摘要:

The demographic performance of a Mediterranean annual arable weed (Diplotaxis erucoides) related to both environmental conditions and disturbance was studied in an agricultural system disturbed by ploughing at various times in the year. Comparative analysis of survival curves reveals that mortality rates are dependent on a variety of environmental conditions, namely competition with neighbouring plants, frost, and availability of water resources. The demographic response ofD.erucoidesmay vary depending upon how the unfavourableness of the environment compares with its physiological tolerance. Under environmental conditions not exceeding its physiological tolerance,D.erucoidesreacts through phenotypic plasticity. However, in arable fields where periodic mechanical disturbance removed all individuals before reproduction, or unfavourable environmental conditions such as frost and drought exceeded the physiological tolerance ofD.erucoides, widespread mortality occurred. Persistence then depended on high fecundity, low emergence rates, and high year-to-year seed survival. The results of our study show that different cultivation treatments will affect the persistence ofD.erucoides. Long-term high-disturbance regimes could produce a progressive decrease in numbers due to drastic reduction, even the absence, of new fresh seed shed onto the field and consequently a progressive depletion of the seed bank. Similarly, low-disturbance regimes or absence of disturbance could produce a rapid decrease in numbers related to an increase of associated species and the low competitive ability ofD.erucoides.Key words: demography, survival, disturbance, Mediterranean weed,Diplotaxis erucoides.

ISSN:0008-4026    

DOI:10.1139/b97-011

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Five inland halophytes,Atriplex prostrata,Hordeum jubatum,Salicornia europaea,Spergularia marina, andSuaeda calceoliformis, were grown in controlled laboratory conditions under three salinity treatments (0.5, 1.5, and 2.5% NaCl) and three density treatments (5, 15, and 30 plants∙100 cm−2) to determine the effects of salinity and density on survival, growth, and ion accumulation. The more salt sensitive species,A.prostrataandH.jubatum, had significant (P < 0.05) density-dependent mortality. Density significantly reduced biomass production for all species, except forH.jubatumin the high-salinity treatment. Succulence inSuaeda calceoliformisshoots increased in the high-salinity treatment, butH.jubatumplants were desiccated at the time of harvest. The ash, sodium, and chloride contents of shoots increased with salinity for all species. Sodium and Cl−ion contents for all species –treatment combinations were an order of magnitude higher than that of Mg2+, Ca2+, and K. AlthoughA.prostrata,Salicornia europaea, andSuaeda calceoliformisaccumulated similar levels of Na+in their shoots,Suaeda calceoliformisplants from the two higher densities in the low-salinity treatment accumulated twice as much total Na+per pot thanA.prostrata, and seven times more Na+thanSalicornia europaea. Based on these laboratory studies,Suaeda calceoliformisplanted in densities ranging from 15 to 30 plants∙100 cm−2would accumulate more Na+from saline-contaminated soils than the other species.Key words: bioremediation,Atriplex, Hordeum,Salicornia,Spergularia,Suae

ISSN:0008-4026    

DOI:10.1139/b97-012

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The effect of nitrogen fertilization on species cover, increment of shrubs, tissue nitrogen, and soil parameters was tested during a 3-year experiment in a low alpine plant community dominated byBetula nanain the Dovre mountains, south-central Norway. The doses used were 1.2 and 6.1 g N/m2, corresponding to 0.72 and 3.6 times, respectively, the annual deposition of nitrogen in southwest Norway. Statistical analysis using SAS ANOVA and GLM procedures were applied to different types of models. The cover of species and growth forms showed no significant response to additional nitrogen supply. The increment of shrubs was not significantly affected by the fertilization, except for the year factor. Incorporation of nitrogen into plant tissue was not evident. No effects were found on soil parameters.Key words: fertilization, alpine tundra, shrubs, nitrogen.

