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Fertilization of hybrid poplar (HP) plantations with papermill by-products is a promising solution to improve soil fertility and nutrient availability, increase plantation productivity, and provide added value to these materials that would otherwise be incinerated or sent to the landfill. We assessed the growth and foliar nutrition of a HP clone (Populus * canadensis * Populus maximowiczii) at six plantation sites aged 3-5 years in southern Quebec, Canada. Sites received a fertilization treatment consisting of a mixture of papermill biosolids (120 to 140 t*[ha.sup.-1], depending on site) and lime mud (10 to 15 t*[ha.sup.-1]) before being planted, or no fertilization (control). Tree growth was significantly improved by fertilization, with fertilized trees showing a mean annual height increment of 1.3 m (all-site mean; SD = 0.2), compared with 0.5 m (SD = 0.4) for unfertilized trees. Foliar calcium and magnesium increased following fertilization and levels met optimal thresholds at all sites, whereas nitrogen, phosphorous, and potassium concentrations also increased, but nutritional deficiencies remained for these elements at several sites. Our results confirm the benefits of fertilizing hybrid poplars with papermill by-products, but they also indicate that adjustments in application rates or type of by-products could be made to fully satisfy nutritional requirements and thus optimize tree growth. Key words: fertilization, foliar nutrition, forest soil, hybrid poplar, papermill by-products, lime mud. La fertilisation des plantations de peuplier hybride avec des sous-produits d'usines de pates et papiers est une solution prometteuse pour ameliorer la fertilite du sol et la disponibilite des nutriments, augmenter la productivite des plantations et valoriser ces materiaux qui autrement seraient incineres ou envoyes dans un site d'enfouissement. Nous avons evalue la croissance et la nutrition foliaire d'un clone de peuplier hybride (Populus * canadensis * Populus maximowiczii) dans six plantations agees de trois a cinq ans dans le sud du Quebec, au Canada. Les plantations ont recu un traitement de fertilisation constitue d'un melange de biosolides papetiers (120 a 140 t*[ha.sup.-1] selon la station) et d'une boue de chaux (10 a 15 t*[ha.sup.-1]) avant d'etre plantees ou aucune fertilisation (temoin). La fertilisation a significativement ameliore la croissance des arbres dont l'accroissement annuel moyen en hauteur a atteint 1,3 m (moyenne de toutes les stations; ecart-type (SD) = 0,2) comparativement a 0,5 m (SD = 0,4) dans le cas des arbres non fertilises. Le calcium et le magnesium foliaires ont augmente apres la fertilisation et atteint les niveaux optimums dans toutes les stations. Par contre, les deficiences nutritionnelles en azote, phosphore et potassium ont persiste dans plusieurs stations meme si la concentration de ces elements a aussi augmente. Nos resultats confirment que la fertilisation du peuplier hybride avec des sous-produits de papetieres est benefique mais indiquent qu'il faudrait ajuster les taux d'application ou les types de sous-produits pour satisfaire pleinement les exigences nutritionnelles et optimiser la croissance des arbres. [Traduit par la Redaction] Mots-cles: fertilisation, nutrition foliaire, sol forestier, peuplier hybride, biosolides papetiers, boue de chaux., Introduction Intensive management of tree plantations can help meet the increasing demand for wood products while increasing carbon sequestration, conserving larger areas of forests, and restoring degraded lands (Paquette and [...]

