摘要:

The dispersal of white spruce (Picea glauca(Moench) Voss) seed through trembling aspen (Populus tremuloidesMichx.) forests was investigated by releasing artificial seed (confetti) from different heights on a meteorological tower, and, secondly, by observing the distribution of spruce regeneration along transects radiating out from small isolated patches of mature spruce seed trees. Mean dispersal distance of confetti increased with height of release. Before leaf fall of the aspen canopy, most confetti landed close to and in all directions around the tower. After leaf fall, no confetti was observed upwind from the tower and the mean dispersal distance increased, with peak densities occurring at a distance of 15 m in the downwind direction. The rate of decrease in regeneration density with distance from patches of mature, seed-bearing white spruce was much less than that observed during confetti release experiments. Furthermore, regeneration densities were significantly greater in the prevailing downwind direction (toward the east). The results indicate that stronger than average winds, primarily from the northwest, west, and southwest, play a major role in the dispersal of white spruce seed. Simulation modelling of the observed distribution of regeneration suggests that long-distance (>250 m) dispersal may be an important mechanism for the persistence of white spruce in the fire-prone boreal forest of western Canada.Key words: seed dispersal, boreal forest, mixedwood, wind dispersal, artificial seed.

ISSN:0008-4026    

DOI:10.1139/b97-179

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

We examined the diversity and distribution of ectomycorrhizal morphotypes on naturally regenerated western hemlock (Tsuga heterophylla(Raf.) Sarg.) seedlings across small forest openings (50-75 m in diameter) in northwest British Columbia. The total and average morphotype richness decreased across the 4-year-old forest openings despite the rapid establishment of western hemlock and lack of soil disturbance. Average fungal richness decreased from 13.1 morphotypes under the forest canopy to 9.6 at the forest edge (27% reduction) and to 7.8 in the forest opening (40% reduction).Cenococcum geophilum,Mycelium radicis atrovirens, andLactariusI were the most abundant ectomycorrhizae at each gap position, and none of the ectomycorrhizal fungi found in openings were eliminated by "late-stage" fungi in mature stands. This fungal distribution supports the "multistage" concept of ectomycorrhizal succession. Seedlings under the forest canopy had a total of 38 fungal morphotypes in a relatively even distribution pattern that corresponded well to the "random niche boundary" hypothesis. Fungal distributions were progressively less even for seedlings at the forest edge and opening than for seedlings beneath the canopy, perhaps because reduced fungal diversity and hyphal inoculum had affected the competitive balance of the ectomycorrhizal community.Key words: ectomycorrhizal community, diversity, succession, forest gaps.

ISSN:0008-4026    

DOI:10.1139/b97-180

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

To examine the causes of spatial variation in overwinter seed survivorship for an early successional plant, an artificial seed bank study was carried out. The design of the study separated vertebrate and nonvertebrate causes of overwinter seed mortality over three spatial scales. Vertebrate activity reduced seed survivorship more in disturbed than in intact forest, and within disturbed forest seed survival in patch types differed by transect, suggesting that vertebrate foraging behavior varies within the landscape context. Nonvertebrate and abiotic effects also suppressed seed survival within disturbed forest to a small but significant extent more than in intact forest, and transects within the disturbed area varied in their effects on survivorship. A second study examined the short-term spatial patterns of vertebrate predation only and showed transect-level patterns of seed predation that differed from those found in the longer term study. These results illustrate not only large spatial variation in vertebrate predation, but also the potentially important influence of less frequently measured effects of seasonal changes, abiotic conditions, and invertebrate and pathogenic attack on seed survival.Key words: seed predation, spatial variation, seed survivorship, disturbance.

ISSN:0008-4026    

DOI:10.1139/b97-170

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Over a period of 2.5 years, mycorrhizal fungal communities in soils of five abandoned surface coal mine sites in western Kentucky were studied in relation to time following reclamation. These sites were reclaimed at different times and were in varying stages of revegetation. At the seeding stage of reclamation, low populations of mycorrhizal fungal spores of only a few species, notablyGlomus microcarpumTul. & Tul.,GlomusaggregatumSchenck & Smith emend. Koske, andGlomusfasciculatum(Thaxter) Gerdemann & Trappe emend. Walker & Koske, were present. Populations of spores of these species increased rapidly during the first 1 or 2 years after reclamation. Other species, notably those with larger spores, appeared with time. Spores of one group of species were a high proportion of the total early after reclamation, then declined in relation to populations of other species. A second group appeared soon after reclamation and maintained a relatively constant proportion of the total population. A third group was inconspicuous for a few years after reclamation but increased in proportion to the total population of spores with time. Species richness was low soon after reclamation, rose slowly and erratically over 5 years, then stabilized at about 10 species. Species dominance, diversity, and evenness were relatively constant after the first 2 years of reclamation.Key words: Glomales mycorrhizal fungi, arbuscular mycorrhizal fungi, abandoned minespoil, succession, community relations.

