摘要:

Tropospheric O3and water stress cause significant reductions in crop growth and yield. The effects of chronic O3exposures on leaf water relations have been less thoroughly studied. Soybeans were grown in two years in open-top field chambers equipped to control O3. The seasonal mean O3concentrations for the charcoal-filtered controls and supplemental O3treatments were 24 and 83 nL∙L−1for the first year (1990) and 20 and 99 nL∙L−1for the second year (1992). In 1990 leaves were sampled during four intervals of the 106-d growing season and subjected to potential–volume analysis. In 1992, leaves were sampled over a 3-week period, centered on 49 days after planting for potential–volume analysis as well as for midday xylem pressure potentials and leaf conductance. Ontogenetic changes in most of the parameters were large compared with treatment effects. O3treatment consistently caused decreased symplastic volume, specific leaf mass, and tissue elasticity. In 1992, these effects were accompanied by decreased leaf conductances with no discernable change in xylem pressure potential, although midday turgor increased by 32% and stomatal competency was maintained. Tissue elasticity decreases may be related to O3-induced changes in cell wall structure during leaf expansion and may result in decreased symplastic volume.Key words:Glycine max, ozone, leaf water relations, pressure–volume analysis, elasticity, elastic modu

ISSN:0008-4026    

DOI:10.1139/b95-053

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Plant and animal macrofossils (vascular plant, moss, fungus, bryozoan, cladoceran and coleoptera remains) were analyzed to reconstitute the development of a palsa peat located at the northwestern forest limit of subarctic Quebec (57°45′N., 76°15′W.) and to detect any black spruce (Picea mariana) remains older than the presumed time of arrival of the species in the study area (4560 BP), after the deglaciation. The oldest peat deposits were formed in a fen with many shallow pools between 5850 and 4500 BP. The flora was mainly composed of aquatic taxa (Ranunculus trichophyllus,Potamogetonspp.,Hippuris vulgaris). Around 4500 BP, there was a shift from a very wet fen to a sedge fen withPotentilla palustrisandMenyanthes trifoliata. From 3700 to 1950 BP, most plant remains were wood fragments of dwarf birch (Betula glandulosa). The formation of the palsa occurred after 1950 BP. The development of this peatland is similar to that of other palsa peatlands of subarctic Quebec, except that it is characterized by the presence of a thick peat layer composed ofBetula glandulosafragments at the top of the palsa. There were no black spruce remains older than 4560 BP. Three peaks of coleoptera abundance were identified at 4400, 3800, and 2700 BP, respectively. Most of the coleoptera taxa being hygrophilous, it was not possible to infer structural changes in the peatland from their fragments.Key words: palsa peatland, macrofossil analysis, subarctic Quebec,Betula glandulosa,Picea mariana, beetles.

ISSN:0008-4026    

DOI:10.1139/b95-054

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Seventeen species of freshwater hyphomycetes were found as endophytes of roots ofMangifera indica,Populus hybrida, andSalix babylonicaextending into the water from crevices in the brick wall of a canal in Lahore, Pakistan. More species were recovered by aerating than by plating bark and xylem segments on malt extract agar. Endophytic species of bark outnumbered those of xylem detected by aeration and plating methods.Anguillospora longissima,Articulospora proliferata,Bacillispora aquatica,Flagellospora curvula,Flagellospora fusarioides,Flagellospora penicillioides,Fusariumsp., andTetracladium marchalianumwere produced in abundance on aerated root segments.Fusariumsp. dominated other endophytic species of three tree species. Fifteen, 14, and 12 species were recovered fromSalix babylonica,Mangifera indica, andPopulus hybrida, respectively.Campylospora chaetocladiawas confined on the bark andHeliscus lugdunensison the bark as well as xylem segments ofSalix babylonica.Clavariopsis azlaniiandTricellula aquaticawere recovered from roots ofMangifera indica.Key words: endophytic freshwater hyphomycetes, submerged roots, canal water.

