bluuebunny/crossref_metadata_2025 huggingface dataset:
Searching for the taxonomic position of the African genus Colletoecema (Rubiaceae): morphology and anatomy compared to an rps16-intron analysis of the Rubioideae
Authors: Piesschaert Frederic , Andersson Lennart , Jansen Steven , Dessein Steven , Robbrecht Elmar , Smets Erik
Published: April 2011

The morphology and anatomy of the African monospecific genus Colletoecema E. Petit (Rubiaceae) is documented and illustrated (including wood anatomy, pollen morphology, gynoecial and exotestal structure). Morphological and anatomical comparison shows that Colletoecema differs in many aspects from the Psychotrieae (e.g., wood anatomy, seed structure). Consequently, the genus' provisional position in the Psychotrieae cannot be maintained. Morindeae, the second tribe Colletoecema has been associated with, has a different gynoecial structure. The oily endosperm and large embryo of Colletoecema is found in several genera that often were or still are included in the Psychotrieae or Morindeae (Trichostachys, Saldinia, Ronabea, and Lasianthus). However, they differ in several other aspects, which makes a close relationship doubtful. Colletoecema exhibits a unique combination of characters including axillary inflorescences, banded parenchyma in the wood, ovules attached around the middle of the septum, bilocular pyrenes, seeds with oily endosperm and large embryo, and verrucate exotestal thickenings, not encountered elsewhere in the Rubioideae. A cladistic analysis based on nucleotide sequence variation in the rps16 intron (chloroplast DNA) confirms that Colletoecema is related neither to Psychotrieae nor to Morindeae. Colletoecema appears as a sister genus of Ophiorrhiza in a weakly supported clade among the basalmost clades of the subfamily Rubioideae, but there is very little morphological support for this relationship.Key words: anatomy, chloroplast DNA, cladistics, morphology, Psychotrieae, Rubioideae.
Peculiar structures occurring in vessel walls of the susceptible carnation cultivar Early Sam infected with Fusarium oxysporum f.sp. dianthi
Authors: Ouellette G B , Baayen R P
Published: April 2011

Ultrastructural and cytochemical studies of infection by Fusarium oxysporum f.sp. dianthi (Prillieux & Delacroix) Snyder & Hansen in susceptible carnation (Dianthus caryophyllus L.) plants have disclosed conspicuous amounts of an unusual dense material that extends long distances in vessel walls. This material, which at times was circumscribed by bands of material that labelled for chitin and was closely linked to large fungal or microhyphal cells, contained membranous and filamentous structures and opaque particles of uniform appearance. At times, the latter aggregated into crystalline bodies.Key words: cytochemical probes, fusarium wilt, microhyphae, wall alterations.
Foliar plasticity of hybrid spruce in relation to crown position and stand age
Authors: Richardson A D , Berlyn G P , Ashton P MS , Thadani R , Cameron I R
Published: April 2011

This study examined the foliar response of putative hybrid Engelmann × white × Sitka spruce (Picea engelmannii Parry × Picea glauca (Moench) Voss × Picea sitchensis (Bong.) Carr) needles in relation to crown position and across three stages of development (15, 55, and 145 years). We focused on the morphological and anatomical response, and used physiological measures (photosynthesis and stomatal conductance) to emphasize the important relationship between structure and function. We found that needles from the upper outer crown position were adaptated to reduce stress from evapotranspiration. Trees from the 15- and 55-year-old stands generally responded the most, and trees from the 145-year-old stand responded the least. As they mature, these spruce trees may have reduced ability to adapt to their environment. Some of our results contradict what the literature considers "typical" for sun-shade dimorphism in temperate forests. For example, in all stands, sun needles were broader than shade needles and, in the two younger stands, sun needles were larger in area, not smaller, than shade needles. Also, in the youngest stand, stomatal pores were longer on sun needles than on shade needles. There were no definite patterns in stomatal spacing with regard to crown position. Our results are indicative of the strategies adopted to increase competitiveness in a resource-limited environment. We suggest that, in the 15-year-old stand, neither water nor light is limiting; in the 55-year-old stand, both water and light are highly limiting; and in the 145-year-old stand, water is most limiting.Key words: drought, foliar plasticity, needle anatomy, photosynthesis, Picea, stand development, sun-shade.
IsRhizoplaca(Lecanorales, lichenized Ascomycota) a monophyletic genus?
Authors: Arup U , Grube M
Published: April 2011

