摘要:

A field survey of eight northernZizania palustrispopulations indicated that there is substantial variation in seed size. Variability is partitioned approximately equally among populations and among individuals within populations. Germination dynamics and temperature sensitivity of germination differed among four populations tested, but the differences were not apparently related to mean population seed size. Mean population seed size did appear to influence the germinability of viable seeds, such that a greater proportion of larger seeds exhibited prolonged dormancy. In a test using three populations differing in mean seed size, those with large seeds produced larger seedlings than populations characterized by small seeds. It appears that inZ.palustrisseed size influences whether or not a viable seed will germinate and the size of the resulting seedling, but not the rate at which germinable seeds are recruited to form a seedling population.Key words:Zizania, seed size, germination.

ISSN:0008-4026    

DOI:10.1139/b91-093

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Starch content and activities of some enzymes of starch metabolism were determined in wild-type, N2-fixing (fix+) nodules and in two non-N2-fixing (fix−) nodules induced byBradyrhizobium japonicummutant strains, T5-95 and T8-1, on soybean (Glycine maxL.) roots. The T5-95 nodules are similar to wild type in ultrastructure, but the T8-1 nodules are different in that the bacteroids are not released from the infection thread. After initial accumulation to relatively high concentration, starch was depleted during nitrogen fixation in fix+nodules. However, in fix−nodules, the accumulated starch was not metabolized. The activity of starch-bound starch synthase (EC 2.4.1.21) declined in fix+nodules but remained high in fix−nodules. The activity of α-amylase (EC 3.2.1.1) was only slightly higher than wild type in T5-95 but was four times higher than wild type in T8-1 nodules. The activity of starch phosphorylase (EC 2.4.1.1) increased in all nodule types from 14 to 21 days postinfection. A positive correlation was observed between the capacity of nodules to fix N2and their capacity to degrade starch. Collectively, these results support the concept that starch accumulated during early stages of nodule development is metabolized to supply energy for nitrogen fixation and to meet the metabolic demands of bacteroids.Key words: nitrogen fixation, starch content, effective and ineffective nodules, starch synthase, starch phosphorylase, α-amylase.

ISSN:0008-4026    

DOI:10.1139/b91-094

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The presence of an abscission zone in the stem of greenhouse roses (Rosa hybrida) between the vegetative and reproductive components was verified. This led to a description of the hydraulic architecture of the rose stem. The structural aspects of the xylem conducting system in stem, abscission zone and peduncle were examined to define their relative roles in the delivery of water via the stem to the transpiring plant surfaces and the extent to which their functional capacity may be influenced by environmental variables such as humidity. The stem exhibited a highly developed xylem with many large-diameter tracheary elements. Contrary to this the distal segment of the peduncle was poorly vascularized. The remainder of the peduncle, which included the abscission zone, was a transition between these two extremes. The abscission zone was a site of reduced hydraulic conductance that was not due to a reduction in the number or size of xylem conduits but to changes in the alignment of the elements. The variable conductances across the abscission zone and peduncle regions may play an important role in floral development and the response of the plant to water stress. Rose plants grown at constantly high humidity (77% RH) did not exhibit significantly different internal anatomical features of the xylem conducting system relative to roses grown in ambient, uncontrolled humidity (30 to 60% RH).Key words: abscission zone, hydraulic conductance, humidity.

