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Aim: Seedling recruitment is a vital process for forest regeneration and is influenced by various factors such as stand composition, climate, and soil disturbance. We conducted a long‐term field experiment (18 years) to study the effects of these factors and their interactions on seedling recruitment. Location: Our study focused on five main species in boreal mixed woods of eastern Canada: trembling aspen (Populus tremuloides), paper birch (Betula papyrifera), white spruce (Picea glauca), balsam fir (Abies balsamea), and white cedar (Thuja occidentalis). Methods: Sixteen 1‐m2 seedling monitoring subplots were set up in each of seven stands originating from different wildfires (fire years ranging from 1760 to 1944), with a soil scarification treatment applied to every other subplot. Annual new seedling counts were related to growing‐season climate (mean temperature, growing degree days and drought code), scarification, and stand effects via a Bayesian generalized linear mixed model. Results: Soil scarification had a large positive effect on seedling recruitment for three species (aspen, birch and spruce). As expected, high mean temperatures during the seed production period (two years prior to seedling emergence) increased seedling recruitment for all species but aspen. Contrary to other studies, we did not find a positive effect of dry conditions during the seed production period. Furthermore, high values of growing degree days suppressed conifer seedling recruitment. Except for white cedar, basal area was weakly correlated with seedling abundance, suggesting a small number of reproductive individuals is sufficient to saturate seedling recruitment. Conclusion: Our findings underscore the importance of considering multiple factors, such as soil disturbance, climate, and stand composition, as well as their effects on different life stages when developing effective forest management strategies to promote regeneration in boreal mixed‐wood ecosystems. [ABSTRACT FROM AUTHOR]

Rapid establishment of closed canopy cover is a key goal in land reclamation. While re-establishment of understory vegetation is likely to positively contribute to this goal, native herbaceous species are not typically planted on reclaimed sites though it is an alternative to reliance on natural regeneration. The objective of the present study was to test the principle of hitchhiker production of a tree species with native herbaceous species on recently reclaimed industrial sites with the aim of (1) understanding growth tradeoffs when mixing these species in the same container and (2) if hitchhiking had negative growth and survival outcomes for white spruce (Picea glauca) seedlings compared with singly grown white spruce seedlings. White spruce seeds were sown in nursery containers of contrasting cavity sizes, followed by sowing a forb species (Eurybia conspicua or Chamerion angustifolium) at different time intervals or grown singly. Larger cavities and earlier sow dates were associated with higher persistence and growth of the forbs, while later sow dates were associated with larger white spruce seedlings. We observed no evidence to suggest that hitchhiked seedlings were at a competitive disadvantage in terms of growth or survival compared with singly grown seedlings that were initially similar in size. [ABSTRACT FROM AUTHOR]

Purpose: Most plants interact with soil biota that positively or negatively affect seedling performance. These plant-soil feedbacks (PSFs) can strongly affect recruitment, potentially for years after death. We tested whether PSFs persisted following death for Populus tremuloides Michx. (aspen) and if these effects were environment dependent using soils collected from live and dead aspen and heterospecific Picea glauca (Moench) Voss in 24 stands across two ecosystems. Methods: We conducted a greenhouse experiment using soils from 24 aspen stands. At each stand, we collected soil from three trees of each tree type and used live and sterilized versions of these soils to inoculate aspen seedlings. We then recorded mortality and growth of the seedlings over three months. Results: Live inocula reduced aspen survival and growth relative to sterilized inocula, suggesting that pathogens drive PSF. Plant responses to live and dead aspen inocula were correlated across environments; however, responses to aspen and heterospecific Picea inocula were uncorrelated, suggesting that specialized pathogens may drive PSF. Conclusions: Pathogen-driven negative PSFs can persist for multiple years irrespective of the environment, potentially limiting the regeneration of aspen stands following dieback. Persistent PSFs thus have potential to cause lagged effects on population and community dynamics. [ABSTRACT FROM AUTHOR]

Herbivores can modify the rate of shrub and treeline advance. Both direct and indirect effects of herbivory may simultaneously interact to affect the growth rates of plants at this ecotone. We investigated the effect of snowshoe hare herbivory on the height of white spruce at two treeline locations in Alaska, USA. White spruce is expanding its distribution both upwards in elevation and northward in latitude because of climate warming, and snowshoe hares are already present in areas likely to be colonized by spruce. We hypothesized that herbivory would result in browsed individuals having reduced height, suggesting herbivory is a direct, negative effect on spruce treeline advance. We found an interactive effect between browsing history and spruce age. When young (under 30 years old), individuals that were browsed tended to be taller than unbrowsed individuals. However, older seedlings (over 30 years old) that had been browsed were shorter than unbrowsed individuals of the same age. Hares suppress faster growing individuals that are initially taller by preferentially browsing them as they emerge above the winter snowpack. This reduced height, in combination with increased mortality associated with browsing, is predicted to slow the advance of both latitudinal and altitudinal treeline expansions and alter the structure of treeline forests. [ABSTRACT FROM AUTHOR]

