Summary 1.We compared the root systems of seven halophytic species that occur at different elevations on a salt marsh, in order to (i) test the hypothesis that variations in root system architecture reflect adaptation to inundation frequency or nitrogen limitation, and (ii) verify the theoretically predicted relationships between root diameter, link magnitude and root topology. Diameters and lengths of individual laterals were determined along root axes, and branching patterns were quantified by calculating a topological index (TI). 2. Chenopodiaceae (annual dicots) showed that with increasing elevation, the branch density and length of individual first-order laterals tended to increase, so that the relative length of the main axes decreased. Root branching of the Chenopodiaceae at lower elevations was herringbone-like, whereas species from higher elevations had smaller TIs because their branching patterns were more complex. 3. The Gramineae, too, showed a tendency to increased length of individual laterals with increasing elevation. However, TI was not related to elevation, did not indicate a herringbone structure for all species, and was within the same range of that of the Chenopodiaceae. 4. As root topology of the Chenopodiaceae is related to elevation, but that of the grasses is not, topology is not necessarily an important adaptive trait in all plant families that inhabit the salt marsh. Short first-and second-order laterals may represent a more general architectural adaptation to frequent inundation, with longer first-order laterals being favourable to competition for nutrients. 5. Diameters at the root base tended to decrease if root branching was herringbone-like (TI close to 1). Roots of first-order laterals were approximately one-third of the diameter of the main axes; second-order laterals were approximately half the diameter of the firstorder laterals. These ratios illustrate the value of using the developmental segment-ordering system in describing roots. The theoretically predicted relationship between root diameter and link magnitude was not present within individual orders of roots, whereas diameter did slowly increase with magnitude when combining different root orders. 6. In the absence of a clear relationship between root diameter and link magnitude, the predicted high carbon costs associated with herringbone root systems disappear, whereas the advantage of minimized inter-root competition remains. Consequently, herringbone root systems will be most efficient in terms of nutrients gained per carbon invested. However, dichotomous root systems offer a greater potential for exploring the soil, which contributes to the potential competitiveness of plants growing in nutrient limited habitats.

ABSTR.ACT. Si-r plant species r,vere germinated in sancl wetted with water extracts of rlssues .,1 hve herd crops and three soils. Deionized water w-as used as a check.-l-he-stud1 ivas conducted rrsing srandard ieed germination te.nniqrer.

A study was made of the manner in which the movement of particles involved in saltation was initiated. The paths of flight of these particles while air borne were also studied.Evidence is presented to show initiation of movement can be caused by impulsive forces generated by differences in wind velocity, and by the distribution of particles, at the soil surface. Photographs of particles in saltation show that the paths of descent are nearly straight lines with an angle of incidence of about 6 ± 4 degrees. The data suggest that constant velocity in both the forward and downward directions is attained very quickly and that these velocities remain in essentially a constant ratio for most of the downward path.

Oats grown with different nutrient treatments in temperature-controlled soil in the greenhouse produced higher yields of grain and straw when soil temperature was increased from 41° to 67°F. Yields were usually less at 80°F. than at 41°F. This relationship between growth and soil temperature was also apparent at the heading stage. At 7th leaf, however, the best temperature for growth varied with nutrient treatment. Root yields usually decreased with increase in soil temperature.Increasing soil temperature from 41° to 67°F. increased uptake of N, P and K. In many instances increases in the concentration of N, P and K in the plant contributed to these increases in uptake. The effect of soil temperature on uptake was more consistent for P than for other elements.Nitrates and native phosphorus in incubated soil samples increased with increase in temperature from 41° to 80°F. but exchangeable K values were not affected.

. 2000. Efficacy of pasture rejuvenation through mechanical aeration or N fertilization. Can. J. Plant Sci. 80: [813][814][815]. Field experiments were conducted in 1991 and 1992 at five sites in central Alberta to determine if mechanical aeration with an Aer-Way™ aerator and/or N application would increase forage production on pasture or hayland. Mechanical aeration did not affect forage yield at any of the five sites. In contrast, forage yields increased significantly with N application in most cases. These results indicate that nutrient deficiency, particularly N, was the likely cause of reduced production on these pasturelands and haylands. Consideration of nutrient deficiency alleviation via inclusion of a legume or via N application may be an appropriate strategy for pastureland and hayland rejuvenation in central Alberta. Key words:Hayland, mechanical aeration, N fertilization, pasture, rejuvenation Malhi, S. S., Heier, K., Nielsen, K., Davies, W. E. et Gill, K. S. 2000. Efficacité du rajeunissement du pâturage par l'aération mécanique ou par la fumure N. Can. J. Plant Sci. 80: 813-815. Des expériences au champ conduites en 1991 et 1992 à cinq emplacements du centre de l'Alberta avaient pour objet d'établir l'effet de l'aération mécanique au moyen de l'aérateur AerWay MD , de la fumure N (ou des deux traitements combinés) sur la production fourragère en régime de fauche ou de pâturage. L'aération mécanique ne causait d'amélioration du rendement fourrager à aucun des 5 emplacements. En revanche dans la plupart des cas, des augmentations significatives des rendements résultaient de l'apport d'engrais N. Il apparaît donc que les carences nutritives, en particulier de N, soient la cause vraisemblable de la piètre production des pâturages et des prairies de fauche dans cette région. L'amélioration de la fertilité du sol, que ce soit par implantation d'une légumineuse ou par apport d'un engrais N, apparaît comme une façon valable de rajeunir les terres à foin et à pâturage de la région du centre de l'Alberta.Mots clés: Prairies de fauche, aération mécanique, fumure azotée, pâturage, rajeunissementResearchers have reported the damaging effects of livestock trampling on pasture (Rosenberg 1964;Watkin and Clements 1978;Wilkins and Garwood 1986;Davies et al. 1989). Livestock treading damages plants directly and also has indirect effects through soil compaction and puddling. Soil compaction by grazing animals has been demonstrated in many studies (Lodge 1954;Orr 1960;Reed and Peterson 1961;Gifford et al. 1977;Watkin and Clements 1978;Wood and Blackburn 1984;Davies et al. 1989;Naeth et al. 1990). It is known that high soil compaction may limit crop yield because of its adverse effects on root growth, soil water and air movement, and the water and air-holding capacity of soil (Bertrand and Kohnke 1957;Smith and Restall 1971;Jaggi et al. 1972).From the literature cited above, it can be concluded that pastureland cannot maintain its initial productivity or plant species composition if poorly managed. The traditional pra...