Wood properties are crucial for the development and application of poplar clones. Here, the effects of clone and age on anatomical and chemical properties were analyzed in eight poplar clones (50, Zhonglin46,108, 36, N179, Danhong, Sangju, and Nanyang) from Henan province, China. The results show that the effects of clone and age are both significant for these wood properties. The eight clones were grouped into three clusters according to their annual ring width, fiber quality, and chemical properties. For some properties, including annual ring width, fiber length, and microfibril angle, all clones displayed the same radial variation trends; however, for other properties, such as holocellulose content, the radial variation trends were different depending on the clones. The culmination of the mean annual increment corresponded to the turning ages of wood properties such as annual ring width in the eight clones, and holocellulose content in the partial clones except for fiber length, microfibril angle, and vessel length. The recommended rotation age of these poplar clones is 8-9 years based on the fiber quality and chemical components. These results indicate strong genetic and age control of the wood properties and highlight the rich source of variation for poplar clone selection. Key words: poplar, clone, anatomical properties, chemical properties, radial variation, rotation age. Les proprietes du bois sont cruciales pour le developpement et l'utilisation des clones de peuplier. Dans cet article, les effets dus au clone et a l'age sur les proprietes anatomiques et chimiques ont ete analysees chez huit clones de peuplier (50, Zhonglin46,108, 36, N179, Danhong, Sangju et Nanyang) provenant de la province de Henan, en Chine. Les resultats montrent que les effets dus au clone et a l'age sont dans les deux cas significatifs. Pour ces deux proprietes du bois. Les huit clones ont ete regroupes dans trois groupes selon la largeur des cernes annuels, la qualite des fibres et les proprietes chimiques. Dans le cas de certaines proprietes, incluant la largeur des cernes annuels, la longueur des fibres et l'angle des microfibrilles, tous les clones montrent les memes tendances de variation radiale. Tandis que pour les autres, telles que la teneur en holocellulose, les tendances de variation radiale etaient differentes dependamment du clone. Le point culminant de l'accroissement annuel moyen correspondait a l'age auquel les proprietes du bois, telles la largeur des cernes annuels, changeaient chez les huit clones et la teneur en holocellulose chez les clones partiels, a l'exception de la longueur des fibres, de l'angle des microfibrilles et de la longueur des vaisseaux. On pouvait etablir l'age d'exploitabilite des clones de peuplier a huit ou neuf ans sur la base de la qualite des fibres et des composantes chimiques. Ces resultats indiquent que les proprietes du bois sont fortement controlees par la genetique et l'age et mettent en evidence la riche source de variation pour la selection des clones de peuplier. [Traduit par la Redaction] Mots-cles: peuplier, clone, proprietes anatomiques, proprietes chimiques, variation radiale, age d'exploitabilite., 1. Introduction Poplars (family Salicaceae; Populus sp.) are primarily distributed in the temperate forests of the Northern Hemisphere (Fang and Yang 2003). Since the 1940s, the favorable properties of poplars, [...]

Modifications to leaf structural components that drive variation in leaf mass per area (LMA) may substantially impact leaf physiology by changing how easily C[O.sub.2] diffuses through intercellular air space to carboxylation sites in mesophyll tissues. Mesophyll conductance ([g.sub.m]) is inversely proportional to the total pathway length for C[O.sub.2], including the structural resistances encountered. In balsam poplar (Populus balsamifera L.), [g.sub.m] increases with latitude, paralleled by an increase in LMA. We investigated a family of P. balsamifera (K4xC) with high variation in LMA for different characteristics (tissues, nitrogen content, ultrastructural attributes). We interpreted trait variability using a developmental scale quantified by the leaf plastochron index (LPI). Developmental age significantly affected LMA, but those effects were lost at LPI ≥ 6. We outlined contributions of anatomical components to LMA and found palisade mesophyll properties were the primary drivers of variation in LMA within mature leaves (LPI [greater than or equal to] 6). Using anatomical data, we derived components corresponding to structural resistances for [g.sub.m]. Perimeters of palisade cells and surface area of palisade exposed to intercellular air space, which may strongly influence C[O.sub.2] diffusion, were correlated to LMA. Variation in LMA is positively related to differences in structural features expected to increase the conductance to C[O.sub.2] diffusion within palisade mesophyll. Keywords: mesophyll conductance, [g.sub.m], balsam poplar, LMA, microanatomy, ultrastructure, leaf physiology. Les modifications apportees aux composantes structurales de la feuille qui sous-tendent la variation de la masse surfacique foliaire (MSF) peuvent avoir un impact important sur la physiologie foliaire en changeant la facilite avec laquelle le C[O.sub.2] diffuse ai travers l'espace aerien intercellulaire aux sites de carboxylation dans le mesophylle. La conductance du mesophylle ([g.sub.m]) est inversement proportionnelle a la longueur totale du sentier parcouru par le C[O.sub.2], incluant les resistances structurales rencontrees. Chez le peuplier baumier (Populus balsamifera L.), la [g.sub.m] augmente en fonction de la latitude parallelement a l'augmentation de la MSF. Les auteurs ont examine une famille de P. balsamifera (K4xC) dont la MSF est hautement variable, sur le plan de differentes caracteristiques (tissus, contenu en azote, attributs ultrastructuraux). Ils ont interprete la variabilite a l'aide d'une echelle developpementale quantifiee par l'indice plastochrone foliaire (IPF). L'age developpemental affectait significativement la MSF, mais ces effets disparaissaient a un IPF ≥ 6. Ils ont defini les contributions des composantes anatomiques a la MSF et trouve que les proprietes du mesophylle palissadique sont les principaux moteurs de la variation de la MSF a l'interieur des feuilles matures (IPF [greater than or equal to] 6). Ils ont deduit a l'aide des donnees anatomiques les composantes correspondant aux resistances structurales du [g.sub.m]. Les perimetres des ellules palissadiques et la surface palissadique exposee a l'espace aerien intercellulaire, qui pourraient influencer fortement la diffusion de C[O.sub.2], etaient correles avec la MSF. La variation de MSF est reliee positivement aux differences des caracteristiques structurales censees accroitre la conductance a la diffusion de C[O.sub.2] a l'interieur du mesophylle palissadique. [Traduit par la Redaction] Mots-cles: conductance du mesophylle, [g.sub.m], peuplier baumier, MSF, micro-anatomie, ultrastructure, physiologie foliaire., Introduction Studies examining the relationships between structure and function that associate anatomical and ecophysiological traits in plants are important because it is possible to obtain information about the carbon exchange [...]

