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This article presents a comprehensive Computational Fluid Dynamics (CFD) assessment of fast pyrolysis of three different agricultural feedstocks representing three different categories: Red oak (hardwood), Switchgrass (herbaceous biomass), and Picea glauca (softwood). The study aimed to evaluate the performance of each feedstock based on particle density, temperature distribution, and volume fraction distribution. The comparison of the simulation results with experimental data showed an average error factor below 13%. The study discovered that Red oak had the highest bio-oil production yield, followed by Switchgrass, which had a yield 10% lower, and Picea glauca , which had the weakest performance having a yield 20% lower than Red oak. Interestingly, optimal operating conditions for the production of bio-oil across all three feedstocks comprised a temperature of 500 °C and particle size of approximately 400 μm. However, increasing the pyrolysis temperature resulted in an increase in gas yield, whereas increasing particle size led to a rise in char production yield. Furthermore, the findings suggest that herbaceous biomass tends to perform better in fast pyrolysis for bio-oil production compared to softwood. This is attributed to the higher hemicellulose content in herbaceous feedstock which has a significant impact on bio-oil yield compared to cellulose and lignin. Moreover, hardwood and herbaceous samples, which have similar levels of cellulose and hemicellulose, demonstrated superior performance compared to softwood, which has lower hemicellulose content. Nonetheless, herbaceous biomass had about 10% extractable content, which made it perform weaker than hardwood. • CFD evaluation/comparison of pyrolysis of hardwood, herbaceous, and softwood feedstocks. • Red oak (hard wood) exhibited the highest bio-oil production, 20% more than Picea glauca. • Optimal conditions for bio-oil production from all feedstocks were 500 °C temperature and 400 μm particle size. • Herbaceous Switchgrass outperformed softwood due to higher hemicellulose content. • CFD approach reliability demonstrated with <13% error, validating product yield predictions. [ABSTRACT FROM AUTHOR]

Merging robust statistical methods with complex simulation models is a frontier for improving ecological inference and forecasting. However, bringing these tools together is not always straightforward. Matching data with model output, determining starting conditions, and addressing high dimensionality are some of the complexities that arise when attempting to incorporate ecological field data with mechanistic models directly using sophisticated statistical methods. To illustrate these complexities and pragmatic paths forward, we present an analysis using tree‐ring basal area reconstructions in Denali National Park (DNPP) to constrain successional trajectories of two spruce species (Picea mariana and Picea glauca) simulated by a forest gap model, University of Virginia Forest Model Enhanced—UVAFME. Through this process, we provide preliminary ecological inference about the long‐term competitive dynamics between slow‐growing P. mariana and relatively faster‐growing P. glauca. Incorporating tree‐ring data into UVAFME allowed us to estimate a bias correction for stand age with improved parameter estimates. We found that higher parameter values for P. mariana minimum growth under stress and P. glauca maximum growth rate were key to improving simulations of coexistence, agreeing with recent research that faster‐growing P. glauca may outcompete P. mariana under climate change scenarios. The implementation challenges we highlight are a crucial part of the conversation for how to bring models together with data to improve ecological inference and forecasting. [ABSTRACT FROM AUTHOR]

Background: R2R3-MYB is a class of transcription factor crucial in regulating secondary cell wall development during wood formation. The regulation of wood formation in gymnosperm has been understudied due to its large genome size. Using Single-Molecule Real-Time sequencing, we obtained full-length transcriptomic libraries from the developmental stem of Cunninghamia lanceolata, a perennial conifer known as Chinese fir. The R2R3-MYB of C. lanceolata (hereafter named as ClMYB) associated with secondary wall development were identified based on phylogenetic analysis, expression studies and functional study on transgenic line. Results: The evolutionary relationship of 52 ClMYBs with those from Arabidopsis thaliana, Eucalyptus grandis, Populus trichocarpa, Oryza sativa, two gymnosperm species, Pinus taeda, and Picea glauca were established by neighbour-joining phylogenetic analysis. A large number of ClMYBs resided in the woody-expanded subgroups that predominated with the members from woody dicots. In contrast, the woody-preferential subgroup strictly carrying the members of woody dicots contained only one candidate. The results suggest that the woody-expanded subgroup emerges before the gymnosperm/angiosperm split, while most of the woody-preferential subgroups are likely lineage-specific to woody dicots. Nine candidates shared the same subgroups with the A. thaliana orthologs, with known function in regulating secondary wall development. Gene expression analysis inferred that ClMYB1/2/3/4/5/26/27/49/51 might participate in secondary wall development, among which ClMYB1/2/5/26/27/49 were significantly upregulated in the highly lignified compression wood region, reinforcing their regulatory role associated with secondary wall development. ClMYB1 was experimentally proven a transcriptional activator that localised in the nucleus. The overexpression of ClMYB1 in Nicotiana benthamiana resulted in an increased lignin deposition in the stems. The members of subgroup S4, ClMYB3/4/5 shared the ERF-associated amphiphilic repression motif with AtMYB4, which is known to repress the metabolism of phenylpropanoid derived compounds. They also carried a core motif specific to gymnosperm lineage, suggesting divergence of the regulatory process compared to the angiosperms. Conclusions: This work will enrich the collection of full-length gymnosperm-specific R2R3-MYBs related to stem development and contribute to understanding their evolutionary relationship with angiosperm species. [ABSTRACT FROM AUTHOR]

Tree-ring data for 1942 - 2013 were used to determine if boreal and subalpine Picea albertiana S. Brown emend. Strong & Hills radial growth rates changed after 1950 in southern Yukon, northwest Canada. The latter year represented the beginning of accelerated atmospheric greenhouse gas accumulation, which has subsequently caused global climate changes. Ring-width chronologies for both boreal and subalpine trees were constructed using 80 trees. Individual ring-width sequences were crossdated, age-detrended, and converted to tree ring-width indices (RWI). In 2013, boreal and subalpine RWI were 41% and 169% greater than in 1950, respectively. In contrast, elevational treeline chronologies in the region typically decreased 20% - 70%. During 1942 - 2013, boreal and subalpine chronologies were significantly, at best modestly (r < |0.36|), and exclusively correlated with either moisture or temperature variables, respectively. Within this same time frame, RWI-climate variable correlates differed between the early and late phases of each chronology. Average pre-1969 or early-phase boreal correlations based on a 19-year moving window reached a maximum of - 0.56. Late-phase chronology correlations typically shifted towards weaker associations with climate variables (typically +0.04 to +0.30). For boreal RWI, 25 of 68 tested climate variables shifted as much as 0.40 - 0.88 correlation coefficient units between the early and late phases of the chronologies. Subalpine RWI were correlated only with July - August precipitation during the early phase of its chronology. These changes suggest responses by spruce to climate have shifted since 1970. The modest 1942 - 2013 RWI-climate variable correlations likely reflect the result of these changing ecological relationships. [ABSTRACT FROM AUTHOR]

Populations of many tree species exhibit synchronous and highly temporally variable seed crops across years. This is called mast seeding, and there are two predominant hypotheses for this pattern of reproduction: pollination efficiency and seed-predator satiation. Mast seeding studies typically involve records of population-level reproduction, with less information on the characteristics of reproductive structures. Here, we use data across 6 years (2012–2017), spanning a range of population-level cone conditions, to characterize (i) white spruce (Picea glauca (Moench) Voss) cone lengths and seeds per cone, and (ii) levels of seed predation. We quantified population-level cone production and collected 1399 cones from a total of 38 trees in the Huron Mountains, Michigan, USA. Linear mixed models showed that mean and minimum cone lengths varied significantly across years; both being longest during the greatest cone production year. Larger cones had more seeds and the slopes of the relationships as well as the intercepts varied significantly across years. Generalized linear mixed models and Akaike's information criterion model selection showed that cones with insect predation damage was greatest when population-level reproduction was the lowest, with a mean proportion of cones damaged 0.82 in that year. Our findings show that white spruce cone characteristics and losses to insect seed predation vary temporally, and follow expectations based on mast seeding hypotheses. [ABSTRACT FROM AUTHOR]