Rhizoplaca Zopf is a genus characterized by an umbilicate thallus with an upper and a lower cortex, as well as a cupulate hypothecium. It has been considered to be related to Lecanora Ach., the type genus of the Lecanoraceae and, in particular, to the lobate species of this genus. The phylogeny of Rhizoplaca, the monotypic Arctopeltis thuleana Poelt, and a number of representatives of different groups of Lecanora is studied, using sequences from the nuclear ribosomal internal transcribed spacer (ITS) regions. The results suggest an origin for Rhizoplaca species within the large genus Lecanora. A well-supported monophyletic assemblage includes the umbilicate type species Rhizoplaca melanophthalma (DC.) Leuck. & Poelt, the lobate Lecanora novomexicana H. Magn., and five vagrant Rhizoplaca species. Rhizoplaca chrysoleuca (Sm.) Zopf and Rhizoplaca subdicrepans (Nyl.) R. Sant. form a separate well-supported group and Rhizoplaca peltata (Ram.) Leuck. & Poelt is more closely related to Lecanora muralis (Schreb.) Rabenh. Together with data on secondary chemistry, the results show that the umbilicate thallus with a lower and an upper cortex, as well as apothecia with a cupulate hypothecium found in Rhizoplaca and A. thuleana, have developed several times in independant lineages in Lecanora. The thallus morphology in lecanoroid lichens is highly variable and does not necessarily reflect phylogenetic relationships.Key words: Rhizoplaca, Lecanora, Lecanorales, phylogeny, ITS.
Differentiation of infection structures of the powdery mildew fungusUncinula necatorand adhesion to the host cuticle
Authors: Rumbolz J , Kassemeyer H -H , Steinmetz V , Deising H B , Mendgen K , Mathys D , Wirtz S , Guggenheim R
Published: April 2011

Development and adhesion of infection structures of the grapevine powdery mildew fungus, Uncinula necator (Schw.) Burr., were investigated during the early stages of leaf colonization. Light microscopy showed that primary appressoria occurred 3.5 h post inoculation (p.i.) and that hyphae on the leaf surface, indicative of successful host colonization, appeared 14 h p.i. Low temperature scanning electron microscopy revealed deposits of extracellular material at the contact zone of fungal structures and plant cuticle, suggesting firm attachment of the pathogen. To investigate whether or not esterase or cutinase activity is involved in establishing the fungus on the host cuticle, histochemical assays and inhibitor studies were performed. Results indicated that esterase activity was associated with conidia and infection structures. A single fungal extracellular protein was identified as a cutinase by its ability to hydrolyze3H-cutin. Probing Southern blots of genomic DNA of U. necator, Magnaporthe grisea, and Fusarium solani f.sp. pisi with the cutinase gene of F. solani f.sp. pisi suggested that the cutinase gene of U. necator shares only limited sequence similarities with the cutinase genes of the other fungi investigated. Adhesion assays showed that the presence of esterase-cutinase inhibitors on the cuticle did not significantly affect adhesion. The role of the enzyme in fungal adhesion is discussed.Key words: grapevine powdery mildew, Vitis vinifera, cutinase, extracellular matrix, cryofixation, low temperature scanning electron microscopy.
Cost of apical dominance in two monocarpic herbs, Erysimum strictum and Rhinanthus minor
Authors: Huhta Ari-Pekka , Tuomi Juha , Rautio Pasi
Published: April 2011

Apical dominance is advantageous in conditions favoring rapid growth in height and unbranched architecture. The cost of apical dominance, on the other hand, should be expressed in conditions where fecundity increases along with an increasing number of branches. Apical damage can be used to measure such costs: when suppressed meristems are released from apical inhibition, the vegetative and reproductive productivity of initially unbranched plants should increase owing to the regrowth and increased branch development following damage. We studied these regrowth responses in two monocarpic herbs, Erysimum strictum P. Gaertn., B. Mey., and Scherb. and Rhinanthus minor L., after both apical damage (10% of the shoot cut) and more extensive damage (50 and 75% cutting). Both species tolerated apical damage, although severe damage had detrimental effects on the performance of both, especially R. minor. Apical damage had positive effects on most of the measured performance parameters of Erysimum. However, the success of seed germination collapsed, presumably due to delayed flowering and less successful pollination. The response was parallel in Rhinanthus; apical damage affected neither the vegetative biomass nor fecundity, but heavier damage, especially 75% clipping, led to severe reductions in most performance measures. The differences in regrowth responses are presumably due to the different habitat requirements of the species. Rhinanthus prefers relatively dense vegetation and starts to branch and produce flowers after a certain threshold in height has been reached, whereas Erysimum prefers gaps in vegetation. In this species, unbranched architecture may be favored in closed vegetation and branched architecture in less competitive habitats. In both species, fruit production correlated positively with the number of branches in both control and clipped plants, which is consistent with the assumption of the cost of apical dominance.Key words: apical dominance, competition, damage, meristem, overcompensation, regrowth.
Thermogenesis in three Philodendron species (Araceae) of French Guiana
Authors: Gibernau Marc , Barabé Denis
Published: April 2011

Spadix temperature was measured in three species of Philodendron: P. acutatum Schott, P. pedatum (Hooker) Kunth, and P. solimoesense A. C. Smith. These species showed two different patterns of spadix temperature during their flowering cycle. In P. acutatum and P. pedatum (subgenus Philodendron), the spadix warmed up twice during the beginning of each flowering night with a temperature not significantly different from that of the ambient air between the two peaks. In P. solimoesense (subgenus Meconostigma), the spadix temperature rose to 14°C above that of the ambient air during the first night, then it progressively cooled down but remained 3-6°C above the ambient air temperature. We propose that the heat production and the spadix temperature patterns observed may reflect different physiological processes and have a taxonomic significance in the genus Philodendron.Key words: Araceae, flowering cycle, flower temperature, heating flower.
Population dynamics response of Lupinus arcticus to fertilization, clipping, and neighbour removal in the understory of the boreal forest
Authors: Graham Stephanie A , Turkington Roy
Published: April 2011