Regional warming has led to increased productivity near the boreal forest margin in Alaska. To date, the effects of warming on seedling recruitment have received little attention, in spite of forecasted forest expansion. Here, we used stand structure and environmental data from 95 white spruce ( Picea glauca) plots sampled across a longitudinal gradient in southwest Alaska to explore factors influencing spruce establishment and recruitment near western treeline. We used total counts of live seedlings, saplings, and trees, representing five life stages, to evaluate whether geospatial, climate, and measured plot covariates predicted abundance, using current abundance distributions as a surrogate for climate conditions in the past. We used generalized linear models to test the null hypothesis that conditions favorable for recruitment were similar along the environmental gradient represented by longitude, by exploring relationships between per-plot counts of each life stage and the covariates hypothesized to affect abundance. We also examined the relationship between growing degree days ( GDD) and seedling establishment over a period of three decades using tree-ring chronologies obtained from cores taken at a subset of our sites ( n = 30). Our results indicated that seedling, sapling, and tree abundance were positively correlated with temperature across the study area. The response to longitude was mixed, with earlier life stages (seedlings, saplings) most abundant at the western end of the gradient, and later life stages (trees) most abundant to the east. The differential relationship between longitude and life-stage abundance suggests a moving front of white spruce establishment through time, driven by changes in environmental conditions near the species' western range limit. Likewise, we found a positive relationship between periods of seedling establishment and GDD, suggesting that longer summers and/or greater heat accumulation might enhance establishment, consistent with the positive relationship we found between life-stage abundance and temperature. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase winter temperatures in boreal climates. White spruce ( Picea glauca (Moench) Voss) is vulnerable to spring frost damage due to its habit of early budbreak, which may be exacerbated or lessened with increasingly warm winters at its southern range edge. We tested the effects of episodic warming during the quiescent stage on budbreak time and growth of seven seed sources grown in a common garden setting in Minnesota, USA. Treatment plots were warmed with infrared lamps for 4 days each in February, March, or February and March to simulate a midwinter thaw. Control plots for each treatment and an overall control were included for comparison. Trees warmed in February experienced a slight delay in spring budbreak, but differences in budbreak time were generally not significant. Terminal growth was significantly and negatively correlated with time of budbreak but not with time to growth cessation. Our results suggest that white spruce is relatively resilient to the effects of intermittent warming but that warming early in the season may delay budbreak time, which is expected to reduce terminal growth. [ABSTRACT FROM AUTHOR]

Climate warming is expected to increase the seasonal duration of photosynthetic carbon fixation and tree growth in high-latitude forests. However, photoperiod, a crucial cue for seasonality, will remain constant, which may constrain tree responses to warming. We investigated the effects of temperature and photoperiod on weekly changes in photosynthetic capacity, leaf biochemistry and growth in seedlings of a boreal evergreen conifer, white spruce [ Picea glauca (Moench) Voss]. Warming delayed autumn declines in photosynthetic capacity, extending the period when seedlings had high carbon uptake. While photoperiod was correlated with photosynthetic capacity, short photoperiods did not constrain the maintenance of high photosynthetic capacity under warming. Rubisco concentration dynamics were affected by temperature but not photoperiod, while leaf pigment concentrations were unaffected by treatments. Respiration rates at 25 °C were stimulated by photoperiod, although respiration at the growth temperatures was increased in warming treatments. Seedling growth was stimulated by increased photoperiod and suppressed by warming. We demonstrate that temperature is a stronger control on the seasonal timing of photosynthetic down-regulation than is photoperiod. Thus, while warming can stimulate carbon uptake in boreal conifers, the extra carbon may be directed towards respiration rather than biomass, potentially limiting carbon sequestration under climate change. [ABSTRACT FROM AUTHOR]

Climate-related variations in functional traits of boreal tree species can result both from physiological acclimation and genetic adaptation of local populations to their biophysical environment. To improve our understanding and prediction of the physiological and growth responses of populations to climate change, we studied the role of climate of seed origin in determining variations in functional traits and its implications for tree improvement programs for a commonly reforested boreal conifer, white spruce (Picea glauca (Moench) Voss). We evaluated growth, root-to-shoot ratio (R/S), specific leaf area (SLA), needle nitrogen (Nmass), total non-structural carbohydrates (NSC) and photosynthetic traits of 3-year-old seedlings in a greenhouse experiment using seed from six seed orchards (SO) representing the different regions where white spruce is reforested in Québec. Height and total dry mass (TDM) were positively correlated with photosynthetic capacity (Amax), stomatal conductance (gs) and mesophyll conductance (gm). Total dry mass, but not height growth, was strongly correlated with latitude of seed origin (SO) and associated climate variables. Amax, gs, gm and more marginally, photosynthetic nitrogen-use efficiency (PNUE) were positively associated with the mean July temperature of the SO, while water use efficiency (WUE) was negatively associated. Maximum rates of carboxylation (Vcmax), maximum rates of electron transport (Jmax), SLA, Nmass, NSC and R/S showed no pattern. Our results did not demonstrate a higher Amax for northern seed orchards, although this has been previously hypothesized as an adaptation mechanism for maintaining carbon uptake in northern regions. We suggest that gs, gm, WUE and PNUE are the functional traits most associated with fine-scale geographic clines and with the degree of local adaptation of white spruce populations to their biophysical environments. These geographic patterns may reflect in situ adaptive genetic differences in photosynthetic efficiency along the cline. [ABSTRACT FROM AUTHOR]