The representation of snow processes in forest growth models is necessary to accurately predict the hydrological cycle in boreal ecosystems and the isotopic signature of soil water extracted by trees, photosynthates and tree-ring cellulose. Yet, most process-based models do not include a snow module, consequently their simulations may be biased in cold environments. Here, we modified the MAIDENiso model to incorporate a new snow module that simulates snow accumulation, melting and sublimation, as well as thermal exchanges driving freezing and thawing of the snow and the soil. We tested these implementations in two sites in East and West Canada for black spruce (Picea mariana) and white spruce (Picea glauca) forests, respectively. The new snow module improves the skills of the model to predict components of the hydrological cycle. The model is now able to reproduce the spring discharge peak and to simulate stable oxygen isotopes in tree-ring cellulose more realistically than in the original, snow-free version of the model. The new implementation also results in simulations with a higher contribution from the source water on the oxygen isotopic composition of the simulated cellulose, leading to more accurate estimates. Future work may include the development of inverse modelling with the new version of MAIDENiso to produce robust reconstructions of the hydrological cycle and isotope processes in cold environments. [ABSTRACT FROM AUTHOR]

In an attempt to comprehensively study the dynamics of non-structural carbon compounds (NCCs), we measured the seasonal changes of soluble sugars, starch, lipids and sugar alcohols in the leaves, branches, stem and roots of the fast-growing Pinus contorta (Loudon) (pine) and slow-growing Picea glauca (Moench) Voss (spruce) trees growing in a boreal climate. In addition to measuring the seasonal concentrations of these compounds, the relative contribution of these compounds to the total NCC pool within the organs of trees (~8 m tall) was estimated and compared across different phenological and growth stages. Both species showed large seasonal shifts from starch to sugars from spring to fall in nearly all organs and tissues; most likely an adaptation to the cold winters. For both species, the total fluctuation of sugar + starch across the year (i.e. the difference between the minimum and maximum observed across collection times) was estimated to be between 1.6 and 1.8 kg for all NCCs. The fluctuation, however, was 1.40 times greater than the minimum reserves in pine, while only 0.72 times the minimum reserves in spruce. By tissue type, NCC fluctuations were greatest in the roots of both species. Roots showed a large build-up of reserves in late spring, but these reserves were depleted over summer and fall. Storage reserves in needles and branches declined over the summer, and this decline may be linked to the sink strength of the stem during diameter growth. Some notable highlights of this holistic study: a late winter build-up of sugars in the stem xylem of both species, but especially spruce; and an increase in sugar alcohols in the bark of spruce in very late winter, which could indicate mobilization to support early growth in spring and high lipid reserves in the bark of pine, which appeared not to be impacted by seasonal changes between summer and winter. Collectively, these observations point toward a more conservative NCC reserve strategy in spruce compared with pine, which is consistent with its stress tolerance and greater longevity. [ABSTRACT FROM AUTHOR]

As boreal forests face significant threats from climate change, understanding evolutionary trajectories of coniferous species has become fundamental to adapting management and conservation to a drying climate. We examined the genomic architecture underlying adaptive variation related to drought tolerance in 43 populations of a widespread boreal conifer, white spruce (Piceaglauca [Moench] Voss), by combining genotype–environment associations, genotype–phenotype associations, and transcriptomics. Adaptive genetic variation was identified by correlating allele frequencies for 6,153 single nucleotide polymorphisms from 2,606 candidate genes with temperature, precipitation and aridity gradients, and testing for significant associations between genotypes and 11 dendrometric and drought‐related traits (i.e., anatomical, growth response and climate‐sensitivity traits) using a polygenic model. We identified a set of 285 genes significantly associated with a climatic factor or a phenotypic trait, including 110 that were differentially expressed in response to drought under greenhouse‐controlled conditions. The interlinked phenotype–genotype–environment network revealed eight high‐confidence genes involved in white spruce adaptation to drought, of which four were drought‐responsive in the expression analysis. Our findings represent a significant step toward the characterization of the genomic basis of drought tolerance and adaptation to climate in conifers, which is essential to enable the establishment of resilient forests in view of new climate conditions. see also the Perspective by Lars Opgenoorth and Christian Rellstab [ABSTRACT FROM AUTHOR]

Nickel (Ni) in trace amounts is important in plant nutrition; it can also be toxic in excess. The objective of this study was to determine if nickel affects gene expression in white spruce (Picea glauca). Nickel toxicity was assessed by treating seedlings with an aqueous solution of nickel nitrate salt [Ni(NO3)2] at different doses (150, 800 mg/kg, and 1600 mg/kg) using a completely randomised design. Expression of the genes encoding 1-aminocyclopropane-1-carboxylic acid deaminase (ACCD) and glutathione reductase (GR) in roots and needles were investigated using RT qPCR analysis. No damage was observed on P. glauca seedlings. This study revealed that Ni induces an upregulation of ACCD at low and high doses tested in roots. Nickel treatments resulted in a downregulation of GR at low dose (150 mg/kg) in needles and an upregulation at low and high doses in roots. This suggests that the low level of bioavailable nickel in mining sites in Ontario and other regions can trigger changes in gene expression. The results also show that potassium nitrate induces a significant effect on gene expression in P. glauca mostly at high concentrations. [ABSTRACT FROM AUTHOR]

Climate change may have spatially variable impacts on growth of trees in topographically diverse environments, making generalizing across broad spatial and temporal extents inappropriate. Therefore, topography must be considered when analyzing growth response to climate. We address these topo-climatic relationships in the Canadian Rocky Mountains, focusing on lodgepole pine (Pinus contorta Douglas ex Louden) and interior spruce (Picea glauca (Moench) Voss × Picea engelmannii hybrid Parry) growth response to climate, Palmer drought severity index (PDSI), aspect, and slope angle. Climate variables correlate with older lodgepole pine growth on south- and west-facing slopes, including previous August temperature, winter and spring precipitation, and previous late-summer and current spring PDSI, but younger lodgepole pine were generally less sensitive to climate. Climate variables correlate with interior spruce growth on all slope aspects, with winter temperature and PDSI important for young and old individuals. Numerous monthly growth–climate correlations are not temporally stable, with shifts over the past century, and response differs by slope aspect and angle. Both species are likely to be negatively affected by moisture stress in the future in some, but not all, topographic environments. Results suggest species-specific and site-specific spatiotemporally diverse climate–growth responses, indicating that climate change is likely to have spatially variable impacts on radial growth response in mountainous environments. [ABSTRACT FROM AUTHOR]

Long-term studies of vegetation succession can inform restoration of degraded forests. We examined resilience of a boreal mixedwood vegetation community, asking whether treatments employed to restore wood production in a degraded ecosystem could also restore diversity and composition of vegetation communities. The Inga Lake trial, established in 1987 in northeastern British Columbia, used mechanical, fire, and chemical and manual treatments, encompassing a gradient of restoration effort, and tree planting to restore a shrubland to white spruce (Picea glauca (Moench) Voss) forest. We monitored vascular plant, bryophyte, and macrolichen composition five times over 31 years on five to seven treatments replicated five times. We used mixed-effects models and nonmetric multidimensional scaling to compare diversity and composition among treatments and with mature reference forests. Low- to high-effort restoration created a gradient from broadleaf- to spruce-dominated overstories. Diversity increased with restoration effort. Four of 253 taxa occurred in mature forests only. There was no evidence that lower versus higher effort treatments followed divergent successional pathways toward broadleaved versus spruce reference communities. Our results suggest that these mixedwood vegetation communities lie within a broad domain of successional attraction that confers high ecological resilience to disturbance. Gap cuttings to stimulate understory re-initiation and provide woody debris are recommended to complete the restoration. [ABSTRACT FROM AUTHOR]

Numerous recent studies have argued that moisture limitation is leading to growth declines and mortality of black spruce (Picea mariana) and white spruce (Picea glauca) in the North American boreal forest. A parallel line of research suggests that increasingly common severe wildfires are altering successional pathways and leading to long‐term replacement of spruce forests with those dominated by paper birch (Betula papyrifera, Betula neoalaskana) and trembling aspen (Populus tremuloides). When both conifers and deciduous trees establish after fire, this biome shift hypothesis implicitly assumes that deciduous species will outcompete the conifers, owing to their more rapid vertical growth and because they might be less sensitive to warm and dry conditions.We established a research site in a white spruce‐paper birch forest on an east‐facing slope in interior Alaska and tested the hypothesis that Alaska paper birch are better adapted to warm and dry conditions than white spruce. Over 6 years (2013–2018), we made hourly measurements of microclimate and xylem sap flux of both species. We also collected increment cores and conducted climate‐growth analyses for both species.During our 6‐year study, growing seasons with low volumetric soil water content (SWC) were those that followed shallow winter snowpacks and had limited summer rainfall, not necessarily those with warm air temperature. Both species were sensitive to moisture limitation. The tree‐ring data revealed significant positive effects of cumulative water year precipitation on radial growth, with a steeper slope for paper birch than for white spruce. Radial growth of both species was also positively related to mean water year air temperature. Sap flux density declined progressively for white spruce over the range of observed SWC and abruptly for paper birch when SWC fell below ~15%.Synthesis. Our results show that, while paper birch might be less sensitive to mild drought than white spruce, it may be more sensitive to severe drought, raising questions about the ability of paper birch to outcompete co‐occurring white spruce in a drier climate. [ABSTRACT FROM AUTHOR]

