摘要:

This study is part of a research program examining the effects of elevated atmospheric carbon dioxide on a pasture. It was designed to examine (i) the interaction between disturbance and the atmospheric CO2concentration at the community level, and (ii) the response of a major weedChenopodium albumto CO2enrichment in a natural field situation. Although both the total number of species and Simpson's index increased upon disturbance, these traits did not respond to CO2fertilization. Counter to our expectation, we found no significant interaction between disturbance and CO2. The composition of the community that established in the open, disturbed spaces was a function of seed availability and as such independent of the atmospheric CO2concentration. Using height of the background vegetation to assess the impact of elevated CO2, we found some evidence for density dependence in the undisturbed quadrats but not in the disturbed ones. ForC.album, the disturbance regimes outweigh the CO2increase in importance. Neighboring plants have a strong influence onC.albumgrowth, this even though theC.albumphotosynthetic mechanisms are potentially responsive to elevated CO2. The present study highlights the complex feed-back interactions occurring when a community is exposed to elevated CO2concentration.Key words: elevated carbon dioxide, disturbance,Chenopodium album, open-top chambers.

ISSN:0008-4026    

DOI:10.1139/b97-874

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Effects of nitrogen and sulphur deposition on the community structure and biomass of ectomycorrhizal fungi in a Norway spruce (Picea abies(L.) Karst.) forest were examined following fertilization with ammonium sulphate. The treated plots had been fertilized three times a year from 1988 with (NH4)2SO3(100 kg N and 114 kg S ∙ ha−1 ∙ year−1). Sampling was carried out in the organic layer of the fertilized and control plots in late autumn in 1992 and 1993. The fungal biomass was estimated in 1992 using ergosterol analysis. The nitrogen treatment reduced the fine-root biomass (to 49% of the control) but did not decrease the mycorrhizal frequency (close to 100%) or concentration of ergosterol in fine roots. To identify mycorrhizas fungal ribosomal DNA was amplified using the polymerase chain reaction and digested with endonucleases. Of the 58 samples analysed, 21 different restriction profiles could be distinguished. Only four of the restriction profiles matched the restriction patterns of the dominant sporocarps on the site. It is suggested that nitrogen deposition will primarily change the community structure of ectomycorrhizal fungi, whereas the number of species may be less affected than has been previously inferred from sporocarp inventories.Key words: air pollution, biomass, diversity, ectomycorrhiza, identification, polymerase chain react

ISSN:0008-4026    

DOI:10.1139/b97-875

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Shrubs in the forest understory may be bent by their own weight or by overstory debris. To maintain height growth they must respond to bending by vertical growth of new shoots, reorientation of older axes, or by releasing preventitious buds to form epicormic shoots. I tested for these responses inIlex verticillataL.,Cornus amomumMill.,Gaylussacia baccata(Wang.) K. Koch,Viburnum cassinoidesL.,Hamamelis virginianaL., andKalmia latifoliaL. For each species, I removed potentially supporting vegetation adjacent to 20 stems, left 10 stems untreated to test for bending by self weight, and bent the remaining 10 stems to 45° to simulate effects of fallen debris. Stem angles and curvatures were measured from before leaf out until just before leaf fall to detect either sagging from self weight or upward bending from tension wood action. Control stems initially leaned out of vertical and five of six species sagged further into a cantilever form. Several control stems failed and bent to the ground. Stems ofH.virginiana,I.verticillata, andC.amomumformed tension wood, but only the first two species bent upward.Viburnum cassinoides,G.baccata, andK.latifoliaformed no tension wood and sagged further down after being bent. Epicormic shoots formed with varying frequencies in all species exceptK.latifolia. Epicormic shoots were the major response inC.amomum,V.cassinoides, andG.baccata. New terminal shoots on bent stems recovered toward vertical inI.verticillataandK.latifolia. Negative gravitropic response of shoots was the only recovery mechanism forK.latifolia.Key words: forest shrubs, tension wood, epicormic shoots, bending, stem architecture.

