Populus Balsamifera Research Articles

Effects of open-range cattle grazing on deciduous tree regeneration, damage, and mortality following patch logging

The impact of summer cattle grazing on deciduous tree regeneration within uncut forests, clearcuts, partially harvested areas, and in-block haul road habitats was examined in four experimental pastures of central Alberta during 2008 and 2009. Sampling of 233 field plots, both inside and outside cattle exclosures, was used to document sapling densities, height, and type of damage. Tree densities (primarily aspen (Populus tremuloides Michx.)) differed among habitats but less so with exposure to cattle. Densities were greatest in clearcuts, followed by partially harvested areas and then uncut forest and haul roads. While exposure to cattle reduced total tree regeneration, sapling densities and sizes remained sufficient to meet postharvest standards for deciduous forest regeneration in Alberta, even with exposure to cattle. Cattle damage in harvested areas was primarily from browsing (≤3.2% of saplings), with proportionally more trees affected in uncut forests (8.6%). Browsing was particularly high on balsam poplar (Populus balsamifera L.) (25%) during 2008. Although sapling damage increased with high cattle stocking in 2008 (to 10.5%), total mortality was limited to 15.5% through 2009. These findings show that despite cattle impacts to some saplings, damage levels were insufficient to alter deciduous regeneration, highlighting the compatibility of cattle grazing and sustainable forest management on public lands in this region.

Comparative resource-use efficiencies and growth ofPopulus trichocarpaandPopulus balsamiferaunder glasshouse conditions

Amongst other traits, ideal poplar genotypes for afforestation programs would be fast growing and have high resource-use efficiencies. Black cottonwood (Populus trichocarpa Torr. & A. Gray) and balsam poplar (Populus balsamifera L.) are closely related species that together extend over much of the forested area of Canada. Within their respective ranges, however, black cottonwood attains much greater size than balsam poplar. Two populations of each species, each with three replicates of 9–10 genotypes, were grown from stem cuttings for 60 days in a greenhouse under long days to examine variation in biomass, height growth, net photosynthesis (A), stomatal conductance (gs), intrinsic water-use efficiency (A/gs), photosynthetic nitrogen-use efficiency (PNUE), leaf and stemwood13C/12C isotope ratios (δ13C), stomatal density (Ds), and leaf amphistomaticity. There were no significant differences in A, PNUE, biomass, or height growth between species. On average, black cottonwood had lower gsand Ds, but higher A/gsand δ13C. Variation within provenances, in most traits, exceeded variation between species or provenances. δ13C and A/gswere highly correlated across all genotypes. Variation in A/gsseemed primarily related to gs, although positive correlations were found between δ13C and A in the P. balsamifera populations, which more generally met expectations for sink-driven differences in water-use efficiency. There is potential to identify fast-growing genotypes with relatively high use efficiencies for both water and nitrogen.

Timing for success: expression phenotype and local adaptation related to latitude in the boreal forest tree, Populus balsamifera

Timing of seasonal dormancy is among the most important traits allowing forest tree populations to span latitudinal gradients of temperature and growing season length. We used RNA-sequencing (RNA-seq) data to identify gene expression differences between latitude-adapted populations and search for elevated genetic differentiation, a signature of adaptation, between northern and southern populations of Populus balsamifera. RNA was extracted from leaf tissues collected from trees originating from two northern (65° N) and two southern (50° N) populations and growing in a common garden. Leaves for RNA-seq were collected on the same day in late July, when southern trees were actively growing and northern trees had set bud. Transcripts of 2,594 genes were more abundant in actively growing leaves, whereas 1,424 were more abundant in leaves of trees that had set bud. The actively growing southern trees exhibited overexpression of genes in the biological process gene ontology (GO) domain, whereas dormant northern trees exhibited overexpression of genes in the cellular component domain. We identified relatively few genes (641) bearing signatures consistent with local adaptation to latitude for three or more SNPs. Exons from differentially expressed (DE) genes were not more likely than non-DE genes to exhibit patterns of latitudinal differentiation consistent with local adaptation. These results indicate that genes associated with differences in the timing of bud set, which is correlated with initiation of dormancy, were not more likely than other categories to exhibit latitudinal differentiation in exonic regions.