ISSN:0008-4026    

DOI:10.1139/b91-095

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

An aluminum-sensitive cultivar (Katepwa) and an aluminum-tolerant experimental line (PT741) ofTriticum aestivumwere grown in nutrient solutions containing 0–400 μM aluminum at pH 4.5. After 18 days of growth, plant fresh weight was reduced in the Al-sensitive and Al-tolerant germ plasm by as little as 100 and 200 μM Al, respectively, and a number of changes in carbon allocation were observed. Shoot to root ratios increased with Al concentration in the Al-sensitive 'Katepwa' and remained constant in the Al-tolerant PT741.In both 'Katepwa' and PT741, shoot carbon was increasingly deposited into starch and fructan pools with increasing Al concentration. However, fructan deposition was more marked in the Al-sensitive 'Katepwa', possibly reflecting a failure to export carbon to the roots. Differences between Al-tolerant and Al-sensitive germ plasm were also observed in some organic acid levels. Contrary to several previous reports, higher concentrations of organic acids were found in the roots of Al-sensitive 'Katepwa'. In shoots, higher concentrations of organic acid were found in the Al-tolerant PT741. These results suggest that allocation of carbon to specific pools is affected by the concentration of Al. However, synthesis of organic acids and subsequent chelation of intracellular Al does not appear to represent a tolerance strategy in wheat. Observed changes in metabolic levels more likely represent a broad array of toxic lesions, with the magnitude of changes being greater in the Al-sensitive 'Katepwa' than in the Al-tolerant PT741.Key words: stress, aluminum tolerance, aluminum sensitivity, fructans.

ISSN:0008-4026    

DOI:10.1139/b91-096

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Post-fire spatial distribution of black spruce (Picea mariana(Mill.) BSP) and jack pine (Pinus banksianaLamb.) regenerations were studied in the Réserve faunique Ashuapmushuan, Quebec. The main factors analysed were (i) effects of organic matter thickness on growth and regneration, (ii) spatial distribution type of the regeneration, (iii) effects of burned stems on this distribution, and (iv) links between spatial distribution of the regeneration and the thickness of the post-fire residual organic matter. A strong correlation was observed between the presence of seedlings and the thickness of the post-fire residual organic matter. However, jack pine was much more efficient in getting established on microsites with thicker organic matter. Spatial distribution of the regeneration has a tendency to spread, following Blackman's dispersion coefficient, while adult individuals of the original population follow a more random pattern; this suggests that some seedling mortality, induced by seedling density, is to be expected. Regeneration shows a spatial link (point correlation coefficient) with trees of the original population, thus showing up the post-fire perpetuation of the individuals on the same microsites. Finally, the residual organic matter thickness on the ground seems without significant influence on the overall growth of jack pine and black spruce seedlings.Key words:Picea mariana,Pinus banksiana, spatial distribution, fire, regeneration. [Journal translation]

ISSN:0008-4026    

DOI:10.1139/b91-097

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Vegetation composition and community structure of boreal inland salt pans near the shore of Dawson Bay, Lake Winnipegosis, Manitoba, were examined. Eight vegetation associations and eight species groups were described from the site. Most of the vegetation associations were dominated by a single graminoid or graminoid-like species. Species composition in the most saline areas was similar to that of prairie salt pans to the south, whereas the vegetation of less saline areas showed affinities to both prairie and boreal forest. Examination of vegetation–environment relationships indicated that soil salinity was the moost important factor determining vegetation pattern. Other soil factors such as nutient levels, bulk density, and percent organic matter were of secondary importance. Species richness increased with decreasing salinity, but trends in Shannon–Weaver diversity and evenness along the salinity gradient were more complex. Despite the salinity gradient being environmentally continuous, strong vegetational discontinuities were noted. It is suggested that these discontinuities arose through interspecific competitive interaction and displacement mediated by differences in the salt tolerance of species.Key words: competition, discontinuity, gradient, halophyte, plant community, salinity.

ISSN:0008-4026    

DOI:10.1139/b91-098

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Ochrolechia, a widespread genus of crustose lichens, includes 19 species growing on bark in North America. These corticolous species and several non-North American taxa are treated in this paper. Six species and one variety are described as new:O. antillarum,O. gowardii,O. montana,O. juvenalis,O. pseudopallescens,O. subisidiata, andO. trochophoravar.pruinirosella. Two species are reduced to synonymy (O.californicaVers, andO.sorediosaHoward); six species are excluded from the North American flora (O.alboflavescens(Wulf.) Zahlbr.,O.apiculataVers.,O.pallescens(L.) Massal.,O.parella(L.) Massal.,O.rhamni-purshianaeSenft,O.subviridis(Höeg) Erichsen, andO.turneri(Sm.) Hasselrot). Several synonymies mentioned in the literature are confirmed (O.trochophora(Vainio) Oshio includingO.rosella(Tuck.) Vers. andO.orientalisVainio;O.androgyna(Hoffm.) Arn. includingO.pergranulosa(Räs.)Vers, andO.mahluensisRäs.; andO.yasudaeVainio includingO.tuckermaniiVers, andO.pennsylvanicaVers.). A key for the determination of all the species treated is presented together with distribution maps and a summary of the chemistry of the group. 5-O-Methylhiascic and 4,5-di-O-methylhiascic acids are reported fromOchrolechiafor the first time.Key words:Ochrolechia, Ascomycotina, Pertusariaceae.

