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Tremula L. (tremula + l)
Kinds of Tremula L. Selected AbstractsDendrogeomorphic reconstruction of past debris-flow activity using injured broad-leaved treesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2010Estelle Arbellay Abstract Tree-ring records from conifers have been regularly used over the last few decades to date debris-flow events. The reconstruction of past debris-flow activity was, in contrast, only very rarely based on growth anomalies in broad-leaved trees. Consequently, this study aimed at dating the occurrence of former debris flows from growth series of broad-leaved trees and at determining their suitability for dendrogeomorphic research. Results were obtained from gray alder (Alnus incana (L.) Moench), silver birch and pubescent birch (Betula pendula Roth and Betula pubescens Ehrh.), aspen (Populus tremula L.), white poplar, black poplar and gray poplar (Populus alba L., Populus nigra L. and Populus x canescens (Ait.) Sm.), goat willow (Salix caprea L.) and black elder (Sambucus nigra L.) injured by debris-flow activity at Illgraben (Valais, Swiss Alps). Tree-ring analysis of 104 increment cores, 118 wedges and 93 cross-sections from 154 injured broad-leaved trees allowed the reconstruction of 14 debris-flow events between AD 1965 and 2007. These events were compared with archival records on debris-flow activity at Illgraben. It appears that debris flows are very common at Illgraben, but only very rarely left the channel over the period AD 1965,2007. Furthermore, analysis of the spatial distribution of disturbed trees contributed to the identification of six patterns of debris-flow routing and led to the determination of preferential breakout locations of events. The results of this study demonstrate the high potential of broad-leaved trees for dendrogeomorphic research and for the assessment of the travel distance and lateral spread of debris-flow surges. Copyright © 2010 John Wiley & Sons, Ltd. [source] Admixture facilitates adaptation from standing variation in the European aspen (Populus tremula L.), a widespread forest treeMOLECULAR ECOLOGY, Issue 8 2010DULCINEIA DE CARVALHO Abstract Adaptation to new environments can start from new mutations or from standing variation already present in natural populations. Whether admixture constrains or facilitates adaptation from standing variation is largely unknown, especially in ecological keystone or foundation species. We examined patterns of neutral and adaptive population divergence in Populus tremula L., a widespread forest tree, using mapped molecular genetic markers. We detected the genetic signature of postglacial admixture between a Western and an Eastern lineage of P. tremula in Scandinavia, an area suspected to represent a zone of postglacial contact for many species of animals and plants. Stringent divergence-based neutrality tests provided clear indications for locally varying selection at the European scale. Six of 12 polymorphisms under selection were located less than 1 kb away from the nearest gene predicted by the Populus trichocarpa genome sequence. Few of these loci exhibited a signature of ,selective sweeps' in diversity-based tests, which is to be expected if adaptation occurs primarily from standing variation. In Scandinavia, admixture explained genomic patterns of ancestry and the nature of clinal variation and strength of selection for bud set, a phenological trait of great adaptive significance in temperate trees, measured in a common garden trial. Our data provide a hitherto missing direct link between past range shifts because of climatic oscillations, and levels of standing variation currently available for selection and adaptation in a terrestrial foundation species. [source] Compatible and Incompetent Paxillus involutus Isolates for Ectomycorrhiza Formation in vitro with Poplar (Populus×canescens) Differ in H2O2 ProductionPLANT BIOLOGY, Issue 1 2004A. Gafur Abstract: Isolates of Paxillus involutus (Batsch) Fr. collected from different hosts and environmental conditions were screened for their ability to form ectomycorrhizal symbiosis with hybrid poplar P.×canescens (= Populus tremula L. ×P. alba) in vitro. The ability to form ectomycorrhiza varied between the fungal isolates and was not correlated with the growth rate of the fungi on agar-based medium. The isolate MAJ, which was capable of mycorrhiza synthesis under axenic conditions, and the incompetent isolate NAU were characterized morphologically and anatomically. MAJ formed a typical hyphal mantle and a Hartig net, whereas NAU was not able to penetrate the host cell walls and caused thickenings of the outer cell walls of the host. MAJ, but not NAU, displayed strong H2O2 accumulation in the outer hyphal mantle. Increases in H2O2 in the outer epidermal walls and adjacent hyphae of the incompetent isolate were moderate. No increases of H2O2 in response to the mycobionts were found inside roots. Suggested functions of H2O2 production in the outer hyphal mantle of the compatible interaction are: growth regulation of the host's roots, defence against other invading microbes, or increasing plant-innate immunity. The system established here for P.