摘要:

Spatial and temporal changes in aquatic hyphomycetes communities were studied in three southwestern French rivers (Tech, Adour, and Nive). The survey was conducted from source to mouth for a year by water filtration. Changes in conidial concentration, species richness, and population diversity were analysed. Concentration of conidia of aquatic hyphomycetes generally increased in the downstream direction. However, these changes varied according to the river and the sampling date. Conidial concentration was higher during autumn than during spring and summer, but there was no difference between the beginning and the end of the leaf fall. Species richness was maximal during autumn and winter. It increased rapidly in downstream direction and reached a plateau. The diversity of conidial community of aquatic hyphomycetes generally remained constant regardless of the river sampled or the sampling date. It approached 75% of the theorical maximum possible diversity value, given the number of species and number of conidia sampled.Key words: Ingoldian fungi, community structure, season, altitude.

ISSN:0008-4026    

DOI:10.1139/b97-155

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Spatial and temporal changes in conidial concentration of species of aquatic hyphomycetes were studied in three southwestern French rivers (Adour, Nive, and Tech). The survey was conducted from source to mouth for a year by water filtration. Fifty-two species were identified.Alatospora acuminataandClavariopsis aquaticawere the most abundant species in all three rivers. Most other species made small contributions to the total amount of conidia, but species such asHeliscella stellataorLemonniera aquaticaoccasionally may be important in a particular river. The timing of seasonal peaks of conidia concentration of some species was studied. Species were classified into three groups according to the similarity or differences among rivers. Peak conidial concentration could appear at the same season on the three rivers (e.g.,Alatospora acuminata,Articulospora tetracladia,Heliscella stellata,Lemonniera aquatica,Lunulospora curvula) or in different seasons on the three rivers (e.g.,Pyricularia submersa,Tetrachaetum elegans). No peak was found forClavariopsis aquaticaorClavatospora longibrachiataon any river. Changes in conidial concentration along the three rivers were analysed. Patterns of individual species varied among rivers and seasons. During summer on the Tech River, conidial concentration ofHeliscella stellataincreased abruptly to the highest values of this study after having remained close to zero in the uppermost 20 km. This coincided with a drastic decrease in community diversity in these reaches. Both altitude and downstream distance influence conidial concentrations in a complex manner.Key words: Ingoldian fungi, conidia concentration, season, elevation.

ISSN:0008-4026    

DOI:10.1139/b97-156

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Spatial and temporal dynamics of individual species of aquatic hyphomycetes in three southwestern French rivers have been previously studied using water filtration techniques. In this paper, relationships between these spatial and temporal dynamics were explored using correspondence analysis. Correspondence analyses were performed for conidial concentration and presence-absence of species. The analysis of conidial concentration data indicated that species temporal dynamics is more important in determining changes in conidial communities than species spatial dynamics. However, the interconnectedness of these dynamics was revealed by a Guttman effect between the first two factorial axes. A linear gradient Tech-Adour-Nive, which corresponds to the geographical disposition of these rivers in southwestern France, was observed on the first three axes of the correspondence analysis of conidial concentrations. This gradient did not exist in the correspondence analysis of species presence-absence, but the analysis revealed a qualitative difference of the communities between the summer season and the beginning of autumn. The comparison of eigenvalues for the two correspondence analyses pointed out that conidial abundance is more significant than presence-absence of species for the structure of the data table.Key words: aquatic hyphomycete, spatial dynamic, temporal dynamic, climatic gradient.

ISSN:0008-4026    

DOI:10.1139/b97-157

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Frost tolerance during the germination stages of four white spruce (Picea glauca(Moench) Voss) provenances (between 45°37' and 50°17'N) was studied at four different developmental stages (imbibed seed, radicle, cotyledon, and young seedling), and their hardening capacity was determined for the latter three stages. Hardening capacity was examined by submitting radicle-stage germinants to two temperature-photoperiod treatments (20:15°C - 16-h photoperiod or 5:5°C - 8 h) for 14 days and by submitting cotyledon and young seedling stage germinants to four treatments (20:15°C - 16 h; 20:15°C - 8 h; 5:5°C - 16 h; 5:5°C - 8 h). Frost tolerance was determined immediately after these treatments. Latitude of origin showed no clear pattern with respect to either frost tolerance or hardening capacity at any of the developmental stages. Imbibed seeds had the greatest degree of frost tolerance. With the exception of the most northern provenance, radicle-stage germinants did not respond to a 5:5°C day:night temperature and 8-h photoperiod hardening treatment. A low-temperature treatment of 5:5°C increased the frost tolerance of cotyledon and young seedling stage germinants, while their response to a shortened photoperiod (8 h) was quite variable. However, an 8-h photoperiod did enhance the effect of the low-temperature treatment at the young-seedling stage. Thus, the timing of germination in the field appears to be an important factor in the ability of germinants to tolerate freezing stress.Key words: germination stage, frost tolerance, hardening capacity, photoperiod, temperature.

