ISSN:0008-4026    

DOI:10.1139/b96-185

出版商:NRC Research Press    

年代:1996

数据来源: NRC

ISSN:0008-4026    

DOI:10.1139/b96-186

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The toxic effects of nickel on maize growth and structure and the accumulation and distribution of Ni in the plant were investigated. Two cultivars of maize, each with a different sensitivity to Ni, were grown on nutrient solution with different nickel concentrations for a period of 8 days. The sensitive and tolerant cultivars exhibited reduction in root and shoot growth with Ni concentrations greater than 20 μM and 40 μM, respectively. The toxic effects of nickel on the structure and ultrastructure of maize roots and leaves were studied by light microscopy and transmission and scanning electron microscopy. With 60 μM Ni, the sensitive cultivar showed a strong reduction in root mitotic activity (80%). Statoliths were absent in cells of the root cap, while leaves contained large amounts of starch in the chloroplasts of their bundle sheath cells. This suggests a decrease in carbohydrate transport between the leaves and the roots. The tissue localization of Ni by the dimethylglyoxim and silver sulphide methods showed important accumulation in the root apex and in the chloroplasts of the bundle sheath cells. These results suggest that Ni reduces maize growth by a reduction in root mitotic activity, probably because of direct action on the meristem. Starch accumulation in the leaves could come directly from a decrease in the root sink effect caused by the reduced mitotic activity or indirectly from an inhibition of carbohydrate transport.Keywords: maize, Ni toxicity, growth, Ni accumulation, Ni distribution, mitotic activity.

ISSN:0008-4026    

DOI:10.1139/b96-187

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Growth characteristics and water uptake were compared on two forest grass species (Agrostis stoloniferaL. andDeschampsia cespitosa(L.) Beauv.) to evaluate their potential competitive effects on young forest seedlings. The two grass species were grown in large containers under two watering regimes (regular irrigation that maintained the soil at field capacity or seasonal water stress). Spring regrowth occurred earlier inDeschampsiathan inAgrostis. During the summer, under irrigated conditions,Agrostishad higher values of leaf and tiller appearance rates thanDeschampsia. Under water-stressed conditions, leaf and tiller appearance rates decreased sharply for both species during the desiccation period, and regrowth was much more pronounced inAgrostisthan inDeschampsiaafter rewatering. Observations of the root systems indicated thatDeschampsiadeveloped deeper roots thanAgrostis. Despite these differences, evapotranspiration in the irrigated and in the dry treatments were similar for both grasses. In the water-stressed treatments, soil water potential decreased rapidly under both grasses and was slightly lower inAgrostisthan inDeschampsia. Although the two grasses had similar soil water uptake, differences in the overall competitive effect of the two grasses on forest tree seedlings might appear because of differences in their phenology, their recovery from drought, and the development of their root system.Keywords:Agrostis stoloniferaL.,Deschampsia cespitosa(L.) Beauv., leaf appearance rate, tiller appearance rate, tiller site-filling index, root growth, evapotranspiration.