Tree improvement programs aim to develop families that are well-adapted to future growing conditions. To gain insight into the stability of the family genetic response to climate change, white spruce (Picea glauca) seedlings from 60 full-sib families were subjected to a combination of two temperature regimes and two levels of CO2over two growing seasons. There was positive effect of warmer temperatures and higher CO2on some growth variables but no significant family × treatment interactions. Instantaneous water use efficiency was the only physiological trait that was affected positively by the CO2treatment, showing a 51% increase that was consistent across families. [ABSTRACT FROM PUBLISHER]

Background and aims: Soil pH is among the major environmental factors affecting plant growth. Although the optimum range of soil pH for growth and the tolerance of pH extremes widely vary among plant species, the pH tolerance mechanisms in plants are still poorly understood. In this study, possible mechanisms were examined to explain the differences in tolerance of boreal plants to root zone pH. Methods: In the controlled-environment solution culture experiments, we compared growth, physiological parameters and tissue nutrient concentrations in aspen, white spruce and tamarack seedlings that were subjected to 8 weeks of root zone pH treatments ranging from 5.0 to 9.0. Results: The pH treatments had little effect on dry weights and net photosynthesis in white spruce seedlings despite reductions in transpiration rates at higher pH levels. In aspen and tamarack, both the growth and physiological parameters significantly decreased at pH higher than 6.0. The chlorosis of young tissues in aspen and tamarack was associated with the reductions in foliar concentrations of several of the examined essential nutrients including Fe and Mn. Although the plants varied in their ability to deliver essential nutrients to growing leaves, there was no direct correlation between tissue nutrient concentrations, chlorophyll concentrations and plant growth. The results also demonstrated strong inhibition of transpiration rates by high pH. Conclusions: The results suggest that high root zone pH can upset water balance in pH sensitive species including aspen. Although the uptake and assimilation of essential elements such as Fe and Mn contribute to plant tolerance of high soil pH, we did not observe a direct relationship between growth and foliar nutrient concentrations to account for the observed differences in growth. [ABSTRACT FROM AUTHOR]

Abstract: White spruce (Picea glauca [Moench] Voss) seedlings produced by somatic embryogenesis were grown both at the Kennedy Space Center and in weightlessness in the ISS for 30days. Plants were placed in closed environment incubators (Advanced Biological Research System) under controlled light, temperature, humidity and CO2 conditions. At the end of the experiment, the leading shoot from three plantlets of each of the three lines tested were sampled and pooled in Kennedy Space Center Fixation Tubes (KFT) containing a RNA stabilization solution. Transcript levels were determined by quantitative real-time polymerase chain reaction (RT-qPCR) for 27 candidate genes and three reference genes on the nine seedlings grown in each environment. About two-thirds of the 27 genes produced a larger number of transcript molecules in microgravity conditions. However, only three genes showed significant differences between the two environments, and all of them were up-regulated in microgravity. These genes appear to be involved in important processes such as cell propagation, plant development and response to stress, and their up-regulation has likely contributed to influencing seedling growth patterns. [Copyright &y& Elsevier]

* Premise of the study: In ecosystems where seed production is low and masting years are sporadic, or with species that have short-lived seeds, regeneration is assured by seedling banks rather than seed banks. Seedling establishment and survival play a critical role in determining the composition of these plant communities by supplying new individuals for their maintenance. Seedling emergence and mortality were investigated to test the hypothesis that recruitment into the seedling bank is periodic. * Materials and methods: Seed production and seedling emergence and survival was monitored during 1994-2007 in balsam fir (Abies balsamea) and white spruce (Picea glauca) in four pristine stands of the boreal forest of Quebec, Canada. Measurements were collected twice per month by sampling one permanent plot of 20 x 20 m per stand. * Key results: Seed-rain abundance reached 9 x 10³ seeds m-2 year-1, and was characterized by synchronous sequences of low and high seed production. New seedlings appeared only during the year following a seed production of at least 1 x 10³ and 1.5 x 10² seeds m-2 year-1 for balsam fir and white spruce, respectively. Seedlings emerged in July and survived 34-52 d on average, with balsam fir showing a longer lifespan and lower mortality, although 85-99% of seedlings died before completing one year of life. * Conclusions: The emergence of young seedlings was coupled with massive seed rains, which allowed synchronous replenish ment of the seedling banks among stands and species, and generated different cohorts, yielding a discontinuous age structure. [ABSTRACT FROM AUTHOR]

