bluuebunny/crossref_metadata_2025 huggingface dataset:
Impacts of trails on cliff-edge forest structure
Authors: Parikesit Pampang , Larson Douglas W. , Matthes-Sears Uta
Published: April 2011

Plant community structure and soil characteristics were quantitatively studied along forested cliff edges of the Niagara Escarpment in southern Ontario, Canada. The objective of the study was to try to differentiate between the effects of two gradients on vegetation structure: the environmental gradient between the cliff edge and dense forest, and an anthropogenic gradient, generated by the presence of major hiking trails parallel to the cliff edges. Species frequencies were determined along 69 transects distributed over eight sites with different amounts of past and present trampling disturbance. The data were analyzed using cluster and ordination analysis as well as analyses of variance. The results showed that soil characteristics were the major influence organizing the vegetation of cliff-edge forests and that soil properties and plant community structure were more strongly influenced by anthropogenic factors than by the environmental gradient between cliff edge and forest. Trampled plots had some properties in common with cliff-edge plots. Species richness was highest at intermediate trail-use levels; abandonment of heavily disturbed trails resulted in the restoration of species richness, but most new colonizing plants were disturbance-tolerant ruderals. Soil properties did not completely recover even after 10 years of trail abandonment. The results suggest that the current use of cliff edges along the Niagara Escarpment is nonsustainable, and reversing its effects on cliff-edge forest structure may take a considerable amount of time. Key words: Niagara Escarpment, plant community ecology, disturbance, trampling, cluster analysis, ordination.
Limacospora gen.nov. and a reevaluation of Ceriosporopsis cambrensis
Authors: Jones E. B. G. , McKeown T. A. , Moss S. T. , Koch J.
Published: April 2011

Fresh collections of Ceriosporopsis sundica enabled an ultrastructural study of ascospores and spore appendage ontogeny. Ascospores are surrounded by an exosporic mucilaginous sheath of variable morphology, initially "slug-shaped" but at maturity ovoid. The fibrous component of the appendage is contiguous with the mesosporium through discontinuities in the episporium. Polar appendages are extensions of the sheath and not discrete mesosporial outgrowths as characteristic of Ceriosporopsis spp. A reexamination of the type material of C. cambrensis shows that spore measurements differ from those given by an earlier researcher, as does the general morphology of the appendages. It is concluded that two species are involved and C. cambrensis must be regarded a nomen dubium. Key words: appendages, Ceriosporopsis, Halosphaeriaceae, Limacospora, taxonomy, ultrastructure.
Wetland management and conservation of rare species
Authors: Doust Lesley Lovett , Doust Jon Lovett
Published: April 2011

The value of wetland is now widely recognized; some legislation requires "no net loss" of wetlands, although economic incentives still exist for wetland conversion. Rare plants may be protected by law; however, wetlands are rarely managed specifically to conserve rare species. Furthermore, it is not always clear how the environment should be manipulated to increase the abundance of such species, since necessary autecological details are rarely available. Species conservation involves demographic and genetic elements, as well as ethical decisions about the merits of transplanting or importing genes through controlled pollinations. Rare species may serve as indicators of habitat quality, although this will depend on the reasons behind the species' rarity. There is a need for multiple-use management plans that incorporate species- and habitat-conservation goals and that implement overall strategies to maintain or enhance the total quantity and quality of wetlands. Key words: rare plants, management, wetland conservation, habitat conservation.
Selection of Puccinia recondita f.sp. tritici virulence phenotypes in three multilines of Thatcher wheat lines near isogenic for leaf rust resistance genes
Authors: Kolmer J. A.
Published: April 2011

A heterogeneous population of Puccinia recondita f.sp. tritici developed from randomly mated pycnial infections on Thalictrum speciosissimum was selected for 12 generations on three multilines composed of Thatcher wheat lines near-isogenic for leaf rust resistance genes. Multiline 1 was composed of 20% each of lines near-isogenic for resistance genes Lr2a, Lr3ka, Lr11, Lr17, and Lr24. Multiline 2 was composed of equal proportions each of Thatcher and the five near-isogenic lines in multiline 1. Multiline 3 was composed of 50% Thatcher and 10% each of the five near-isogenic lines. Diversity of virulence phenotypes as measured by the Shannon index declined most in the population selected on multiline 1. Phenotypes of P. r. tritici with virulence to three of the five resistance genes in the multilines were the predominant isolates in all three populations after 12 generations of selection. Frequency of phenotypes with virulence to resistance genes Lr2a and Lr11 significantly increased in all three populations. Virulence to Lr11 significantly increased in the multiline 3 population, and virulence to Lr24 increased in populations from multilines 2 and 3. Frequency of phenotypes with virulence to Lr3ka did not significantly change in any of the populations. Virulence phenotypes with an intermediate number of virulences appeared to have fitness advantage relative to other isolates on the three host multilines. These results indicate that use of wheat multilines may not necessarily stabilize selection for virulence complexity in P. r. tritici populations. Key words: mixtures, Triticum aestivum, wheat leaf rust.
Antennaria howellii subsp. gaspensis comb, et stat. nov. (Asteraceae : Inuleae): justification for change
Authors: Chmielewski Jerry G.
Published: April 2011

