摘要:

Soil from cottongrass (Eriophorum vaginatum) tussock tundra at Eagle Creek, Alaska, was analyzed with respect to the distribution, abundance, and germination patterns of buried viable seeds. Seeds ofCarex bigelowii, Eriophorum vaginatum, andLedum palustrewere abundant. Smaller amounts ofEmpetrum nigrumandBetulaspp. were also present. Buried seeds were found to 21 cm below the soil surface. Germination was rapid in the first 3 weeks of exposure to greenhouse conditions and continued at a slower rate for 5 more weeks. The ecological importance of seed banks in arctic regions and their possible implications for management of cotton-grass tussock tundra vegetation are discussed.

ISSN:0008-4026    

DOI:10.1139/b80-195

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Macrofossil actinorhizal root nodules discovered in sediments about 11 500 radiocarbon years old in northern Vermont, U.S.A., were studied by scanning electron microscopy. Evidence of an endophytic microsymbiont was observed within the cortex of the fossil nodules. A comparative study as undertaken using root nodules from species ofAlnus, Dryas, Elaeagnus, Myrica, Shepherdia, andVicianative to eastern North America in an effort to determine the identity of the fossils. From qualitative and quantitative differences observed among the root nodule endophytes, it was concluded that the fossil nodules contained actinomycetes morphologically similar to those of extant Elaeagnaceae. The fossils are probably from plants ofElaeagnus commutataand (or)Shepherdia canadensisbased on independent evidence of the representation of these species in the plant macrofossil assemblage.

ISSN:0008-4026    

DOI:10.1139/b80-196

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

This taxonomic revision of OntarioCrataegus(Rosaceae) indicates the presence of 39 good species in 14 series in the province. This appears to represent about one-third of the taxa of North AmericanCrataegus. Additionally, six "little-known" species are briefly described. The reasons for taxonomic difficulty inCrataegusin eastern North America are fully discussed and attention is drawn to the care with which specimens must be collected and the characteristics known to be of diagnostic value. A key to and descriptions of the series are provided. A key to species is followed by descriptions of each. Line drawings of 25 species at anthesis are provided to indicate the range of variation in OntarioCrataegusand to underline discriminating features. This is the only pictorial record of this detail for OntarioCrataegus. Thirty-two colour figures emphasize the differences among fruitingCrataegus, which have hitherto caused much confusion to collectors. Thirty-five species are mapped for their Ontario distribution and exemplar specimens are cited for all taxa. Seven new combinations have been made. Our species concepts are not consistent because of the range of variation patterns found in the genus, from ordinary sexual outbreeders through polytypic forms with various cytotypes to situations where hybrid swarms may be suspected. The taxonomic situation is known to be complicated by apomixis and polyploidy.

ISSN:0008-4026    

DOI:10.1139/b80-197

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Vapor fixation for 96 h with 1% osmium tetroxide (OsO4) and 3–4 days air drying produced distortion-free specimens ofBeauveriaspp. for examination with the scanning electron microscope. A combination of 4 h OsO4vapor fixation and freeze-drying also reduced disruption satisfactorily but specimens were not as well preserved as with the first method. Preparation methods that were ineffective in preventing collapse of hydrophilic structures were Cling Free® sprayed on specimens prior to examination, freeze-drying, critical-point drying (of unfixed material), and vapor fixation with glutaraldehyde.

ISSN:0008-4026    

DOI:10.1139/b80-198

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The biomass, community composition, and metabolic activity of soil microorganisms were studied in adjacent burnt and unburnt areas of spruce–fir subalpine forest razed 6 years previously by a moderately severe natural fire. Similar levels of microbial biomass were observed at comparable burnt and unburnt sites, although the ratio of fungal to bacterial biomass was higher in the unburnt soils. The decreased acidity of the surface horizons in the burn probably tended to favor the development of a bacterial flora rather than a fungal flora. Microbial biomass in the burnt sites peaked earlier in the season than in the unburnt sites in response to the warmer soil temperatures and earlier thaw in the spring in the burn area.Significant differences in the species composition of the mycoflora in the organic soil horizons were observed between the burnt and unburnt sites. Apparently, these were related to qualitative differences in the recent litter.Phoma, Cladosporium, andBotrytis, which are usually associated with early stages of decomposition of herbaceous litter, were more common in the burnt soil. The mycoflora of the mineral soil horizons varied considerably from one burn site to another, possibly reflecting the geographical variation in the intensity of the burn. In overall composition, however, the mycoflora in the mineral soil horizons of the burn was not appreciably different from that of the unburnt sites.Higher laboratory rates of respiration and cellulose decomposition were observed for soil samples from the undisturbed forest. However, the rate of decomposition of cellulose in the field was much higher in the burnt sites, probably as a result of the higher soil temperatures in the burn area. Low soil temperature was concluded to be the main factor limiting microbial activities in the study area, and the removal of the insulating plant canopy and increased heat absorption by the ash in the burn area were found to increase decomposition rates, at least at this stage in the succession following the disturbance of fire.

ISSN:0008-4026    

DOI:10.1139/b80-199

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Forest soils and litter in the vicinity of a large nickel–copper smelter at Sudbury, Ont. are known to be contaminated with a variety of heavy metals. In view of this, studies were carried out to determine if forest litter decomposition processes have been affected. The effects of nickel and copper on the decomposition of forest litter were investigated using a variety of techniques in which contaminated and control sites were compared. At contaminated sites an increase in litter standing crop was found. This was related to lower rates of litter decomposition at these sites, as evidenced by reduced rates of breakdown of litter in mesh bags, compared with uncontaminated sites. Lower rates of CO2flux and acid phosphatase activity were also found at the contaminated sites. In a laboratory experiment, the addition of copper and (or) nickel to a homogenate of leaf litter was shown to depress the rate of dry weight loss and CO2flux. Negative effects commenced at metal concentrations comparable to those observed in litter at contaminated sites in the field.

ISSN:0008-4026    

DOI:10.1139/b80-200

出版商:NRC Research Press    

年代:1980

数据来源: NRC