×canescens compatible and incompetent fungal associations will be useful to take advantage of genomic information now available for poplar to study tree-fungal interactions at the molecular and physiological level. [source] Antioxidant and Pigment Composition during Autumnal Leaf Senescence in Woody Deciduous Species Differing in their Ecological TraitsPLANT BIOLOGY, Issue 5 2003J. I. García-Plazaola Abstract: Photoprotection mechanisms have been studied during autumnal senescence in sun and shade leaves of woody plants with different ecological characteristics and senescence patterns. Three of them belonging to the same family, Betulaceae: the shade-intolerant and early successional species (Betula alba L.), the shade-tolerant and late successional species (Corylus avellana L.), and an N-fixing tree with low N resorption efficiency (Alnus glutinosa L.). The other two species: a shade-intolerant (Populus tremula L.) and a shade-tolerant (Cornus sanguinea L.), were chosen because of their ability to accumulate anthocyanins during autumnal leaf senescence. The study of plants with different ecological strategies allowed us to establish general trends in photoprotection mechanisms during autumnal senescence, when nutrient remobilisation occurs, but also during whole leaf ontogeny. We have not found a clear relationship between shade tolerance and the level of photoprotection; the main difference between both groups of species being the presence of ,-carotene in shade leaves of shade-tolerant species. Preceding autumn, nitrogen resorption started in mid-summer and occurred in parallel with a slight and continuous ascorbate, chlorophyll and carotenoid degradation. However, the ascorbate pool remained highly reduced and lipid oxidation did not increase at this time. Contrasting with ascorbate, ,-tocopherol accumulated progressively in all species. Only during the last stages of senescence was chlorophyll preferentially degraded with respect to carotenoids, leading to the yellowing of leaves, except in A. glutinosa in which a large retention of chlorophyll and N took place. Senescing leaves were characterised, except in C. sanguinea, by a relative increase in the proportion of de-epoxidised xanthophylls: zeaxanthin, antheraxanthin and lutein. The light-induced accumulation of anthocyanins in C. sanguinea could play an additional protective role, compensating for the low retention of de-epoxidised xanthophylls. These different strategies among deciduous species are consistent with a role for photoprotective compounds in enhancing nitrogen remobilization and storage for the next growing season. [source] Development of molecular markers to assess the level of introgression of Populus tremula into P. alba natural populationsPLANT BREEDING, Issue 4 2004T. Fossati Abstract Morphological traits traditionally adopted to discriminate between Populus alba L. and P. tremula L. have frequently led to misclassifi-cation of their spontaneous hybrid P. × canescens Sm. Moreover, they may not be of any help in cases of spontaneous backcross phenomena. These limitations can be overcome by molecular markers, which are not environmentally influenced nor subjectively assessed. In this study, the effectiveness of amplified fragment length polymorphism (AFLP) and simple sequence repeat (SSR) markers in species and hybrid discrimination was evaluated by analysing a set of reference samples of P. alba, P. tremula and P. × canescens. Species-specific and species-indicative AFLPs, as well as diagnostic SSR alleles, were recorded in both P. alba and P. tremula reference samples. The results allowed a clear distinction between the two poplar species and their hybrid. Using these diagnostic markers, a natural population of P. alba trees sampled along the Ticino river basin in northern Italy was analysed, and P. × canescens individuals, intermingled with P. alba trees, were detected. [source] Low night temperature and inhibition of gibberellin biosynthesis override phytochrome action and induce bud set and cold acclimation, but not dormancy in PHYA overexpressors and wild-type of hybrid aspenPLANT CELL & ENVIRONMENT, Issue 12 2005JØRGEN A. MØLMANN ABSTRACT Juvenile trees of temperate and boreal regions cease growth and set buds in autumn in response to short day-lengths (SD) detected by phytochrome. Growth cessation and bud set are prerequisites for the development of winter dormancy and full cold hardiness. In this study we show that the SD-requirement for bud set and cold hardening can be overcome in hybrid aspen (Populus tremula L. × tremuloides Michx.) by low night temperature and inhibition of gibberellin (GA) biosynthesis. Bud set and increased cold hardiness were observed under normally non-inductive long day-length (LD) in wild-type