A demographic study was conducted on field populations of Lupinus arcticus S. Wats. growing in the understory of a white spruce dominated forest, near Kluane Lake, Yukon. The relative effects of soil fertility level, neighbours, and herbivory were assessed using a factorial experiment of ± fertilizer (N-P-K), ± neighbour removal, and ± clipping. We monitored the dynamics of leaves and collected data on reproduction, survival, and size for two growing seasons. Fertilizing increased the incidence of disease on leaves and reduced reproductive efficiency. Clipping reduced leaf cohort survivorship, total leaf density, and the incidence of disease on leaves. Removing neighbours increased the percent cover of L. arcticus and decreased total leaf mortality. Treatments had no effect on the survival of leaves in early cohorts. Although there were some significant responses to treatments, the overall tendency was a lack of response, especially pertaining to leaf population dynamics. This low response to the treatments imposed is consistent with the argument that plants growing in low productivity, infrequently disturbed habitats should show little response to short-term changes in local environmental conditions. The results are also consistent with suggestions that plants in moderately stressed habitats should be more adapted to withstand grazing than competition.Key words: boreal forest, competition, demography, fertilization, population dynamics, Lupinus arcticus.
The vascular flora of Terra Nova National Park, Newfoundland, Canada: a biodiversity analysis from a biogeographical and life form perspective
Authors: Charest René , Brouillet Luc , Bouchard André , Hay Stuart
Published: April 2011

Terra Nova National Park, located on the east coast of Newfoundland, has a vascular flora of 535 taxa, including 33 rare species and 94 introduced taxa. About 75% of the native flora of the Park is composed of hemicryptophyte and cryptophyte species. Phanerophytes and nanophanerophytes represent only 13% of the flora, but the percentages of occurrence of these life forms reaches 31%. The flora of the Park is mainly boreal (56%), composed mainly of Boreal North American, Boreal Eastern North American, and Circumboreal elements. Arctic-alpine species are infrequent. We report two species as new to Newfoundland: Festuca richardsonii Hooker (Poaceae) and Carex communis L.H. Bailey var. communis (Cyperaceae). Significant positive and negative associations between (i) life forms and (ii) phytogeographical elements, and the distribution of species within the habitats of the Park were established using the Fourth Corner Method. Distribution of life forms and phytogeographical elements within habitats of the Park appears to be explained more by ecological characteristics of species than by their history.Key words: life form, biogeography, biodiversity, Terra Nova National Park, Newfoundland, Canada.
The role of climate on the developmental history of Frontenac Peatland, southern Quebec
Authors: Lavoie Martin , Richard Pierre JH
Published: April 2011

The developmental stages, hydrological conditions, and net peat accumulation rates at three coring sites of Parc de Frontenac Peatland (Quebec) were reconstructed to examine the role of climate on peat accumulation. During the early to mid-Holocene, elevated temperatures proved to be a more critical factor for sustained peat production than precipitation, because peatland development occurred mostly under a dry climate according to a low lake-level stage lasting from 11 000 to 7000 calibrated (cal.) BP in a nearby lake. Between 7000 and 6000 cal. BP, elevated net peat accumulation rates roughly correspond with a rise in lake water level, suggesting that higher precipitation and (or) less evapotranspiration then favored peat growth. A decrease in peat accumulation occurred from 5000 to 2500-1500 cal. BP, while the lake level was high from 4400 cal. BP. An important increase in net peat accumulation rate is recorded for this entire peatland from 1500 cal. BP. Lack of close timing between lake level changes and changes in peat accumulation rates or surface hydrology suggest that temperature and autogenic processes were often more important than regional water balance in the developmental history of the peatland.Key words: peatlands, paleohydrology, pollen, plant macrofossils, rhizopods, Quebec.
Effects of natural habitat fragmentation on the species richness, diversity, and composition of cliff vegetation
Authors: Haig A R , Matthes U , Larson D W
Published: April 2011

Plant species richness, diversity, and some aspects of species composition were measured on natural limestone cliff fragments of varying size within the Niagara Escarpment Biosphere Reserve, Canada. This information was collected because knowledge about how different components of community structure change in response to natural fragmentation may permit the prediction of the effects of future anthropogenic fragmentation. The number and relative abundance of vascular plant, bryophyte, and lichen species were determined on cliff fragments that varied in area from 185 to 126 000 m2. Latitude, aspect, percent available photosynthetically active radiation on the cliff face, distance from the nearest neighbouring cliff, and length of the nearest neighbouring cliff were also measured. Regression analysis was used to test for a significant relationship between fragment area and diversity of vascular plants, bryophytes, and lichens both separately and combined. Multiple regression with all subsets selection was used to find the best predictors of species richness from among all variables measured for the 21 cliff fragments. Multivariate analyses were used to study the effect of fragmentation on the structure of the vegetation as a whole. The results showed no significant relationship between cliff fragment area and richness or diversity for vascular plants and bryophytes, and only a marginally significant increase in richness with area for lichens. The multivariate analyses also showed that only one community type exists, and that its structure mainly varies as a function of latitude. These results indicate that very small fragments of cliff face can support a similar plant biodiversity as do large continuous portions of the Niagara Escarpment.Key words: habitat fragmentation, plant species richness, lichens, bryophytes, cliff vegetation.
Moss distribution in streams of the Quebec Laurentian Mountains
Authors: Cattaneo Antonella , Fortin Lucie
Published: April 2011