ISSN:0008-4026    

DOI:10.1139/b97-013

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The species composition and the depth distribution of the soil propagule banks of bryophytes and vascular plants from three different soil layers in a boreal old-growth spruce forest in SE Norway were studied using the emergence method. A total of 34 taxa germinated with a predominance of ferns and mosses. The frequency of the different species exhibits a common community pattern with a few common and a large number of low frequency species. The treeBetula pubescens, the fernsAthyrium filix-femina,Gymnocarpium dryopteris, andPhegopteris connectilis, and the mossesPlagiothecium laetumagg. andPolytrichumspp. were the most frequent. There is only a moderate correspondence, decreasing with soil depth, between the propagule bank and the aboveground vegetation in the sampled plots. In the soil profile, the litter layer on average had more taxa than the peaty mor and bleached layer (7.7, 6.0, and 5.5 taxa, respectively). Five of the 17 taxa occurring in more than 10% of the soil samples from the different soil layers were significantly more frequent in the upper soil layer, while two taxa were more frequent in either peaty mor and (or) the bleached layer than in the uppermost layer. The propagule bank in the different soil layers represents an in situ potential for regeneration of the vegetation after different degrees of disturbance in the forest floor.Key words: disturbance, soil propagule bank, boreal forest, bryophytes, vascular plants.

ISSN:0008-4026    

DOI:10.1139/b97-014

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Blooms of the marine flagellateChrysochromulinahave resulted in mortality of marine organisms in Scandinavian waters, including fish in aquaculture. Eight species ofChrysochromulina, namelyC.apheles,C.brevifilum,C.ericina,C.hirta,C.leadbeateri,C.parva,C.polylepis, andC.simplex, isolated into unialgal culture, were examined for haemolytic activity and toxicity to the brine shrimp,Artemia salina. Haemolytic fractions were obtained from all species, but onlyC.polylepiscells were toxic toArtemia. Thin-layer chromatography (TLC) analysis in chloroform –methanol–water (75:25:4) and in chloroform–methanol (9:1) yielded up to six haemolytic spots. Except for one spot, these all occurred in extracts of the species examined, includingIsochrysissp., which was used as a control,C.polylepis, and the well-known fish killerPrymnesium parvum. The single unique haemolytic spot(Rfvalues 0.45 and 0.16 in solvents I and II, respectively) occurred in the extract fromC.polylepis. When isolated by TLC, the contents of the single spot were toxic toArtemia.Key words:Chrysochromulina, toxicity, haemolytic,Artemia, thin-layer chromatography (TLC).

ISSN:0008-4026    

DOI:10.1139/b97-015

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

This study examines experimentally the influence of limiting factors on seed to ovule ratio and seed weight in three alpine populations of the perennial herbRanunculus acrisL. at Finse, southwest Norway. To test for pollen and resource limitation, seed production of supplementally pollinated or completely defoliated plants was compared to that of untreated plants. In one population the experiment was repeated twice during the season. In mid-season, supplemental hand-pollination had no significant effect on seed to ovule ratio, but significantly increased the seed weight, whereas complete defoliation resulted in a significant decrease in seed to ovule ratio and a marginally significant decrease in seed weight. These results indicate that pollen limitation occurred on seed weight and resource limitation mainly on seed to ovule ratio. Seed production in late-flowering control and defoliated plants in one population was nearly completely absent, whereas supplemental pollination increased seed production substantially. Most seeds were produced at the lowest elevation, and frost damage on developing seeds was most pronounced at the highest elevation population, suggesting that severe weather conditions at the highest altitudes had a negative influence on reproductive processes. Significant positive relationships between seed number and seed weight were found, possibly reflecting a large among-plant variation in total resource availability.Key words: altitude gradient, climate, defoliation, pollen and resource availability, seasonal variation, seed size.

ISSN:0008-4026    

DOI:10.1139/b97-016

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Development of staminate flowers in double-floweringBegonia semperflorens-cultorumcultivars 'Cinderella', 'Goldie Locks', and 'Lucy Lockett' was examined using epi-illumination microscopy, focussing on later stages when secondary partial floral buds formed on the floral apex. This process, switching from floral to inflorescence-like development, is an example of homeosis, the expression of inflorescence features on a floral apex. Floral development began as in a normal begonia flower with the formation of a perianth consisting of two sepals and two petals, but sepaloid and (or) petaloid appendages then developed in what corresponded to stamen positions in normalBegoniaspecies. This was usually followed by lateral elongation, distortion of the primary floral apex, and formation of secondary partial floral buds. The pattern of primordial inception on the secondary apices tended to be irregular, but in some cases, appendage primordia formed in groups of twos, threes, and fours, and in a somewhat alternating formation on the apices. Often, primordial initiation seemed to continue on secondary apices even after anthesis of the staminate flower. Appendage primordia that formed on the secondary buds usually were laterally elongate and bifacial, giving them a phyllomic appearance. Others were, on occasion, more hemispherical at inception, but as they developed they became phyllomic.Key words: homeosis, polyaxial, floral development, intermediate inflorescence.