ISSN:0008-4026    

DOI:10.1139/b97-876

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

A dematiaceous hyphomycete,Leptodontidium quercuum, was found to be an extremely deleterious antagonistic fungus for log cultivation ofLentinula edodes, or Shiitake. In response to the approach ofLentinula edodeshyphae, the antagonist formed distinct, narrow, and shiny black zone lines in outer sapwood, cambium, and inner bark regions ofQuercusbed logs. The zone line was a pseudosclerotic plate consisting of several layers of thick-walled, highly pigmented cells, and caused deadlock of the two fungi. Abundant slime material was exuded fromLeptodontidium quercuumhyphae during the formation of pseudosclerotic plates. Neither bleaching nor decay occurred in the regions occupied byLeptodontidium quercuumwhere lumens of wood fibers, tracheids, vessels, and ray parenchyma were filled with its black sclerotic cells. Conidia ofLeptodontidium quercuumformed on agar culture media after 2 to several months of incubation at 20 °C. Scanning electron microscopy revealed that development of conidia was either sympodial or phialidic. However, their occurrence in nature and function in dispersal and colonization remain unknown.Key words:Leptodontidium quercuum,Lentinula edodes, mushroom cultivation,Quercusbed logs, antagonism, conidiogenesis.

ISSN:0008-4026    

DOI:10.1139/b97-877

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

We report the results of the first screening of 89 seaweeds collected from British Columbia, Canada, and Korea for antiviral activity. Various concentrations of methanol extracts of dried algae were tested against 100 plaque-forming units of herpes simplex virus type 1 and Sindbis virus in Vero cell monolayers. Eleven extracts inhibited both viruses, and 22 extracts were active against only one of the viruses. Thus, in total 37% of the species were active, and only two of these extracts also showed cytotoxicity at the concentrations tested. The antiviral activities were proportionately more frequent in the Korean extracts (56% compared with 27% of Canadian extracts), but in general the more potent extracts were of Canadian origin.Analipus japonicuswas the most potent anti-herpes species, and the Korean species ofCodium fragilewas the most potent against both viruses. This high yield of antiviral extracts illustrates the potential of seaweeds as a resource for bioactive compounds.Key words: seaweeds, algal extracts, antiviral activities.

ISSN:0008-4026    

DOI:10.1139/b97-878

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Seeds of the terrestrial orchid,Spiranthes sinensis, were germinated in vitro in association with the symbiotic fungus,Ceratobasidium cornigerum. Resulting colonized protocorms were prepared for light microscopy, transmission electron microscopy, and fluorescence labelling of actin filaments for examination with laser scanning confocal microscopy. Fungal hyphae invaded the suspensor end of embryos, formed typical hyphal coils (pelotons) within parenchyma cells, and then underwent lysis resulting in degraded hyphal masses. Hyphae and hyphal masses were enveloped by host-derived membrane. Changes in actin filament arrays accompanied fungal colonization. Uncolonized cells had a network of actin filaments and actin bundles (cables) located in the cortical region of the cell cytoplasm; some of these were associated with the nucleus and amyloplasts. Although actin filament arrays were still present in protocorm cell cytoplasm during fungal entry and peloton formation, most of the cortical network disappeared and instead actin filaments radiated from the periphery of developing pelotons towards the cell wall. Degraded hyphal masses also had actin filament arrays associated with them, again radiating toward the cell periphery; a network of cortical actin filaments reappeared in the protocorm cell cytoplasm at this stage. Actin filaments did not appear to have a close physical association with fungal hyphae except in the epidermal hairs that developed from protocorms; this differs from our previous observations on microtubules in this system.Key words: actin, actin filaments, orchids, mycorrhizas, laser scanning confocal microscopy.

ISSN:0008-4026    

DOI:10.1139/b97-879

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Soil fungi are important components of terrestrial ecosystems. They function as decomposers, pathogens, parasites, and mutualistic symbionts. Their main mode of dispersal is to liberate spores into the atmosphere. In this study we tested the hypothesis that a higher atmospheric CO2concentration will induce greater sporulation in common soil fungi, leading to higher concentrations of fungal propagules in the atmosphere. In our field experiment, the concentration of airborne fungal propagules, mostly spores, increased fourfold under twice-ambient CO2concentrations. Analysis of decomposing leaf litter (likely the main source of airborne fungal propagules) indicated that the fungi produced fivefold more spores under elevated CO2. Our results provide evidence that elevations in atmospheric CO2concentration can directly affect microbial function, which may have important implications for litter decay, fungal dispersal, and human respiratory health.Key words: atmospheric CO2, fungal spores, global change,Populus tremuloides.