Fitness dynamics within a poplar hybrid zone: I. Prezygotic and postzygotic barriers impacting a native poplar hybrid stand.

Hybridization and introgression are pervasive evolutionary phenomena that provide insight into the selective forces that maintain species boundaries, permit gene flow, and control the direction of evolutionary change. Poplar trees (Populus L.) are well known for their ability to form viable hybrids and maintain their distinct species boundaries despite this interspecific gene flow. We sought to quantify the hybridization dynamics and postzygotic fitness within a hybrid stand of balsam poplar (Populus balsamifera L.), eastern cottonwood (P. deltoides Marsh.), and their natural hybrids to gain insight into the barriers maintaining this stable hybrid zone. We observed asymmetrical hybrid formation with P. deltoides acting as the seed parent, but with subsequent introgression biased toward P. balsamifera. Native hybrids expressed fitness traits intermediate to the parental species and were not universally unfit. That said, native hybrid seedlings were absent from the seedling population, which may indicate additional selective pressures controlling their recruitment. It is imperative that we understand the selective forces maintaining this native hybrid zone in order to quantify the impact of exotic poplar hybrids on this native system.

Characteristics of Barred Owl (<em>Strix varia</em>) nest sites in Manitoba, Canada

During 2009 and 2010, nine Barred Owl (Strix varia) nest sites were located in Manitoba, Canada, and data on nest trees, nest structure, and nest site habitat were collected. Nests were located in a variety of tree species, including Balsam Poplar (Populus balsamifera), Paper Birch (Betula papyrifera), Trembling Aspen (Populus tremuloides) and Burr Oak (Quercus macrocarpa). All nests were in tree cavities, and the majority of nests were in dead trees (67%) and had lateral openings (67%). Habitat surrounding nest trees and estimated canopy cover were highly variable. Diameter at breast height of nest trees, cavity width, and cavity depth were consistent and were determined to be the most reliable indicators of nest suitability for breeding Barred Owls. We conclude that the distribution of nesting Barred Owls is influenced more by availability of suitable nest sites than by nest tree species or nest site habitat.

Propolis from Northern California and Oregon: Chemical Composition, Botanical Origin, and Content of Allergens

Propolis is a beehive product that bees manufacture by mixing their own wax with vegetable resins collected from different species of trees and bushes. The chemical composition of propolis is very variable because it depends on the flora locally available, and specimens from different geographical and climatic areas display unique properties. In this paper, the results of the chemical characterization of some propolis specimens collected in northern California and in Oregon are presented. Their chemical compositions show that all specimens contain resins from poplars of the Tacamahaca section (balsam poplars)--characteristic of the western part of the North American continent. Nevertheless, some of the specimens are of mixed origin because they also contain resins from poplars of the Aigeiros section (cottonwoods)--also present in this part of the world. Propolis causes allergies in sensitive human individuals, which are due to the presence of certain esters. The contents of known propolis allergenic esters--phenylethyl caffeate, 1,1-dimethylallyl caffeate, benzyl cinnamate, and benzyl salicylate--have been investigated in these specimens and found to depend on the botanical origin.

Balsacones D-I, dihydrocinnamoyl flavans from Populus balsamifera buds

A phytochemical investigation of an ethanolic extract from Populus balsamifera L. buds resulted in the isolation and characterization of twelve new flavan derivatives consisting of six pairs of enantiomers. Structures of (+) and (−)-balsacones D-I were elucidated based on spectroscopic data (1D and 2D NMR, MS) and their absolute configurations were established using X-ray single crystal diffraction analysis and ECD computational calculations. Antibacterial activity and cytotoxicity of all purified enantiomers were evaluated in vitro against Staphylococcus aureus and human skin fibroblast cells, respectively.