The present study documents the changes in carbon and nitrogen metabolites occurring in apical buds and previous year stems of white spruce seedlings ( Picea glauca [Moench] Voss) with contrasting growth phenotypes (tall vs. small) after transfer to short day (SD; 8 h) photoperiod to induce bud formation. Concentrations of total nonstructural carbohydrates markedly increased in the developing buds within the days after transfer to SD, mainly as a result of increased concentrations of monosaccharides such as glucose, fructose, and pinitol. At the same time, starch levels declined, with the resulting carbohydrates presumably used to meet early carbon requirements of the SD-induced apical bud. Concentrations of glutamine, glutamic acid and proline also decreased immediately after transfer to SD in both organs. Later stages of SD-induced bud formation were characterized by an increase in starch, sucrose, and glutamine concentrations in previous year stems, concomitant with an increase in the steady-state levels of UDP-glucose pyrophosphorylase and glutamine synthetase protein. In contrast, arginine levels increased after 2 weeks of SD exposure, indicating a transition in arginine metabolism at the time of initiation of shoot stem primordia and bud elongation. Higher accumulation of total nonstructural carbohydrates and total amino acids in previous year stems of small trees could indicate lower sink strength of apical bud during its development, which could in turn impact subsequent tree growth. [ABSTRACT FROM AUTHOR]

CO2–light interactions can influence the competition among boreal plants, but are poorly understood. We investigated the effect of such interactions on the growth and biomass of 1-year-old black spruce (Sb) (Picea mariana (Mill.) BSP) and white spruce (Sw) (Picea glauca (Moench) Voss) grown with CO2 concentrations ([CO2]) of 360 and 720 µmol·mol–1 under 30%, 50%, and 100% light, in greenhouses. There were significant two-way and three-way interactions. Root collar diameter (RCD) of Sw decreased with decreasing light, while in Sb, there was no significant difference in RCD for plants grown under 50% or 30% light. Height was greater for plants grown under 100% light than if the plants were shaded. Elevated [CO2] increased RCD by 33% and enhanced stem volume by 67%, 98%, and 84% under 100%, 50%, and 30% light, respectively. The CO2 enhancement of total biomass was relatively higher under lower light, and greater for Sb than Sw. Elevated [CO2] decreased specific leaf area under 50% light only. Root mass was generally higher under 100% light than when shaded. Elevated [CO2] increased the root mass of Sb under 100% light, but decreased it under 30% light. Elevated [CO2] decreased the shoot/root ratio under 100% light, but increased it under 30% light. Our data suggest that raising [CO2] will likely increase species competitiveness under low light conditions, and that the increase will be greater in species that are relatively shade tolerant. [ABSTRACT FROM AUTHOR]

Black spruce ( Picea mariana), white spruce ( Picea glauca) and jack pine ( Pinus banksiana) were inoculated with Suillus tomentosus and subjected to potassium fluoride (1 m M KF and 5 m M KF) in the presence and absence of 60 m M NaCl. The NaCl and KF treatments reduced total dry weights in jack pine and black spruce seedlings, but they did not affect total dry weights in white spruce seedlings. The addition of 60 m M NaCl to KF treatment solutions alleviated fluoride-induced needle injury in ectomycorrhizal (ECM) black spruce and white spruce, but had little effect in jack pine seedlings. Both KF and 60 m M NaCl treatments reduced E values compared with non-treated control seedlings. However, with the exception of small reductions of Kr by NaCl treatments in black spruce, the applied KF and NaCl treatments had little effect on Kr in ECM plants. Chloride tissue concentrations in NaCl-treated plants were not affected by the presence of KF in treatment solutions. However, shoot F concentrations in ECM black spruce and white spruce treated with 5 m M KF + 60 m M NaCl were significantly reduced compared with the 5 m M KF treatment. The results point to a possible competitive inhibition of F transport by Cl. We also suggest that the possibility that aquaporins may be involved in the transmembrane transport of F should be further investigated. [ABSTRACT FROM AUTHOR]