Canonical discriminant analysis was used to assess the taxonomic status of Antennaria neodioica Greene var. gaspensis Fernald. Results based on these analyses indicate that Antennaria howellii Greene, Antennaria microphylla Rydberg, A. neodioica var. gaspensis, Antennaria pulvinata Greene, and Antennaria rosea Greene are morphologically distinct. High cross-validation assignment rates as well as high Geisser assignment probabilities for each of the taxa support this statement. Elevating var. gaspensis to the rank of species is in part supported by the data analysis, but doing so would be contrary to the species standard method and inconsistent with recent practice in revisions of the genus. The presence of scarious appendages at the tips of the upper cauline leaves, the open pedicellate inflorescence, the whitish-green capitula, general growth form, agamospermous reproduction, chromosome number, provenance, and quantitative morphology, in addition to the results of the canonical discriminant analysis, support recognition of var. gaspensis at an infraspecific rank. In keeping with the criteria utilized in recent revisions of the genus, var. gaspensis should more appropriately be treated as a subspecies. Recent nomenclatural rearrangements in A. neodioica and A. howellii founded on the priority of the latter lead to the following new combination: Antennaria howellii subsp. gaspensis (Fernald) Chmielewski. Key words: Antennaria howellii var. gaspensis, Asteraceae, Newfoundland flora, Gaspé Bay Peninsula flora.
Phytochrome-induced structural changes and protein degradation prior to radicle protrusion in Datura ferox seeds
Authors: Mella R. A. , Sànchez R. A. , Maldonado S.
Published: April 2011

In Datura ferox L. seeds induced to germinate by the far-red light absorbing form of phytochrome (Pfr) and alternating temperatures, protein degradation started before radicle protrusion. Proteolysis was, however, restricted to the micropylar region of the endosperm in which the protein content decreased 51% by 48 h after red light treatment. There was no change during that time in the protein content of the rest of the endosperm or in the embryo. Light and electron microscopy preparations show the vacuolation of protein bodies along with other changes in cellular structure in the micropylar portion of the endosperm in seeds treated with red light (R). No changes were detected in the rest of the endosperm or in the micropylar portions of far-red light (FR) treated seeds. In the embryonic axes there were some alterations but only in a small sector of the calyptra. In contrast, shortly after radicle protrusion (5 h), there was extensive degradation of protein bodies in the embryonic axes. A Pfr is required for the induction of protein degradation in the micropylar portion of the endosperm in the intact seed before radicle protrusion. Incubation of isolated micropylar portions induced protein degradation in tissues from seeds treated with either R or FR. The results do not support a source–sink type of control of protein degradation in the endosperm driven by the beginning of embryo growth but suggest the participation of regulatory signals in the determination of a temporal and spatial pattern of protein degradation in both the endosperm and the embryo. Key words: germination, dormancy, phytochrome, protein degradation, micropylar endosperm.
The chemical composition of newly shed needle litter of Scots pine and some other pine species in a climatic transect. X Long-term decomposition in a Scots pine forest
Authors: Berg B. , Johansson M.-B. , Anta R. Calvo de , Escudero A. , Gärdenäs A. , Laskowski R. , Madeira M. , Mälkönen E. , McClaugherty C. , Meentemeyer V. , Santo A. Virzo De
Published: April 2011

Significant differences in the chemical composition of falling needle litter were found among various pine species. A comparison between the needle litter of northern species (Scots pine and lodgepole pine) and that of 17 other, southern species combined showed that concentrations of N, P, Mg, K, and lignin were significantly lower in the northern group. In contrast, the Mn concentration was significantly higher in this northern group. Along a transect from the Barents Sea (69°45′N) to the Carpathian Mountains (49°53′N), concentrations of N, P, S, and K in Scots pine litter fall increased significantly. The best-fit regression models described asymptotic curves, suggesting that concentrations of these major nutrients approach their maximum values at sites with high values for actual evapotranspiration (AET). Low values were found in the north. By contrast, Mn concentrations, increased with latitude and decreased with increasing AET. High covariation among concentrations of the major nutrients (N, P, S, and K) can be attributed to their being major constituents of structural compounds. Analysis of various regression models relating the chemical composition of needle litter fall to latitude and AET, together with a factor analysis, suggested that concentrations of N, P, S, and K were related mainly to climatic conditions, whereas those of Mg and Mn were related more to site-specific properties such as soil fertility. A high level of predictability was found for concentrations of N, P, S, and K using multiple regression, with values for R2adjbetween 0.63 and 0.93. Key words: litter fall, chemical composition, interspecific variability, geographical variability, climate, soil fertility.
Sexual composition of populations of Fragaria virginiana (Rosaceae) collected from Minnesota and western Wisconsin
Authors: Stahler Margaret M. , Ascher Peter D. , Luby James J. , Roelfs Alan P.
Published: April 2011