The influence of regional gradients in climate and air pollution on epiphytes in riparian forest galleries of the upper Fraser River watershed

Epiphyte diversity and abundance were examined along the Fraser River and its tributaries in central-interior British Columbia at varying distances from point-source air pollution discharges. Black cottonwood (Populus balsamifera L. ssp. trichocarpa (Torr. & A. Gray ex Hook.) Brayshaw trunks near discharges in Prince George had comparatively low epiphyte diversity and supported an unusual acidiphilic lichen community, including Tuckermannopsis chlorophylla (Willd.) Hale, Usnea lapponica Vain., and Vulpicida canadensis (Räsänen) J.-E. Mattsson & M.J. Lai. At a greater distance from air pollution sources, a more characteristic flora was observed, including Collema Wigg. spp., Lecidea erythrophaea Flörke, Leptogium (Ach.) Gray spp., Lobaria pulmonaria (L.) Hoffm., Nephroma parile (Ach.) Ach., Peltigera Willd. spp., and Strangospora moriformis (Ach.) Stein. These changes were accompanied by large differences in bark pH; mean values ranged from 3.7 in Prince George to 6.7 in upriver stands for black cottonwoods, from 3.5 to 5.4 for live spruce branches (Picea glauca (Moench) Voss), and from 3.1 to 4.9 for dead spruce branches, respectively. Epiphyte communities proximal to Prince George were characterized by many nitrophilous species. Our data showed a strong covariate influence of climate, with Lobarion community lichens more abundant in the easternmost high-precipitation plots. Numerous provincial- and global-level conservation priority species were found, including Collema quadrifidum D.F. Stone & McCune, newly discovered for Canada; Collema coniophilum Goward, a Species at Risk Act listed species; and provincially at risk Heterodermia speciosa (Wulf.) Trev., Physcia tribacia (Ach.) Nyl., and Santessoniella saximontana T. Sprib., P.M. Jørg. & M. Schultz, mostly in sites distant from air pollution sources.

The Role of Aggregated Forest Harvest Residue in Soil Fertility, Plant Growth, and Pollination Services

While post‐harvest residue (“slash”) is increasingly viewed as a source of biofuel, few studies have considered the potential ecological impact of the spatial distribution of forest harvest residue. We hypothesized that slash piles create islands of high soil fertility and light, leading to greater abundance, growth, and reproduction of plants. In 6‐yr‐old intensively managed hybrid poplar (Populus balsamifera L. × P. maximowiczii A. Henry) plantations, we showed that soluble organic N, NO3–N, NH4–N, and P decreased as a negative exponential function with distance from the pile. Pin cherry (Prunus pensylvanica L. f.) relative growth rate was fastest near piles in the first few years after harvest. We found significantly greater stem size, flowers per plant, and foliar P near piles for cherry, and this inverse gradient sharpened in a 16‐yr‐old white spruce [Picea glauca (Moench) Voss] plantation. For the two other flowering species, strawberry (Fragaria virginiana Mill.) and raspberry (Rubus idaeus L.), flower and fruit abundance were also significantly and strongly negatively correlated with distance to the pile. Further, directly correlating soil nutrient availability with plant traits, we found significant positive relationships between plant growth, reproductive output, and N availability. Partial correlation analysis indicated that more of the variance in plant traits was explained by distance than by soil nutrition. We conclude that in industrial forests, piles replace canopy gaps as sites where understory plant species can episodically reproduce and are therefore important for many plant species as well as the pollinators and frugivores dependent on them.

The influence of lignin–carbohydrate complexes on the cellulase-mediated saccharification I: Transgenic black cottonwood (western balsam poplar, California poplar) P. trichocarpa including the xylan down-regulated and the lignin down-regulated lines

The influence of the putative lignin–carbohydrate complexes (LCCs) on enzymatic saccharification was elucidated for the first time by examining two groups of transgenic black cottonwood (P. trichocarpa) comprised of the lignin down-regulated and the xylan down-regulated lines. Any adventitious contaminants that could affect the characterization of LCCs and the enzymatic saccharification were removed by performing a thorough extraction on the samples. The crude milled wood lignin was subsequently isolated from which the phenyl glycoside, benzyl ether and γ-ester linkages representative of the LCCs were identified and quantified with the combination of 13C and 1H–13C Heteronuclear Single Quantum Coherence (HSQC) NMR. The result indicated that the samples showed different levels of the three LCC linkages, depending on the xylan and/or lignin content. The correlation between the LCCs and enzymatic saccharification nearly conclusively demonstrated that the LCCs accounting for the recalcitrance of lignocellulosic biodegradation.