Aim The objectives of the study are: (1) to evaluate the dynamics of the maritime tree line and forest limit of white spruce, Picea glauca, within the dual framework of primary succession induced by the rapid post-glacial land emergence on the eastern coast of Hudson Bay and the impacts of recent and past climate changes; and (2) to determine the time lapse between land emergence and seedling, tree, and forest establishment in the context of the primary chronosequence occurring on rising, well-drained sandy beaches and terraces. Location The study area was located on the eastern coast of Hudson Bay (56°20′ N, 76°32′ W) in northern Québec, Canada. Methods We evaluated the colonization dynamics of white spruce as seedlings, tree-line trees and primary-forest trees at eight sites distributed along a 200-km latitudinal gradient based on a mean land emergence rate of 1.2 m century−1. A 30-m wide by 140–300-m long quadrat was positioned at random at the centre of each site. The elevation above sea level, position and age of all individuals of spruce present in the quadrat areas were determined, and the soils of each chronosequence were described. Results The main stages of primary succession along the emerging coast were common to all the sites, regardless of latitude, but occurred at different elevations above sea level (a.s.l.). White spruce seedlings colonized near-shore beaches 2 m a.s.l., whereas the tree line and forest limit tended to form only at about 3–4 m and 4–8 m a.s.l., corresponding approximately to 180–825 years and 310–1615 years after land emersion, respectively. White spruce establishment at the tree line occurred about 50 years ago. Climatic conditions at this time were probably more favourable to tree colonization than when the species established at the forest limit. Soil formation was influenced primarily by distance from the seashore and elevation above sea level, with podzolization being accelerated by white spruce cover. Main conclusions The current tree-line and forest-limit positions on the rising coast of eastern Hudson Bay correspond to ecological limits established during the course of primary succession within a context of changing climatic conditions. The recent establishment of trees at the tree line and forest limit at relatively old coastal sites is associated with warmer conditions over the last 100 years. Although white spruce was present nearby, coastal sites were devoid of trees before the 20th century. [ABSTRACT FROM AUTHOR]

We characterized the ectomycorrhizae (ECM) of planted white spruce (Picea glauca (Moench) Voss) seedlings as affected by mechanical site preparation (MSP) of clear-cut conifer-dominated boreal mixedwood forest. Relative abundance, richness, and composition of the ECM community were compared among untreated control, mixed, mounded, and scalped site preparation treatments. On >11 000 root tips, we observed 16 ECM morphotypes. Those common to the nursery in which the seedlings were raised were most abundant (Thelephora americana, Wilcoxina-like (E-strain), Amphinema byssoides, Phialocephala-like (MRA)). Seedlings in the untreated controls had lower abundances of these, but higher abundances of other ECM, which were not present in the nursery of origin but were indigenous to these forest stands. In terms of ECM composition, the “mixed” treatment was most similar to the untreated control, while the “scalped” and “mound” treatments showed significantly different ECM communities than the controls. Our results suggest that MSP may facilitate continued dominance by ECM that establish on seedlings in the nursery while slowing the natural succession towards the natural forest ECM. MSP treatments that leave some surface organic matter relatively intact may impact ECM less than those that remove or bury the organic layer. Nous avons caractérisé les ectomycorhizes (ECM) de plants d’épinette blanche (Picea glauca (Moench) Voss) affectés par la préparation mécanisée de terrain (PMT) à la suite d’une coupe à blanc dans une forêt mixte dominée par des résineux. L’abondance relative, la richesse et la composition de la communauté d’ECM a été comparée entre un témoin non traité et des traitements de préparation de terrain mixtes, d’aménagement de buttes et de scalpage. Nous avons observé 16 morphotypes d’ECM sur plus de 11 000 apex racinaires. Ceux qui étaient communs dans la pépinière où les semis avaient été produits étaient les plus abondants (Thelephora americana, le type Wilcoxina (souche E), Amphinema byssoides, le type Phialocephala (MRA)). L’abondance de ces ECM était plus faible chez les semis des témoins non traités qui comportaient, cependant, une plus forte abondance d’autres ECM qui n’étaient pas présentes dans la pépinière d’origine, mais qui étaient indigènes à ces peuplements forestiers. En termes de composition en ECM, le traitement mixte était le plus semblable au témoin non traité alors que le scalpage et l’aménagement de buttes étaient associés à des communautés d’ECM significativement différentes de celle du témoin. Nos résultats indiquent que la PMT peut faciliter le maintien de la dominance des ECM établies sur les plants en pépinière tout en ralentissant la succession naturelle vers les ECM de la forêt naturelle. Les traitements de PMT qui laissent des superficies relativement intactes de matière organique peuvent avoir moins d’impact sur les ECM que ceux qui enlèvent ou enfouissent la couche de matière organique. [ABSTRACT FROM AUTHOR]

This study examined the impact of increased irrigation efficiency on the hardening and frost tolerance of 2-year-old containerized white spruce seedlings in the context of groundwater protection, irrigation management and the maintenance of seedling quality in northern climates. The seedlings were grown under three different irrigation regimes (IR =30%, 40% and 55% v/v; cm3 H2O/cm3 substrate) and were hardened under conditions of natural photoperiod and temperature. After being subjected to artificial frost tests on four sampling dates during autumn, the seedlings were compared for bud development and frost tolerance. IR had no influence on frost tolerance as determined by measurements of physiological (electrolyte leakage, root water loss) and morphological (shoot damage, root initiation) variables. At the end of the second growing season, there was no significant difference between IRs in seedling height, root collar diameter, shoot dry mass and root dry mass. The results indicate that the amount of water applied to large-dimension 2-year-old white spruce seedlings during the growing season can be significantly decreased without prematurely impeding their growth or hindering their acquisition of frost tolerance. [ABSTRACT FROM AUTHOR]

