Search

Conifers are long-lived and slow-evolving, thus requiring effective defences against their fast-evolving insect natural enemies. The copy number variation (CNV) of two key acetophenone biosynthesis genes Ugt5/Ugt5b and βglu-1 may provide a plausible mechanism underlying the constitutively variable defence in white spruce (Picea glauca) against its primary defoliator, spruce budworm. This study develops a long-insert sequence capture probe set (Picea_hung_p1.0) for quantifying copy number of βglu-1-like, Ugt5-like genes and single-copy genes on 38 Norway spruce (Picea abies) and 40 P. glauca individuals from eight and nine provenances across Europe and North America respectively. We developed local assemblies (Piabi_c1.0 and Pigla_c.1.0), full-length transcriptomes (PIAB_v1 and PIGL_v1), and gene models to characterise the diversity of βglu-1 and Ugt5 genes. We observed very large copy numbers of βglu-1, with up to 381 copies in a single P. glauca individual. We observed among-provenance CNV of βglu-1 in P. glauca but not P. abies. Ugt5b was predominantly single-copy in both species. This study generates critical hypotheses for testing the emergence and mechanism of extreme CNV, the dosage effect on phenotype, and the varying copy number of genes with the same pathway. We demonstrate new approaches to overcome experimental challenges in genomic research in conifer defences. [ABSTRACT FROM AUTHOR]

The demand for exterior wood siding is stagnating in North America due in part to perceptions of low durability and the need for frequent maintenance. One way to address these concerns is to modify the wood to improve its physical properties, while maintaining its appearance. In this study, white spruce was treated with organosilanes and a combination of aluminum treatments followed by a thermal treatment to improve the dimensional stability and the wood durability. Anti-swelling efficiency (ASE), leaching and decay tests were performed on the treated Canadian wood species. The quantity of hydroxyls available after treatment was evaluated by water vapor sorption. The results showed that the treatment improved the dimensional stability up to 50%. Available hydroxyls decreased by as much as 37%. The organosilanes treatment was resistant to leaching, while the aluminum was observed to leach. Organosilanes in combination with aluminum showed brown rot resistance. The addition of aluminum to the organosilanes treatment did not have effect on dimensional stability but it had a great impact on the brown rot resistance. [ABSTRACT FROM AUTHOR]

The spruce bark beetle Ips typographus is the most damaging pest in European spruce forests and has caused great ecological and economic disturbances in recent years. Although native to Eurasia, I. typographus has been intercepted more than 200 times in North America and could establish there as an exotic pest if it can find suitable host trees. Using in vitro bioassays, we compared the preference of I. typographus for its coevolved historical host Norway spruce (Picea abies) and two non-coevolved (naïve) North American hosts: black spruce (Picea mariana) and white spruce (Picea glauca). Additionally, we tested how I. typographus responded to its own fungal associates (conspecific fungi) and to fungi vectored by the North American spruce beetle Dendroctonus rufipennis (allospecific fungi). All tested fungi were grown on both historical and naïve host bark media. In a four-choice Petri dish bioassay, I. typographus readily tunneled into bark medium from each of the three spruce species and showed no preference for the historical host over the naïve hosts. Additionally, the beetles showed a clear preference for bark media colonized by fungi and made longer tunnels in fungus-colonized media compared to fungus-free media. The preference for fungus-colonized media did not depend on whether the medium was colonized by conspecific or allospecific fungi. Furthermore, olfactometer bioassays demonstrated that beetles were strongly attracted toward volatiles emitted by both con- and allospecific fungi. Collectively, these results suggest that I. typographus could thrive in evolutionary naïve spruce hosts if it becomes established in North America. Also, I. typographus could probably form and maintain new associations with local allospecific fungi that might increase beetle fitness in naïve host trees. [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]

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]

Copyright of Forestry Chronicle is the property of Canadian Institute of Forestry and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

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]