plants, when exposed to low night temperature and paclobutrazol. In addition, the effect of PHYA overexpression could be overcome in transgenic plants, producing bud set and cold acclimation by treatment with: SD, low night temperature and paclobutrazol. After cold acclimation, the degree of bud dormancy was lower for wild-type plants prior treated with LD and transgenic plants (overexpressing PHYA), than SD-treated, wild-type plants. Thus, low night temperature in combination with reduced GA content induced bud set and promoted cold hardiness under normally non-inductive photoperiods in hybrid aspen, but was unable to affect development of dormancy. This might suggest separate signalling pathways from phytochrome regulating the induction of cold/cold hardiness and bud dormancy in hybrid aspen or alternatively, there might be one pathway that fails to complete its action in the transgenic and paclobutrazol treated plants. [source] Environmental and auxin regulation of wood formation involves members of the Aux/IAA gene family in hybrid aspenTHE PLANT JOURNAL, Issue 6 2002Richard Moyle Summary Indole acetic acid (IAA/auxin) profoundly affects wood formation but the molecular mechanism of auxin action in this process remains poorly understood. We have cloned cDNAs for eight members of the Aux/IAA gene family from hybrid aspen (Populus tremula L. × Populus tremuloides Michx.) that encode potential mediators of the auxin signal transduction pathway. These genes designated as PttIAA1-PttIAA8 are auxin inducible but differ in their requirement of de novo protein synthesis for auxin induction. The auxin induction of the PttIAA genes is also developmentally controlled as evidenced by the loss of their auxin inducibility during leaf maturation. The PttIAA genes are differentially expressed in the cell types of a developmental gradient comprising the wood-forming tissues. Interestingly, the expression of the PttIAA genes is downregulated during transition of the active cambium into dormancy, a process in which meristematic cells of the cambium lose their sensitivity to auxin. Auxin-regulated developmental reprogramming of wood formation during the induction of tension wood is accompanied by changes in the expression of PttIAA genes. The distinct tissue-specific expression patterns of the auxin inducible PttIAA genes in the cambial region together with the change in expression during dormancy transition and tension wood formation suggest a role for these genes in mediating cambial responses to auxin and xylem development. [source] Willow (Salix spp.) and aspen (Populus tremula) regrowth after felling by the Eurasian beaver (Castor fiber): implications for riparian woodland conservation in ScotlandAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2009Kevin Jones Abstract 1.A proposed trial reintroduction of the Eurasian beaver (Castor fiber L.) to Scotland has recently been approved (May 2008). A previous proposal was turned down by the licensing authority, partly over the perceived risks to woodland within a Special Area of Conservation. 2.This paper presents data on two years of willow (Salix spp.) and aspen (Populus tremula L.) regrowth following tree felling by captive beavers within two large semi-natural enclosures in eastern Scotland. Both willow and aspen are highly preferred by beavers. 3.Regrowth of willow stems was quantified from cut stumps, felled logs and partially severed (,incompletely felled') trees, and compared with growth of stems in the canopies of untouched willows. 4.Maximum annual regrowth was observed in incompletely felled trees, followed by cut stumps and then unfelled control trees. Mean regrowth rates were ca 18 m regrowth per metre of measured tree section per year in incompletely felled trees. This was approximately 12 times more annual regrowth than that observed in unfelled trees, despite apparently selective browsing of the regrowth of incompletely felled trees by roe deer. 5.Although incompletely felled willows represent a relatively small component of felling activity (9% of all felled willow), they contribute disproportionately to the biomass of beaver-engineered riparian woodlands, creating a more multi-layered habitat structure. 6.Willow regrowth in inundated areas was avoided by deer, and harvesting of regrowth by beavers was rare. 7.Significant regrowth from 11 stumps of aspen in 2 years post-felling occurred by suckering, with 85 suckers of mean height 2.1 m being recorded, all of which were subsequently avoided by browsing deer and beavers. 8.These data suggest that rapid regeneration of willow and aspen will occur in riparian woodlands in the event of major felling activity by Eurasian beaver, even in the presence of low to moderate levels of roe deer browsing, and that the conservation status of both these trees or the wider habitats that they form would not be threatened by a well planned and managed reintroduction of beavers to Scotland. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||