To model the distribution of aquatic mosses, we measured their cover in 33 Quebec streams. The variation in moss cover among streams was explained mostly (42%) by substratum size (percentage >25 cm in diameter). Water pH and depth also explained a significant amount of variation (9 and 10%, respectively). Within a stream, moss cover was again positively correlated to the availability of large substrata and negatively to water depth. There was a strong inverse relationship between covers of moss and of the filamentous cyanobacterium Stigonema, suggesting a competitive interaction. This study confirms previous observations that moss distribution is mainly controlled by substratum size. Chemistry explains part of the among-stream variation. Stigonema-moss competition partly accounts for the patchy distribution within a stream.Key words: aquatic mosses, Fontinalis, streams, Quebec.
The effect of leaf phenology of overstory trees on the reproductive success of an understory shrub, Staphylea bumalda DC
Authors: Maeno Hanako , Hiura Tsutom
Published: April 2011

The effects of the leaf phenology of canopy trees on the reproductive success of an entomophilous, self-incompatible shrub, Staphylea bumalda DC. were examined in a deciduous broad-leaved forest in northern Japan. The amount of light reaching a particular understory shrub from spring to early summer was determined by the leafing date of surrounding canopy species. Variation in leafing date of canopy species affected flower and fruit production by the understory shrub. These results suggest that reproductive success of understory shrubs depends in part on the leaf phenology of canopy trees.Key words: phenology, deciduous broad-leaved forest, fruit set, resource limitation.
Flavonoid chemistry and chromosome numbers of Fallopia section Pleuropterus (Polygonaceae)
Authors: Kim Min-Ha , Park Jin Hee , Won Hyosig , Park Chong-Wook
Published: April 2011

Flavonoid chemistry and chromosome numbers of Fallopia sect. Pleuropterus were examined to gain insights into the relationships among the taxa within the section. Twenty-seven flavonoid compounds were isolated and identified from taxa of section Pleuropterus; most of them were glycosylated derivatives of the flavonols kaempferol, quercetin, and myricetin, and of the flavones apigenin and luteolin. The flavonoid data appear to be useful for taxon delimitation, because all taxa examined are readily distinguished by their flavonoid profiles. In addition, the flavonoid data revealed the presence of two chemical entities in the section; the first group includes Fallopia multiflora (Thunb. ex Murray) Haraldson (with varieties) and Fallopia ciliinervis (Nakai) Hammer and the second group includes Fallopia baldschuanica (Regel) Holub and Fallopia koreana Oh & Kim. These groupings suggested by the flavonoid chemistry are well-corroborated by the chromosome number of these taxa. Taxa of the first group have chromosome numbers based on x = 11 (2n = 22, 44), whereas chromosome numbers of the second group are based on x = 10 (2n = 20). Our counts for F. multiflora var. hypoleuca (Nakai ex Ohwi) Yonekura & H. Ohashi (2n = 44), Polygonum multiflorum Thunb. ex Murray (= F. multiflora) var. angulatum S.Y. Liu (2n = 22), F. ciliinervis (2n = 22), and F. koreana (2n = 20) are the first reports for these taxa. Based on these results, and in conjunction with morphological evidence, it is strongly suggested that the two groups of section Pleuropterus revealed by this study are not closely allied and may represent separate lineages in the genus Fallopia.Key words: Polygonaceae, Fallopia sect. Pleuropterus, flavonoids, chromosome number, chemotaxonomy.
Effect of branch position and light availability on shoot growth of understory sugar maple and yellow birch saplings
Authors: Goulet Julie , Messier Christian , Nikinmaa Eero
Published: April 2011

Phenotypic plasticity enables tree saplings to change their morphology according to their environment to grow toward a better light micro-habitat. Therefore, processes of crown development could be expected to vary as a function of light. The objectives of this study were to (i) evaluate the effects of position and light availability on shoot growth within the crowns of understory saplings of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula alleghaniensis Britton.); (ii) develop a new vigour index for shoots; and (iii) evaluate the possible factors relating to branch mortality in the crown of sugar maple saplings. The results revealed that there is a clear branch position effect on shoot growth in the crown for yellow birch saplings and that it is partly related to the presence of two types of shoots. Dead branches were located at the bottom of the crown of sugar maple saplings; they were smaller in size, had wider angles and had lower indexes of vigour than live branches found nearby. Preliminary results obtained on the vigour index indicate that it is a potentially useful tool for predicting the growth and vigour status of a branch.Key words: shoot growth, branch position, light availability, branch mortality, sugar maple, yellow birch.
Effect of the lower lip of Monarda didyma on pollen removal by hummingbirds
Authors: Temeles Ethan J , Rankin Adam G
Published: April 2011