Populations of Fragaria virginiana Miller collected from 39 sites in Minnesota and western Wisconsin were gynodioecious, in that 35% of the plants were pistillate, 65% were hermaphroditic with perfect flowers, and none were staminate, when scored for gender expression in greenhouse or field plantings. Instability of gender expression across environments was apparent in 15% of the collections and these genotypes that appeared to change gender were termed weak hermaphrodites. Variation in gender composition of collections was not related in any consistent manner with the plant communities characterizing the collection sites. The proportions of pistillate plants, total hermaphrodites, strong hermaphrodites, and weak hermaphrodites in collections from the northern forest floristic province in the northeastern part of the region were not significantly different from those of collections from the southwestern prairie-forest floristic region, although collections from the prairie-forest province were more variable for gender composition than populations from the northern forest province. Lack of staminate plants and increased percentages of hermaphrodite plants, relative to reports in the literature, suggest that the gender composition of F. virginiana populations in Minnesota has changed, perhaps as a result of introgression from hermaphroditic Fragaria ×ananassa or Fragaria vesca. Key words: Fragaria chiloensis, Fragaria vesca, Fragaria ×ananassa, dioecy, introgression, evolution.
Étude de la croissance et du développement chez le frêne commun, Fraxinus excelsior, cultivé en conditions contrôlées
Authors: Collin P. , Badot P. M. , Millet B. , Barnola P.
Published: April 2011

Under controlled conditions (14 h light : 10 h dark; 27 ± 1 and 19 ± 1 °C), common ashes, Fraxinus excelsior L., display a rhythmic growth. The average duration of the first growth flush is 106 days, followed by a phase of nonlengthening from 9 to 11 months, depending on individuals. This rhythm was materialized in the shoot organization. The end of each growth stage was characterized by progressively shorter internodes and by the presence of scales around the bud. Histological studies reveal that no leaf is preformed at the embryo stage and that the meristem activity carried on after the stem growth stops. The common ash growth rhythm is therefore not the direct consequence of the arrest of meristem activity. The nonlengthening phase is an apparent resting phase during which the initiation of new leaves carries on. Key wordsff growth, development, common ash, meristem, plastochron, rhythm. [Author's translation]
Ultrastructure of conidia and conidium germination in the plant pathogenic fungus Alternaria cassiae
Authors: Mims C. W. , Rogers M. A. , Dyke C. G. Van
Published: April 2011

Transmission electron microscopy of plunge-frozen and freeze-substituted samples was used to examine germinating conidia of Alternaria cassiae, a plant pathogenic fungus used as a biological control agent for sicklepod (Cassia obtusifolia). Hydrated conidia on small pieces of dialysis membrane were incubated for 1, 2, or 3 h on the surface of corn meal agar prior to fixation. Conidia were large, darkly pigmented, and surrounded by a thick, two-layered wall. Each conidium was divided by transverse and longitudinal septa into multiple cells, a few of which sometimes appeared necrotic. Each septum tapered to a small central pore region with which Woronin bodies were associated. Each healthy cell of a conidium contained a typical complement of cellular organelles including multiple nuclei. With the exception of lipid bodies, all the various organelles were well preserved by plunge freezing and freeze substitution. Evidence of germ tube development was visible by 2 h post-incubation and well-developed germ tubes were present by 3 h. Two modes of germ tube development were observed. In the less common mode germ tubes developed inside conidia and grew internally through one or more adjacent cells before emerging from the conidium surface. Cells penetrated by internal germ tubes appeared necrotic. In the more common mode of germination, germ tubes developed directly from the conidium surface. Multiple germ tubes usually arose from each conidium and grew out in all directions. Germ tubes that contacted the underlying dialysis membrane continued to grow along its surface. Extracellular material was produced in association with developing germ tubes and coated the sides of germinated conidia and covered germ tubes growing along membranes. Key words: transmission electron microscopy, cryofixation, freeze substitution, germ tube development.
Effects of gap area and shape on recolonization by grassland plants with differing reproductive strategies
Authors: Kotanen Peter M.
Published: April 2011

Species with poor dispersal ability initially should be slower to colonize larger or rounder gaps than smaller or less circular gaps. Conversely, dispersive and seed-banking species should be less sensitive than poor dispersers to gap size and shape, and less confined near the edges of a gap. I tested these ideas with a 3-year experiment in which I monitored the revegetation of gaps in grassland vegetation. Initially, species reproducing largely by clonal growth (bulbs and perennial graminoids) were the most sensitive to gap size and (to a lesser extent) shape, reaching their greatest abundances in small and (or) rectangular openings. Species relying on seed dispersal (annual grasses) also tended to do best in smaller plots, but were less concentrated near the edges of the plots. Species relying on seed dormancy (dicots and J uncus bufonius) were least sensitive to plot size, shape, and distance from an edge. In subsequent years, these patterns often were obscured or reversed, reflecting continuing seed immigration and environmental and competitive conditions within gaps. These results indicate that species respond to gap size and shape in ways consistent with their reproductive biologies, and suggest that the importance of the dimensions of gaps may vary among plant communities. Key words: disturbance, gap shape, gap size, grasslands, revegetation, succession.
The role of endogenous ethylene in the expansion of Helianthus annuus leaves
Authors: Lee Siew Hwee , Reid David M.
Published: April 2011