ISSN:0008-4026    

DOI:10.1139/b96-188

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Interference between 1-year-old sessile oak (Quercus petraea(Mattus.) Liebl.) seedlings and two grass species (Agrostis stoloniferaL. andDeschampsia cespitosa(L.) Beauv.) was evaluated during 3 years after seedling transplantation. The seedlings were grown in large containers under crossed levels of watering regimes (regular irrigation that maintained the soil at field capacity or seasonal water stress) and grass competition (withAgrostis,Deschampsia, or bare soil). After 3 years, seedling basal diameter was 2.5 times greater in the absence of competing vegetation than with one of the two grasses. Within the grass-competition treatments, diameter was 1.3 times as great for the seedlings grown in the irrigated treatments than for the seedlings grown in the water-stressed treatments and was 1.3 times greater for the seedlings grown withAgrostisthan for the seedlings grown withDeschampsia. During the first 2 years, the seedlings grew much faster in the bare soil than in the weedy treatments, whatever the watering level. During the 3rd year, the seedlings in all the irrigated treatments showed similar relative growth rate values, which were much higher than those in the water-stressed treatments. Each year, soil water potential reached −2.5 MPa under the two grasses and −0.7 MPa under bare soil by the end of summer. On the contrary, competition for nutrients seemed to be low. Assessments of plant carbon isotope composition showed that the seedlings in the weedy water-stressed treatments had higher intrinsic water-use efficiency, and also suggested that the competition exerted by the two grasses occurred mainly for water. We conclude that during the first 2 years, the negative effects of the two grass species on seedling growth seemed to be largely independent of any competition for water. Conversely, during the 3rd year, the influence of the grasses on the seedlings seemed to be related only to competition for water.Keywords: root interactions, water stress, osmotic adjustment, carbon isotope discrimination, classical growth analysis.

ISSN:0008-4026    

DOI:10.1139/b96-189

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

We examined the species diversity of an ectomycorrhizal community in natural stands of bishop pine (Pinus muricataD. Don) to determine the correspondence between above- and below-ground views of species composition, spatial frequency, and abundance. We addressed this question by simultaneously sampling fruit bodies and ectomycorrhizae over a 4-year period. By using molecular methods based on polymerase chain reaction, we were able to identify the fungal symbionts directly from mycorrhizae in nearly all of the mycorrhizal morphotypes we found. Most species were either rare or low in abundance. Among the common species we observed three patterns: (i) some species, such asRussula xerampelinas.l. andAmanita franchetiwere well represented both above- and below-ground; (ii) some common fruiting species such asSuillus pungenswere rare components belowground; (iii) some species that were common as mycorrhizae were represented poorly or unrepresented in the aboveground fruiting record. The latter was the case forRussula amoenolens, thelephoroid types (i.e.,Tomentella sublilacinaand thelephoroid-2), and a boletoid type. These results show that (i) the pattern of resource allocation to production of fruit bodies versus ectomycorrhizae varied among species, and (ii) the correspondence between above- and below-ground is imprecise at best at the community level.Keywords: mycorrhizal types, basidiocarps, sporocarps, fungal community, ecology of fungi, PCR, molecular ecology.

ISSN:0008-4026    

DOI:10.1139/b96-190

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Vegetative fragmentation of clonal aquatic plants is considered a form of asexual reproduction. Although vegetative fragmentation of eelgrass (Zostera marinaL.) is considered a mode of asexual reproduction and dispersal, no data exist to evaluate the potential contribution of fragments (rhizomes with meristems and green leaf shoots) to eelgrass populations. We estimated (i) the size of the fragment population relative to the size of adjacent eelgrass populations, and (ii) the potential for fragments to re-establish in eelgrass beds in Mission Bay, San Diego, Calif. We surveyed the abundance of fragments on adjacent beaches and determined the survival and growth of detached fragments and of fragments re-established in eelgrass beds after varying time spent in the water column. Although vegetative fragments occurred throughout the year, but mostly in winter, they represented a loss of <4% of the leaf shoots in adjacent eelgrass populations. Only 60% of the fragments survived in the water column after 6 weeks, and growth and survivorship of re-established fragments declined with time spent in the water column. Thus, fragmentation represents a small net loss to the eelgrass beds studied and is not a common recruitment mechanism. This result does not support the hypothesis that asexual reproduction in the form of vegetative fragments contributes to eelgrass population growth. Because successful re-establishment is improbable, vegetative fragments also are not likely to contribute substantially to eelgrass dispersal, at least in Mission Bay.Keywords: eelgrass, asexual reproduction, clone fragmentation,Zostera marina.