• Higher temperature heightened growing season drought despite more precipitation. • Mature white spruce increased mortality and reduced growth in southeasterly Ontario. • Climate warming will likely cause white spruce range retraction in southern Ontario. • Increasing drought may cause white spruce to decline in Ontario's boreal forests. The adaptive capacity of boreal tree species to thrive in a warming, more variable climate has significant implications for boreal forest ecosystem structure and function. Dendrochronological and other empirical data indicate reduced growth and increased mortality of white spruce (Picea glauca [Moench] Voss) growing in warmer, drier portions of its natural range in western North America due to recent climate change. Comparatively, little is known of potential climate change effects on white spruce in the more mesic, eastern portion of its range where mean annual precipitation is relatively high. In this study, we examined the potential long-term consequences of climate warming on annual rates of mortality and height growth of mature white spruce by substituting space for time using data from 10, 31- to 40-year-old large common garden experiments (CGEs) established in Ontario, Canada. Across these CGEs, white spruce was exposed to differences of up to 5.0 °C in mean annual temperature and 405 mm in mean annual precipitation. During a 12- to 16-year measurement interval, mortality increased from the colder, more northern CGEs to the warmer CGEs near the species' southern range margin. Along this climatic gradient, white spruce was also exposed to more frequent, severe growing season moisture deficits, with southern CGEs sometimes subject to extreme drought events with a low probability based on historical occurrence. Our results indicate that the severity of recent growing season drought events at more southern CGEs may have exceeded the drought tolerance capacity of white spruce and resulted in significantly increased mortality and reduced height growth rates. These results suggest that with projected increases in temperature and frequency/severity of growing season drought by the end of this century, white spruce is likely to experience maladaptation over a larger portion of its range in Ontario and gradually retract from its current southern range edge. [ABSTRACT FROM AUTHOR]

Vast areas of hardwood and mixedwood forests of eastern North America have been high-graded in the past and need silvicultural treatments to increase their value and productivity. To rehabilitate a high-graded temperate mixedwood stand, in Quebec, Canada, we used a split–split-split plot design with three replicates to assess different seed-tree and strip cutting systems, in combination with scarification and planting. The experiment consisted of three regeneration cuts in main plots: 10 seed-trees/ha, 40 seed-trees/ha and a 40-m wide strip clearcut (0 seed-tree/ha) with 60 seed-trees/ha in leave strips, thereby resulting in four levels of tree retention, and all included understory brushing. We applied two types of scarification (patch scarification or disk-trenching) to subplots, two regeneration modes (natural regeneration or planting with white spruce [Picea glauca]) to sub-subplots and two mechanical release treatments (softwood or mixedwood production) to planted sub–sub-subplots. Density of seed-trees did not affect the natural regeneration dynamics after 5 years, but disk-trenching was more efficient for the establishment of yellow birch (Betula alleghaniensis) and sugar maple (Acer saccharum). Few seed-trees of desirable white spruce were present and most died standing, confirming the importance of supplemental planting. Height growth of planted seedlings was 15% higher in the 0 and 10 (26–27 cm/year) than in the 40 and 60 (23 cm/year) seed-trees/ha treatments, and release doubled mean height growth (33.1 vs. 16.6 cm/year). Despite intensive site preparation, pre-established beaked hazel (Corylus cornuta) and mountain maple (Acer spicatum) were present at high densities in the regeneration stratum. Controlling this recalcitrant layer might be the greatest challenge for rehabilitating degraded stands of the mixedwood forest, especially since the use of herbicides is prohibited on Quebec's public lands. [ABSTRACT FROM AUTHOR]