The possible role of ethylene in leaf expansion of the primary leaves of sunflower plants (Helianthus annuus) was studied. Our lowest application of ethephon promoted expansion of primary leaves. Higher concentrations of ethephon, and a range of concentrations of 1-aminocyclopropane-1-carboxylic acid, increased endogenous ethylene concentration and caused a reduction in the area of the primary leaves. The inhibition in leaf expansion induced by ethephon and 1-aminocyclopropane-1-carboxylic acid was reversed by pretreating the plants with an inhibitor of ethylene action, namely silver thiosulphate. Treating leaves with lower concentrations of aminoefhoxyvinylglycine reduced ethylene production and stimulated leaf expansion. This effect of aminoethoxyvinylglycine could be nullified by pretreating the plants with 1-aminocyclopropane-1-carboxylic acid. Treatment with silver thiosulphate enhanced leaf expansion. This indicates that endogenous ethylene normally plays a significant role in leaf expansion. Flooded and gravistimulated plants produced more ethylene and had smaller leaves. This could suggest that the increased ethylene is the main cause of the slowed leaf growth, however, only in some cases were we able to partially reverse the effect of flooding with silver thiosulphate. This indicates that there are probably many factors, in addition to increased ethylene, that inhibit leaf expansion in flooded and gravistimulated plants. Key words: ethylene, leaf expansion.
Two alternative pathways of somatic embryo origin from polyembryonic mature stored seeds of Pinus koraiensis Sieb et Zucc.
Authors: Bozhkov P. V. , Ahn I. S. , Park Y. G.
Published: April 2011

Individual mature stored seeds of Pinus koraiensis sometimes contain several viable zygotic embryos originated through the processes of simple and cleavage polyembryony. To induce the embryonic process, isolated zygotic embryos were cultured on five different media all supplemented with 10 μM 2,4-dichlorophenoxyacetic acid and 5 μM 6-benzyladenine. Two alternative pathways of somatic embryo origin were revealed. The first pathway was associated with the production of a friable, translucent callus in the hypocotyls–cotyledon region of the dominant zygotic embryo. The second pathway was related to the proliferation of a translucent, moist, and mucilaginous tissue (termed embryonal–suspensor mass) in the suspensor region of the dominant zygotic embryo. Both types of tissues contained early somatic embryos. Regression analysis has shown a strong negative correlation between the frequencies of formation of embryogenic callus and embryonal–suspensor mass both at 3 and 8 weeks of culture (r = − 0.85; p = 0.07 and r = −0.71; p = 0.17, respectively). Key words: Pinus koraiensis; polyembryonal seeds; somatic embryogenesis; embryogénie callus; embryonal–suspensor mass.
Accumulation of mansonones in callus cultures of Ulmus americana L. in the absence of a fungal-derived elicitor
Authors: Meier F. G. , Remphrey W. R.
Published: April 2011

The Dutch elm disease pathogens Ophiostoma ulmi (Buism.) Nannf. and Ophiostoma novo-ulmi Brasier elicit the production of phytoalexins called mansonones in the American elm (Ulmus americana L.). As part of a larger investigation, it was revealed that mansonone elicitation in callus culture does not require the Dutch elm disease pathogens, as has been reported in other studies. The objective of this study was to determine the nature and timing of the nonfungal elicited mansonone accumulation in U. americana callus. Initially, 7-week-old calli were subjected to inoculations with various fungal growth medium components. Mansonone production occurred in all treatments, indicating that it was stimulated prior to the addition of the medium components. Next, cotyledons and calli at various stages of development were analysed for the production of mansonones to determine the timing of its production. Mansonone production appeared to be correlated with the initiation of callus production and may be related to the callus wound reaction. As the callus aged, its colour changed from white–green to brown possibly as a result of phytoalexin accumulation. Additional experiments in which the cotyledon source, agar source, and type of plant tissue culture media were modified resulted in no change to the mansonone accumulation ability of the callus. The discrepancy between our results and those of other researchers could be due to differences in the method of mansonone quantification, namely, that our method is more sensitive and led to the detection of mansonones where previously none had been found. Further research must be done in this area to investigate this mansonone accumulation. Key words: phytoalexin, Dutch elm disease, mansonone, Ulmus americana, callus.
Phylogeny of Gremmeniella spp. based on sequences of the 5.8S rDNA and internal transcribed spacer region
Authors: Hamelin Richard C. , Rail Jimmy
Published: April 2011