ISSN:0008-4026    

DOI:10.1139/b97-149

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Lodgepole pine (Pinus contortaDougl. ex Loud.) seedlings, originating from seed in three southwestern Alberta cut blocks, were sampled to identify their ectomycorrhizal associates. Fourteen ectomycorrhizal taxa were identified, 10 were common to all three cut blocks, and 12 to two cut blocks. Individual seedlings were colonized by two fungal associates on average and never had more than six fungal associates at one sampling time. Total percent colonization of seedling roots was greater than 50% one year after seed germination and greater than 90% two years after seed germination. Species richness increased throughout the course of the study; however, all but two ectomycorrhizal taxa were found in mature forests nearby. Typical late-stage ectomycorrhizal fungi colonized regenerating lodgepole pine seedlings in the absence of refuge host plants; therefore, either these fungi remained viable in situ between harvesting and regeneration or they migrated back into the cut block once revegetation was initiated.Key words: lodgepole pine seedlings, ectomycorrhiza, percent relative abundance, Alberta cut blocks.

ISSN:0008-4026    

DOI:10.1139/b97-171

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The ectomycorrhizal community associated with regenerating lodgepole pine (Pinus contortaLoud.) after clear-cutting in southwestern Alberta was investigated in 6-, 10-, and 19-year-old cut blocks and their adjacent 90-year-old undisturbed control stands. Twenty different mycorrhizal taxa were found in the 90-year-old undisturbed stands. Of these 20, 13 mycorrhizal taxa were found in the 6-year-old cut blocks, and 15 mycorrhizal taxa were found in both the 10- and 19-year-old cut blocks. The most common associate of all stand ages wasMycelium radicis atrovirensMelin (MRA), which overall colonized 29% (weighted average) of the root tips. Species or groups accounting for greater than 10% of the mycorrhizas in one or more age classes includedPiloderma fallax(Karst.) Jül. (15% overall),Piloderma byssinum(Karst.) Jül. (11%),Cenococcum geophilumL. (8%),Russula-like (8%),Suillus brevipes(Pk.) Kuntze (5%),Suillus tomentosus(Kauff.) Sing., Snell & Dick (5%), andLactarius deliciosus(L.:Fr.) S.F. Gray (2%). Although several mycorrhizal fungi exhibited significant differences in percent relative abundance of root tips colonized, when comparing cut blocks to their controls, there was no evidence to suggest that the suite of mycorrhizal fungi colonizing roots of young lodgepole pine trees was replaced by a different suite of mycorrhizal fungi in mature stands. Extensive fruit body collections, totalling 43 species of ectomycorrhizal fungi, throughout the study sites support this contention.Key words:Pinus contortaectomycorrhizas, clear-cutting, second-rotation forests, succession.

ISSN:0008-4026    

DOI:10.1139/b97-172

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

A specific chloroplast DNA sequence was compared in 34 populations representing 10 wildBrassicaspecies (2n= 18). Species studied wereBrassica bourgeaui(Webb) O. Kuntze,Brassica creticaLam.,Brassica hilarionisG.E. Post,Brassica incanaTen.,Brassica insularisMoris,Brassica macrocarpaGuss.,Brassica montanaPourret,Brassica oleraceaL.,Brassica rupestrisRaf., andBrassica villosaBiv. The sequence was located between thetrnLandtrnFgenes in the large, single-copy region of the chloroplast genome. Site-specific primers were used to amplify the region via the polymerase chain reaction technique. Products of the same size were amplified from all populations. Sequence differences in the DNA fragments were detected by denaturing gradient gel electrophoresis. Ten different haplotypes defined by 20-base sequence differences were detected. Haplotype did not always reflect species classification. Haplotypes were shared by the species pairsB. rupestris - B. villosa,B. cretica - B. incana, andB. bourgeaui - B. oleracea. Populations carrying divergent haplotypes were discovered forB. cretica,B. montana, andB. insularis. Possible introgression of theB. macrocarpacytoplasm into aB. insularispopulation was observed. DNA sequences for the 10 haplotypes were determined and subjected to phylogenetic analysis using maximum parsimony. In the phylogenetic tree, theB. rupestris-B. villosahaplotype formed a basal clade, theB. macrocarpahaplotype diverged next, while all other species fell into a third clade.Key words:wild Brassicaspecies,B. oleraceacytodeme, haplotype, cpDNA, phylogeny.