Understanding the magnitude and cause of variation in tree growth and forest productivity is central to sustainable forest management. Measurements of annual growth rings allow assessments of individual-tree, tree population, and forest ecosystem vulnerabilities to drought stress or other changing forest disturbance regimes (insects, diseases, fire), which can be used to identify areas at greatest risk of forest losses. Given a heightened demand for tree-ring data, we consolidated and synthesized tree-ring studies and datasets gathered over the past 30 years in Canada by scientists with the Canadian Forest Service and research partners. We incorporated these datasets into a data repository that currently contains tree-ring measurements from 40 206 tree samples from 4594 sites and 62 tree species from all Canadian provinces and territories. Through our synthesis, we demonstrate the value of such large ensembles of tree-ring data for identifying patterns in tree growth over large spatial scales by mapping pan-Canadian drought sensitivity. Overall, we found high coherence in the samples analyzed; low coherence was generally limited to data-poor regions and species. Drought sensitivity was widespread across species and regions: 34% of sampled trees displayed a significant positive relationship between annual growth increment and summer soil moisture index. Dependence upon water availability in species Picea mariana (Mill.) BSP, Pinus banksiana Lamb., Pinus contorta Douglas ex Loudon, and Pseudotsuga menziesii (Mirb.) Franco was more strongly expressed in the warmest regions of the species' range; for species Picea glauca (Moench) Voss and Populus tremuloides Michx., drought sensitivity was stronger in the driest regions. This unprecedented consolidation and synthesis of tree-ring data will enable new research initiatives (e.g., meta-analyses) aimed at improved understanding of the drivers, patterns, and implications of changes in tree growth, as well as facilitating new research collaborations in earth and environmental sciences. Among other things, there is a need for expanding the spatial distribution of sites across Canada's northern regions, increasing the number of samples collected from older stands and angiosperm species, and integrating datasets from studies that evaluate the effects of silvicultural experiments, including provenance and progeny trials, on tree growth. [ABSTRACT FROM AUTHOR]

Norway spruce (Picea abies L. Karst) is one of the most important forest tree species with significant economic and ecological impact in Europe. For decades, genomic and genetic studies on Norway spruce have been challenging due to the large and repetitive genome (19.6 Gb with more than 70% being repetitive). To accelerate genomic studies, including population genetics, genome‐wide association studies (GWAS) and genomic selection (GS), in Norway spruce and related species, we here report on the design and performance of a 50K single nucleotide polymorphism (SNP) genotyping array for Norway spruce. The array is developed based on whole genome resequencing (WGS), making it the first WGS‐based SNP array in any conifer species so far. After identifying SNPs using genome resequencing data from 29 trees collected in northern Europe, we adopted a two‐step approach to design the array. First, we built a 450K screening array and used this to genotype a population of 480 trees sampled from both natural and breeding populations across the Norway spruce distribution range. These samples were then used to select high‐confidence probes that were put on the final 50K array. The SNPs selected are distributed over 45,552 scaffolds from the P. abies version 1.0 genome assembly and target 19,954 unique gene models with an even coverage of the 12 linkage groups in Norway spruce. We show that the array has a 99.5% probe specificity, >98% Mendelian allelic inheritance concordance, an average sample call rate of 96.30% and an SNP call rate of 98.90% in family trios and haploid tissues. We also observed that 23,797 probes (50%) could be identified with high confidence in three other spruce species (white spruce [Picea glauca], black spruce [P. mariana] and Sitka spruce [P. sitchensis]). The high‐quality genotyping array will be a valuable resource for genetic and genomic studies in Norway spruce as well as in other conifer species of the same genus. [ABSTRACT FROM AUTHOR]

The use of wood ash as a soil amendment in afforestation and reforestation efforts is increasing. While most studies suggest benefits or neutral results on tree growth and survival, a few studies indicate adverse effects. Hybrid larch, jack pine and white spruce were studied at three northwestern Quebec plantation sites after they received wood ash at two application rates. Soil chemical properties, foliar nutrients and seedling growth and mortality were monitored over a period of eight years. The response of soil to ash application was mostly observed in the forest floor and was more pronounced in year 3 than year 8, likely due to the acidifying nature of the boreal soils studied. Jack pine growth increased linearly with wood ash application rates, white spruce growth showed an inconsistent and delayed positive response under the higher application rate, and hybrid larch growth and survival were either increased or decreased under the lower application rate depending of site but decreased at all sites under the higher application rate. The divergence in growth response between tree species underlines a trade-off between species with rapid acquisition of resources (e.g., pine, larch) to species that use more conservative strategies and store nutrients in their tissues for longer periods (e.g., spruce). In the case of hybrid larch, it accumulated larger amounts of Mn in its needles under the higher application rate and thus, the high bioavailabil - ity of Mn appears to have been detrimental to its survival and growth. Its higher sensitivity to Mn addition from ash is likely due to its highly acquisitive (nutrients) nature compared to other coniferous species as well as the initial levels of available Mn levels in the soil. The contrasted growth responses reported here under similar growing conditions highlight the importance of identifying suitable species, sites and application rates to maximize the benefits of wood ash amendments for future tree plantations in the boreal forest. [ABSTRACT FROM AUTHOR]

Biodiversity effects on productivity and other ecosystem functions are strongly dependent on climate and resource availability. Based on the stress‐gradient hypothesis, under conditions of greater abiotic stress, diversity effects on plant performance are intensified due to the increased relative importance of positive plant interactions. However, whether this hypothesis is consistently applicable in forest systems remains unclear. A field trial was established to test the stress‐gradient hypothesis and examine diversity effects on above‐ground biomass production of young trees in mixtures exposed to different water availability.Six native tree species of northern temperate forests (Acer saccharum, Betula papyrifera, Larix laricina, Picea glauca, Pinus strobus and Quercus rubra) were planted as monocultures and as mixtures of two, four and six species. For five growing seasons, four replicates of each community were exposed to conditions of either low‐ or high‐water availability created by rainfall exclusion and weekly irrigation, respectively. Growth‐years 4 and 5 were significantly different when the climatic water balance of the growing seasons was compared. We tested the effects of functional diversity on: (a) total growth of mixtures under low‐ and high‐water availability, and (b) annual growth in years 4 (higher water availability, 2017) and 5 (lower water availability, 2018).Annual growth of most species in both years was greater under high‐ versus low‐water availability. Functional diversity had a significant positive effect on total biomass production and annual growth, and this effect was more strongly expressed under high‐water availability. Functional diversity effects on annual growth did not differ between years 4 and 5 regardless of their climatic water balance. Functional and species identity were key to understanding productivity responses to mixture and treatment effects.Synthesis. Contrary to the stress‐gradient hypothesis, the positive effects of functional diversity on productivity were enhanced by high‐water availability and were independent of seasonal water balance. [ABSTRACT FROM AUTHOR]

Nine open-pollinated families of Picea glauca (Moench) Voss from the Region D1 Controlled Parentage Program (Alberta, Canada) were systematically chosen from fast, medium and slow-growth rankings based on breeding values for height from field progeny tests at age 30 years. Seeds from these families were sown and grown to age 3 years to analyze the performance and correlations of growth, physiological traits and expression of gibberellin-related genes, with and without elevated gibberellic acid 3 (GA3) application, under greenhouse conditions. We observed a significant interaction effect between families and growth groups subjected to 50 μg μl−1 of GA3 treatment, causing a decrease in apical internode length, diameter, volume and absolute transcript level for fast-growing families but an increase for families in the slow-growth group for the same traits. We also observed that in the apical internode, the gene PgGA20ox1 had significantly more relative expression under the elevated GA3 treatment than the control trees. In the stem, PgGA3ox1 showed a significantly higher relative expression under elevated GA3 treatment compared with control trees. Also, the slow-growth group showed more relative expression of PgGA20ox1 (in the apical internode) and PgGA3ox1 (in the stem) than the fast-growth group. The apical internode length and diameter significantly increased by 24% and 16%, respectively, with the hormone treatment in the slow growing group. In general, the PgGID1 and PgDELLA1 genes were upregulated and downregulated respectively, in spruce shoots under the GA3 treatment, meaning a positive feedback regulation by those genes were influencing PgGA20ox1 and PgGA3ox1 expression in that tissue type. Moreover, there was a significant correlation between absolute transcript levels of PgGA20ox1 in the apical internode and apical internode length, and absolute transcript levels of PgGA3ox1 in the stem and the diameter, in the fast-growth group families. This study shows that expression of GA genes is a limiting factor for growth in certain white spruce families with a complex feedback mechanism. Finally, absolute transcript levels of endogenous GA relative to growth parameters in juvenile seedlings could potentially be used to accelerate the early selection of families with inherently rapid apical and radial growth expansion. [ABSTRACT FROM AUTHOR]