Sequences in the 5.8S rDNA and internal transcribed spacer region were obtained for taxa belonging to Gremmeniella spp., and a phylogenetic analysis was carried out using parsimony and distance methods. A set of hypotheses concerning evolutionary relationships between members of that genus was tested. The hypothesis that all members of Gremmeniella abietina var. abietina are closely related was rejected. It appears that the Asian race is quite divergent from the European and North American races, but could be more closely related to G. abietina var. balsamea. The phylogeny was consistent with host specificity: members of G. abietina var. abietina generally do not infect Abies or Picea spp. but the Asian race occurs on Abies sachalinensis in Japan. The hypothesis that host specialization has created divergence within G. abietina var. balsamea was supported by our analysis because the levels of divergence between isolates originating from Picea spp. and Abies spp. were similar to those found between the North American and European races of G. abietina var. abietina. The hypothesis that greater divergence occurred between Gremmeniella abietina and Gremmeniella laricina than between G. abietina var. abietina and G. abietina var. balsamea was not supported. The level of divergence was as large between the two varieties within G. abietina as between the two species G. abietina and G. laricina. These results indicate that similar taxonomic levels should be applied to these three taxa. Key words: scleroderris canker, internal transcribed spacer (ITS).
Phosphorus acquisition from compacted soil by hyphae of a mycorrhizal fungus associated with red clover (Trifolium pratense)
Authors: Li Xiao-Lin , Zhang Jun-Ling , George Eckhard , Marschner Horst
Published: April 2011

The influence of an arbuscular mycorrhizal fungus, Glomus mosseae, on the adverse effects of soil compaction on growth and phosphorus (P) uptake of red clover was studied in a model experiment. The pots used in the experiment had three compartments, a central one with a soil bulk density of 1.3 g ∙ cm−3 and two outer compartments with three different levels of soil bulk density (1.3, 1.6, or 1.8 g ∙ cm−3). The soil in the outer compartments was fertilized with P and was either freely accessible to roots and hyphae, or separated by nets and accessible to hyphae only. At a soil bulk density of 1.3 g ∙ cm−3, mycorrhizal plants did not absorb more P than nonmycorrhizal plants except when access of roots to the outer compartments was restricted by nets. At high soil bulk density, root growth was drastically decreased. However, hyphae of G. mosseae absorbed P even from highly compacted soil, and induced a P-depletion zone of about 30 mm from the root surface. In consequence, at higher soil bulk density shoot P concentration and the total amount of P in the shoot were higher in mycorrhizal than in nonmycorrhizal plants. This experiment showed that hyphae of G. mosseae are more efficient in obtaining P from compacted soil than mycorrhizal or nonmycorrhizal roots of red clover. Key words: arbuscular mycorrhiza, phosphorus, red clover (Trifolium pratense L.), soil bulk density, soil compaction.
Taxonomic and ecological characterization of chrysophyte stomatocysts from northwestern Canada
Authors: Brown Kimberly M. , Zeeb Barbara A. , Smol John P. , Pienitz Reinhard
Published: April 2011

Chrysophyte stomatocysts from the surface sediments of 49 lakes located on a north–south transect in the Yukon and Northwest Territories, Canada, were investigated for their potential use as indicators of environmental change in northern latitudes. Photographic plates and descriptions, following International Statospore Working Group guidelines, illustrate 19 new stomatocyst morphotypes. The main patterns of floristic variation in the data set were explored using canonical correspondence analysis, which indicated that gradients of chloride (r2 = 0.73), dissolved inorganic carbon (r2 = 0.63), and surface-water temperature (r2 = 0.55) were important in influencing species assemblages. Compared with the diatom-temperature inference model developed from the same set of lakes, the stomatocysts provided a slightly less robust model. These results suggest that stomatocysts are weakly, though significantly, related to some of the gradients in lake water chemistry in this data set and can provide a complement to other paleoecological markers. Key words: chrysophyte stomatocysts, inference models, northwestern Canada.
Inhibition of Fusarium oxysporum f-sp. dianthi in the non-VAM species Dianthus caryophyllus by co-culture with Tagetes patula companion plants colonized by Glomus intraradices
Authors: St-Arnaud M. , Vimard B. , Fortin J. A. , Hamel C. , Caron M.
Published: April 2011

The effect of the mycorrhizal fungus Glomus intraradices on disease development caused by Fusarium oxysporum f.sp. dianthi in the nonmycorrhizal species Dianthus caryophyllus was studied by co-culture of carnation plants with the mycorrhizal species Tagetes patula. Presence of VAM T. patula plants more than doubled the survival of D. caryophyllus, significantly reduced the disease symptoms, and decreased F. o. dianthi propagules by 4:1 in soil. Non-VAM T. patula plants had no effect. Dianthus caryophyllus shoot biomass was reduced by F. o. dianthi in non-VAM controls but was not affected in presence of G. intraradices. Glomus intraradices alone has no effect on T. patula or D. caryophyllus shoot biomass. Dianthus caryophyllus mineral shoot content was not modified by G. intraradices. In absence of T. patula, G. intraradices did not colonize D. caryophyllus, whereas in its presence, 14–20% of the carnation root length contained abundant vesicles and hypha but very rarely arbuscules. The presence of G. intraradices clearly reduced the disease caused by F. o. dianthi in D. caryophyllus. Reduction in disease severity was associated with reduced F. o. dianthi propagule number in the substrate and was clearly unrelated to plant nutrition. Our results may be explained either by the induction of D. caryophyllus disease resistance mechanisms by the mycorrhizal fungus or by direct or indirect microbial interactions in the soil. Key words: vesicular–arbuscular mycorrhizae, marigolds, carnation, disease, biocontrol.
Organisation de la richesse et de la composition floristiques d'îles de la Méditerranée occidentale (sud-est de la France)
Authors: Médail Frédéric , Vidal Éric
Published: April 2011