Two herbivore-induced cytochrome P450 enzymes CYP79D6 and CYP79D7 catalyze the formation of volatile aldoximes involved in poplar defense.

Aldoximes are known as floral and vegetative plant volatiles but also as biosynthetic intermediates for other plant defense compounds. While the cytochrome P450 monooxygenases (CYP) from the CYP79 family forming aldoximes as biosynthetic intermediates have been intensively studied, little is known about the enzymology of volatile aldoxime formation. We characterized two P450 enzymes, CYP79D6v3 and CYP79D7v2, which are involved in herbivore-induced aldoxime formation in western balsam poplar (Populus trichocarpa). Heterologous expression in Saccharomyces cerevisiae revealed that both enzymes produce a mixture of different aldoximes. Knockdown lines of CYP79D6/7 in gray poplar (Populus × canescens) exhibited a decreased emission of aldoximes, nitriles, and alcohols, emphasizing that the CYP79s catalyze the first step in the formation of a complex volatile blend. Aldoxime emission was found to be restricted to herbivore-damaged leaves and is closely correlated with CYP79D6 and CYP79D7 gene expression. The semi-volatile phenylacetaldoxime decreased survival and weight gain of gypsy moth (Lymantria dispar) caterpillars, suggesting that aldoximes may be involved in direct defense. The wide distribution of volatile aldoximes throughout the plant kingdom and the presence of CYP79 genes in all sequenced genomes of angiosperms suggest that volatile formation mediated by CYP79s is a general phenomenon in the plant kingdom.

Photosynthetic and morphological responses of white birch, balsam poplar, and trembling aspen to freezing and artificial defoliation

Comparative stress resistance of 1-year-old white birch (Betula papyrifera Marsh.), balsam poplar (Populus balsamifera L.), and trembling aspen (Populus tremuloides Michx.) seedlings was evaluated after exposure to freezing or defoliation. Photosynthesis in leaves surviving freezing (−5 °C) declined immediately after treatment, but nearly fully recovered within 3 weeks. Defoliation did not significantly increase photosynthesis in the remaining leaves. Refoliation occurred after freezing that killed terminal shoots and released current buds from apical dominance, while new leaves of larger size were produced through continuous growth of terminal shoots in 50% or 100% defoliation. Freezing and complete defoliation significantly reduced diameter and height growth in all species, whereas 50% defoliation did not affect growth. These results indicate some of the physiological and morphological responses to foliage loss in broadleaved boreal species that can help to maintain growth and productivity under a warming climate, which may result in more frequent damaging spring frosts and insect defoliation.

Host Genotype Shapes the Foliar Fungal Microbiome of Balsam Poplar (Populus balsamifera)

Foliar fungal communities of plants are diverse and ubiquitous. In grasses endophytes may increase host fitness; in trees, their ecological roles are poorly understood. We investigated whether the genotype of the host tree influences community structure of foliar fungi. We sampled leaves from genotyped balsam poplars from across the species' range, and applied 454 amplicon sequencing to characterize foliar fungal communities. At the time of the sampling the poplars had been growing in a common garden for two years. We found diverse fungal communities associated with the poplar leaves. Linear discriminant analysis and generalized linear models showed that host genotypes had a structuring effect on the composition of foliar fungal communities. The observed patterns may be explained by a filtering mechanism which allows the trees to selectively recruit fungal strains from the environment. Alternatively, host genotype-specific fungal communities may be present in the tree systemically, and persist in the host even after two clonal reproductions. Both scenarios are consistent with host tree adaptation to specific foliar fungal communities and suggest that there is a functional basis for the strong biotic interaction.