Objectives: Rehabilitation of edentulous ridges to promote the insertion of dental implants has been the key indicator for retaining osseous structures since tooth extraction. Recombinant Bone Morphogenetic Protein-2(rhBMP-2) is exploited for bone augmentation due to its osteoinductive capacity. The objective of the study to determine the effectiveness of bone induction for implant placement by rhBMP-2 delivered on beta-tricalcium phosphate graft (β-TCP) and PRF following tooth extraction. Results: Minimal changes in the width of the crestal bone relative to baseline values were found three months after socket grafting. A bone loss in the mesiodistal and buccolingual aspects of 0.6 ± 0.13 mm and 0.5 ± 0.13 mm was found, respectively. While drilling before the implant placement, the bone's clinical hardness evaluated through tactile was analogous to drilling into spruce or white pine wood. Total radiographic bone filling was seen in 3 months and no additional augmentation was needed during implant placement. Besides, histology shows no residual graft of bone particles. Therefore, the data from this study demonstrated that the novel combination of rhBMP-2 + β-TCP mixed with PRF has an effect on de novo bone formation and can be recommended for socket grafting before implant placement. [ABSTRACT FROM AUTHOR]

• We assessed tree water stress from leaf temperature and changes in stem radius. • Both approaches revealed responses to similar environmental variables over the summer. • Pinus contorta was more sensitive to decreasing soil moisture than Picea glauca. • UAV-based thermal imagery can identify water stress in a natural forest environment. With a warming climate and greater evaporative demand, many forest ecosystems are increasingly affected by water limitation as prolonged water deficits reduce tree-level growth and survival. Water deficit can be monitored in several ways, including from daily measurements of sap flow or changes in stem radius from automated sensors mounted on individual trees. As an alternative approach, we evaluated the use of airborne thermal imagery from unmanned aerial vehicles as a rapid, scalable tool for assessing tree-level water stress. Plant water stress leads to higher leaf temperatures when soil moisture is low and evaporative demand is high. To detect this response, we modeled the difference between leaf and air temperature (∆T) as a function of local soil moisture, vapor pressure deficit, and wind speed for two tree species, lodgepole pine (Pinus contorta var. latifolia) and white spruce (Picea glauca). We used those same weather and soil conditions to model dendrometer-based measurements of daily changes in internal tree water deficit (∆TWD). While canopy leaf temperature and daily change in tree water deficit showed little direct correlation with one another, these variables both responded to soil moisture, vapor pressure deficit, and wind speed in a manner that reflects responses to water stress as soil became progressively drier over the summer months. The two species showed some differences related to species-specific strategies for drought avoidance. The application of thermal imagery to detect water stress in natural forest ecosystems can improve understanding of how trees experience water stress across species and environmental conditions. [ABSTRACT FROM AUTHOR]

The intensity of extreme heat and drought events has drastically risen in recent decades and will likely continue throughout the century. Northern forests have already seen increases in tree mortality and a lack of new recruitment, which is partially attributed to these extreme events. Boreal species, such as paper birch (Betula papyrifera) and white spruce (Picea glauca), appear to be more sensitive to these changes than lower-latitude species. Our objectives were to investigate the effects of repeated heatwaves and drought on young paper birch and white spruce trees by examining (i) responses in leaf gas exchange and plant growth and (ii) thermal acclimation of photosynthetic and respiratory traits to compare ecophysiological responses of two co-occurring, yet functionally dissimilar species. To address these objectives, we subjected greenhouse-grown seedlings to two consecutive summers of three 8-day long, +10 °C heatwaves in elevated atmospheric CO2 conditions with and without water restriction. The data show that heatwave stress reduced net photosynthesis, stomatal conductance and growth—more severely so when combined with drought. Acclimation of both photosynthesis and respiration did not occur in either species. The combination of heat and drought stress had a similar total effect on both species, but each species adjusted traits differently to the combined stress. Birch experienced greater declines in gas exchange across both years and showed moderate respiratory but not photosynthetic acclimation to heatwaves. In spruce, heatwave stress reduced the increase in basal area in both experimental years and had a minor effect on photosynthetic acclimation. The data suggest these species lack the ability to physiologically adjust to extreme heat events, which may limit their future distributions, thereby altering the composition of boreal forests. [ABSTRACT FROM AUTHOR]

With climate change, the pressure on tree breeding to provide varieties with improved resilience to biotic and abiotic stress is increasing. As such, pest resistance is of high priority but has been neglected in most tree breeding programs, given the complexity of phenotyping for these traits and delays to assess mature trees. In addition, the existing genetic variation of resistance and its relationship with productivity should be better understood for their consideration in multitrait breeding. In this study, we evaluated the prospects for genetic improvement of the levels of acetophenone aglycones (AAs) in white spruce needles, which have been shown to be tightly linked to resistance to spruce budworm. Furthermore, we estimated the accuracy of genomic selection (GS) for these traits, allowing selection at a very early stage to accelerate breeding. A total of 1,516 progeny trees established on five sites and belonging to 136 full‐sib families from a mature breeding population in New Brunswick were measured for height growth and genotyped for 4,148 high‐quality SNPs belonging to as many genes along the white spruce genome. In addition, 598 trees were assessed for levels of AAs piceol and pungenol in needles, and 578 for wood stiffness. GS models were developed with the phenotyped trees and then applied to predict the trait values of unphenotyped trees. AAs were under moderate‐to‐high genetic control (h2: 0.43–0.57) with null or marginally negative genetic correlations with other traits. The prediction accuracy of GS models (GBLUP) for AAs was high (PAAC: 0.63–0.67) and comparable or slightly higher than pedigree‐based (ABLUP) or BayesCπ models. We show that AA traits can be improved and that GS speeds up the selection of improved trees for insect resistance and for growth and wood quality traits. Various selection strategies were tested to optimize multitrait gains. [ABSTRACT FROM AUTHOR]

Increase in frost damage to trees due to earlier spring dehardening could outweigh the expected increase in forest productivity caused by climate warming. We quantified the impact of growing‐season frosts on the performance of three spruce species (white, black, and Norway spruce) and various seed sources with different frost tolerance in two plantations, established on both sides of the eastern Canadian boreal‐temperate forest ecotone. The objectives of this study were to determine (a) if spruce species and seed sources planted in sites far from their natural provenance would be less adapted to local site conditions, leading to increased frost damage and reduced height growth; (b) at which height above the ground growing‐season frosts ceased to damage apical meristems; and (c) if height growth was best predicted by extreme climatic events (growing‐season frosts) or by mean annual or summer temperature. At each site and for all spruce species and seed sources, we cross‐sectioned spruce trees at different heights above the ground. Tree rings were cross‐dated and screened for frost rings, which were then given a severity score based on cellular damage. Frost severity reduced height growth of all spruce species and provenances at both sites. Height growth of the non‐native Norway spruce was the most reduced by frost severity and was the smallest species at both sites. Frost caused the highest growth reduction in white spruce at the boreal mixedwood site and had the least effect on black spruce at both sites. For all spruce species, height growth was affected up to 2 m above the ground. Model selection based on corrected Akaike's information criteria (AICc) identified that minimum temperature in May was by far the best climate variable predicting tree growth (AICc weight = 1), highlighting the importance of considering extreme climatic events, which are likely to increase in the future. [ABSTRACT FROM AUTHOR]