The effects of physiographic variables (area, isolation, elevation, and substrate) and habitat diversity on plant species richness and composition have been investigated on some Mediterranean islands (southeastern France). The number of species - area relationship is significant but there are more diverse vegetation patterns on smallest islands (area smaller than 3.5 ha and, ultimately, 0.2 ha). Although the species composition is positively correlated to the distance from the continent, the effect of isolation is not so obvious because of the small distance of these continental islands from the continent. Some islands nearest to shore show very different plant species composition, suggesting a nonselective plant dispersal through some narrow stretches of sea. Habitat diversity represents one of the major explanatory factors of the species richness; nevertheless, it is not possible to settle between the two hypotheses effect of habitat diversity versus effect of area per se because of the correlation between the two factors. Key words: Mediterranean islands, insular biogeography, number of species - area relationship, isolation, habitat diversity, islets.
Aquatic hyphomycetes in three rivers of southwestern France. I. Spatial and temporal changes in conidial concentration, species richness, and community diversity
Authors: Fabre Eric
Published: April 2011

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.
Floral syndrome in Amelanchier nantucketensis (Rosaceae). I. Floral density, bee activity, and characterization of andropetaly
Authors: Dibble Alison C. , Drummond Francis A.
Published: April 2011

The clonal shrub Amelanchier nantucketensis is andropetalous; a variable number of petals as well as normal anthers both bear germinable pollen. To determine whether floral density associated with andropetaly is related to activity of native bees on flowers, we compared Amelanchier nantucketensis to Amelanchier humilis and Amelanchier stolonifera, which have sterile petals. In samples from four Maine sites, floral density in Amelanchier nantucketensis was 30.3% greater than that for Amelanchier humilis and 39.5% greater than that for Amelanchier stolonifera; in Amelanchier nantucketensis, flowers were more numerous per cubic metre and distance between flowers was shorter. There was a significant correlation across all sites and species between the number of flowers per plant and number of inflorescences visited per bee in 10 min (r = 0.711, p = 0.0001). Statistical t tests separated Amelanchier nantucketensis from both Amelanchier humilis and Amelanchier stolonifera by plant height, nearest stem, nearest flower, and number of inflorescences visited per bee during 10 min. Plant species classification in a canonical discriminant analysis was 83–93% correct with four plant variables, namely distance to nearest flower, distance to nearest inflorescence, plant width, and plant height. Our findings support optimal foraging theory in that bee visits increase with floral density in these Amelanchier species. Key words: Amelanchier, andropetaly, bees, floral density, morphology, Maine.
Floral syndrome in Amelanchier nantucketensis (Rosaceae). II. Bee preference and diversity associated with andropetaly
Authors: Dibble Alison C. , Drummond Francis A. , Laberge Wallace E.
Published: April 2011

Pollinator preference has been demonstrated to depend on floral morphology in some plant groups. We tested bee preference for Amelanchier nantucketensis, which has pollen-bearing petals or andropetals, over Amelanchier humilis with its normal petals when these flower together at two Maine sites. In an array experiment with equal floral display for Amelanchier nantucketensis and Amelanchier humilis, almost twice as many bees approached the latter first. Bees responded to some aspect of the larger flowers of Amelanchier humilis when number of inflorescences and height above the ground were similar. We captured 539 bees in 43 species individually on flowers, in malaise traps, and in sweeps; most were common, widely distributed solitary and eusocial bees. Bee species diversity differed slightly between plant species, and guilds differed; 11 bee species were unique to Amelanchier nantucketensis, including 39 individuals of Andrena milwaukiensis, and three species were unique to Amelanchier humilis. For 29 bee species shared by both plant species, abundance on Amelanchier nantucketensis was greater than on Amelanchier humilis for 62%, less for 14%, and the same for 24%. Bees might be attracted to Amelanchier nantucketensis less by andropetaly than by proximity of flowers to the ground, floral density, or unidentified features. Key words: Amelanchier, bees, foraging, morphology, Maine, species diversity.
Negative heterosis not apparent in 22-year-old hybrids of Picea mariana and Picea rubens
Authors: Johnsen Kurt H , Major John E , Loo Judy , McPhee Donald
Published: April 2011