ISSN:0008-4026    

DOI:10.1139/b97-880

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Isozyme and random amplified polymorphic DNA (RAPD) analyses have been used in combination with numerical taxonomy to study the taxonomic relationships among the toxigenic speciesFusarium acuminatumEllis & Everh. sensu Gordon (subsp.acuminatumand subsp.armeniacum),Fusarium sporotrichioidesSherb. andFusarium tricinctum(Corda) Sacc. Eight enzymes, selected among 23 enzyme systems tested initially for activity, resolution, and consistent formation of bands, were used for isozyme analysis of 75 strains. Both cluster analysis grouping by average linkage method and correspondence analysis of the isozyme data set resulted in an arrangement of the four taxa inconsistent with their classical taxonomic classification in theFusariumsectionsGibbosumandSporotrichiella. Isolates ofF.acuminatumsubsp.acuminatumwere more closely related toF.tricinctumthan toF.acuminatumsubsp.armeniacum. Correspondingly, theF.acuminatumsubsp.armeniacumgroup was closer toF.sporotrichioidesthan toF.acuminatumsubsp.acuminatum. Twenty-seven strains of the four taxa, representative of the variability found by isozyme analysis, were studied using a RAPD analysis with five different decamer primers. All the primers produced polymorphic amplification patterns with taxon-specific bands, in addition to individual-specific bands. Correspondence analysis of the RAPDs distinguished four compact groups corresponding to the four taxa studied. These data support the separation of the varieties ofF.acuminatuminto two different species, and suggest a revision of theFusariumsectionsGibbosumandSporotrichiellamay be necessary.Key words:Fusarium, isozymes, RAPDs, numerical taxonomy, mycotoxins.

ISSN:0008-4026    

DOI:10.1139/b97-881

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The objective of this study was to determine whether Arctic grasses from different sites along a snow deposition gradient respond similarly to grazing. The effects of laboratory simulated grazing (two levels of clipping frequency, clipping height, and nutrition) on accumulated biomass of different plant parts and number of tillers were measured in the reindeer forage grassesPoa arcticaR. Br. from a dry ridge habitat,Festuca rubraL. from a moist lee-side habitat, andDeschampsia alpinaL. from a wet snowbed habitat in Svalbard. BothP.arcticaandF.rubraincreased the proportion of biomass allocated belowground at the cost of the aboveground structures in response to high clipping frequency combined with high clipping height, leaving total accumulated biomass unchanged. InD.alpina, on the contrary, the percentage of aboveground biomass increased at the cost of belowground structures in response to high clipping frequency and low clipping height. This results in higher vulnerability to clipping and reduced total biomass. These two contrasting response patterns may reflect differences in adaptations in the habitats. Stress tolerance is more important on wind-blown ridges and in lee-side habitats where the grazing season is longer. On the other hand, rapid growth is more important in the snowbed where the growing season is shorter. These strategies may be of great importance in regulating and driving the local foraging patterns of Svalbard reindeer.Key words: herbivory, Arctic, graminoids, plant strategy, forage.

ISSN:0008-4026    

DOI:10.1139/b97-882

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The seed germination behaviour of six cold-temperate, cespitoseCarexspecies occurring either in wet forests or wet, open habitats was investigated under different light and temperature conditions. Germination tests were conducted in the laboratory with cold and wet stratified seeds in light and darkness, under four constant-temperature regimes and one fluctuating regime. Other germination tests were carried out in an experimental garden where freshly matured seeds sown on the soil surface were exposed to conditions typical for a sun-exposed site and a shaded (forest) site for 2 years. In the garden experiments, seeds at the sun-exposed site germinated soon after sowing in three species, whereas late-shedding species or species exhibiting primary dormancy germinated the following spring. Under the dense leaf canopy at the forest site, germination was inhibited completely during the first season in all species. Wet-forest species (Carex elongata,Carex remota) germinated the following spring before the leaf canopy closed, whereas the sedges adapted to open habitats (Carex canescens,Carex cespitosa,Carex pseudocyperus,Carex paniculata) failed to germinate, or only a low percentage germinated. Following transfer of ungerminated seeds from the shaded site to the sun-exposed site in the summer of the second year of the investigation, almost all of the hitherto ungerminated seeds germinated within 10 days. Results of laboratory experiments supported the findings in the garden experiments. At low mean temperatures (7 and 10 °C) in light, sedges adapted to open habitats did not germinate at all or showed a low percentage of germination, whereas forest sedges showed good germination. A high diurnal temperature amplitude and (or) a high constant temperature was needed to trigger the germination of a fraction of the seeds in dark treatments. It is suggested that the forest sedges are adapted to using a brief temporal regeneration niche during mid-spring, when mean temperatures are close to 10 °C and the leaf canopy has yet to close in central European, wet deciduous forests. In contrast, sedges adapted to open habitats probably fail to germinate under forest conditions because of their higher temperature requirements.Key words:Carex, germination, light, temperature, dormancy.

ISSN:0008-4026    

DOI:10.1139/b97-883

出版商:NRC Research Press    

年代:1997

数据来源: NRC