Aims: The Sub-Boreal Pine-Spruce xeric-cold (SBPSxc) biogeoclimatic region in British Columbia, Canada is characterized by weakly-developed soils, thin organic forest floor and limited plant-available nitrogen. Yet, lodgepole pine trees are thriving in this region unaffected by these nitrogen-limitations, which led us to hypothesize that endophytic nitrogen-fixing bacteria could be playing a potential role in sustaining pine tree growth. Methods: We evaluated these endophytes in a yearlong greenhouse experiment with their native host (lodgepole pine) for in planta nitrogen-fixation (15N isotope dilution assay) and growth-promotion (length and biomass). These endophytes were also evaluated with a foreign host native to the SBPSxc region (hybrid white spruce) in another yearlong greenhouse trial. Results: Each bacterial strain considerably enhanced seedling length and biomass of pine and spruce along with fixing significant amount of nitrogen from atmosphere (15–50%). Notably, Caballeronia sordidicola HP-S1r strain fixed 49–50% of the host nitrogen from atmosphere and enhanced seedling length and biomass by up to 1.5-fold and 4-fold, respectively. Conclusions: Endophytic bacteria could be playing a crucial role in the survival of lodgepole pine trees in the SBPSxc region by providing them with significant amounts of fixed nitrogen. Their effectiveness with a foreign host (hybrid white spruce) shows the lack of plant x microbe specificity, indicating their potential role in supporting the growth of multiple boreal forest trees. [ABSTRACT FROM AUTHOR]

The resource budget model for mast seeding hypothesizes that soil nutrients proximately influence reproduction. Plants in high soil nutrient (particularly N) areas are predicted to have lower reproductive variability over time and higher mean reproduction. While often examined theoretically, there are relatively few empirical tests of this hypothesis. We quantified cone production of 110 individual white spruce (Picea glauca) trees over seven years and quantified plant-available soil macronutrients (N, Ca, K, Mg, P, S) in natural forest conditions across three years with different cone crop conditions. Each of these plant-available soil nutrients were correlated across years (rs = 0.55–0.89; all > 0.81 for total-N); spatially, total-N availability varied 366-fold across trees. Plant-available soil nutrients did not influence variability or mean annual reproduction, contrary to nutrient perturbation experiments. We examined within-year nutrient and cone-production relationships, and observed significant positive relationships between reproduction and plant-available soil nutrients only in a low-reproduction year preceding a mast event. Both during a mast event and the following year, when overall cone production was very high or very low, there were no relationships. Both external drivers (e.g., weather) and internal resource budgets likely influence soil nutrient-reproduction relationships. These results suggest that plant-available soil nutrients may not be a large factor influencing mast-seeding patterns among individuals in this species. [ABSTRACT FROM AUTHOR]

Understanding the factors influencing the current distribution of genetic diversity across a species range is one of the main questions of evolutionary biology, especially given the increasing threat to biodiversity posed by climate change. Historical demographic processes such as population expansion or bottlenecks and decline are known to exert a predominant influence on past and current levels of genetic diversity, and revealing this demo‐genetic history can have immediate conservation implications. We used a whole‐exome capture sequencing approach to analyze polymorphism across the gene space of red spruce (Picea rubens Sarg.), an endemic and emblematic tree species of eastern North America high‐elevation forests that are facing the combined threat of global warming and increasing human activities. We sampled a total of 340 individuals, including populations from the current core of the range in northeastern USA and southeastern Canada and from the southern portions of its range along the Appalachian Mountains, where populations occur as highly fragmented mountaintop "sky islands." Exome capture baits were designed from the closely relative white spruce (P. glauca Voss) transcriptome, and sequencing successfully captured most regions on or near our target genes, resulting in the generation of a new and expansive genomic resource for studying standing genetic variation in red spruce applicable to its conservation. Our results, based on over 2 million exome‐derived variants, indicate that red spruce is structured into three distinct ancestry groups that occupy different geographic regions of its highly fragmented range. Moreover, these groups show small Ne, with a temporal history of sustained population decline that has been ongoing for thousands (or even hundreds of thousands) of years. These results demonstrate the broad potential of genomic studies for revealing details of the demographic history that can inform management and conservation efforts of nonmodel species with active restoration programs, such as red spruce. [ABSTRACT FROM AUTHOR]

Population of the spider mite Oligonychus ununguis (Jacobi, 1905) was monitored on introduced species of coniferous plants in the Fomin Botanical Garden, Kyiv, Ukraine in 2012-2019. The mite material was collected by shaking method, fixed, mounted on slides and then processed according to standard techniques. Severity of damage (R, %) was calculated. Eight varieties of the introduced genera Pseudotsuga and Picea of coniferous plants were chosen as study objects. The pest was found on Pseudotsuga plants for the first time. It was revealed that different species and varieties of conifers differ in attractiveness as host plants for this pest species. The mite O. ununguis was the most numerous on plants of Pseudotsuga menziesii, Ps. menziesii var. viridis Franco, and Picea glauca (Moench.) Vossf. «Conica». The dependence of shoot growth parameters on pest density is strong according to the value of the coefficient of determination, R² = 0.8781. The populations of spruce spider mites mostly increase in spring and autumn in Kyiv. In summer, the increase of air temperatures about 30-32 °C slowed the mite development, suppressing its density and the levels of damage on the conifers. Two species of Phytoseiidae, Typhlodromus laurae and Amblydromella inopinata and their activity in colonies of the pests on plants were observed in 2019. These predaceous mites can colonize the investigated coniferous plants together and control the O. ununguis population. روي گونههاي وارداتي مخروطيان در باغ گياهشناسي فومين، كيف، اكراين در Oligonychus ununguis (Jacobi, جمعيت كنة تارتن (1905 2019 بررسي شد. نمونههاي كنه به روش تكاندن جمعآوري، ثابت و روي اسلايد نصب و سپس بر اساس روشهاي - سالهاي 2012 مخروطيان براي Picea و Pseudotsuga محاسبه شد. هشت رقم از جنسهاي وارداتي (R, %) استاندارد مطالعه شدند. شدت خسارت پيدا شد. مشخص شد كه گونهها و رقمهاي Pseudotsuga موضوع مورد مطالعه انتخاب شدند. آفت براي نخستين بار روي گياهان جنس Pseudotsuga روي گياهان O. ununguis مختلف مخروطيان در جلب شدن به عنوان گياه ميزبان براي اين گونه آفت تفاوت دارند. كنة بيشتزين فراواني را داشتند. Picea glauca (Moench.) Vossf. «Conica» و ، Ps. menziesii var. viridis Franco ، menziesii بسيار زياد بود. جمعيت كنة تارتن كاج در كيف در بهار R² = 0/ وابستگي آمارههاي رشد جوانه به انبوهي آفت بنابر ميزان ضريب تعيين، 8781 32 درجة سلسيوس رشد كنه را آهسته كرده، انبوهي و ميزان خسارت آن را - و پاييز بسيار افزايش مييابد. در تابستان، افزايش دما به حدود 30 و فعاليت آنها در كلنيهاي Amblydromella inopinata و Typhlodromus laurae ،Phytoseiidae محدود ميكند. دو گونة از خانوادة آفت روي گياهان در سال 2019 مشاهده شد. اين كنههاي شكارگر ميتوانند با همديگر روي مخروطيان مورد بررسي تجمع يافته و جمعيت را مهار كنند. O. ununguis. [ABSTRACT FROM AUTHOR]

Lodgepole pine, a prominent Pinaceae tree species native to western North America, is well-known for its ability to thrive in highly disturbed and degraded areas. One such area is the Sub-Boreal Pine-Spruce xeric-cold (SBPSxc) region in British Columbia, Canada, which is characterized by weakly-developed, parched soils that lack an organic forest floor and essential plant-available nutrients. We hypothesized that plant growth-promoting bacteria could play a significant role in sustaining the growth of lodgepole pine trees in the SBPSxc region. Testing this hypothesis, we evaluated plant growth-promoting abilities of six endophytic bacterial strains previously isolated from lodgepole pine trees growing in this region. These bacterial strains significantly enhanced the length and biomass of their natural host (lodgepole pine) as well as a foreign host (hybrid white spruce) in a 540-day long greenhouse trial. This growth stimulation could be linked to the diverse plant growth-promoting (PGP) abilities detected in these strains using in vitro assays for inorganic/organic phosphate-solubilization, siderophore production IAA production, ACC deaminase activity, lytic enzymes (chitinase, β-1,3-glucanase, protease, and cellulase) activity, ammonia production and catalase activity. ACC deaminase activity was also detected in vivo for all strains using ethylene-sensitive plants–canola and tomato. Notably, strains belonging to the Burkholderiaceae family (HP-S1r, LP-R1r and LP-R2r) showed the greatest potential in all PGP assays and enhanced pine and spruce seedling length and biomass by up to 1.5-fold and 4-fold, respectively. Therefore, such bacterial strains with multifarious PGP abilities could be crucial for survival and growth of lodgepole pine trees in the SBPSxc region and could potentially be utilized as bioinoculant for Pinaceae trees in highly disturbed and nutrient-poor ecosystems. [ABSTRACT FROM AUTHOR]