We examined the effect of the lower lip of Monarda didyma L. on pollen removal by ruby-throated hummingbirds (Archilochus colubris L.) through comparisons of hummingbird visits to natural, lipped flowers versus those that had their lower lip experimentally removed. Birds missed the openings of lipless flowers more often than lipped flowers and thus spent more time attempting to insert their bills into them. Once their bills entered the floral tube, handling times of hummingbirds were significantly longer at lipped than at lipless flowers. Contact durations with anthers and amounts of pollen removed by hummingbirds were significantly greater at lipped than at lipless flowers. Videotapes indicated that lips enhanced pollen removal by slowing a hummingbird's bill insertion into the floral tube, which increased the amount of time that a bird was positioned under a flower's anthers. Unlike the conventional view of hummingbird-flower evolution, which argues for the loss or reduction of lips, our results suggest that lower lips may be maintained in some hummingbird flower species, because they are preadaptations that act as nectar guides for hummingbirds and positioners for optimum pollen removal, in addition to possibly serving as landing platforms or attractants for secondary pollination by bees.Key words: Monarda didyma, pollination, flower morphology, hummingbirds.
In situ field measurements of photosynthetic rates of tropical tree species: a test of the functional group hypothesis
Authors: Ellis Alexander R , Hubbell Stephen P , Potvin Catherine
Published: April 2011

We examined photosynthetic characteristics of 21 tree species from a Panamanian forest differing in successional status. We hypothesized that functional guilds of species, grouped by successional status, would differ in photosynthetic performance and that pioneers would be more sensitive to seasonality and more variable in response to light than intermediate or shade tolerants. Steady-state leaf-level photosynthesis (A) was measured in situ on eight trees per species. Light response curves were generated by fitting a hyperbolic model to these data. Average light saturated photosynthetic rates (Amax) were then calculated for each species. Variability of light, photosynthesis, and leaf characteristics were quantified using coefficients of variation (CV). Significant differences were detected among species and functional groups for A, Amax, and leaf N concentration. Functional group explained 46% of the observed variation in A. Pioneers exhibited higher light-saturated photosynthetic rates than intermediates; both were higher than shade tolerants. Intermediates were the most seasonally plastic group and had the highest leaf N concentration. Shade tolerants were found in lower, more variable light environments than pioneers. A strong positive correlation between diameter growth rate and photosynthetic rate (r2= 0.55, p = 0.004) was observed across species. Our results tend to confirm the hypothesis that physiological traits can be used to differentiate among functional groups of plants. However, no evidence was found for higher plasticity of pioneer compared with shade-tolerant species.Key words: tropical trees, physiological plasticity, photosynthesis, nitrogen, growth, tropical succession.
Clonal diversity within and among introduced populations of the apomictic vine Bryonia alba (Cucurbitaceae)
Authors: Novak Stephen J , Mack Richard N
Published: April 2011

Bryonia alba L. (Cucurbitaceae) is a herbaceous Eurasian vine that predominantly reproduces clonally (asexually) through apomixis. We assessed the magnitude and distribution of clonal diversity within and among 23 recently established populations of B. alba in its new range in the western United States, based on the distribution of multilocus isozyme genotypes. Fifty-two unique clones were detected: 30 in the nine populations from eastern Washington and northern Idaho, and the remaining 22 in 14 populations from western Montana, northern Utah, and southern Idaho. On average, each population of B. alba was composed of 6.4 clones, and the proportion of distinguishable clones was 0.275. Multilocus diversity (D) was 0.632 and multilocus evenness (E) was 0.556. Twenty-six of 52 clones (50%) were restricted to a single population, and, on average, each clone occurred in 2.83 populations. Compared with other clonally reproducing plant species, this vine possesses moderate to high levels of clonal diversity in its new range in the western United States. This diversity appears to be a consequence of the events associated with its introduction (including multiple introductions), founder effects, and the proportion of sexual to apomictic reproduction within populations.Key words: invasive vine, apomixis, multilocus genotypes, clonal diversity and evenness, Bryonia alba, Cucurbitaceae.
Modifications expérimentales de la morphogenèse du système racinaire de jeunes semis d'hévéa (Hevea brasiliensis)
Authors: Roux Yannick Le , Pagès Loïc
Published: April 2011

Determining factors involved in root polymorphism were studied in young hevea seedlings (Hevea brasiliensis Mull. Arg.) following an experimental block of the tap root in the laboratory, using minirhizotron grown plants. The authors show that this block promotes different morphogenetic modifications in the root system: regrowth of the early secondary roots having the largest external apex, high density of the ramification zone in the taproot apical area, large growth (associated with an important external diameter at the apex), and orthogeotropism of the sequential secondary roots emerging after the treatment in the zone close to the blockage site. The evolution of morphogenetic potentialities of sequential secondary roots following an inhibition of the taproot growth was confirmed using other cultivation set ups, under controlled (aeropinic) or natural (underground observation windows) conditions. Overall results show that the expression of the early morphogenetic potential acquired by the roots can be modulated by the environmental conditions exerting their effect during their development. Notably, the active growth correlations existing between the taproot and the secondary axes confer a high plasticity to the root system which will permit its adaptation to heterogeneous or restricting environments. These correlative influences are discussed in the frame of an hormono-trophic model for the root morphogenetic determinism, essentially based on taproot dominancy.Key words: articial block, growth correlations, root system, morphogenesis, minirhizotron, Hevea brasiliensis.[Journal translation]
Influence de la densité du couvert forestier sur le développement architectural de jeunes chênes sessiles, Quercus petraea (Matt.) Liebl. (Fagaceae), en régénération forestière
Authors: Nicolini Eric , Barthélémy Daniel , Heuret Patrick
Published: April 2011