ISSN:0008-4026    

DOI:10.1139/b97-168

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Four aquatic plants were tested for the occurrence of unusual polyamines. The leaves of the aquatic plants tested ubiquitously contained homospermidine in addition to usual polyamines such as diaminopropane, putrescine, cadaverine, spermidine, spermine, and agmatine.Brasenia schreberiandNuphar japonicumbelonging to the family Nymphaeaceae contained aminopropylhomospermidine. Norspermidine and norspermine were detected in the blackweedHydrilla verticillatabelonging to Hydrocharitaceae. Thermospermine was detected inBrasenia schreberi. Anovel tetraamine,N,N'-bis(3-aminopropyl)-1,2-ethanediamine (NH2(CH2)3NH(CH2)2NH(CH2)3NH2), was discovered in the aquatic plantNuphar japonicum.This is the first report of the occurrence ofN4-methylspermidine (NH2(CH2)3N(CH3)(CH2)4NH2) in the water chestnutTrapa natasbelonging to the family Hydrocaryaceae.Key words:aquatic plants, polyamine, bis(aminopropyl)ethandiamine, methylspermidine.

ISSN:0008-4026    

DOI:10.1139/b97-175

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Parthenocarpy (the production of seedless fruits) and abortion of reproductive structures at different developmental stages are important processes limiting female fecundity inPistacia lentiscus(Anacardiaceae), a Mediterranean endozoochorous dioecious shrub. This paper tests (i) the effects of water and pollen as the ecological causes of abortion and parthenocarpy, (ii) the function of abortion and parthenocarpy regarding the uncertainty on resources and predispersal seed predation, and (iii) reviews the evolution of parthenocarpy across the phylogeny of the genusPistaciaand the family Anacardiaceae. Using experimental manipulations, we examined the effects of pollen and water availability on female fecundity. The components of female fecundity were the four sequential developmental stages in the reproductive cycle: (i) flower survival after pollination, (ii) latent ovary survival, (iii) final-sized fruit survival, and (iv) seed viability. The survival of reproductive structures along the four developmental stages in response to pollination was highly variable. The survival of pollen-excluded flowers was negligible. Water addition increased the survival of reproductive structures in the first two developmental stages but this effect was lost in the other two stages. However, irrigation had a delayed effect, significantly increasing the number of viable seeds per number of flowers at the following reproductive season. The irrigated females significantly increased the percentage of viable seeds, whereas nonirrigated females did not. These data support the hypothesis that the adjustment of progeny size to the available resources is an individual feature inherent to the life history of each individual and therefore independent on the present resource level. This adjustment may have an adaptive value in relation to uncertainty of water availability. An advantage for parthenocarpy in terms of reducing seed predation was not found and it may be a nonadaptive plesiomorphic character within the genusPistaciaand within the family Anacardiaceae. A significant negative relationship was found between the rate of seed abortion and predispersal seed predation by wasps, suggesting that abortion reduces insect predation. In support of this hypothesis, we found that fruits with aborted seeds abscised in a lower proportion than expected, while fruits with seeds parasitized by wasps fell in a greater proportion than expected.Key words: abortion, parthenocarpy, predispersal seed predation, seed production.

ISSN:0008-4026    

DOI:10.1139/b97-166

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Three new species ofCanalisporium, namelyCanalisporium exiguumGoh & K.D. Hyde,Canalisporium kenyenseGoh, W.H. Ho & K.D. Hyde, andCanalisporium pallidumGoh, W.H. Ho & K.D. Hyde, are described and illustrated. New records ofCanalisporium caribense,Canalisporium pulchrum, andCanalisporium elegans, are given. They are also illustrated from fresh material and briefly discussed. Comparisons of conidial morphology of all species from different localities are made and a key to the species of the genus is provided.Key words:Berkleasmium, dematiaceous hyphomycetes, freshwater fungi, lignicolous fungi, systematics.