Increasing the production of wood fibre from conifer species such as white spruce (Picea glauca (Moench) Voss) is one of many challenges in the management of boreal mixedwood forests. The effects of various competition measures on relative growth and relative growth rate variables were calculated for individual white spruce subject trees. Correlation analysis was used to explore relationships with competitor structural features, including the ratio of competitor basal area to subject tree basal area (CBAS), the ratio of competitor height to subject tree height (AHCS), and the proportion of softwood (FSW). Regression analysis was used to explore relationships with three distance-dependent competition indices. The ratio of subject tree height to diameter at breast height (DBH) (HDR), crown ratio (CR), and crown relative increment rate (CRIR) were significantly correlated with CBAS and AHCS. HDR, CR, CRIR, and DBH relative growth rate were all statistically significantly related to the competition indices. Results indicated that (i) relative growth and relative growth rate measures successfully captured a range of competition, (ii) crowns of trees with larger diameters used their horizontal growing space more efficiently to produce stemwood, and (iii) the proportion of softwood contributing to competition did not appear to influence subject tree production efficiency. Growth efficiency variables have the potential to improve our understanding of boreal mixedwood dynamics. [ABSTRACT FROM AUTHOR]

Summary: Drought intensity and frequency are increasing under global warming, with soil water availability now being a major factor limiting tree growth in circumboreal forests. Still, the adaptive capacity of trees in the face of future climatic regimes remains poorly documented.Using 1481 annually resolved tree‐ring series from 29‐yr‐old trees, we evaluated the drought sensitivity of 43 white spruce (Picea glauca (Moench) Voss) populations established in a common garden experiment.We show that genetic variation among populations in response to drought plays a significant role in growth resilience. Local genetic adaptation allowed populations from drier geographical origins to grow better, as indicated by higher resilience to extreme drought events, compared with populations from more humid geographical origins. The substantial genetic variation found for growth resilience highlights the possibility of selecting for drought resilience in boreal conifers.As a major research outcome, we showed that adaptive genetic variation in response to changing local conditions can shape drought vulnerability at the intraspecific level. Our findings have wide implications for forest ecosystem management and conservation. [ABSTRACT FROM AUTHOR]

Plant mitochondrial genomes vary widely in size. Although many plant mitochondrial genomes have been sequenced and assembled, the vast majority are of angiosperms, and few are of gymnosperms. Most plant mitochondrial genomes are smaller than a megabase, with a few notable exceptions. We have sequenced and assembled the complete 5.5-Mb mitochondrial genome of Sitka spruce (Picea sitchensis), to date, one of the largest mitochondrial genomes of a gymnosperm. We sequenced the whole genome using Oxford Nanopore MinION, and then identified contigs of mitochondrial origin assembled from these long reads based on sequence homology to the white spruce mitochondrial genome. The assembly graph shows a multipartite genome structure, composed of one smaller 168-kb circular segment of DNA, and a larger 5.4-Mb single component with a branching structure. The assembly graph gives insight into a putative complex physical genome structure, and its branching points may represent active sites of recombination. [ABSTRACT FROM AUTHOR]

Many forest tree species have characteristics that make the study of their evolutionary ecology complex. For example, they are long‐lived and thus have long generation times, and their often large, complex genomes have hampered establishing genomic resources. One way to tackle this challenge is to access multiple complementary data sources and analytical approaches when attempting to infer patterns of adaptive evolution. In the cover article of this issue of Molecular Ecology, Depardieu et al. (2021) combine large amounts of environmental, genomic, dendrochronological, and gene expression data in a common garden to explore the polygenic basis of drought resistance in white spruce (Picea glauca), a long‐lived conifer. They identify candidate genes involved in growth and resistance to extreme drought events and show how multiple data sets may deliver complementary evidence to circumvent the manifold challenges of the research field. [ABSTRACT FROM AUTHOR]

Summary: Phenology is an important indicator of environmental variation and climate change impacts on tree responses. In conifers, monitoring phenology of photosynthesis through remote sensing has been unreliable, because needle foliage varies little throughout the year. This is challenging for modelling ecosystem carbon uptake and monitoring phenology for enhanced breeding (genomic selection) and forest health.Here, we demonstrate that drone‐based carotenoid‐sensitive spectral indices, such as the Chl/carotenoid index (CCI), can be used to track phenology in conifers by taking advantage of the close relationship between seasonally changing carotenoid levels and the variation of photosynthetic activity.Physiological ground measurements, including photosynthetic pigments and maximum quantum yield of Chl fluorescence, indicated that CCI tracked the variation of photosynthetic activity better than other vegetation indices for 30 white spruce seedlings measured over 1 yr. A machine‐learning approach, using CCI derived from drone‐based multispectral imagery, was used to model phenology of photosynthesis for the entire pedigree population (6000 seedlings).This high‐throughput drone‐based phenotyping approach is suitable for studying climate change impacts and environmental variation on the physiological status of thousands of field‐grown conifers at unprecedented speed and scale. [ABSTRACT FROM AUTHOR]

Background: The presupposition of genomic selection (GS) is that predictive accuracies should be based on population-wide linkage disequilibrium (LD). However, in species with large, highly complex genomes the limitation of marker density may preclude the ability to resolve LD accurately enough for GS. Here we investigate such an effect in two conifer species with ~ 20 Gbp genomes, Douglas-fir (Pseudotsuga menziesii Mirb. (Franco)) and Interior spruce (Picea glauca (Moench) Voss x Picea engelmannii Parry ex Engelm.). Random sampling of markers was performed to obtain SNP sets with totals in the range of 200–50,000, this was replicated 10 times. Ridge Regression Best Linear Unbiased Predictor (RR-BLUP) was deployed as the GS method to test these SNP sets, and 10-fold cross-validation was performed on 1,321 Douglas-fir trees, representing 37 full-sib F1 families and on 1,126 Interior spruce trees, representing 25 open-pollinated (half-sib) families. Both trials are located on 3 sites in British Columbia, Canada. Results: As marker number increased, so did GS predictive accuracy for both conifer species. However, a plateau in the gain of accuracy became apparent around 10,000–15,000 markers for both Douglas-fir and Interior spruce. Despite random marker selection, little variation in predictive accuracy was observed across replications. On average, Douglas-fir prediction accuracies were higher than those of Interior spruce, reflecting the difference between full- and half-sib families for Douglas-fir and Interior spruce populations, respectively, as well as their respective effective population size. Conclusions: Although possibly advantageous within an advanced breeding population, reducing marker density cannot be recommended for carrying out GS in conifers. Significant LD between markers and putative causal variants was not detected using 50,000 SNPS, and GS was enabled only through the tracking of relatedness in the populations studied. Dramatically increasing marker density would enable said markers to better track LD with causal variants in these large, genetically diverse genomes; as well as providing a model that could be used across populations, breeding programs, and traits. [ABSTRACT FROM AUTHOR]

Defoliation level and site type are thought to influence tree response during spruce budworm (Choristoneura fumiferana (Clemens)) outbreaks. We determined the effects of four manual defoliation treatments (0%, 50%, 100%, and 100% + bud removal of current foliage) for 3 years on foliage production of balsam fir (Abies balsamea (L.) Mill.), black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.), and white spruce (Picea glauca (Moench) Voss) trees on four site-quality classes. After 3 years of defoliation and 2 years of recovery, foliage biomass was reduced by 34%–98%. During defoliation, the number of shoots generally increased and shoot length of spruce generally decreased, especially on rich sites. During recovery, the number of shoots increased substantially, shoot length decreased, and bud destruction reduced the number of shoots by about 50% compared with that of trees that received the 100% defoliation treatment. Defoliation did not substantially affect needle length. Trees on rich sites had two- to fourfold greater foliage production than trees on poor sites. Effects of site and defoliation differed among species, but site quality, especially nutrition, played an important role in production of shoots and needles and the tree's ability to withstand defoliation. Black spruce had more limited ability to recover foliage biomass, only producing more shoots, whereas balsam fir and white spruce had stronger ability to recover needle and shoot length, respectively. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase woody vegetation abundance in the Arctic, yet the magnitude, spatial pattern and pathways of change remain uncertain. We compared historical orthophotos photos (1952 and 1979) with high‐resolution satellite imagery (2015) to examine six decades of change in abundance of white spruce Picea glauca and tall shrubs (Salix spp., Alnus spp.) near the Agashashok River in northwest Alaska. We established ~3000 random points within our ~5500 ha study area for classification into nine cover types. To examine physiographic controls on tree abundance, we fit multinomial log‐linear models with predictors derived from a digital elevation model and with arctic tundra, alpine tundra and 'tree' as levels of a categorical response variable. Between 1952 and 2015, points classified as arctic and alpine tundra decreased by 31% and 15%, respectively. Meanwhile, tall shrubs increased by 86%, trees mixed with tall shrubs increased by 385% and forest increased by 84%. Tundra with tall shrubs rarely transitioned to forest. The best multinomial model explained 71% of variation in cover and included elevation, slope and an interaction between slope and 'northness'. Treeline was defined as the elevation where the probability of tree presence equaled that of tundra. Mean treeline elevation in 2015 was 202 m, corresponding with a June–August mean air temperature > 11°C, which is > 4°C warmer than the 6–7°C isotherm associated with global treeline elevations. Our results show dramatic increases in the abundance of trees and tall shrubs, question the universality of air temperature as a predictor of treeline elevation and suggest two mutually exclusive pathways of vegetation change, because tundra that gained tall shrubs rarely transitioned to forest. Conversion of tundra to tall shrubs and forest has important and potentially contrasting implications for carbon cycling, surface energy exchange and wildlife habitat in the Arctic. [ABSTRACT FROM AUTHOR]

