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Increased nutrient availability reduces vesicular?arbuscular mycorrhizal (VAM) associations with plants, but whether increased nutrients in small volumes of soil affect local VAM colonization is not known. In a field experiment we investigated VAM colonization at different times following fertilization of small soil patches. Soil volumes of ~ 1000 cm3 were treated with a nutrient solution (enriched patch) or distilled water (control patch) on opposite sides of individual plants of the tussock grass Agropyron desertorum and the shrub Artemisia tridentata. Agropyron had significantly lower (p = 0.03) arbuscular infection in the locally enriched patches compared to control patches (32 and 40%, respectively). This reduced...
Blue grama (Bouteloua gracilis (HBK.) Griffiths), an important C4 species in the Great Plains grasslands of the north-central United States, was grown under three concentrations of CO2: 350, 675, and 1000 ?L?L?1. Growth of blue grama was significantly enhanced by enrichment to 675 but not to 1000 ?L?L?1. At the end of the experiment, 7 weeks after planting, plants grown at 675 ?L?L?1 had 35% more total biomass and nearly 90% greater leaf area than controls grown at 350 ?L?L?1. This growth enhancement is large for a C4 species, but is modest compared with the response typical of C3 species. It is concluded that blue grama may experience increasing competition from its C3, associates if atmospheric CO2 continues to...
Cheatgrass (Bromus tectorum L., Poaceae), an introduced winter annual, has invaded a variety of habitats in western North America. This study examines variation in cheatgrass germination response and after-ripening patterns that are related to differences in habitat and to yearly differences in weather conditions during seed maturation. Seeds collected from five contrasting populations in 1992 and 1993 were subjected to controlled dry storage and then incubated across a range of temperatures. Recently harvested seeds were dormant and germinated slowly, while fully after-ripened seeds were nondormant and germinated rapidly. The optimal incubation temperature for mean germination time shifted from 5:15 to 20:30 °C...
The articles in this issue of the Canadian Journal of Botany arose from presentations given at The Fifth International Symposium on Inorganic Carbon Utilization by Aquatic Photosynthetic Organisms held from 24 to 28 August 2004 at Saint-Sauveur, Quebec, Canada. They represent the current state of our understanding of CO2-concentrating mechanisms in these organisms and highlight recent molecular, physiological, and ecological advances made in this field of study. The influence of CO2-concentrating mechanisms on global carbon sequestration, species diversity, and population dynamics are also explored.Key words: algae, CO2-concentrating mechanisms, cyanobacteria, photosynthesis.Les articles dans ce numéro de la Revue...
During a survey of fungi associated with boreal bryophytes in Alberta, Canada, an isolate of Coniochaeta velutina (Coniochaetaceae, Coniochaetales), an opportunistic tree-pathogen and saprobe, was obtained from Hylocomium splendens (Hedw.) Schimp. (Hylocomiaceae, Hypnales). This isolate exhibited phylogenetic affinities to C.velutina isolated from vascular plants. In vitro characterization of its interactions with the model host Funaria hygrometrica Hedw. (Funariaceae, Funariales) demonstrated that it readily forms both anamorph and teleomorph states on the moss. Infected hosts exhibited no macroscopic symptoms or, occasionally, became weakly chlorotic, suggesting that the fungus is a parasite. However, cellulase...
Shadscale (Atriplex confertifolia (Torr. & Frem.) Wats.) is a dominant shrub species of western North American deserts. Its one-seeded utricles are enclosed in bracteoles, and its seeds are highly dormant at dispersal. We examined the role of soluble inhibitors, bracteole effects, after-ripening, and chilling in regulating dormancy for six shadscale populations. Seeds in bracteole-enclosed fruits required chilling to become germinable, and the fraction responsive to chilling was small for recently harvested seeds. This fraction increased during dry storage for 24 weeks, but the rate of increase decreased asymptotically. After-ripening rate was an exponential function of storage temperature over the range 22?50�C....


    map background search result map search result map Local reduction of mycorrhizal arbuscule frequency in enriched soil microsites