amounts of Si deposited in the endodermis of upland rice cultivars. This might be related to a higher drought resistance of these types of rice. In leaves, silica deposits were present in all epidermal cells with the highest concentration in silica cells. The amount of Si deposited in leaves was several times higher than in the root endodermis. No relationship between extent of leaf epidermal silicification was found when lowland and upland cultivars were compared.Key words: endodermis, environmental scanning electron microscope (ESEM), rice, root, silica deposits, X-ray microanalysis.

ISSN:0008-4026    

DOI:10.1139/b99-043

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The water-soluble polysaccharides (F1SS) obtained from the alkali extracts of the cell wall of two strains ofPenicillium vermoeseniiBiourge,Fusarium javanicumKoorders,Fusarium solani(Martius) Saccardo, andFusarium oxysporumSchlechtendahl represented 8.7 to 10.7% of the dry cell wall material. All polysaccharides were composed of galactose (22.0-27.4%), glucose (18.4-30.3%), mannose (7.8-23.1%), and glucuronic acid (3.0-6.0%, except inF. oxysporumthat contained 16.8%). Methylation analysis and1H-NMR spectra of the polysaccharides of these fungi were similar except forF. oxysporum, which showed a higher peak of glucuronic acid than of glucose. The chemical and structural analyses performed indicated that F1SS polysaccharides of the species studied have a skeleton of beta-(1–>6) galactofuranose, fully substituted at positionsO-2 by a single residue of glucopyranose or by short side chains containing one glucuronic acid residue and beta-mannopyranose. This polysaccharide is linked to a mannose core consisting of a short chain of alpha-(1–>6)-linked D-mannopyranose. Immunological methods confirm the structural relatedness among these polysaccharides. No similarities were found with the1H-NMR spectra of F1SS polysaccharides from other species ofPenicilliumorGliocladium. These results show thatP. vermoeseniiis closer to the genusFusariumthan toPenicilliumorGliocladium.Key words:Penicillium vermoesenii, cell wall polysaccharides, chemotaxonomy, NMR, polyclonal antibodies.

ISSN:0008-4026    

DOI:10.1139/b99-046

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Two experiments were conducted onPhillyrea latifoliaL. plants exposed to increasing NaCl concentrations at the root zone in hydroponic culture. Growth, ion fluxes within the plant, and rates of excretion by glandular trichomes were measured during both salinity stress and relief periods. The reduction in relative growth rate (RGR) of plants treated with 100 and 200 mM external NaCl was more marked when RGR was calculated on a fresh weight (FW) basis than on a dry weight (DW) basis. The RGR of previously salt-treated plants, expressed on a FW basis, did not differ from that of the controls over 5 weeks of relief from stress, whereas RGR calculated on a DW basis did not fully recover. Fluxes of Na+and K+appeared highly regulated. Sodium transport to the leaf of 100 mM salt-treated plants equalled that of the controls, whereas Na+transport to the leaf was higher in 200 mM salt-treated plants. Selectivity ratio for K+and Na+transport to the leaf was increased by salt treatments. The exclusion ability for Cl-was markedly lower than that for Na+at 300 and 400 mM external NaCl. The excretion of Na+and Cl-by glandular trichomes was very low at all external NaCl concentrations and substantially higher in basal leaves than in apical leaves. These results indicate that inP. latifolia, mechanisms of salt tolerance operate by excluding sodium and maintaining high selectivity for uptake and transport of K+, whereas the excretion of toxic ions is of minor significance.Key words: chloride, excretion, growth,Phillyrea latifolia,potassium, sodium.

ISSN:0008-4026    

DOI:10.1139/b99-049

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The avifrugivore availability hypothesis predicts that summer-fruiting species will have an extended fruiting season and slow fruit removal, and the foliar flag hypothesis predicts that fruit dispersal in autumn-fruiting species coincides with fall bird migration. Phenology of fruit removal from plants of the early summer-fruiting shrubRhus aromaticaAit. (var.aromatica) and of the later summer-fruiting shrubRhus glabraL. (Anacardiaceae) was studied primarily to test the avifrugivore availability and foliar flag hypotheses of fruit dispersal, respectively. Fruits ofR.aromaticaripened synchronously in early June, and 77-89% of them were gone from the plants by the early July, thus failing to support the avifrugivore availability hypothesis. The pattern of rapid fruit removal in this species, which was consistent throughout a 3-year period, is in contrast with previous reports of dispersal until September and even the next summer. Display size (at both infructescence and clump levels) had no effect on removal rate inR.aromatica. Fruits ofR.glabramatured in August, and about 20% of them remained undispersed the following spring. In both species, fruit removal was mostly due to dispersers rather than to natural fruit fall. No correlations were found between fruit characteristics (pulp weight, pulp-to-seed ratio, moisture content of pulp) and probability of removal during the dispersal season in either species. Browsing by mammals, most likely white-tailed deer, was responsible for the rapid removal of fruits fromR.aromaticaplants during the 1st week after they turned mature-red; thereafter, most fruit removal was by birds. Two removal peaks were found forR.glabrafruits: a small one in September and a large one in winter to early spring. These peaks correspond to the fall migration season for migratory birds and the scarcity of food for winter-resident birds, in the study area, respectively. Thus, the dispersal pattern ofR.glabrafruits does not support the foliar flag hypothesis.Key words: avifrugivore availability hypothesis, foliar flag hypothesis, fruit characteristics, fruit dispersal by birds or mammals, fruiting phenology,Rhus aromatica,Rhusglabra.

ISSN:0008-4026    

DOI:10.1139/b99-050

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

TheFestuca violaceaaggregate in the Alps and Apennines was the subject of full morphological, biosystematic, chorological, and ecological investigations carried out on herbarium specimens, living plants under cultivation, and wild populations. In the two mountain ranges, seven taxa were found to occur in the summit area:Festuca violaceaGaudin ssp.violacea,Festuca violaceassp.puccinellii(Parl.) Foggi, Graz. Rossi et Signorini,Festuca violaceassp.italicaFoggi, Graz. Rossi et Signorini,Festuca melanopsisFoggi, Graz. Rossi et Signorini,Festuca norica(Hack.) K. Richt.,Festuca picturataPils, andFestuca nitidaSchultes ssp.nitida. Synonyms, descriptions, original iconography, karyological data (new data forF. violaceassp.puccinellii), distribution, and ecology were gathered for each taxon, together with original identification keys. The possible origin and diffusion of the different entities are discussed. Special attention was given toF. melanopsisand to the three subspecies ofF. violacea, for which morphometric multivariate analyses (cluster analysis and discriminant analysis) were performed. A new taxonomic treatment of the aggregate is proposed.Key words:Festuca, Poaceae, Europe, morphometric analyses, systematics.

ISSN:0008-4026    

DOI:10.1139/b99-054

出版商:NRC Research Press    

年代:1999

数据来源: NRC