The growth and branching patterns of the main axis of 6-year-old sessile oak, growing in a natural regeneration in the north of France, were analysed each year retrospectively according to three increasing canopy density conditions: large gap, small gap, and dense canopy. Increasing gap size is associated with an increase in the total height, basal diameter, branching probability, and global polycyclism rate of the trees. At the growth unit or annual shoot level, from dense canopy to large gaps these botanical entities also show an increase in their total length, number of nodes, polycyclism, and branching rate as well as mean number of branches and mean internode length. A discussion of our results revealed some endogenous features of growth and branching patterns in young sessile oak trees. It is also shown that increasing canopy density generally tends to reduce the expression of the endogenous architectural sequence of differentiation of young sessile oak trees. Young trees growing below dense canopy thus seem to be "delayed" in their sequence of differentiation and appear to be in a "waiting" status, whereas young trees growing in large gaps exhibit an architecture very similar to trees growing in nurseries under nonlimiting growth conditions.Key words: architecture, Quercus petraea, growth, morphology, canopy density.
Microfungus communities of white spruce and trembling aspen logs at different stages of decay in disturbed and undisturbed sites in the boreal mixedwood region of Alberta
Authors: Lumley Trevor C , Gignac L Dennis , Currah Randolph S
Published: April 2011

Fallen logs of trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) at various stages of decomposition were sampled from undisturbed and 1-, 14-, and 28-year-old post-fire and post-harvest sites in northern Alberta and studied for differences in the associated microfungus communities. Wood samples were plated directly onto each of six different media and, from these, fungal species were identified and enumerated over a 24-month period. Approximately 10 000 isolates were obtained, representing 292 species of filamentous microfungi, including 41 ascomycetes, 29 zygomycetes, and 222 mitosporic fungi. The most commonly isolated species were Trichoderma viride (Gray) Pers., Rhinocladiella atrovirens Nannf., Penicillium pinophilum Hedgcock, and Mortierella ramanniana (Moller) Linnem. Cluster analysis and ordination of microfungus communities in logs showed that the tree species of the log had the greatest influence on the species composition of communities. Fungus community composition was also correlated with the stage of decomposition. Species richness was highest in logs from undisturbed sites and lowest in logs from the most recently disturbed sites. Species diversity (Shannon-Weaver) was only slightly higher at undisturbed sites than at disturbed sites. The most significant environmental factor was log moisture, which increased proportionately with stage of decomposition and was significantly correlated with climatic factors.Key words: ecology, fungi, ordination, succession, species richness, diversity.
Comparison of decomposition of belowground and aboveground plant litters in peatlands of boreal Alberta, Canada
Authors: Thormann Markus N , Bayley Suzanne E , Currah Randolph S
Published: April 2011

Studies examining the decomposition rates of belowground plant tissues in peatlands are scarce despite the significant contribution these tissues make to total plant production. Therefore, we measured mass losses of Carex aquatilis Wahlenb. leaves and rhizomes and Salix planifolia Pursh leaves and roots in a rich, sedge-dominated fen and Sphagnum fuscum (Schimp.) Klinggr. plants in a forested bog using the litter bag technique over a 2-year period in southern boreal Alberta. After 2 years, mass losses of C. aquatilis rhizomes (75%) were significantly higher than those of C. aquatilis leaves and Salix planifolia leaves, which were similar to each other (54 and 48%, respectively). Sphagnum fuscum and Salix planifolia root mass losses also were similar to each other (21 and 29%, respectively), but they were significantly lower than those of the other three litter types. Different tissue nutrient concentrations as well as alkalinity- and phosphorus-related surface water chemistry variables correlated significantly with mass losses of different litter types; however, they alone did not explain all of the mass loss trends. The majority of sedge peat and carbon in the fen originates from C. aquatilis leaves (188 and 86 g·m-2, respectively), with the remainder originating from C. aquatilis rhizomes (102 and 47 g·m-2, respectively) after the first 2 years of decomposition. Conversely, the majority of Salix planifolia peat and carbon originates from its roots (33 and 16 g·m-2, respectively) and the remainder from its leaves (24 and 11 g·m-2, respectively) over the same period. After the first 2 years of decomposition, 150 g·m-2of peat and 71 g·m-2of carbon remained from the decomposing Sphagnum fuscum in the bog.Key words: bog, fen, mass losses, Carex aquatilis, Salix planifolia, Sphagnum fuscum.
Root contrast enhancement for measurement with optical scanner-based image analysis
Authors: Costa C , Dwyer L M , Hamel C , Muamba D F , Wang X L , Nantais L , Smith D L
Published: April 2011