From 2001 to 2004 we experimentally warmed 40 large, naturally established, white spruce [ Picea glauca (Moench) Voss] seedlings at alpine treeline in southwest Yukon, Canada, using passive open-top chambers (OTCs) distributed equally between opposing north and south-facing slopes. Our goal was to test the hypothesis that an increase in temperature consistent with global climate warming would elicit a positive growth response. OTCs increased growing season air temperatures by 1. 8°C and annual growing degree-days by one-third. In response, warmed seedlings grew significantly taller and had higher photosynthetic rates compared with control seedlings. On the south aspect, soil temperatures averaged 1. 0°C warmer and the snow-free period was nearly 1 month longer. These seedlings grew longer branches and wider annual rings than seedlings on the north aspect, but had reduced Photosystem-II efficiency and experienced higher winter needle mortality. The presence of OTCs tended to reduce winter dieback over the course of the experiment. These results indicate that climate warming will enhance vertical growth rates of young conifers, with implications for future changes to the structure and elevation of treeline contingent upon exposure-related differences. Our results suggest that the growth of seedlings on north-facing slopes is limited by low soil temperature in the presence of permafrost, while growth on south-facing slopes appears limited by winter desiccation and cold-induced photoinhibition. [ABSTRACT FROM AUTHOR]

Early height growth of eastern white spruce (Picea glauca (Moench) Voss) rooted cuttings was compared with that of seedlings using annual measurements collected over 5 years in a farm field test replicated on three sites. The experiment included 148 full-sib families obtained from controlled crossings of superior trees selected for a white spruce breeding population in Quebec. Fifteen additional seedlots were used as controls. The average growth rate of seedlings (37.3 cm·year–1) was slightly larger than that of rooted cuttings (36.2 cm·year–1). The yearly growth rate increased over the test period, and it did so at a somewhat higher rate for the seedlings. The relative size of the estimated variance components and the moderate rank correlations of full-sib family height growth features between the two propagule types suggest that tree breeders should favour seedlings over rooted cuttings to rank families for selection purposes, but vegetative propagation would prove useful for bulking up scarce valuable genotypes. [ABSTRACT FROM AUTHOR]

We examined the growth of understory conifers, following partial or complete deciduous canopy removal, in a field study established in two regions in Canada. In central British Columbia, we studied the responses of three species (Pseudotsuga menziesii var. glauca (Beissn.) Franco, Picea glauca (Moench) Voss × Picea engelmannii Parry ex Engelm., and Abies lasiocarpa (Hook.) Nutt.), and in northwestern Quebec, we studied one species (Abies balsamea (L.) Mill.). Stem and root diameter and height growth were measured 5 years before and 3 years after harvesting. Both root and stem diameter growth increased sharply following release but seedlings showed greater root growth, suggesting that in the short term, improvement in soil resource capture and transport, and presumably stability, may be more important than an increase in stem diameter and height growth. Response was strongly size dependent, which appears to reflect greater demand for soil resources as well as higher light levels and greater tree vigour before release for taller individuals. Growth ratios could not explain the faster response generally attributed to true fir species or the unusual swift response of spruces. Good prerelease vigour of spruces, presumably favoured by deciduous canopies, could explain their rapid response to release. [ABSTRACT FROM AUTHOR]

Previous studies conducted in growth chambers had demonstrated the successful experimental inoculation of white spruce seedlings with anti-insectan toxin producing needle endophytes. Needles colonized with the rugulosin-producing endophyte 5WS22E1 (DAOM 229536) contained rugulosin in concentrations that impaired spruce budworm growth. Here we report experimental inoculations conducted under nursery conditions. To improve the reliability of detecting successful colonization, a polyclonal assay was developed for the target endophyte 5WS22E1. It was able to reliably detect the fungus in 500 ng subsamples of colonized needles. Seventeen months post-inoculation, 330 seedlings from 1235 inoculated were colonized. A random selection of 113 colonized seedlings was analyzed for rugulosin. Needles of most (90%) contained detectable concentrations of rugulosin. The range and distribution of the rugulosin concentrations was similar to that found in earlier tests done in growth chambers. [ABSTRACT FROM AUTHOR]