ISSN:0008-4026    

DOI:10.1139/b97-017

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The Osse River is a plain river (southwest of France) fed by the Neste Canal flowing from the Pyrénées. From 1988 to 1993, 46 samples taken from the foam in the river have shown a great temporal variability in densities of aquatic hyphomycete conidia, especially during winter. In 1992, the winter maximum density, related to the latest leaf breakdown, was 1522 conidia/mm3, and the winter minimum, in 1989, 2 conidia/mm3. This variability was much lower during spring. The water temperature varied between 3.0 and 23.5 °C. Several species of hyphomycetes appeared as extremely sensitive to temperature variations, whereas no significant correlation with pH variations was found. The effects of floods on the fungal community varied according to the flood intensity and timing and to the composition of the riparian vegetation. The role of the species composition and the phenology of the riparian vegetation on the fungal community stucture and dynamics was discussed in relation to leaf litter decomposition. This paper emphasizes the need to take into account the flood intensity for the study of hyphomycetes dynamics and the significant role of hydrodynamics in freshwater nutrient cycle.Key words: aquatic hyphomycetes, temperature, pH, vegetation phenology, vegetation composition, decomposition, hydrodynamic.

ISSN:0008-4026    

DOI:10.1139/b97-018

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The rotated-lamina syndrome is a condition most commonly found in dorsiventral shoots with distichous phyllotaxis. Typically, young laminae in bud appear to be rotated to face towards the upper side of the shoot. The syndrome arises by asymmetrical growth from leaf primordia that initially face the shoot apex in approximately the normal way. It was previously described inTilia. Further genera of Tiliaceae and the closely related Sterculiaceae were examined for the presence of the syndrome. Altogether it was found in 9 genera of the 30 examined. The syndrome is well developed in representatives ofCommersonia,Corchorus, andPterospermum, and less well developed inLuehia seemannii. Expression of the syndrome is minimal inLuehia divaricata,Theobroma,Byttneria, andGrewia. In all cases with distichous phyllotaxis that were examined in these families, the leaf primordia show at least some asymmetry in development and consequently there appears to be a predisposition to lamina rotation within the group. The syndrome is probably becoming suppressed in cases with minimal expression. The situation in dorsiventral shoots ofCorchorusandByttneriais complicated by the presence of inflorescences that arise in a leaf-opposed position.Key words: Sterculiaceae, Tiliaceae, leaf, development, dorsiventrality, lamina rotation.

ISSN:0008-4026    

DOI:10.1139/b97-019

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

The genusPterospermumpresents an extreme case of lamina rotation in their dorsiventral distichous shoots. InPterospermum suberifoliumand an unidentified species, the young laminae emerge from the bud with their upper surfaces facing towards the upper side of the shoot, and, in this, they resemble most other cases of lamina rotation. InPterospermum heterophyllumandPterospermum acerifolium, the lamina emerge in hyper-rotated orientation, with the upper surface of the lamina facing outwards away from the parent axis inP.heterophyllumor outwards and towards the lower side of the shoot inP.acerifolium. The early development of the lamina is unusual in all cases, since it appears to arise directly in the rotated position. This unusual mode of lamina development appears to be a case of saltational evolution. InP.acerifoliumandP.heterophyllum, the leaf buttress also develops asymmetrically in the manner of other lamina rotators previously described, so that the lamina is rotated further with the formation of a triangular axillary site. This may be a relic of a more "normal" form of lamina rotation. Shoots with spiral phyllotaxis also occur inP.acerifolium, and inP.heterophyllumto a lesser extent, and these shoots have palmately lobed peltate leaves in contrast with the simple leaves of the dorsiventral shoots. The laminae in these shoots arise in a peculiar orientation, so that the upper surface of the lamina faces in the direction of growth of the shoot and never faces towards the shoot apex on which it formed. The mode of early lamina development in the spiral shoots is very similar to that of the dorsiventral shoots, but in the spiral shoots, the lamina is symmetrically placed instead of facing to one side of the shoot. It is suggested that the peculiar orientation of the lamina in the dorsiventral shoots arose first, and then a symmetrical form of this mode of development became incorporated into the leaves of the spiral shoots.Key words: Sterculiaceae, leaf, development, dorsiventrality, lamina rotation, hyper-rotation.

ISSN:0008-4026    

DOI:10.1139/b97-020

出版商:NRC Research Press    

年代:1997

数据来源: NRC