Fine roots (diameter <0.30 mm) account for about 80% of total root length in many species but are often underestimated owing to their small size and near transparency. We have assessed a technique for rapid and accurate estimation of root length when using image analysis. To allow the collection of clear images, several stains were tested to determine when staining is beneficial. Plants of six species (barley (Hordeum vulgare L.), maize (Zea mays L.), oat (Avena sativa L.), soybean (Glycine max (L.) Merr.), strawberry (Fragaria × ananassa), and wheat (Triticum aestivum L.)) were grown for either 3 or 5 weeks after emergence. Roots of five woody species (honey locust (Gleditsia triacanthos L.), Norway maple (Acer platanoides L.), red ash (Fraxinus pennsylvanica Marsh.), silver maple (Acer saccharinum L), and hackberry (Celtis occidentalis L.)) were collected outdoors. Stains were evaluated over a range of concentrations and for three staining times. Root variables were measured with WinRHIZO, an interactive scanner-based image analysis system. Two approaches were used: (i) measuring specific amounts of roots at several stain concentrations and contrasting the results with an unstained control and (ii) measuring unstained roots, recovering the roots, staining them and measuring them again. The tristimulus coordinates (L*a*b*) of unstained root colour were measured by spectrophotometer to determine if root colour might be used as an indicator as to whether or not staining improved the image contrast. Staining improved image contrast and substantially increased measured root length estimates for species with low root contrast (maize, barley, and wheat), gave small improvements for hackberry, Norway maple, and honey locust, but had no effect on other species. Staining for 10 min was sufficient to maximally enhance the image contrast of species with a high proportion of fine roots. Tristimulus coordinates indicated that differences among species correlated with the distribution of root diameter. Establishing whether staining of root samples is required should be accomplished before any study of root systems with a high proportion of fine roots is undertaken.Key words: root measurement, staining, imaging analysis, root colour measurement, stains.
Functional specialization of current shoots as a reproductive strategy in Japanese alder (Alnus hirsuta var. sibirica)
Authors: Hasegawa Shigeaki , Takeda Hiroshi
Published: April 2011

Current shoots, which form the crown of a tree, are specialized in various functions such as crown expansion, reproduction, and assimilation. We examined the temporal and spatial distribution of reproductive shoots in Alnus hirsuta Turcz. var. sibirica (Fischer) C.K. Schn., assessed their direct and indirect costs of reproduction, and explained their distribution in the crown as the reproductive strategy of a current shoot population. The upper and lower limits to the lengths of current shoots for reproductive growth (flower formation) were 40 and 10 cm, respectively. Reproductive 1-year-old shoots produced fewer shoots in the following year than non-reproductive 1-year-old shoots. In current shoots longer than 40 cm, the increment of reproductive output in the following year by abandonment of reproduction surpassed the decrement of reproductive output in the current year by abandonment of reproduction. This may be one reason for the upper limit of reproductive shoot length. Thus, the current shoot population of A. hirsuta var. sibirica may be divided into three functionally specialized subpopulations: reproductive, maintenance, and exploratory. This specialization is considered to be a reproductive strategy to maximize their lifetime reproductive success.Key words: current shoot population, reproductive ecology, functional specialization, cost of reproduction, Japanese alder.
Five new species of lichenicolous conidial fungi from Spain
Authors: Calatayud Vicent , Etayo Javier
Published: April 2011

Five new species of lichenicolous conidial fungi from Spain are described. The genus Lichenohendersonia Calatayud & Etayo gen.nov. is introduced to accommodate three new coelomycetes: Lichenohendersonia squamarinae Calatayud & Etayo sp.nov. (on Squamarina lentigera), Lichenohendersonia uniseptata Etayo & Calatayud sp.nov. (on Parmelina tiliacea), and Lichenohendersonia varians Calatayud & Etayo sp.nov. (type on Rhizoplaca chrysoleuca, but also occurring on other saxicolous crustose lichens). Two further species are also described: Phoma aggregata Calatayud & Etayo sp.nov. (on Diploschistes ocellatus), with numerous and densely aggregated pycnidia, and Feltgeniomyces dichotomus Etayo & Calatayud sp.nov., a sporodochial fungus occurring on Physcia biziana and Heterodermia sp. All these taxa are known only from the Iberian Peninsula, except F. dichotomus, which is also reported from Colombia. Keys to the known Feltgeniomyces and Lichenohendersonia species are provided.Key words: Lichenicolous fungi, deuteromycetes, Feltgeniomyces, Lichenohendersonia, Phoma, Spain.
Isozyme variation and its environmental correlates inElymus glaucusfrom the California Floristic Province
Authors: Wilson Barbara L , Kitzmiller Jay , Rolle Wayne , Hipkins Valerie D
Published: April 2011

Genetic variation in the self-fertile, allotetraploid grass Elymus glaucus Buckley was assessed using isozymes in 133 populations from southwestern Oregon and from the San Francisco Bay area and central Sierra Nevada mountains in California. Elymus glaucus was highly (98.5%) homozygous but also highly variable; 77% of loci were polymorphic, and the mean number of alleles per locus was 2.96. Populations were highly differentiated, with 40% of variation among populations. Geographic and genetic distances among populations were not correlated, except that populations collected within 5 km were generally more similar than average. Genetic distance among populations could not be predicted from geographic distance, geographic location, foliage pubescence, serpentine substrate, or habitat moisture. However, two genetic clusters, associated with elevation, did emerge. The taxonomic status of Elymus glaucus ssp. jepsonii (Burtt Davy) Gould, based on leaf pubescence, was not supported.Key words: Elymus glaucus, isozyme, genetic variation, Poaceae, polyploid, seed transfer.
An evaluation of methods for breaking seed dormancy in kudzu (Pueraria lobata)
Authors: Susko David J , Mueller J Paul , Spears Janet F
Published: April 2011