DEVELOPMENT AND APPLICATION OF CVA, DRIS, AND CND NORMS FOR THREE HYBRIDS OF POPULUS MAXIMOWICZII PLANTED IN SOUTHERN QUEBEC

Plantations of hybrid poplars adapted to relatively poor soils and cold conditions are being established in abandoned fields and forest sites in southern Quebec. Hybrids of Populus maximowiczii are well adapted to these sites but little is known about their nutritional requirements. The objectives of this study were to develop nutritional norms (CVA, DRIS, CND) for three of these hybrids: 915508, Populus euramericana or canadensis X Populus maximowiczii; 3729, Populus nigra X Populus maximowiczii; and 915303, Populus maximowiczii X Populus balsamifera, and to apply the norms on some sites recently planted in southern Quebec. Six plantations (two per clone) were used for the determination of nutritional norms. In each plantation, individual trees were fertilized with nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) according to a factorial design with three levels of application for each nutrient (35 = 243 treatments). Tree diameter and height, unit foliar mass and foliar chemistry (N, P, K, Ca, and Mg) of each tree were determined two years after fertilization. CVA, DRIS and CND norms were determined using a boundary-line approach with each plantation. Nutritional norms could be established for most combinations of clones and nutrients. CVA, DRIS and CND indices produced with published optimum nutrient concentrations for hybrid poplars closely related to P. maximowiczii were generally in agreement with the ones developed in our study. Differences in nutritional norms among P. maximowiczii hybrids/clones were small but hybrid/clone specific norms could provide more precise estimates of tree nutrition. The application of the norms on some representative sites of southern Quebec revealed more frequent nutrient imbalances than true nutrient deficiencies with generally excessive Ca and Mg, and limiting N, P, and K.

Natural Products for the Treatment of Obesity, Metabolic Syndrome, and Type 2 Diabetes

Globally, the incidence of obesity, metabolic syndrome, and diabetes (OMD) are continuously on the rise because of rapid changes in human life-style and dietary habits. Herbal extracts are of special interest in treating combination of these diseases because of their multipronged mode of action. The list of potential herbals to control metabolic diseases is ever-expanding. However, because of poor characterization and safety issues, these herbs face limitations for their clinical usage. This special issue is a collection of research and review articles on preclinical and clinical benefits of herbals in controlling OMD. This special issue contains 24 articles accepted from a total of 37 submissions consisting of 20 research articles, 3 review articles, and 1 clinical study. The research articles in this issue can be broadly divided into three disease categories—nonalcoholic steatohepatitis (NASH), obesity, and diabetic complications. Four articles of this special issue focus on evaluating the protective role of herbal extracts on NASH. The studies by X. R. Yang et al. “Effect of dietary cocoa tea (Camellia ptilophylla) supplementation on high-fat diet-induced obesity, hepatic Steatosis, and hyperlipidemia in mice” and H.-Y. Jung et al. “The Korean mistletoe (Viscum album coloratum) extract has an antiobesity effect and protects against hepatic steatosis in mice with high-fat diet-induced obesity” report the potential benefits of Camellia ptilophylla and Viscum album coloratum extracts against HFD-induced NASH. Another two articles evaluated protective effects of biherbal combination (S. miltiorrhiza, G. jasminoides and Grape Pomace, Omija Fruit) in ameliorating experimental NASH. This special issue also contains five articles that focus on antiobesity potential of herbal extracts. These detailed studies evaluated the benefits of 10 herbs and their potential mechanisms responsible in controlling obesity using experimental HFD-fed mice/rat in vivo and 3T3L1 preadipocyte in vitro models. Modulation of PPARγ was a key antiobesity mechanism of Artemisia iwayomogi, Codonopsis lanceolata, Populus balsamifera and its active component (salicortin), and beta-glucan-rich extract from Pleurotus sajor-caju (Fr.) Singer. H.-Y. Shin et al. reported an activation of AMP-activated protein kinase by extract of six herbal medicines (OB-1). In this special issue, 11 articles focus on the potential benefits of various herbal extracts/phytocompounds on diabetes-induced insulin resistance, nephropathy, retinopathy, cardiomyopathy, and inflammation. A. l. Al-Malki showed oat extract to be beneficial for diabetic nephropathy and retinopathy by modulating nuclear factor kappa B (NF-kB). Inhibition of aldose reductase activity by scopoletin ameliorated cataractogenesis in galactose-fed rats (J. Kim et al.). Boehmeria nivea extract (S. H. Kim et al.) and swertiamarin (T. P. Patel et al.) regulated experimental insulin resistance by modulating PPARγ. In another report, S. Kadan et al. evaluated effect of eight antidiabetic medicinal plants extracts on GLUT 4 translocation. The benefits of fisetin and an ayurvedic herbal formulation (Kal-1) on diabetes-induced inflammation was also reported. Further, quercetin was shown to preserve β-cell mass and function in fructose-fed hyperinsulinemic rats via modulating pancreatic akt/foxo1 activation. Berberine ameliorated glucose- and insulin-induced cardiomyocyte hypertrophy by modulating PPARα/NO. In an interesting article by S. E. Martinez et al. pharmacometrics of an antidiabetic compound, 3-methoxypterostilbene was reported. 3-Methoxypterostilbene inhibited α-glucosidase and α-amylase activity and exhibited approximately 50% bioavailability. Three review articles were also incorporated in this special issue. A review by Y. Liu et al. (recent updates on beneficial role of berberine in controlling NASH) provides detailed account on molecular regulation of lipid metabolism and NASH by berberine. In another review by C. D. Lorenzo et al. the use of in vitro and clinical approaches to assess the benefits of plant food supplements is critically discussed. The potential benefits of Kampo, a Japanese traditional medicine, in treating obesity was reviewed by J.-i Yamakawa et al. based on basic and clinical evidence. The only clinical study as a part of this special issue focuses on evaluating body weight lowering effects of herbal extract-THI (target herbal ingredient) on exercising healthy overweight humans following a two-month randomized double-blind, placebo-controlled trial. The study reports a significant reduction in body weight indicating its potential antiobesity effect. We envisage that this special issue will attract broad interest in the fields of obesity, metabolic syndrome, and type 2 diabetes and encourage the perusal of in-depth molecular and cellular mechanistic investigations into the use of natural products, in particular the herbal therapies for metabolic disorders and their complications.