Work from the 1970s indicated that, relative to either parent species, crosses between red spruce (Picea rubens Sarg.) and black spruce (Picea mariana (Mill.) B.S.P.) were inferior with respect to both growth and photosynthesis. We re-examined the hypothesis that there is negative heterosis in hybrids of red and black spruce using 22-year-old trees in a common garden study planted on two sites. The trees were the product of controlled crossings and represent a continuum from hybrid class 0 (pure black spruce) to hybrid class 1 (pure red spruce). Progeny of all controlled crosses were measured for height and diameter. A subset of families were measured for gas exchange and were assessed using a hybrid index based on needle color, needle configuration, twig ridges, twig bark color, vegetative bud color, and cone scale morphology. Tree growth rate linearly declined with the increasing proportion of red spruce germplasm (increasing hybrid index). In 1994, intermediate hybrid index classes did not differ in gas exchange from either pure black spruce (hybrid index class 0) or pure red spruce (hybrid index class 1), and in 1996, hybrids displayed slightly higher rates of gas exchange. Thus, negative heterosis was not apparent in 22-year-old trees. Individual tree hybrid index generally agreed with expectation based on midparent means, although the relationship was stronger on the higher productivity site (r2 = 0.91) than the poorer productivity site (r2 = 0.54).Key words: black spruce, heterosis, hybrid, photosynthesis, red spruce.
Analyzing leaf margins with the use of a shape feature description language
Authors: Moraczewski Ireneusz R
Published: April 2011

A method for automated analysis of leaf margins is presented. A detailed algorithm for the decomposition of a leaf into its central part and marginal projections (teeth) is given. Cut-off projections that cannot be decomposed any further are approximated to simple geometrical figures. The set of cut-off projections is then characterized by tens of attributes, which in turn, can constitute an input for multivariate methods. In contrast to well-known shape descriptor systems (e.g., moment invariants, elliptic Fourier coefficients, chain codes) this method is highly specific, permits plausible botanical interpretation, and is computationally inexpensive. Some limitations of the approach are discussed. It seems that the technique can be utilized in computer identification systems and for purely taxonomical purposes. The paper is rounded off with cluster analysis of a small set of leaves described by marginal characters only. It is shown that leaves differing in indentation pattern but otherwise similar can be discriminated by the method. On the other hand, even considerable blade damage does not prevent the leaves of one species from being grouped together. It is also demonstrated that dendrograms based on moment invariants and elliptic Fourier coefficients do not match the predefined partition.Key words: biometrics, identification aids, image acquisition, shape descriptors.
Une méthode d'estimation de l'indice foliaire mort d'une culture à partir des masses de feuilles. Application au cas du topinambour
Authors: Denoroy Pascal
Published: April 2011

The quantification of the equivalent area of the dead leaves of a canopy is necessary for any quantitative study dealing with the dynamics of leaf area index. A method to estimate this area from measurements normally performed in growth analysis is presented and tested. The method is parameterized and validated for two varieties of Jerusalem artichoke. Cautions for use are presented.Key words: Leaf area index, dead leaves, growth analysis, method, Helianthus tuberosus L., Jerusalem artichoke.
Persistent, systemic, asymptomatic infections of Albugo candida, an oomycete parasite, detected in three wild crucifer species
Authors: Jacobson David J , LeFebvre Siobhan M , Ojerio Ryan S , Berwald Nicole , Heikkinen Erja
Published: April 2011

Field observations and published data suggested that the oomycete parasite Albugo candida (Pers.) Kuntze could exist as latent, asymptomatic, systemic infections. The wild crucifer species Lepidium campestre (L.) R.Br., Arabis lyrata L., and Erysimum menziesii ssp. eurekense R.A. Price were chosen as models to test this hypothesis. Detection of the parasite in asymptomatic host tissue was based on polymerase chain reaction amplification of ribosomal DNA internal transcribed spacer region I of A. candida using primers designed to discriminate between plant and parasite DNA template. Albugo candida was detected in high proportions of asymptomatic field plants (vegetative and reproductive), greenhouse grown vegetative rosettes, and laboratory germinated seedlings of each species. For example, A. candida appeared to be systemic in all 20 field plants and 10 inoculated rosettes of L. campestre. Albugo candida was present in uninoculated rosettes and seedlings (up to 98%) suggesting seed borne transmission of the pathogen. Although the parameters controlling symptom development are still unclear, presence of the pathogen appeared not to be sufficient for symptom expression. Persistent, asymptomatic, systemic infections that are vertically transmitted through seed suggest that A. candida may possibly form endophytic relationships with at least some of its crucifer hosts.Key words: fungal endophyte, latent infection, PCR detection, rDNA ITS I.
Kinetics of Douglas-fir (Pseudotsuga menziesii) somatic embryo development
Authors: Taber Ryan P , Zhang Chun , Hu Wei-Shou
Published: April 2011