Populus balsamifera L., Betula papyrifera Marsh., Populus tremuloides Michx. and Picea glauca (Moench) Voss seedlings were grown in specialized pots that maintained a constant water-table height and allowed monitoring of water use by the tree/pot under high water-table conditions and different soil temperatures. The trees were grown at imperfectly and poorly drained water table conditions and at 5, 10 or 20°C soil temperature. In P. balsamifera , net assimilation and transpiration remained high under wet soil conditions and increased with higher soil temperatures. Populus balsamifera growth and leaf area development were severely restricted at soil temperatures of 5°C. Both B. papyrifera and P. tremuloides had low transpiration and pot level water-use rates at both water-table conditions and these did not significantly increase with increasing soil temperature. Picea glauca was negatively affected by high water tables but showed minimal response to soil temperature changes. The study suggests that P. balsamifera would be a good hydrological nurse crop to lower the water table when soils are warm, while B. papyrifera is likely to be a good nurse species in cool and imperfectly drained sites. [ABSTRACT FROM AUTHOR]

Mortality of transplanted somatic seedlings at the stage of acclimatization is often high and likely due to rapid change in environmental conditions. To investigate the potential of in vitro acclimatization of somatic seedlings before soil transfer, somatic seedlings of white spruce (Picea glauca [Moench] Voss) were germinated on a liquid medium supplemented with sucrose. After 6 weeks in germination, sucrose was omitted from the medium for a supplementary 6 weeks at which time somatic seedlings were acclimatized in vitro in their germination tubes before transfer to soil. In vitro acclimatization of somatic seedlings was realized by transferring the test tubes containing the germinated somatic seedlings to the greenhouse for 9 days. During this period, the culture tube lids of acclimatized somatic seedlings were lifted progressively increasing air exchange between the tube and the greenhouse whereas, for non-acclimatized somatic seedlings the culture tubes were maintained closed during in vitro acclimatization. In vitro acclimatized somatic seedlings had higher asymptotic net photosynthesis (P n ) at light saturation than non-acclimatized seedlings (6 versus 4.5 µmol m-2 s-1 ). At the end of the in vitro acclimatization period, a lower rate of epidermal transpiration was also observed for acclimatized somatic seedlings (3.85 versus 4.75% h-1 ). Microscopic observations showed that starch granules were more abundant in needles of acclimatized somatic seedlings than in non-acclimatized somatic seedlings, probably as a result of their greater photosynthetic capacity. Needles from acclimatized somatic seedlings also showed more epicuticular wax projections than needles from non-acclimatized somatic seedlings. These structural changes may help somatic seedlings to restrict epidermal water loss and stomatal aperture. [ABSTRACT FROM AUTHOR]

Fungi colonizing fine roots of containerized Picea glauca seedlings were assessed in four large conifer nurseries in northern Alberta. PCR amplification of fungal rDNA (internal transcribed spacer and a portion of the 5? end of the large subunit gene) from random samples of fine feeder roots gave between 1 and 4 amplicons per seedling. Amplicons were either separated by electrophoresis and sequenced directly, or cloned and sequenced. The resulting sequences were compared to sequences obtained from cultures established from seedling roots and from GenBank by maximum parsimony analysis. ITS sequences formed 11 distinct clades, each including at least one reference sequence. The ectomycorrhizal basidiomycetes Thelephora americana and Amphinema byssoides were dominant, whereas ascomycetes were less common. Fungi with sequences similar to members of the Heleotiales which form ericoid mycorrhizas were also present. Correspondence analysis revealed strong positive and negative associations among fungal taxa as well as an influence of applied fertilizer level on fungal diversity and species composition. [ABSTRACT FROM AUTHOR]

Compares the relative competitiveness of three early successional boreal forest species, trembling aspen (Populus tremuloides Michx.), fireweed (Epilobium angustifolium L.), and calamagrostis (Calamagrostis canadensis (Michx.) Beauv.), on 15N uptake and the growth response by containerized white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb.) seedlings. Focus on belowground competition for nitrogen (N) between boreal forest species; Method; Findings; Conclusion.

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO[sub 2] uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage. [ABSTRACT FROM AUTHOR]

The effect of nitrogen stress on needle δ13C, water-use efficiency (WUE) and biomass production in irrigated and dry land white spruce (Picea glauca (Moench) Voss) seedlings was investigated. Sixteen hundred seedlings, representing 10 controlled crosses, were planted in the field in individual buried sand-filled cylinders. Two nitrogen treatments were imposed, nitrogen stressed and fertilized. The ranking of δ13C of the crosses was maintained across all combinations of water and nitrogen treatments and there was not a significant genetic versus environmental interaction. The positive relationships between needle δ13C, WUE and dry matter production demonstrate that it should be possible to use δ13C as a surrogate for WUE, and to select for increased WUE without compromising yield, even in nitrogen deficient environments. Nitrogen stressed seedlings had the lowest needle δ13C in both irrigated and dry land conditions. There was a positive correlation between needle nitrogen content and δ13C that was likely associated with increased photosynthetic capacity. There was some indication that decreased nitrogen supply led to increased stomatal conductance and hence lower WUE. There was a negative correlation between intrinsic water use efficiency and photosynthetic nitrogen use efficiency (NUE). This suggests that white spruce seedlings have the ability to maximize NUE when water becomes limited. There was significant genetic variation in NUE that was maintained across treatments. Our results suggest that in white spruce, there is no detectable effect of anaplerotic carbon fixation and that it is more appropriate to use a value of 29‰ (‘Rubisco only’) for the net discrimination against 13C during CO2 fixation. This leads to excellent correspondence between values of Ci/Ca derived from gas exchange measurements... [ABSTRACT FROM AUTHOR]