Successful establishment of fast-growing trees could depend on early root development and the access to belowground resources. Boreal podzolic soils present a distinctive vertical zonation wherein nutrient availability and the presence of plant roots decline sharply with depth. Mechanical soil preparation that modifies the vertical arrangement of soil layers creates microsites with improved physical conditions but potentially lower nutrient availability. We compared the vertical distribution of proximal roots of young hybrid poplars in soil layers of mechanically prepared (by mounding) and unprepared microsites. We also evaluated the relationship between root distribution and the availability and mineralization of soil nitrogen. Hybrid poplar roots were less abundant in the surface organic layer of unprepared soils, whereas they proliferated in the buried organic layer of mounds. Total mineralized N was highest in the upper mineral layer of mounds, whereas it was similar between the buried organic layer of mounds and the unprepared organic layer. Altogether, mounding created conditions conducive to greater soil N mineralization and greater production and vertical distribution of proximal roots. This possibly provided access to a larger soil volume and greater soil nutrient pools, which may explain the success of mounding in terms of aboveground growth of hybrid poplars. Resume: L'etablissement des arbres a croissance rapide pourrait dependre du developpement precoce des racines et de l'acces rapide aux ressources du sol. Les podzols de la region boreale ont une zonation verticale caracteristique ou la disponibilite des nutriments et la presence des racines diminuent abruptement avec la profondeur. La preparation mecanique du sol qui modifie l'organisation verticale des horizons du sol cree des microsites ou les conditions physiques sont meilleures mais ou la dis-ponibilite des nutriments est potentiellement reduite. Nous avons compare la distribution verticale des racines proximales de jeunes peupliers hybrides dans les horizons du sol de microsites ayant subi ou non une preparation mecanique par creation de monticules. Nous avons aussi evalue la relation entre la distribution des racines et la disponibilite ainsi que la mineralisation de l'azote du sol. Les racines des peupliers hybrides etaient moins abondantes a la surface de l'horizon organique des sols non prepares tandis qu'elles proliferaient dans l'horizon organique enfoui dans les monticules. L'horizon mineral superieur dans les monticules contenait la plus grande quantite d'azote mineralise total tandis que l'horizon organique enfoui dans les monticules et l'horizon organique non prepare en contenaient a peu pres la meme quantite. Dans l'ensemble, la creation de monticules a cree des conditions propices a une plus forte mineralisation de l'azote du sol ainsi qu'a une production et une distribution accrues des racines proximales. Cela fournit possiblement l'acces a un plus grand volume de sol et a de plus grandes reserves de nutriments; ce qui peut expliquer le succes des monticules en termes de croissance aerienne des peupliers hybrides. [Traduit par la Redaction], Introduction Early root development of the target species is a fundamental factor in the successful establishment of plantations, as it can favour juvenile tree growth and survival (Grossnickle 2005). Indeed, [...]

A fundamental goal of systems biology is to identify genetic elements that contribute to complex phenotypes and to understand how they interact in networks predictive of system response to genetic variation. Few studies in plants have developed such networks, and none have examined their conservation among functionally specialized organs. Here we used genetical genomics in an interspecific hybrid population of the model hardwood plant Populus to uncover transcriptional networks in xylem, leaves, and roots. Pleiotropic eQTL hotspots were detected and used to construct coexpression networks a posteriori, for which regulators were predicted based on cis-acting expression regulation. Networks were shown to be enriched for groups of genes that function in biologically coherent processes and for cis-acting promoter motifs with known roles in regulating common groups of genes. When contrasted among xylem, leaves, and roots, transcriptional networks were frequently conserved in composition, but almost invariably regulated by different loci. Similarly, the genetic architecture of gene expression regulation is highly diversified among plant organs, with less than one-third of genes with eQTL detected in two organs being regulated by the same locus. However, colocalization in eQTL position increases to 50% when they are detected in all three organs, suggesting conservation in the genetic regulation is a function of ubiquitous expression. Genes conserved in their genetic regulation among all organs are primarily cis regulated (~92%), whereas genes with eQTL in only one organ are largely trans regulated. Trans-acting regulation may therefore be the primary driver of differentiation in function between plant organs. eQTL | gene network | gene regulation | systems biology | Populus doi/ 10.1073/pnas.0914709107

