摘要:

Seedling emergence may be suppressed by dense ground cover causing species frequency to vary where ground cover ranges from moderate to dense. An experiment was conducted to determine how many community members showed matching patterns of variation in seedling emergence and frequency on a gradient of ground cover density in an abandoned pasture. Seedling emergence and species frequency were recorded on ridges, where ground cover was moderately dense, and in hollows, where ground cover was much denser. Eight of the 10 species examined showed ridge-hollow variation in seedling emergence and seven of the eight species showed a matching pattern of ridge-hollow variation in their frequency. When ground cover was removed experimentally, seedling emergence increased more in hollows than on ridges for all but one of the eight species. This suggests that ridge-hollow variation in seedling emergence resulted from greater suppression of seedling emergence by ground cover in hollows than on ridges. The close relationship between ridge-hollow variation in seedling emergence and species frequency in the community studied here indicates that models of spatial variation in community structure need to include spatial variation in seedling emergence as well as plant survival.Key words: ground cover, old field, seedling emergence.

ISSN:0008-4026    

DOI:10.1139/b91-179

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Dwayaangam heterosporais described as a new Hyphomycete attacking the eggs of rotifers and nematodes. The fungus attaches to the eggshell by an appressorium-like swelling. After penetration a postinfection bulb is produced from which haustorium-like assimilative hyphae develop and consume the contents of the egg. The fungus produces several morphologically different types of conidia from inconspicuous conidiogenous cells. The conidia are solitary, hyaline and septate and are either scolecospores or staurospores.Key words: egg parasite, rotifers,Dwayaangam,Triposporina, aquatic hyphomycetes.

ISSN:0008-4026    

DOI:10.1139/b91-180

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Vegetative compatibility groups were determined for 914 isolates of the chestnut blight fungus,Cryphonectria(Endothia)parasitica, collected over a 5-year period from American chestnut trees in eight regenerating clear-cut plots. We tested the hypothesis that the average distance between individuals in the same vegetative compatibility group is not different from the average distance between individuals with vegetative compatibility assigned at random. Nonrandom patterns were detected in all plots at least once during the study, indicating that vegetative compatibility groups were often aggregated. However, when multiple occurrences of vegetative compatibility groups on the same tree were eliminated from the analysis, there was only one test (out of 98 in total) in which the null hypothesis was rejected. We conclude that nonrandom patterns of vegetative compatibility groups are due primarily to multiple occurrences of vegetative compatibility groups on the same trees. Nearly half of all new cankers detected once the epidemic got started were in the same vegetative compatibility groups as cankers previously resident on the same tree. These data are consistent with the hypothesis that populations ofC.parasiticaare partly clonal in structure.Key words:Endothia parasitica, hypovirulence, Mantel test, matrix comparison, spatial autocorrelation.

ISSN:0008-4026    

DOI:10.1139/b91-181

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Effects of prolonged light irradiation on seed germination of wild oat (Avena fatuaL.) were studied in three nondormant and three dormant genetic lines. Light responses were observed in each of the lines tested. The expression of the light reaction is related to the genetic variability and dormancy states of the seeds. The light reaction can be observed in the dormant lines by removing the dormancy blocks in the seeds either through afterripening or by treatment with gibberellic acid or azide. Prolonged far-red, blue, and white light are inhibitory to germination. Prolonged red light had neutral, or inhibitory, effects compared with the corresponding dark germination. Germination responses to light depend on both the condition of phyto-chrome established by the light environment and the state of dormancy in wild oat seeds.Key words: phytochrome, dormancy, afterripening, genotype, gibberellin, azide.

ISSN:0008-4026    

DOI:10.1139/b91-182

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The envelopes of isolated algal packets from cyanobiont-containing and cyanobiont-freeAzollawere examined with the electron microscope. Both types of envelope were 10–20 nm thick and composed of three layers. The three-layer structure was also observed when algal packets were treated with cellulase, pectinase, lipase, protease, sodium hydroxide, nitric acid, or sodium dodecylsulfate. Thus, the envelopes do not appear to be membrane-like in nature and the presence and ultrastructure of the envelopes are not affected by cyanobiont filaments.Key words: algal packet, cyanobiont-freeAzolla,Azolla, electron microscopic studies, envelope.

ISSN:0008-4026    

DOI:10.1139/b91-183

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A 15-month field experiment was performed in the emergent zone of a freshwater riverine marsh along the Ottawa River, Canada, to determine whether the mechanisms producing plant zonation along the exposure gradient of freshwater shorelines also accounted for the zonal pattern along the water depth gradient. Three species (Carex crinita,Acorus calamus, andTypha angustifolia) were chosen, having contiguous distributions along a gradient of water depth. Ramets of each were planted within and beyond the field distributions of each, both in the presence and in the absence of the natural vegetation of each site. Although there was strong evidence of growth depression due to the presence of neighbouring plants (interference), there was no evidence of a differential response between species, between sites on the water depth gradient, or a combination of the two. As well, thee was no evidence that the water depth gradient represents a general gradient of decreasing productivity; rather, there was a qualitative change below the low-water level. These results are contrary to previously published results obtained along the exposure gradient of freshwater shorelines, where the effects of plant interference do vary both along the exposure gradient and among species.Key words: plant zonation, interference, water depth, exposure gradient.