White spruce [ Picea glauca (Moench) Voss.] seedlings were used to study the changes in cell wall composition and elasticity in mature needles before and after the resumption of growth following winter dormancy. Dormant seedlings showed high cell wall elasticity that decreased after the resumption of shoot growth. Cell wall hemicellulose content increased 3 days after planting and decreased after the buds flushed. Non-cellulosic glucose and arabinose were the sugars showing the most pronounced changes related to shoot growth. Arabinose was the most abundant sugar residue in the pectin and hemicellulose fractions and it decreased until day 10 after planting. At the same time, the levels of glucose in pectin and hemicellulose increased. The results provide evidence for cell wall carbohydrate turnover in dormant and active seedlings before and after bud flushing. [ABSTRACT FROM AUTHOR]

The fate of carbamoyl phosphate in white spruce seedlings revolves around the production of spontaneous degradation products, cyanate, bicarbonate, and carbamate. When [14C]-carbamoyl phosphate and [14C]-cyanate are assimilated, urea is a common early metabolic intermediate that appears in the alcohol soluble N, By contrast, urea is not detected among the products of [14C]-bicarbonate. Carbamoyl phosphate and glutamic acid are implicated as having pivotal roles in the production of amides, arginine, and biotin. Within 2-h exposures to radioactive substrates considerably more carbon from bicarbonate was diverted into amino acids incorporated into proteins than with carbon-nitrogen substrates. Specific activities of bound amino acid residues support the view that proteins formed from these [14C]-substrates have different rates of metabolic turnover. [ABSTRACT FROM AUTHOR]

The relationship among water use efficiency (WUE), productivity and carbon isotopic composition (δ13C) in white spruce (Picea glauca (Moench) Voss) seedlings was investigated. Sixteen hundred seedlings representing 10 controlled crosses were planted in the field in individual buried sand-filled cylinders. The soil water content in the cylinders was measured using time domain reflectometry over two growing seasons and seedling water use deters mined by water balance, Two watering treatments were imposed: irrigation and dry land. There was significant (1.6-2.0%o) genetic variation in needle δ13 C. Ranking of crosses in terms of δ13C was generally maintained over watering treatments and there was not a significant genetic versus environmental interaction. There was a positive correlation between δ13C and both intrinsic and long-term WUE (more positive δ13C with increased WUE) and between δ13C and productivity, suggesting a correlation due to variation in photosynthetic capacity. Root to shoot ratios did not increase in water-stressed plants, indicating that responses to drought were primarily at the level of gas exchange, rather than through morphological changes. Our results indicate that it should be possible to use δ13C as a surrogate for WUE and to select white spruce genotypes for high WUE without compromising yield. [ABSTRACT FROM AUTHOR]

Effect of hexazinone (Pronone TM5G) at 3 levels of application equivalent to field rates of 1, 2 and 4 kg a. i/ha on the seedling growth and mycorrhizal development in lodgepole pine (pinus contorta Dougl. var. latifolia Engelm.) and white spruce (Picea glauca [Monech] Voss) was studied in a greenhouse trial . Both species responded similarly except that phytotoxic effects were more intense in pine than in spruce. There was an initial reduction in seedling growth and mycorrhizal development at 1 kg a./ha rate, however, a recovery to control conditions occurred after 4 months. At application rates of 2 and 4 kg a. i/ha there was significant (P=0.05) reduction in growth parameters and mycorrhizal development compared to control and 1kg a. i/ha treatment. Though within 6 months after planting, seedling growth and mycorrhizal infection significantly (P=0.05) improved over the initial reduction, these parameters were still significantly lower than the control and 1kg a.i/ha treatment. [ABSTRACT FROM AUTHOR]

A white spruce seedling, Picea glauca (Moench) Voss, was found at the northern edge of the Brooks Range in Alaska, more than 50 km north of the latitudinal tree line. The seedling, 19 cm tall and about nine years old, was growing at the side of the Dalton Highway to Prudhoe Bay. It most likely sprouted from a seed transported across the Brooks Range on a vehicle and has survived on the well-drained gravel road berm, where site conditions are more favorable for germination and survival than in the surrounding tundra. This spruce has survived for about a decade under current climatic conditions. Even with a warming climate, natural seed dispersal is severely hampered by the rugged topographic barrier of the Brooks Range. Considering the amount of vehicle traffic on the Dalton Highway, however, it is likely that more pioneering spruce seedlings will turn up along this corridor. Once over the Brooks Range, a spruce population can potentially develop and expand. [ABSTRACT FROM AUTHOR]