ISSN:0008-4026    

DOI:10.1139/b95-055

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

This study addresses the hypothesis that the spatial pattern of four bryophyte species on the forest floor of boreal woodland represents habitat partitioning, corresponding to microhabitat heterogeneity. Temperature, vapour pressure deficit, photosynthetically active radiation, incident precipitation, and litter fall were monitored at locations of pure colonies ofPleurozium schreberi,Ptilium crista-castrensis,Dicranum polysetum, andPtilidium ciliare. From May through November 1990, the species received a mean total of 51.20 ± 1.09 cm of rain and 1.034 ± 0.639 g of litter, primarily spruce needles. They experienced temperatures as high as 40 °C, vapour pressure deficits to 7.3 kPa, and photosynthetically active radiation to 3200 μmol∙m−2∙s−1. The results do not support habitat partitioning by the species on the basis of the variables examined: all four species tolerated the full range of conditions and their combinations that occurred in the study season, and experienced the same ranges during > 90% of the sampling period, with equally broad within-species variation. Although large pure colonies ofP.ciliarewere delimited by microsites receiving greater spruce needle litter fall and lower incident precipitation per rainfall event, smaller colonies and individual shoots were often found in mixture with other species. Overall, the spatial pattern did not correlate with microsite conditions, and we see no evidence of habitat partitioning in terms of currently occupied microsites.Key words: community structure, microclimate,Pleurozium schreberi,Ptilium crista-castrensis,Dicranum polysetum,Ptilidium cili

ISSN:0008-4026    

DOI:10.1139/b95-056

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The existence of annulate lamellae is detailed for the first time in the ultrastructure of a plant flagellated cell lineage. In early spermatogenous cells ofLycopodium obscurum, annulate lamellae are abundant and located adjacent to either the nucleus or plastid. Individual organelles consist of 1–11 parallel cisternae bearing tightly compacted pores that are similar in size and substructure to nuclear pores. In cross section, the pores measure 95–130 nm in diameter. Frequently, endoplasmic reticulum is continuous with the annulate lamellae cisternae. The existence of annulate lamellae inLycopodiumextends the known distribution of these organelles to rapidly proliferating spermatogenous tissue of seedless plants. Moreover, spatial associations between annulate lamellae and plastids are reported for the first time in any plant tissue.Key words: Annulate lamellae,Lycopodium, plastid, "pteridophyte," spermatogenesis, ultrastructure.

ISSN:0008-4026    

DOI:10.1139/b95-057

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Verticillium dahliaeinfection may reduce growth and yield of eggplant (Solanum melongenaL.) by inhibiting gas exchange per unit leaf area, and (or) by reducing leaf area. To quantify this inhibition, eggplants were grown in a field in fumigated soil or soil naturally infested withV.dahliae. Photosynthesis, dark respiration, transpiration, leaf area, disease symptoms, and yield were measured. Whole plants were enclosed in clear-walled chambers to measure gas exchange for 24-h periods. Before fruit set, there were no symptoms of wilt and no difference in leaf area or in gas exchange of plants grown in infested or fumigated soil. After fruit set, plants grown in theVerticillium-infested soil became symptomatic and had less leaf area, smaller leaves, and less photosynthesis per plant under high irradiance than plants grown in the fumigated soil. When whole plant gas exchange was normalized per unit leaf area there was no significant effect of disease on photosynthesis or transpiration. Although verticillium wilt reduces photosynthesis per unit leaf area in other species, our findings suggest that verticillium wilt reduced gas exchange of the entire eggplant predominantly by reduced leaf area rather than by reduced photosynthetic efficiency.Key words:Verticillium dahliae,Solanum melongenaL., photosynthesis, transpiration, leaf area.