Summary: Lignin is a complex phenolic biopolymer found mainly in the secondary cell walls of vascular plants, where it contributes to mechanical strength, water conduction, and plant defence. We studied the lignin of eastern leatherwood (Dirca palustris) because this slow‐growing woody shrub is known for its flexible stems.Various analytical techniques and microscopy methods were employed to examine the composition and distribution of lignin and structural polysaccharides in leatherwood xylem in comparison with trembling aspen (Populus tremuloides) and white spruce (Picea glauca).We found that leatherwood has low overall levels of lignin, a high syringyl lignin content, and a unique distribution of lignin. Most remarkably, the cell corners and middle lamellae remain unlignified in mature xylem.These findings help explain the flexibility of leatherwood and also call into question the classical model of lignification, which purports that lignin polymerization begins in the cell corners and middle lamellae. This atypical lignification regime vividly illustrates the diversity in plant secondary cell wall formation that abounds in nature and casts leatherwood as a new model for the study of lignin biogenesis. [ABSTRACT FROM AUTHOR]

The onset of lifetime reproduction is central to processes of plant adaptation and population changes. The relative contributions of size and age to the onset of reproduction are important to predicting that key event in individuals. To estimate respective size and age effects on first reproduction in a conifer, I observed white spruce (Picea glauca (Moench) Voss) trees in forest stands in Alaska, United States, over ranges of cumulative growth rates. Age was estimated by counting annular growth rings, size was indicated by tree height, and reproductive status was indicated by seed cones. Multiple logistic regression showed the relative contributions of tree height and age, adjusted for each other, to statistical predictions of reproductive maturity. Trees selected for having little competition for light first produced cones at heights between 1 and 5 m with little additional effect of age. Tree height contributed approximately 50% to regression predictions of reproductive maturity. In contrast, tree age contributed ≤1.5% and bore little relation to reproductive maturity other than as a component of growth rate. This is among the first reports to partial the effect sizes of tree size and age on the commencement of lifetime reproduction in a conifer. [ABSTRACT FROM AUTHOR]

Understanding interactions between competition and climate in relation to their effects on individual tree growth is crucial to the development of climate-sensitive growth models required for modelling boreal forest succession in a changing climate. We used data from permanent growth and yield sample plots in western Canada and Alaska to investigate the impact of competition within a regional gradient of climatic conditions for lodgepole pine (Pinus contorta Douglas ex Loudon), jack pine (Pinus banksiana Lamb.), trembling aspen (Populus tremuloides Michx.), balsam poplar (Populus balsamifera L.), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.). We characterized the effects of competition (basal area of spruce–fir, deciduous, and pine trees larger than the focal tree) and climate (mean annual temperature and precipitation) and their interactions on basal area growth of individual trees using linear mixed-effects models. Our results indicated that intraspecific competition had stronger effects on growth than interspecific competition and climate. Moreover, significant interactions between intraspecific competition and climate suggest that an increase in intraspecific competition will lead to a reduction in tree growth for warmer regions (lodgepole pine, trembling aspen, balsam poplar, and white spruce) and wetter regions (jack pine). The manner in which interspecific competition altered tree growth responses to climate was variable, depending on tree species and competition type. These results indicate that the relationships between growth and climate may differ according to the degree of competition and the structure of the stand. [ABSTRACT FROM AUTHOR]

Synchronous pulses of seed masting and natural disturbance have positive feedbacks on the reproduction of masting species in disturbance‐prone ecosystems. We test the hypotheses that disturbances and proximate causes of masting are correlated, and that their large‐scale synchrony is driven by similar climate teleconnection patterns at both inter‐annual and decadal time scales.Hypotheses were tested on white spruce (Picea glauca), a masting species which surprisingly persists in fire‐prone boreal forests while lacking clear fire adaptations. We built masting, drought and fire indices at regional (Alaska, Yukon, Alberta, Quebec) and sub‐continental scales (western North America) spanning the second half of the 20th century. Superposed Epoch Analysis tested the temporal associations between masting events, drought and burnt area at the regional scale. At the sub‐continental scale, Superposed Epoch Analysis tested whether El Niño‐Southern Oscillation (ENSO) and its coupled effects with the Atlantic Multidecadal Oscillation (AMO) in the positive phase (AMO+/ENSO+) synchronize drought, burnt area and masting. We additionally tested the consistency of our synchronization hypotheses on a decadal temporal scale to verify whether long‐term oscillations in AMO+/ENSO+ are coherent to decadal variation in drought, burnt area and masting.Analyses demonstrated synchronicity between drought, fire and masting. In all regions the year before a mast event was drier and more fire‐prone than usual. During AMO+/ENSO+ events sub‐continental indices of drought and burnt area experienced significant departures from mean values. The same was observed for large‐scale masting in the subsequent year, confirming 1‐year lag between fire and masting. Sub‐continental indices of burnt area and masting showed in‐phase decadal fluctuations led by the AMO+/ENSO+. Results support the 'Environmental prediction hypothesis' for mast seeding.Synthesis. We provide evidence of large‐scale synchronicity between seed masting in Picea glauca and fire regimes in boreal forests of western North America at both inter‐annual and decadal time scales. We conclude that seed production in white spruce predicts changes in disturbance regimes by sharing the same large‐scale climate drivers with drought and fire. This gives new insides in a mechanism providing a fire‐sensitive species with higher than expected adaptability to changes in climate. [ABSTRACT FROM AUTHOR]

Climate change is altering phenology; however, the magnitude of this change varies among taxa. Compared with phenological mismatch between plants and herbivores, synchronization due to climate has been less explored, despite its potential implications for trophic interactions. The earlier budburst induced by defoliation is a phenological strategy for plants against herbivores. Here, we tested whether warming can counteract defoliation‐induced mismatch by increasing herbivore‐plant phenological synchrony. We compared the larval phenology of spruce budworm and budburst in balsam fir, black spruce, and white spruce saplings subjected to defoliation in a controlled environment at temperatures of 12, 17, and 22°C. Budburst in defoliated saplings occurred 6–24 days earlier than in the controls, thus mismatching needle development from larval feeding. This mismatch decreased to only 3–7 days, however, when temperatures warmed by 5 and 10°C, leading to a resynchronization of the host with spruce budworm larvae. The increasing synchrony under warming counteracts the defoliation‐induced mismatch, disrupting trophic interactions and energy flow between forest ecosystem and insect populations. Our results suggest that the predicted warming may improve food quality and provide better growth conditions for larval development, thus promoting longer or more intense insect outbreaks in the future. [ABSTRACT FROM AUTHOR]

Tree growth at northern treelines is generally temperature‐limited due to cold and short growing seasons. However, temperature‐induced drought stress was repeatedly reported for certain regions of the boreal forest in northwestern North America, provoked by a significant increase in temperature and possibly reinforced by a regime shift of the pacific decadal oscillation (PDO). The aim of this study is to better understand physiological growth reactions of white spruce, a dominant species of the North American boreal forest, to PDO regime shifts using quantitative wood anatomy and traditional tree‐ring width (TRW) analysis. We investigated white spruce growth at latitudinal treeline across a >1,000 km gradient in northwestern North America. Functionally important xylem anatomical traits (lumen area, cell‐wall thickness, cell number) and TRW were correlated with the drought‐sensitive standardized precipitation–evapotranspiration index of the growing season. Correlations were computed separately for complete phases of the PDO in the 20th century, representing alternating warm/dry (1925–1946), cool/wet (1947–1976) and again warm/dry (1977–1998) climate regimes. Xylem anatomical traits revealed water‐limiting conditions in both warm/dry PDO regimes, while no or spatially contrasting associations were found for the cool/wet regime, indicating a moisture‐driven shift in growth‐limiting factors between PDO periods. TRW reflected only the last shift of 1976/1977, suggesting different climate thresholds and a higher sensitivity to moisture availability of xylem anatomical traits compared to TRW. This high sensitivity of xylem anatomical traits permits to identify first signs of moisture‐driven growth in treeline white spruce at an early stage, suggesting quantitative wood anatomy being a powerful tool to study climate change effects in the northwestern North American treeline ecotone. Projected temperature increase might challenge growth performance of white spruce as a key component of the North American boreal forest biome in the future, when drier conditions are likely to occur with higher frequency and intensity. [ABSTRACT FROM AUTHOR]