Highlights • Four pines and four spruces in a 2 × 2 factorial of CO 2 and soil moisture. • Overall, pines respond better to eCO 2 and soil moisture stress. • Shade-tolerant spruces perform better in eCO 2 than shade-intolerant spruces. • Greater the mass, greater the response to eCO 2 and soil moisture. • Supports shift toward increased use of pines in NE N. America. Abstract Growth, components of growth, and biomass allocation were quantified for eight species in two commercially important genera, Pinus and Picea , grown in a 2 × 2 factorial of atmospheric CO 2 and soil moisture stress. Four of the pines and three of the spruces are native to eastern North America; a fourth spruce, Norway spruce (NS: P. abies), is native to Europe but is used for reforestation in northeastern North America. Height, basal diameter (BD), and total biomass response of pines were often more than two times greater than that of spruces under elevated CO 2 (eCO 2). A significant species × CO 2 interaction for total biomass was a result of species' differential response to eCO 2 : Pinus rigida had the greatest biomass stimulation (59%), followed by P. resinosa (39%), P. strobus (26%), and P. banksiana (19%). Among spruces, Picea glauca showed the greatest response (30%), and P. mariana the least response under eCO 2 (5%). Overall, soil moisture stress reduced total productivity by 12%. Most pines did have greater growth under moisture stress, and NS and BS grew well. Percent needle mass was lower under eCO 2 , but this was not due directly to eCO 2 but to ontological changes. Controlling for size, pines had 20% greater needle biomass than spruces, while having a negative relationship to total biomass. A comparison of total biomass under eCO 2 in relation to aCO 2 by species showed that overall, the greater the species mass, the greater the mass gain under eCO 2, and the greater the mass loss under drought conditions. In addition, our results for spruces lend strong support to the theory that late-successional species have greater growth response under eCO 2 than early to mid-successional species. A diverse portfolio of tree species for artificial reforestation would help forest management adapt to the many uncertainties over future environments and markets, but our results on responses in spruces and pines to eCO 2 and soil moisture stress support a shift toward increased use of pines in forest management and artificial reforestation. [ABSTRACT FROM AUTHOR]

• We exposed seedlings of conifer species to three realistic simulated future climates. • Seedlings of conifer species experienced high mortality (75%) induced by drought. • Conifer species are highly vulnerable at the seedling stage to future drought. • Hydraulic safety margins are good indicators of mortality risk for conifer species. The future climate of northern temperate forests is projected to be drier and warmer by the end of this century. As a result, more drought-induced forest dieback events are anticipated in northeastern North America, and assessing the vulnerability of dominant tree species to drought is critical for understanding the future composition of these forests. In a greenhouse experiment, we exposed two-year-old seedlings of Picea glauca (Moench) Voss, Picea mariana (Mill.) B.S.P. and Pinus strobus L. to three future climate treatments for southern Quebec, Canada, and evaluated their mortality, growth, and foliage water status responses to soil water availability and atmospheric drought. Using a unique approach, climate treatments emulated droughts of different frequencies, durations, and intensities. Treatments closely simulated one growing season, with changes in air temperature and relative humidity every six hours and daily adjustment in the amount of water delivered to the seedlings. The three species experienced high mortality (75%) in all water-limited treatments compared to a control treatment that provided non-limiting soil moisture (0% mortality). The biomass of the seedlings that survived was 40% lower than that of control seedlings. Our results confirmed that the hydraulic safety margins, defined as the difference between seasonal minimum water potential and xylem water potential leading to 12, 50 and 88% of hydraulic conductivity loss, were good predictors of probability of tree mortality. Therefore, hydraulic safety margins are useful functional traits that can be used to compare the vulnerability of various species to drought and then provide crucial information to practitioners and policymakers to adjust forest management to climate change. We showed that three dominant conifer species of northern temperate forests were highly vulnerable to drought in future climates. Because drought is projected to be a significant threat to forests, understanding potentially adaptive physiological responses to drought, such as hydraulic safety margins of tree seedlings, is important for predicting the response of forest regeneration and composition in warmer and drier climates. [ABSTRACT FROM AUTHOR]