ISSN:0008-4026    

DOI:10.1139/b95-058

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

The taxonomic status of the species complexHedysarum spinosissimumL. (s.l.) has been evaluated on the basis of the phenetic variation within and between populations. Twenty-five characters were measured on plants grown from seeds of 9 populations ofH.spinosissimumssp.capitatumand 12 populations ofH.spinosissimumssp.spinosissimumfrom the western Mediterranean basin. Data were analyzed by means of multivariate methods. Stepwise discriminant analysis led to conclusions similar to those derived from principal components analysis. The results are discussed from a systematic point of view. On the basis of vegetative and floral characters, numerical analyses supported two morphologically distinct groups of operational taxonomic units corresponding to the predominantly selfingH.spinosissimumand the mostly outcrossingH.capitatum.Key words:Hedysarum spinosissimumL., phenetic variation, morphological contrast, Mediterranean basin, multivariate analysis.

ISSN:0008-4026    

DOI:10.1139/b95-059

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Six fungal species previously placed inLeptosphaeriaand originally described on plant species in the Ranunculaceae were reevaluated for their proper taxonomic position and redescribed and illustrated from the type and authentic materials. The original position ofLeptosphaeria nigromaculataasOphiobolus nigromaculatais confirmed.Metasphaeria rupicolais transferred toMassarina, and a lectotype is designated.Leptosphaeria scotophilaandLeptosphaeria thoraeare transferred toPhaeosphaeria, and a lectotype is designated forL.scotophila. The previous transfer ofLeptosphaeria anthostomoidestoMontagnula anthostomoidesis confirmed. The new genusBarrellais established and typified byLeptosphaeria thalictri, and a neotype is designated.Key words: systematics, Loculoascomycetes,Leptosphaeria.

ISSN:0008-4026    

DOI:10.1139/b95-060

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Pollen tube growth rates and pollen tube attrition were examined inCucurbita pepoplants grown in an experimental garden. Two separate studies were performed utilizing controlled hand-pollinations. First, female flowers were hand-pollinated and collected at intervals over a 22-h period. Examination of stained pollen tubes in these pistils under reflected UV light revealed variation in growth rate: after approximately 7 h, the fastest growing pollen tubes grew at nearly twice the rate of the mass of the pollen tubes. The faster growing tubes reached the top of the ovary well ahead of most of the pollen tubes. Second, density of pollen application was varied and counts of germinated pollen and pollen tubes were made at four points from the stigmatic surface to the receptacle. Attrition was high for all pollen densities, but significantly higher rates occurred at high and medium densities just below the stigmatic surface. Pollen tube attrition at other points in the pistil was associated with constrictions in the stylar tissue and possibly with levels of nutrients in the pistil.Key words:Cucurbita pepo, pollen competition, pollen tube attrition.

ISSN:0008-4026    

DOI:10.1139/b95-061

出版商:NRC Research Press    

年代:1995

数据来源: NRC

摘要:

Pseudostilbellaanam. gen.nov. andPseudostilbella euphorbiaeanam. sp.nov. are proposed to accommodate a fungus isolated from lesions on living stems ofEuphorbia resiniferaBerg. collected in Morocco. The conidioma is a sporodochium borne on a rudimentary, brownish to greyish-brown, diffuse, KOH−stroma that is an extreme development of prosenchyma. The sparingly branched conidiophores develop from underlying pseudoparenchymatous cells. Conidiogenous cells form palisades and produce filiform, straight, or sinuous conidia. The conidiogenous system is holoblastic. Orange, slimy conidial masses accumulate on the colony surface or at the apex of synnema-like aggregations according to the location of the sporodochia. Sporodochia are sessile when colonies are grown under intense light, whereas they form at the apex of white stalks under diffuse light. Cultures grown in continuous darkness produce mycelial, synnema-like aggregations but do not sporulate. Light is thus needed for sporulation.Key words: Hyphomycetes,Euphorbia, fungal taxonomy, photomorphogenesis, sporodochial fungi.

ISSN:0008-4026    

DOI:10.1139/b95-062

出版商:NRC Research Press    

年代:1995

数据来源: NRC