ISSN:0008-4026    

DOI:10.1139/b91-184

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Taxonomically useful descriptors were provided by the banding patterns of seed storage proteins obtained when extracts of bulked, ungerminated seed samples from commercially available North American native species ofFestucawere analyzed by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS–PAGE). The banding patterns for three species of rough fescues (sectionBreviaristataeKrivot) indicate that although the taxa are closely related,F.campestrisRydb. (2n = 56) does not appear to be an autoploid of eitherF.altaicaTrin. (2n = 28) orF.hallii(Vasey) Piper (2n = 28). A distinct band corresponding to a molecular weight of 57 000 occurred in the seed protein profiles of all native and commercial samples ofFestucaL. analyzed. The profile forF.californicaVasey, questionably sectionBreviaristatae, also has a band at this position, and is very different from that ofF.altaica,F.campestris, andF.hallii. Species-specific banding patterns were observed forF.brachyphyllaSchultes,F.saximontanaRydb.,F.idahoensisElmer, andF.trachyphylla(Hackel) Krajina (F.ovinaL. s.l.,F.longifoliaThuill.,F.ovinavar.duriusculaauct. amer.). The results support the recognition of subgenusSchedonorus(Beauv.) Peter., and sectionsBreviaristataeKrivot andFestuca.Key words: Poaceae,Festuca, SDS–PAGE seed proteins.

ISSN:0008-4026    

DOI:10.1139/b91-185

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Taxa included in theAntennaria monocephalaDC. polyploid complex were previously circumscribed at the specific, subspecific, or varietal levels without concensus. The purpose of this phenetic study was to construct a taxonomy that not only reflects the presumed evolutionary history of the complex but also presents a taxonomy that is both functional and informative, regardless of an individual's gender or more importantly, the reproductive mode of the population. The rank of subspecies (A.monocephalassp.monocephalaandA.monocephalassp.angustata(Green) Hultén) was accepted as the most appropriate level of gender independent circumscription that satisfied the purpose of the phenetic study. These subspecies differ with respect to tomentum, chromosome number, reproductive biology, and (in part) provenance. The former taxon,A.monocephalassp.monocephala, is a sexual diploid (2n = 28); the latter taxon,A.monocephalassp.augustata, is an apomictic polyploid, with chromosome numbers ranging from tetraploid (2n = 56) to octoploid (2n = 112). InA.monocephalassp.monocephalathe adaxial surface of the basal and cauline leaves is glabrous-strigose, as is the stem. InA.monocephalassp.angustatathe adaxial surface of both basal and cauline leaves is floccose-tomentose, as is the surface of the stem.Key words:Antennaria monocephalapolyploid complex, multivariate analyses.

ISSN:0008-4026    

DOI:10.1139/b91-186

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The decomposition dynamics of four types of needle litter and three types of leaf litter were followed for 4 years. Mass losses and certain chemical changes were studied. Most of the nutrient-rich litters appeared to decompose relatively quickly during the first 12–18 months. After 3–4 years, however, their accumulated mass losses were lower compared with litter types that intially had lower rates. Thus the more nutrient-rich litters had considerably lower mass-loss rates in the later stages. This pattern was even more pronouced for extract-free lignocellulose: its mass-loss rate was negatively related to the lignin concentration, which increased progressively as litter decomposition proceeded. During late stages in litter with a high nitrogen content, there was also a clear negative relation between nitrogen concentration and lignin mass-loss rate, as well as between nitrogen concentration and litter mass-loss rate. By extrapolation of measured mass-loss values, maximum values for accumulated litter–mass loss were estimated. A nonlinear statistical model predicted that the proportion of mass lost through decomposition should be 50% for grey alder leaves, 54% for green leaves of white birch, and 57% for brown leaves of white birch. For Scots pine the predicted maximums for accumulated mass loss were 68% for green needles and 89% for brown needles, whereas corresponding values for lodgepole pine needles were 81% (green) and 100% (brown). Lodgepole pine is an introduced species in this system.Key words: litter, decomposition, lignin, nitrogen, maxium mass loss.

ISSN:0008-4026    

DOI:10.1139/b91-187

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Greenhouse studies were conducted to determine the effects of partial removal of endosperm or cotyledons from seeds of seven dune species on seed germination, seedling emergence, seedling size, and dry matter allocation. Different proportions (0, 30, and 60%) were surgically removed from seeds ofAgropyron psammophilum,Calamovilfa longifolia,Elymus canadensis,Leymus arenarius,Panicum virgatum,Lupinus perennis, andStrophostyles helvola. Partial removal of seed reserves caused a significant reduction in seedling variables 1 or 2 weeks after planting in sand. For example, seedling height, leaf area, dry weight of leaves, stem, and roots were significantly lower than control. The data suggest that the principal determinant of seedling size at an early stage was the amount of energy reserves in the endosperm or cotyledons of seeds. In addition to reduction in food reserves, partial removal of seed reserves caused some physiological damage to seedlings. In grass species, seedlings from surgically treated seeds devoted more dry matter to the roots and less to the leaves and stem than control seedlings. In dicot species, however, plants from treated seeds devoted more dry matter to the leaves and less to the roots.Key words: seed injury, seed germination, seedling size, energy allocation, dune plants.

ISSN:0008-4026    

DOI:10.1139/b91-188

出版商:NRC Research Press    

年代:1991

数据来源: NRC