Logistic survival probability models were developed for seven tree species in northwestern North America using Permanent Sample Plot (PSP) data from: six Canadian provincial and territorial governments, the government of Alaska (USA), and four forestry companies; for a total of 1,250,257 trees within 11,673 PSPs. The survival probability of: white/Engelmann spruce ( Picea glauca (Moench) Voss /Picea engelmannii Parry ex Engelm . ), black spruce ( Picea mariana (Mill.) BSP.), lodgepole pine ( Pinus contorta Douglas ex Loudon), jack pine ( Pinus banksiana Lamb.), trembling aspen ( Populus tremuloides Michx.), balsam poplar ( Populus balsamifera L.), and balsam fir ( Abies balsamea (L.) Mill . ) was modeled using tree size (dbh), competition estimates (basal area of the larger trees by species group), climate normal, tagging limits and the time elapsed between consecutive measurements. Survival increased nonlinearly with tree size and the effect of competition on tree survival was related to the shade-tolerance of the species and to stand composition, with shade intolerant conifer species (i.e. lodgepole and jack pine) being more negatively affected by competition compared to shade intolerant deciduous species (trembling aspen and balsam poplar) and shade tolerant spruce species (white and black spruce). Competition from larger spruce ( Picea spp.), fir ( Abies spp.) and deciduous species (e.g. Populus spp. and Betula spp.) had stronger influences on survival than pine species ( Pinus spp.). Intraspecific competition also had significant effects on survival of the majority of the species. Climate Moisture Index provided better results than other climate variables for most species and survival probability increased with increasing values of CMI (i.e. relatively cooler and wetter climate), while for pine species survival probability decreased with increasing CMI and showed higher levels of survival on warmer and drier sites for the range of conditions included in our data. The predictive equations developed in this study could be used to improve the predictive ability of existing growth and yield models such as the Mixedwood Growth Model. [ABSTRACT FROM AUTHOR]

• Recovery in absence of treatments showed the resilient nature of mixedwood stands. • Understory conifers largely contributed to recovery of stand basal area and vigor. • Active rehabilitation could speed improvement of composition, quality and structure. • Shelterwood combined to scarification during good seed year is recommended. • Prescriptions should include provision of conifers in lower and upper strata. In northeastern North America, mixed hardwood-conifer forests have commonly been harvested with selective practices such as diameter-limit cutting. By removing trees of highest commercial value, these cuts often left stands with highly variable density and reduced volume, less species diversity, and lower wood quality. The lack of care to the regenerating layer also resulted in regeneration deficiencies, especially on productive sites supporting yellow birch (Betula alleghaniensis Britton)-conifer stands. We assessed the 15-yr effects of four rehabilitation scenarios on stand growth, quality, vigor and regeneration in an experiment established in Quebec, Canada. The trial compared untreated experimental units (e.g. control), uniform shelterwood method (50 overstory trees/ha), strip clearcutting (20-m strips), and seed-tree method (10 overstory trees/ha), all combined with 3 site preparation treatments (no scarification, mechanical raking, and spot scarification). After 15 years, the ongoing recovery of growth, vigor and regeneration in the control and untreated part of the strip clearcut plot reflected the resilient nature of these mixedwood stands, with conifer (Abies balsamea [L.] Mill. , Picea rubens Sarg., Picea glauca [Moench] Voss) saplings and poles contributing to the recovery of total BA and that of vigorous trees (i.e. acceptable growing stock [AGS]). The control and strip clearcut treatments, however, had high BA of unacceptable growing stock. Shelterwood plots recovered more slowly in BA and AGS, but had greater BA of high-quality trees than the control. Seed-tree method was less optimal because of its slow recovery and high understory competition. The lack of synchronization with a good seed year limited the efficiency of scarification, and increased the abundance of non-commercial species. An active rehabilitation strategy combining shelterwood system and ground disturbance (e.g. raking) during a good seed year should help to improve stand quality and regeneration. Yet, our results indicate that retaining conifers in the understory and overstory would ensure a seed source and accelerate recovery. Where seed sources and conifer advance regeneration are lacking, enrichment planting may be necessary to maintain a mixedwood composition over time. [ABSTRACT FROM AUTHOR]

• Climate change may cause reduced forest productivity and higher tree mortality. • We infer white spruce growth limitations from 9795 tree cores from 227 sample sites. • Water deficits make trees vulnerable to climate change in its west-central range. • Future climate projections imply water deficits in the southwest and central boreal. • The north-east may be a climate change refugium due to lack of water deficits. Climate change may cause reduced forest productivity and higher tree mortality due to water deficits that result from increased evapotranspiration. Such limitations may occur in some areas of the North American boreal forest where precipitation is low and warming trends are high. This paper analyzes climatic factors that limit the growth of a commercially important and widespread boreal tree species, white spruce (Picea glauca (Moench) Voss), based on a range-wide dendroclimatological analysis of 9795 trees from 227 sample sites across the North American boreal forest. A bootstrapped response function analysis was conducted for monthly temperature and precipitation variables, and a multivariate regression tree analysis was used to group white spruce populations with similar response coefficients where climatic factors explained 46% of the total variance in response coefficients. The results of this study show that white spruce populations in the west-central boreal forest of North America are the most precipitation-limited group and therefore likely to be most susceptible to climate change. Populations both to the north and south of this group appear less vulnerable, and eastern populations generally do not experience growth-limiting moisture deficits. Regional climate change projections suggest that moisture limitations will become more pronounced in the future, especially for southwest and west-central boreal tree populations. [ABSTRACT FROM AUTHOR]