ISSN:0008-4026    

DOI:10.1139/b91-099

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

In midsuccessional old fields, seedlings are often concentrated in patches of disturbed ground, such as earth mounds created by burrowing mammals. An experiment was conducted to determine whether interspecific variation in seedling density on mounds reflected interspecific variation in potential seedling establishment (i.e., the number of seedlings established per 1000 seeds sown). Seeds of 13 old-field forbs were sown on experimentally created mounds in an abandoned pasture. Their potential seedling establishment ranged from 0 to 156 seedlings per 1000 seeds sown, and seedling establishment was directly related to seed mass. The number of seedlings becoming established naturally on mounds ranged from 0.1 to 41 seedlings per mound for the 13 species. Natural seedling establishment and potential seedling establishment were not directly related. Instead, natural seedling establishment on mounds was correlated with species' frequency of occurrence off mounds. This suggests that seed availability may be more important than seedling establishment in controlling seedling density on mounds. However, if seed availability is unlimited or equal among species, then seedling establishment could control seedling density on disturbed ground.Key words: disturbance, seedling density, old field.

ISSN:0008-4026    

DOI:10.1139/b91-100

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Conifer–feather moss ecosystems dominate large areas of the boreal forest regions of the world, but the interrelations between these two components of the system are poorly understood. Mycorrhizal roots of the trees grow in close association with the mosses. The possibility that nutrients can be transferred from moss shoots to trees through mycorrhizal fungi was investigated using the feather mossPleurozium schreberiand mycorrhizal seedlings ofPinus contorta. Shoots of the moss were divided into three categories, viz. green, senescent, and dead, and nutrient contents of aqueous leachates from the segments were measured before and after drying. Significant quantities of nitrogen and phosphorus were released from moss shoots especially after drying. Senescing segments consistently released more N than those that were dead and generally released more than did the green segments. All categories of segments released some protein nitrogen, and drying induced leakage of glucose, fructose, and sucrose. Leachates of entire moss shoots were capable of supporting growth of three mycorrhizal fungi in pure culture. Moss shoots added to chambers containing mycorrhizal plants were colonized by the fungal associates of the plants, particularly intensive growth occurring in the senescent region of the moss shoots. Phosphate (32P) and carbon (14C), previously fed to the moss shoots, was absorbed by mycorrhizal mycelia and transferred over distances of centimetres to infected roots of pine plants and then to their shoots. The significance of these uptake and transfer processes for nutrient cycling in boreal forest ecosystems is discussed.Key words: leachate, nitrogen, phosphorus, sugars, protein, radioisotope.

ISSN:0008-4026    

DOI:10.1139/b91-101

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Pollen stratigraphy from three peat sections near Yakutat, Alaska, suggests that lodgepole pine only recently arrived in southeastern Alaska. In contrast with this palynological interpretation, however, are lodgepole pine (Pinus contorta) macrofossils that are present throughout one entire peat core.14C dating by accelerator mass spectrometry confirms the establishment of lodgepole pine in this region of Alaska about 10 000 BP. The surprising disparity between the pollen and macrofossil results has important implications for paleomigration research. These results imply that the use of assigned pollen percentages to indicate the presence of a species within a region may not be valid, particularly where a species is at the edge of its geographic range. Comparison of the timing of the first appearance of lodgepole pine pollen from a dozen sections along the north Pacific coast suggests either a late Wisconsin refugium for this pine in southeastern Alaska or extremely rapid late-glacial coastal migration northwestward following ice retreat.Key words: Alaska, pollen, macrofossils, lodgepole pine, phytogeography.

ISSN:0008-4026    

DOI:10.1139/b91-102

出版商:NRC Research Press    

年代:1991

数据来源: NRC