ISSN:0008-4026    

DOI:10.1139/b97-164

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Cell wall electrical potentials were recorded from external hyphae, appressoria, and associated hyphae of the vesicular-arbuscular (VA) mycorrhizal fungusScutellospora calospora(Nicolson & Gerdemann) Walker & Sanders colonizing leek (Allium porrumL.) roots. As colonization progressed the hyphal walls became more polarized with similar values to the walls of the leek root. These changes, which may reflect changes in fungal wall composition, have important implications for nutrient uptake by the fungus. There were no differences in wall or intracellular potentials between leek roots colonized by eitherS. calosporaorGlomussp. ("City Beach") and non-mycorrhizal roots. These results are further evidence of the close compatibility between roots and VA mycorrhizal fungi.Key words: vesicular-arbuscular mycorrhiza, cell wall, electrical potential difference, leek,Alliumporrum,Scutellospora calospora.

ISSN:0008-4026    

DOI:10.1139/b97-163

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Flow cytometry (FCM) has been used to estimate the nuclear DNA content of 11Salixspecies and 5 hybrids. One hundred and sixty nine individuals were studied including 159 individuals from a sequence of 32 communities along a stretch of river in France and 10 individuals from French and English collections for comparison. Isolated nuclei were stained with propidium iodide. FCM was a significantly more practical and rapid technique than that of establishing the karyotype to survey many samples ofSalixfor variation in ploidy. The 2C DNA amounts for diploid species ranged from 0.76 to 0.98 pg, and tetraploid values ranged from 1.62 to 1.80 pg. The DNA values were consistent with the known ploidy levels. With the exception of a doubtfulSalix xquercifolia,ploidy levels and DNA amounts of hybrids were intermediate compared with those of their parents. Intraspecific variation of nuclear DNA values including instrumental variation was low (i.e., 6-11% at the same ploidy level). FCM appeared to be an accurate tool for determination ofSalixtriploid hybrids. However, it remains limited concerning hybrids from crosses between species of the same ploidy level. Results suggest that natural hybridization might not be frequent in the communities studied, although they have been subject to disturbance. Previous overestimates of hybridization frequency in willows were probably due to misinterpretation of the effects of the environment onSalixspp. morphology; however, the extent and mechanisms of introgression in the genus remain to be further investigated.Key words: flow cytometry,Salix,hybridization, nuclear DNA content, riparian vegetation, disturbance.

ISSN:0008-4026    

DOI:10.1139/b97-153

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Reproductive effort in dandelions (Taraxacum officinaleWeber) from two different habitats was compared. One dandelion population occupied a 5-year-old alfalfa (Medicagospp.) field, an environment subject to regular disturbance but with a relatively low density of neighbours. Individuals from the second population were derived from a number of undisturbed sites where the density of neighbouring grasses was high. Three hypotheses were evaluated with respect to the observed patterns of reproductive effort. One hypothesis, that reproductive effort was a function of differences between habitats in resource availability, did not provide an explanation for our results. A second hypothesis considered patterns of reproductive effort when mortality rates varied with degree of disturbance and neighbour density, which was a consequence of each habitat representing a different successional environment. A third hypothesis used a life-history approach to predict reproductive effort when mortality schedules were size dependent. Both of these hypotheses received support for their predictions. There was more than a sixfold variation in reproductive effort among individuals from the alfalfa field and a fourfold variation on the undisturbed sites. Much of this variation, however, was attributable to a size-dependent relationship between reproductive effort and vegetative mass. Total reproductive effort (total seed plus scape mass) in both populations increased linearly with vegetative mass, but the slope for the population from the alfalfa field was significantly higher. In contrast, proportional reproductive effort (total seed plus scape mass per vegetative mass) showed a curvilinear increase for the alfalfa field population but was linear and negative for the undisturbed population. There were also important differences between the populations in reproductive morphology. Larger plants on the alfalfa field had longer average scape lengths, produced more flower heads (capitula) per plant, had greater seed production, and had a lower ratio of seed mass per pappus area; only mean scape and mean seed mass did not differ significantly. We suggest that dandelions on the alfalfa field have a different reproductive morphology to facilitate colonization of open areas on the field.Key words:Taraxacum, dandelion, reproductive effort, biomass, life history, neighbour density, agriculture, weed.

ISSN:0008-4026    

DOI:10.1139/b97-176

出版商:NRC Research Press    

年代:1998

数据来源: NRC