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is one of the most economically important softwood species in the Pacific Northwest region. Somatic embryogenesis is a potential mass propagation technology for increasing the productivity of existing forest acreage. Combined with traditional breeding methods and recent advances of genetic engineering in plant species, somatic embryos can shorten the elite clone selection process significantly. Somatic embryo culture of Douglas-fir involves three stages: maintenance, abscisic acid (ABA) singulation, and maturation. At the beginning of all stages of culture, the population of cells with embryogenic potential is increased through the weekly subcultured maintenance stage; transfer into the ABA singulation stage initiates embryo development, while cotyledonary embryos are formed in the maturation state. The first two stages were carried out in submerged suspension culture, while during the maturation stage the developing embryos were placed on a polyester pad in a Petri dish. The growth kinetics in these stages were investigated. Fresh and dry weights were observed to double in the maintenance stage, while a smaller increase occurred in the ABA singulation stage. NH4+ was consumed preferentially to NO3- in all culture stages. Sucrose, the primary carbon source, was hydrolyzed to glucose and fructose rapidly. During cultivation, glucose and fructose were consumed simultaneously. The hydrolysis of sucrose resulted in a slight osmolarity increase at the beginning of all culture stages, while the subsequent consumption of glucose and fructose coincided with a gradual decrease in osmolarity. This dynamic osmolarity pressure profile is most profound in the maturation stage, in which the initial high osmotic pressure of 600 ± 20 mOsm/kg (mean ± SD) increased to 700 ± 27 mOsm/kg after sucrose was hydrolyzed but decreased to 350 ± 14 mOsm/kg after the depletion of sugars at the end of cultivation. The complete process of embryo development, from the week-long maintenance culture, through the weekly subcultured ABA singulation culture, to the maturation of embryos took between 70 and 80 days. Each millilitre of culture present at the onset of maintenance culture gave rise to approximately 420 mature embryos. During that same time period, the biomass increased approximately 100 times. Prolonging the cultivation time failed to increase the yield of mature embryos. These results give a more complete view of the kinetic behavior of developing Douglas-fir embryos and will aid in the optimization and scale-up of this important process.Key words: somatic embyrogenesis, Douglas-fir, Pseudotsuga menziesii, growth kinetics, ABA, osmolarity, development.
Architecture et gradients morphogénétiques chez de jeunes hêtres Fagus sylvatica L. Fagaceae) en milieu forestier
Authors: Nicolini Eric
Published: April 2011

The objective of this study was to describe the different morphological gradients being used as the basis for the development of the shape of the stem system in young forest-grown 7-year-old beeches, while characterizing the structural evolution of successively produced annual shoots in relation to the timing of their formation as well as their topological situation among tree stem systems. Three simple morphogenetic gradients explain the developmental dynamics of their overall stem system and the evolution in time and space of the morphogenetic functioning of their primary meristem structure. The first one illustrates structure settings by progressive increase of annual growth rate (increase of foliated node number and of annual shoot length) and of the branching angle of the trunk, as well as of successively produced twigs. The second gradient is represented by the "primary acrotonic" phenomenon described by Rauh in beech, which encourages formation and development of the highest lateral axes on the annual shoot. The third one is characterized by a gradual reduction in annual growth rate as well as of the branching angle of the lowest axes of the tree, indicating their decline and their imminent elimination by natural pruning.Key words: beech, architecture, growth, ramification, polycyclism, morphology.[Translated by editorial staff]
Effect of sink size on growth response to elevated atmospheric CO2 within the genus Brassica
Authors: Reekie Edward G , MacDougall Glenn , Wong Ivan , Hicklenton Peter R
Published: April 2011

Many plants grown at elevated CO2 concentrations exhibit enhanced photosynthetic rates. However, this increase in photosynthesis is often reduced after prolonged exposure to elevated CO2. This reduction may be related to the capacity of plants to utilize the extra photosynthate produced at elevated CO2. This study examined the effect of source to sink ratio on the capacity of plants to respond to elevated CO2. Seven species or cultivars within the genus Brassica were germinated and grown at either 350 or 1000 ppm CO2. Broccoli (Brassica oleracea L.) and cauliflower (B. oleracea L.) have large carbon sinks in the reproductive structures; Chinese broccoli (Brassica campestris L.) and marrow stem kale (B. oleracea) have carbon sinks in the stem; turnip (B. campestris) stores carbon in the root; rape (Brassica napus L.) and white mustard (Brassica alba (L.) Rabenh.) have no obvious carbon storage structures and were assumed to have a lower sink strength relative to the above cultivars. Plants were harvested at three stages of development and total plant weight, leaf area ratio, and allocation to leaf, root, and stem determined. As young seedlings, all cultivars responded positively to elevated CO2. The long-term growth response of different cultivars to CO2 was independent of sink location, but was dependent on sink size. Cultivars with no obvious carbon storage structures showed no significant growth enhancement by elevated CO2 by the end of the experiment. However, neither leaf area ratio nor biomass allocation pattern were reliable predictors of response to CO2 suggesting that assessing differences in source to sink ratio is not necessarily straightforward.Key words: biomass allocation, sink strength, functional groups, elevated carbon dioxide, leaf area ratio.