p-Coumaroyl-CoA 3'-hydroxylase (C3'H) is a cytochrome P450-dependent monooxygenase that catalyzes the 3'-hydroxylation of p-coumaroyl shikimate and p-coumaroyl quinate. We used RNA interference to generate transgenic hybrid poplar suppressed in C3'H expression and analyzed them with respect to transcript abundance, cell wall structure and chemical composition, and soluble metabolite levels. RT-PCR expression profiles confirmed the down-regulation of C3'H in a number of lines, which generally correlated very well with reduced total cell wall lignin content. The most strongly repressed line was chosen for further analysis and compared with the wild-type trees. In-depth characterization revealed that along with the significant decrease in total lignin content, a significant shift in lignin monomer composition was observed, favoring the generation of p-hydroxyphenyl units at the expense of guaiacyl units while the proportion of syringyl moieties remained constant. Suppression of C3'H also resulted in the accumulation of substantial pools of 1-O-p-coumaroyl-[beta]-D-glucoside and other phenylpropanoid glycosides, and p-coumaroyl shikimate, providing further insight into the role of C3'H in the lignin biosynthetic pathway. The data presented indicate that when down-regulated, C3'H becomes a rate-limiting step in lignin biosynthesis and further support the involvement of hydroxycinnamic acid shikimate esters in the lignin biosynthetic pathway. phenolic glucosides | syringyl lignin | CYP98 | C3'H

Although it is understood that the composition of riparian trees can affect stream function through leaf litter fall, the potential effects of genetic variation within species are less understood. Using a naturally hybridizing cottonwood system, we examined the hypothesis that genetic differences among two parental species (PopuIus fremontii and P. angustifolia) and two groups of their hybrids ([F.sub.1] and backcrosses to P. angustifolia) would affect litter decomposition rates and the composition of the aquatic invertebrate community that colonizes leaves. Three major findings emerged: (1) parental and hybrid types differ in litter quality, (2) decomposition differs between two groups, a fast group (P. fremontii and [F.sub.1] hybrid), and a slow group (P. angustifolia and backcross hybrids), and (3) aquatic invertebrate communities colonizing P. fremontii litter differed significantly in composition from all other cross types, even though P. fremontii and the [F.sub.1] hybrid decomposed at similar rates. These findings are in agreement with terrestrial arthropod studies in the same cottonwood system. However, the effects are less pronounced aquatically than those observed in the adjacent terrestrial community, which supports a genetic diffusion hypothesis. Importantly, these findings argue that genetic interactions link terrestrial and aquatic communities and may have significant evolutionary and conservation implications. Key words: aquatic decomposition; aquatic-terrestrial interaction; cottonwood hybridization; ecological genetics; genetic introgression; genetic variation; hybrids; leaf litter decomposition; macroinvertebrate communities; Populus.

Phoradendron hexastichum is a bird-dispersed mistletoe that infects the dioecious tree Cecropia schreberiana. Because both species share frugivore seed dispersers, we hypothesized that female Cecropia would have a greater probability and intensity of mistletoe infection than males due to more frequent visitation by shared frugivores. Over 50% of female Cecropia were infected, in contrast with 25% of males. On average, female trees had twice as many mistletoes as male trees. Infection probability and intensity increased with basal area in females but not in males, suggesting that lifetime reinfection was also female biased. We found mistletoe frugivores visiting uninfected fruiting females twice as often as males. Although mistletoes were mostly consumed by the mistletoe specialist Euphonia musica, we did not record Euphonia visiting uninfected Cecropia trees. Uninfected Cecropia trees were frequently visited by generalist frugivores (such as Spindalis portoricensis) that used both mistletoes and Cecropia fruits. The Cecropia--frugivores--Phoradendron network of interactions seems to have led to the spatial linkage of the two plant species through directional dispersal, to plant--plant facilitation through shared frugivores, and to bird--bird facilitation in which generalist frugivores start new foci of infection that specialist frugivores can use. Key words: Cecropia schreberiana; dioecious trees; directed dispersal; Euphonia musica; facilitation; frugivory; generalist consumers; mistletoes; Phoradendron hexastichum; Puerto Rico; seed dispersal.