ISSN:0008-4026    

DOI:10.1139/b96-191

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

The impact of root herbivory by larvae of the weevilSitona flavescens(Marsh.) on the growth and carbon and nitrogen economies of seedlings of white clover (Trifolium repensL.) and the nature and extent of nitrogenous compounds found in the root exudates taken from the rhizosphere were investigated. The seedlings were grown in sand culture in a system of microlysimeters that enabled sequential sampling of root exudates. Weevil infestation significantly reduced foliar biomass and total N and C contents and impaired N-fixation. The C:N ratios of the infested plants were significantly increased compared with those of uninfested seedlings. The most abundant amino acids in the exudates were aspartic acid and serine.Keywords: nitrogen fixation,Sitonaspp., root exudates, white clover.

ISSN:0008-4026    

DOI:10.1139/b96-192

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Phenotypic gender in the evergreen shrubThymelaea hirsutawas studied at regular intervals over 3–6 years in five natural populations in the western desert of Egypt. Quantitative estimates of gender were calculated for each plant, each year over the entire study period. Plants were also classified using a typological framework, allowing discrimination between plants that followed different flowering phenologies (e.g., dichogamy) but that may have had the same quantitative values of phenotypic gender. Two contrasting patterns of gender were revealed. Approximately one-third of all plants were stable in their gender expression (i.e., they produced the same floral pattern and quantitative gender on every occasion); the remainder had labile gender phenotypes, showing varying degrees and patterns of gender lability. The relative frequency of gender phenotypes differed significantly between sites. Stable unisexual forms were most prevalent at the depression sites, where the water table is closer to the soil surface. Patterns of gender variation inT.hirsutacan be interpreted in terms of a complex evolutionary pathway to dioecy, represented by several intermediate stages, including dichogamous, monoecious, and subdioecious individuals. Alternatively, there may be no directionality to the array; gender phenotypes may reflect localized selection that confers differential fitness on the phenotypes, to the extent that such phenotypes may be heritable.Keywords: dioecy, evolution,Thymelaea hirsuta, labile sex expression, gender variation.

ISSN:0008-4026    

DOI:10.1139/b96-193

出版商:NRC Research Press    

年代:1996

数据来源: NRC

摘要:

Sediment lithology, pollen, and plant-macrofossil data from the Paynter Site, southern Ontario, revealed three wetland developmental stages during the past 11 000 years: (i) aCarex,Eupatorium, andEleocharisdominated marsh with someLarix,Abies, andPicea(ca. 11 000–8300 cal years BP); (ii) aVerbena hastataandMentha arvensismarsh (ca. 8300–7460 cal years BP); and (iii) a white cedar (Thuja occidentalis) swamp (7460 cal years BP to present). There were no significant successional changes in the initial diverse marsh (stage 1) for about 2700 years; its high taxon richness was maintained by fluctuating water levels. The succession from marsh to swamp at 7460 cal years BP was caused by mid-Holocene warm and dry climate, which corresponded with cedar expansion elsewhere in Ontario. The swamp peat record was interrupted at ca. 6400 cal years BP by declining water levels, culminating in a dry period, as indicated by a sandy layer, rare macrofossils, and a low sediment-accumulation rate (0.012 cm/year). The reappearance of cedar swamp macrofossils since 3200 cal years BP corresponded with the recovery of water levels owing to a more humid late Holocene climate and flooding from isostatic tilt. Human disturbance such as damming and logging caused the development of historical cedar and thicket swamps with abundantAlnus rugosaand weedy taxa. This sequence of wetland development did not match the present vegetational gradients fromCarex–Typhaherb marsh, throughMyrica–Decodonshrub marsh andAlnus–Fraxinusthicket, toThujaswamp. At this site, the wetland development was mainly influenced by allogenic factors such as water levels and climate rather than autogenic factors.Keywords: wetland succession, climate change, hydrological change, Holocene, paleoecology, disturbance, space-for-time substitution, plant macrofossils,Thujaexpansion, Ontario.

ISSN:0008-4026    

DOI:10.1139/b96-194

出版商:NRC Research Press    

年代:1996

数据来源: NRC