Quantifying remobilization of pre-existing nitrogen from cuttings to new growth of woody plants using 15N at natural abundance

BackgroundFor measurements of nitrogen isotope composition at natural abundance, carry-over of pre-existing nitrogen remobilized to new plant growth can cause deviation of measured isotope composition (δ15N) from the δ15Nof newly acquired nitrogen. To account for this problem, a two-step approach was proposed to quantify and correct for remobilized nitrogen from vegetative cuttings of Populus balsamifera L. grown with either nitrate (δ15N = 58.5‰) or ammonium (δ15N = −0.96‰). First, the fraction of carry-over nitrogen remaining in the cutting was estimated by isotope mass balance. Then measured δ15N values were adjusted for the fraction of pre-existing nitrogen remobilized to the plant.ResultsMean plant δ15N prior to correction was 49‰ and −5.8‰ under nitrate and ammonium, respectively. Plant δ15N was non-linearly correlated to biomass (r2 = 0.331 and 0.249 for nitrate and ammonium, respectively; P < 0.05) where the δ15N of plants with low biomass approached the δ15N of the pre-existing nitrogen. Approximately 50% of cutting nitrogen was not remobilized, irrespective of size. The proportion of carry-over nitrogen in new growth was not different between sources but ranged from less than 1% to 21% and was dependent on plant biomass and, to a lesser degree, the size of the cutting. The δ15N of newly acquired nitrogen averaged 52.7‰ and −6.4‰ for nitrate and ammonium-grown plants, respectively; both lower than their source values, as expected. Since there was a greater difference in δ15N between the carried-over pre-existing and newly assimilated nitrogen where nitrate was the source, the difference between measured δ15N and adjusted δ15N was also greater. There was no significant relationship between biomass and plant δ15N with either ammonium or nitrate after adjusting for carry-over nitrogen.ConclusionHere, we provide evidence of remobilized pre-existing nitrogen influencing δ15N of new growth of P. balsamifera L. A simple, though approximate, correction is proposed that can account for the remobilized fraction in the plant. With careful sampling to quantify pre-existing nitrogen, this method can more accurately determine changes in nitrogen isotope discrimination in plants.