ISSN:0008-4026    

DOI:10.1139/b97-183

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Azospirillumhas been shown to improve coleoptile growth in seedlings growing in darkness under osmotic stress. However, the changes in water relations that may occur in this experimental system have not yet been studied. Two-centimetre longTriticum aestivumcv. Buck Pucará andTriticum durumcv. Balcarceño-INTA seedlings were inoculated with viable or autoclaved (control)Azospirillum brasilenseSp. 245 bacteria, at approximately 108cells per seedling. Three days after inoculation, seedlings were exposed to osmotic stress by immersing their roots in 20% polyethylene glycol 6000 for up to 72 h. Germination and seedling growth were at 20°C in darkness. Shoots were excised after 72 h of stress, and water-status parameters were determined through pressure-volume analyses. While osmotic potential at full turgor remained constant,Azospirillum-stimulated growth in Buck Pucará seedlings was accompanied by significant decreases in osmotic potential and relative water content at zero turgor, in volumetric cell wall modulus of elasticity, and in absolute symplastic water volume and by a significant rise in apoplastic water fraction parameters. Except for a constant volumetric cell wall modulus of elasticity, similar results were obtained with Balcarceño-INTA seedlings. However, bacterial growth promotion was evident only in the less tolerant cv. Buck Pucará. Turgor at low water potential was higher in inoculated seedlings in both wheat cultivars under osmotic stress. These results are consistent with a better water status inAzospirillum-inoculated wheat seedlings under water stress, where both effects on cell wall elasticity and (or) apoplastic water are evident.Key words:Azospirillum, drought, seedlings, water status, wheat.

ISSN:0008-4026    

DOI:10.1139/b97-178

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Monthly changes in the endophytic mycobiota inPinusthunbergiiParl. andPinusdensifloraSieb. et Zucc. needles were detected by tissue culture. Endophytic mycobiota of these pine needles were dominated by four taxa: theLeptostromaanamorph of theLophodermiumpinastri(Schrad. ex Hook.) Chev. complex,Phialocephalasp.,CenangiumferruginosumFr.:Fr., and an unidentified hyphomycete species (BrS). The mycobiota differed with host pine species, position on the needle, and needle age. Virtually no endophytes were detected in needles just after emergence, but most segments of the older needles harbored endophytes. The endophytic mycobiota changed slowly with needle aging, except for the periods of rapid increase in the detection frequency ofLeptostromaandPhialocephalasp. Detection frequency ofLeptostroma, the most frequently detected endophyte taxon in the needles of the two pine species, continuously increased with needle aging, while that ofPhialocephalasp., the endophyte mainly detected from the basal segments ofPinusdensiflora, slowly decreased with needle aging after a massive emergence in current-year needles.Key words:Pinusthunbergii,Pinusdensiflora, pine needle, endophytic fungi.

ISSN:0008-4026    

DOI:10.1139/b97-177

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Epilithic diatoms were sampled at 48 sites along the St. Lawrence River, from Salaberry de Valleyfield to Québec City, in an attempt to determine how diatom assemblages were related to measured water quality variables. Canonical correspondence analysis was used to explore the relationships between environmental variables and patterns in the epilithic diatom assemblages. "Distance downstream from Cornwall" was determined to be the strongest variable influencing the structure of epilithic diatom assemblages, likely due to the effect of tides (favouring aerophilic species) closer to the river outlet. Variables related to pollution (suspended solids, fecal coliforms, chlorophylla) also explained significant (P< 0.05) amounts of variance in the diatom assemblages. The optima of common diatom species to suspended solids were explored further. Reconstructive models using weighted-averaging calibration and regression illustrated that "distance from Cornwall" and concentrations of suspended solids, fecal coliforms, and chlorophylla, the most influential variables, could be inferred from the diatom assemblages. When compared with the inference models developed for pollution variables using epiphytic diatom assemblages (attached to macrophytes orCladophora), the epilithon model appears to perform better.Key words: diatoms, rocks, epilithic, St. Lawrence River, water quality, calibration.

ISSN:0008-4026    

DOI:10.1139/b97-173

出版商:NRC Research Press    

年代:1998

数据来源: NRC