The article discusses that 12-g migratory blackpoll warbler has one of the most spectacular migrations in the world; and mentions the use of miniaturized devices to track the movements of blackpolls breeding at four northern locations.

High northern latitude regions are experiencing some of the most rapid environmentalchanges. Carbon sequestration might be enhanced by increased forest productivity due towarming temperatures and potentially higher atmospheric CO2, but declines in tree growthand mortality due to drought stress could counteract this enhancement by releasing CO2 tothe atmosphere. Observed changes in boreal forest dynamics are already altering theglobal carbon and hydrological cycles, albedo and land surface feedbacks. Here, wecombined ring-width data with annually resolved stable carbon (δ13C) and oxygenisotope (δ18O) records to investigate the physiological responses of white spruce(Picea glauca [Moench] Voss) trees to warming and increased atmospheric CO2concentrations at northern treeline sites. We developed an extensive network of δ13Cand δ18O tree-ring chronologies covering the 20th century derived from 10 sitesacross North America (NA) spanning from 60.5º to 68.7ºN and 104º to 162ºW. Weused a range of observational data and a climate model to interpret signals in theseannually-resolved tree-ring series. At most sites, the inter-tree correlations werehigher for δ18O than δ13C series. Both δ13C and δ18O were highly influenced bytemperature variations, although the dominant season was different: summer and spring,respectively. This suggests that different processes associated with temperature variationsmay be operating. Physiological processes occurring at leaf level during summermainly influenced δ13C. Spring climate had the strongest influence on tree-ringδ18O via temperature effects on the δ18O of source water, and to a lesser degree,in summer, physiological process at leaf level may also occur. Accordingly, wefound weak relationships between the tree-ring δ18O and atmospheric circulation(such as integrated moisture transport) during summer using the GISS ModelE2isotopically-equipped general circulation model. Calibration and simulations of tree-ring datain the process-based mechanistic model MAIDENiso will help us to elucidate thecomplex linkages between increases in temperature and CO2 driven tree responses.This tree-ring isotope network provides a unique opportunity to disentangle theclimatic and physiological controls driving growth patterns at the northern treeline. [ABSTRACT FROM AUTHOR]

Background: Outbreaks of spruce budworm (SBW, Choristoneura fumiferana Clem.) cause major recurrent damage in boreal conifers such as white spruce (Picea glauca [Moench] Voss) and large losses of forest biomass in North America. Although defensive phenolic compounds have recently been linked to chemical resistance against SBW, their genetic basis remains poorly understood in forest trees, especially in conifers. Here, we used diverse association genetics approaches to discover genes and their variants that may control the accumulation of acetophenones, and dissect the genetic architecture of these defence compounds against SBW in white spruce mature trees. Results: Out of 4747 single nucleotide polymorphisms (SNPs) from 2312 genes genotyped in a population of 211 unrelated individuals, genetic association analyses identified 35 SNPs in 33 different genes that were significantly associated with the defence traits by using single-locus, multi-locus and multi-trait approaches. The multi-locus approach was particularly effective at detecting SNP–trait associations that explained a large fraction of the phenotypic variance (from 20 to 43%). Significant genes were regulatory including the NAC transcription factor, or they were involved in carbohydrate metabolism, falling into the binding, catalytic or transporter activity functional classes. Most of them were highly expressed in foliage. Weak positive phenotypic correlations were observed between defence and growth traits, indicating little or no evidence of defence-growth trade-offs. Conclusions: This study provides new insights on the genetic architecture of tree defence traits, contributing to our understanding of the physiology of resistance mechanisms to biotic factors and providing a basis for the genetic improvement of the constitutive defence of white spruce against SBW. [ABSTRACT FROM AUTHOR]