We evaluated several methods for breaking dormancy in seeds of the invasive weed Pueraria lobata (Willd.) Ohwi (kudzu). Seedlings from untreated seeds emerged from late March to early October 1999 in trays placed outdoors under natural weather conditions; mean cumulative percentage emergence was low (11%). In growth chamber experiments, germination percentages of untreated seeds ranged from 6 to 17%. All hand-scarified seeds germinated, whereas only 6% of intact seeds germinated. Other dormancy-breaking methods that produced higher germination percentages included exposure to ethyl alcohol for 6-12 h (24-86%), exposure to concentrated sulfuric acid for 1-2 h (65-81%), and exposure to moist heat for 5-300 s (30-80%). The influence of temperature on germination percentages of seeds following dry heat treatments depended on the duration of exposure. At 60 and 80°C, germination percentages increased with longer exposures to dry heat and were greatest after 720 min (27 and 60%, respectively). At 100°C, percent germination was greatest when seeds were exposed to dry heat for only 10 min (93%). Cold stratification at 5°C for 0-6 weeks did not increase seed germination percentages after exposure to a range of alternating thermoperiods. Similarly, dry storage at room temperature for 0, 200, or 400 days did not affect germination percentages in light or dark treatments.Key words: Pueraria lobata, physical dormancy, germination, phenology, acid scarification, warm stratification, cold stratification.
The role of epicormic shoot production in maintaining foliage in old Pseudotsuga menziesii (Douglas-fir) trees
Authors: Ishii Hiroaki , Ford E David
Published: April 2011

Shoots and foliage on branches of old Pseudotsuga menziesii (Mirb.) Franco var. menziesii (coastal Douglas-fir) trees are constantly renewed by epicormic shoot production. Epicormic shoots are produced in all parts of the crown, and epicormic buds remain dormant for 5 or 6 years on average. Epicormic shoot production results in reiteration of shoot cluster units (SCUs), an architectural unit of shoot organization within branches. Five phases of SCU development were identified based on relative age structures of regular and epicormic shoots. SCUs produce epicormic branchlets as early as 3 or 4 years of age, and peak production occurred around 6-13 years. Epicormic branchlets occur toward the proximal end of main axes of SCUs, where regular lateral branchlets are no longer producing new shoots. In some lower-crown branches, nearly 50% of shoots and foliage are epicormic shoots. Demographic analysis of SCUs showed that upper-crown branches are still growing in size, while mid- and lower-crown branches have reached maximum size, and are being maintained by reiteration of SCUs. Epicormic shoot production maintains shoots and foliage of old P. menziesii trees after height growth and crown expansion have stopped and may contribute to prolonging tree longevity.Key words: aging, branch growth, epicormic shoots, longevity, Pseudotsuga menziesii, reiteration.
Ecological effects of the non-native Pinus nigra on sand dune communities
Authors: Leege Lissa M , Murphy Peter G
Published: April 2011

Owing to their successional nature, sand dunes provide an opportunity to examine the effects of non-native species introduced into multiple habitats. We investigated the biotic and abiotic effects of non-native Pinus nigra in four habitats on the dunes of the eastern shore of Lake Michigan. The 26 000 pines were planted in foredunes, forest edges, wetpannes, and inland blowouts as a stabilization measure in 19561972, and in 1995 the surviving trees ranged in stand density from 2741176 trees per hectare. Pinus nigra stands were associated with reduced cover of dune vegetation except in forest edges, and with depressed species richness only in wetpanne sites. Higher densities of woody stems occurred in P. nigra stands at the edge of native forest than in sites lacking P. nigra, suggesting that pines accelerate succession to a woody community. Pinus nigra stands were associated with lower light levels than native stands of comparable or greater stand densities (Pinus banksiana in wetpannes and Populus deltoides in foredunes). In addition, P. nigra sites were drier than P. banksiana sites in wetpannes. The non-native pines may have modified the four dune habitats and appear to be functionally different from stands of native trees.Key words: functional equivalency, non-native species, Pinus nigra, plant invasion, sand dunes.
Gradient analysis of Larix laricina dominated wetlands in Canada's southeastern boreal forest
Authors: Girardin Martin-Philippe , Tardif Jacques , Bergeron Yves
Published: April 2011

With the objective of understanding how vegetation was structured in four Larix laricina (Du Roi) K. Koch dominated wetlands in north-western Quebec, 186 point-centred quarters were sampled in four stands. For each point, both biotic and abiotic variables were collected and species cover was recorded. Divisive hierarchical classification analysis (Twinspan) identified nine vegetation clusters: i) Larix laricina & Spiraea alba, ii) Larix laricina & Kalmia angustifolia, iii) Larix laricina, Picea mariana & Alnus rugosa, iv) Larix laricina & Betula pumila, v) Thuja occidentalis & Trientalis borealis, vi) Abies balsamea & Betula papyrifera, vii) Fraxinus nigra & Onoclea sensibilis, viii) Alnus rugosa, and ix) Eleocharis smallii. Results of the canonical correspondence analyses indicated that the distribution of these clusters was mainly related to (i) distance from shore, (ii) shade (canopy cover), (iii) substrate nitrate concentration (in relation to the abundance of Kalmia angustifolia and Alnus rugosa), (iv) substrate pH (in relation to the abundance of Sphagnum spp.), and (v) substrate conductivity. Several characteristics of the water table also affected species distribution, including pH, depth, and carbon concentration. Further studies should address the effect of the presence of Kalmia angustifolia and Alnus rugosa on larch growth.Key words: larch, wetland, vegetation analysis, flooding, boreal forest.