Climate-sensitive height–age models were developed for top height trees of trembling aspen (Populus tremuloides Michx.), jack pine (Pinus banksiana Lamb.), and white spruce (Picea glauca (Moench) Voss) in natural and reclaimed oil sands stands. We used stem analysis data collected from the Athabasca oil sands region in northern Alberta, Canada, and climate data generated by the ClimateWNA model. Height–age trajectories differed between top height trees in natural and reclaimed stands for jack pine and white spruce, but not for trembling aspen. At a given age, white spruce top height trees were taller and jack pine top height trees were shorter in reclaimed stands than those in natural stands, suggesting that it is easier to achieve similar forest productivity for oil sands sites reclaimed with white spruce stands than for sites reclaimed with jack pine stands. The principal climate variables were growing season (May to September) precipitation averaged over the previous 10 years for trembling aspen and jack pine and summer (June to August) precipitation averaged over the previous 10 years for white spruce. These variables had positive effects on the height–age trajectories. [ABSTRACT FROM AUTHOR]

Summary: Laimaphelenchus pannocaudus, isolated in Ningbo port from Picea gluaca, is redescribed based upon characteristic morphological details elucidated by light and scanning electron microscopy photographs. The recovered population is characterised by 907 (771-1024) μ m long females with 11.2 (8.9-12.2) μ m long stylet, four incisures in the lateral field, excretory pore located at the same level as, or slightly anterior to the nerve ring, vulva lacking a flap and located at 68.7 (63.9-73.4)% of the body, elongate post-vulval uterine sac 78.5 (55.6-101.1) μ m long, and tail 40.6 (33.4-45.6) μ m long. Males are common and characterised by 16.5 (15.7-17.8) μ m long spicules (chord) with their condylus slightly recurved, squared to rounded in shape with a blunt rounded tip and rostrum triangular with a bluntly pointed tip, and six visible caudal papillae. The female tail is ventrally curved, conoid and bears a stalk-like terminus with 4-8 pedunculate projections. Phylogenetic analyses using partial 18S and 28S rDNA D2-D3 data revealed that L. pannocaudus formed a sister relationship with L. suberensis in both phylogenies. [ABSTRACT FROM AUTHOR]

The spruce budworm, Choristoneura fumiferana, is presumed to be panmictic across vast regions of North America. We examined the extent of panmixia by genotyping 3,650 single nucleotide polymorphism (SNP) loci in 1975 individuals from 128 collections across the continent. We found three spatially structured subpopulations: Western (Alaska, Yukon), Central (southeastern Yukon to the Manitoba–Ontario border), and Eastern (Manitoba–Ontario border to the Atlantic). Additionally, the most diagnostic genetic differentiation between the Central and Eastern subpopulations was chromosomally restricted to a single block of SNPs that may constitute an island of differentiation within the species. Geographic differentiation in the spruce budworm parallels that of its principal larval host, white spruce (Picea glauca), providing evidence that spruce budworm and spruce trees survived in the Beringian refugium through the Last Glacial Maximum and that at least two isolated spruce budworm populations diverged with spruce/fir south of the ice sheets. Gene flow in the spruce budworm may also be affected by mountains in western North America, habitat isolation in West Virginia, regional adaptations, factors related to dispersal, and proximity of other species in the spruce budworm species complex. The central and eastern geographic regions contain individuals that assign to Eastern and Central subpopulations, respectively, indicating that these barriers are not complete. Our discovery of previously undetected geographic and genomic structure in the spruce budworm suggests that further population modelling of this ecologically important insect should consider regional differentiation, potentially co‐adapted blocks of genes, and gene flow between subpopulations. [ABSTRACT FROM AUTHOR]

Analyses of maximum early tree ring growth within a regional curve standardization (RCS) framework were used to construct ring width chronologies in mm year−1 to estimate historical growth rates in southwest Yukon (Canada), without the necessity of correcting for age related changes. The analysis relied on the use of the 11th–50th year growth rings to standardize chronology comparisons. This age range represents the period of peak radial growth for Picea albertiana and P. glauca (white spruces), which are common trees on upland boreal sites in the study area. Of 1,460 available Picea ring series, 1,029 fit the criteria for inclusion in the study and they represented five commonly occurring RCS curve types. When converted to chronologies, all curve types had year-to-year fluctuations in average ring widths (RW11–50), but nine of the 12 RCS types (four types in three study areas) also had long-term growth rate increases of 15–132% between ad 1850 and 2000, based on regression modeling (R/r = 0.54–0.76, p < 0.001). Associated with these increases were changes through time in RCS curve type and the timing of peak growth. Among studied areas, RW11–50 values on average increased 47% from 1.59 to 2.35 mm year−1 between 1850 and 2000. The greatest increase (71% vs 35–38%) occurred in the coldest study area. RW11–50 values were significantly (p < 0.001) and strongly correlated (r > 0.94, n > 100) with conventional tree ring width index values derived from multiple RCS curves. This indicates that the two chronology construction approaches have very similar temporal patterns despite the maximum early growth analysis technique representing ring widths in mm. [ABSTRACT FROM AUTHOR]

We review a recently discovered white spruce (Picea glauca) chemical defense against spruce budworm (Choristoneura fumiferana) involving hydroxyacetophenones. These defense metabolites detected in the foliage accumulate variably as the aglycons, piceol and pungenol, or the corresponding glucosides, picein and pungenin. We summarize current knowledge of the genetic, genomic, molecular, and biochemical underpinnings of this defense and its effects on C. fumiferana. We present an update with new results on the ontogenic variation and the phenological window of this defense, including analysis of transcript responses in P. glauca to C. fumiferana herbivory. We also discuss this chemical defense from an evolutionary and a breeding context. [ABSTRACT FROM AUTHOR]

Wood products, especially those used in outdoor conditions, can be damaged by dimensional changes and decay fungi. It is therefore advised to use impregnation treatments to mitigate these hazards. While the potency of the chemicals employed in the treatments is important, characterization of the treatments is also crucial to ensure deep and durable protection. In this study, eastern white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss) were impregnated with propiconazole and 3-iodo-2-propynyl butylcarbamate (IPBC) through diffusion. Instead of using pressure treatments, the samples were dipped in solutions containing amine oxides, which can diffuse into the wood. The treatments were characterized by the mass of fungicide impregnated, fungicide leaching, and the impregnation depths of both the fungicides and the amine oxides. It was found that the treatment impregnated slightly more than 0.040 kg/m³ of both fungicides, meeting EU standards. It was also shown that the presence of amine oxides slightly prevented the leaching of the fungicides in white pine. The penetration of the amine oxides was several millimeters deep in all directions, but the penetrations of the fungicides were much shorter and only longitudinal. [ABSTRACT FROM AUTHOR]

Depletion of white spruce (Picea glauca) in mixedwood forest is a frequent problem, particularly in stands that were high-graded as a result of inadequate silviculture and spruce budworm (Choristoneura fumiferana) epidemics. To provide information that will help guide restoration efforts, we assessed the effect of four seed-tree retention (STR: 0, 10, 40 and 60 trees/ha) levels and two scarification (SC: patch scarification and disk-trenching) types on white spruce reintroduced by planting in a high-graded yellow birch (Betula alleghaniensis)–conifer stand. We present the 9-year results from the seedling physiology, nutrition and morphology. Physiology and nutrition changed with years, but did not vary with STR levels and SC types. Significant increases in the number of internodal branches, height growth, and total height at the two lowest STR levels and after release suggest that the performance of white spruce in terms of morphology and growth is sensitive to small variations in available light. Because seedling morphology and growth were similar between SC types, a moderate disturbance of the forest floor by disk-trenching would be sufficient at a relatively low cost. Our findings highlight that the STR levels influenced the morphology and growth of planted white spruce seedlings more than the SC types. [ABSTRACT FROM AUTHOR]