New antibacterial dihydrochalcone derivatives from buds of Populus balsamifera

Three new dihydrochalcone derivatives, balsacones A, B, and C, along with seven known compounds, were isolated from the buds of Populus balsamifera. The structures of the new compounds were elucidated by the analysis of spectroscopic data. Only balsacone A, B, and C were significantly active against Staphylococcus aureus with MIC values ranging from 3.1 to 6.3μM.

The adaptive potential of Populus balsamifera L. to phenology requirements in a warmer global climate

The manner in which organisms adapt to climate change informs a broader understanding of the evolution of biodiversity as well as conservation and mitigation plans. We apply common garden and association mapping approaches to quantify genetic variance and identify loci affecting bud flush and bud set, traits that define a tree's season for height growth, in the boreal forest tree Populus balsamifera L. (balsam poplar). Using data from 478 genotypes grown in each of two common gardens, one near the southern edge and another near the northern edge of P. balsamifera's range, we found that broad-sense heritability for bud flush and bud set was generally high (H(2) > 0.5 in most cases), suggesting that abundant genetic variation exists for phenological response to changes in the length of the growing season. To identify the molecular genetic basis of this variation, we genotyped trees for 346 candidate single nucleotide polymorphisms (SNPs) from 27 candidate genes for the CO/FT pathway in poplar. Mixed-model analyses of variance identified SNPs in 10 genes to be associated with variation in either bud flush or bud set. Multiple SNPs within FRIGIDA were associated with bud flush, whereas multiple SNPs in LEAFY and GIGANTEA 5 were associated with bud set. Although there was strong population structure in stem phenology, the geographic distribution of multilocus association SNP genotypes was widespread except at the most northern populations, indicating that geographic regions may harbour sufficient diversity in functional genes to facilitate adaption to future climatic conditions in many sites.

EFFECT OF PLANTS ON THE BIOAVAILABILITY OF METALS AND OTHER CHEMICAL PROPERTIES OF BIOSOLIDS IN A COLUMN STUDY

The effects of metal-accumulating plants (Salix x reichardtii and Populus balsamifera) on the chemical properties and dynamics of metals in biosolids were investigated using different techniques including diffusive gradients in thin films (DGT), sequential extraction procedures and partitioning coefficient (Kd). Plants could effectively extract Cd, Ni, and Zn and decreased dissolved organic carbon (DOC). The presence of plants increased the potential bioavailability of these metals, as assessed by an increase in the ratio of metal measured by DGT and metals in the solution. The plants affected the Cd, Ni, and Zn pools (soluble/exchangeable; Fe/Mn oxide and organic matter bound) characterised by sequential extraction and Kd but did not reduce the total metals in either substrate. However, plants had no effect on Cu, presumably because of the effective buffering of available Cu by organic matter in both solution and solid phases. A high density of plant roots was associated with increased leaching of metals.

Natural Revegetation of a Boreal Gold Mine Tailings Pond

AbstractUnderstanding the natural revegetation of forests disturbed by the dumping of mine wastes is vital for the success of reclamation strategies. The Gunnar gold mine tailings pond in southeast Manitoba has remained largely unvegetated since the mine was closed in 1942, with limited vegetation developed on one side of the pond. We examined the natural Picea mariana/Larix laricina forest that has developed on the pond to determine how the plant community develops and what changes in the tailings are associated with this development. Vegetation sampled along transects showed a consistent pattern of succession from Equisetum palustre to Salix spp., and Populus balsamifera, to Larix laricina and finally to P. mariana. Larix laricina and P. mariana are moving into the site at the rate of 1.5 m per year with L. laricina invading 4 years ahead of P. mariana. Both tree species show a similar pattern of annual growth, showing positive correlations with spring precipitation, a pattern also occurring on L. laricina growing on a nearby site. The establishment of E. palustre was accompanied by initially rapid decreases in compaction and conductivity of the tailings, and an increase in inorganic nitrogen. Surface organic matter depth, coarse organic matter mass, and soil organic carbon increased at a constant rate, whereas subsurface coarse organic matter had an initial rapid increase followed by a gradual increase. As fern allies (and specifically members of the Equisetaceae family) have a number of properties that facilitate succession on mine wastes, their use should be explored further.