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1.
  • Andreasson, Frida (författare)
  • Comparison of ingrowth cores and ingrowth meshes in root studies: 3 years of data on Pinus pinaster and its understory
  • 2016
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 30, s. 555-570
  • Tidskriftsartikel (refereegranskat)abstract
    • Key message Pine fine root biomass, live fraction and specific root length studied after collection with ingrowth cores do not correspond with those collected with ingrowth meshes. Abstract Root studies are a challenging task, yet they are primordial to improve our understanding of biogeochemical cycles in many ecosystems. Methods reducing operator time and minimizing disturbance while permitting adequate assessment of root dimensions in space and time would naturally be of great relevance. Recently, ingrowth meshes have been proposed as a valuable alternative to existing methods, deployable in remote areas and potentially yielding smaller disturbances along with a reduction in time spent per sample. In this study, we used flexible mesh material in Pinus pinaster production forests. The mesh material (pore size 6 by 6 mm) was either applied as cores (15 cm deep, 8 cm diameter) or as linear meshes (15 cm deep, 50 cm long), and left in soils for 9, 24, or 36 months. Roots were retrieved from both devices and separated over plant species (pine and understory species), diameter class and vitality (live or dead). We expected 1) improved assessment of larger diameter roots in the linear meshes due to a larger mesh surface and 2) less disturbance of the soil for the linear meshes. Results indicate that most patterns were similar between both devices and species, but the meshes resulted in lower ingrowth for all diameter classes, and the cores better reflected the standing biomass. The larger surface of the linear meshes resulted in larger disturbance and did not permit to reduce time per sample. Future research may target ingrowth meshes of reduced size and perhaps of more rigid material.
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2.
  • Beyer, Friderike, et al. (författare)
  • Relationship between foliar δ13C and sapwood area indicates different water use patterns across 236 Salix genotypes
  • 2018
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 32:6, s. 1737-1750
  • Tidskriftsartikel (refereegranskat)abstract
    • The relationship between leaf δ13C and plant size (represented by e.g. total leaf area) has been used to analyze different water use patterns of plants. However, the total leaf area (TLA) is difficult to assess in trees. Our aims were to (i) identify a feasible predictor for TLA; (ii) estimate the effects of TLA on leaf-level δ13C and δ18O values; and (iii) evaluate whether the relationship between leaf-level δ13C and a TLA proxy can be used to discriminate between different water use patterns. Various leaf and shoot traits of up to 236 Salix genotypes field-grown in Sweden and Italy were assessed and analyzed. Accumulated shoot diameter and sapwood area (SA) calculated from it were the best predictors for TLA. The SA was significantly correlated with foliar δ13C, but not δ18O values in some genotypes. The effects of SA on foliar δ13C values varied significantly among genotypes, and the foliar δ13C–SA relationship could be used to discriminate between different water use patterns across 236 Salix genotypes. Our results demonstrate a great variability of water use patterns across taxonomically closely related plants, and may also have implications for Salix pre-breeding and selection for different drought conditions.
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3.
  • Bonosi, Lorenzo, et al. (författare)
  • Growth responses of 15 Salix genotypes to temporary water stress are different from the responses to permanent water shortage
  • 2010
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 24, s. 843-854
  • Tidskriftsartikel (refereegranskat)abstract
    • Hybrids of willow (Salix spp.) are today grown as biomass crops for energy in several cool-temperate regions including Sweden. These trees have great growth potential also under warmer climates, but may suffer from drought and heat. Research on tree growth under drought has often focused on the responses to permanent water stress. Less attention has been paid to the effects of temporary water stress on tree growth, although periods of strong water shortage are recurrent in many regions of the world. We performed a greenhouse experiment to assess the impact of five treatments including permanent (PWS; 30 days of water shortage) and temporary (TWS; 4-12 days of water shortage followed by normal watering) water stress on growth and leaf traits of 15 Salix genotypes. Plant biomass and height increment decreased across treatments in the order control (well-watered) > TWS > PWS, but there was also a significant genotype x treatment interaction. The pattern in growth traits was not directly reflected by the leaf traits, for which there was no significant genotype x treatment interaction (except for leaf angle). The significant genotype x treatment interactions for growth traits indicate a potential for breeding. Permanent water shortage does not necessarily represent an appropriate environment for the selection of genotypes for environments characterised by temporary water stress.
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4.
  • Canales, Javier, et al. (författare)
  • Gene expression profiling in the stem of young maritime pine trees : detection of ammonium stress-responsive genes in the apex
  • 2011
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 26:2, s. 609-619
  • Tidskriftsartikel (refereegranskat)abstract
    • The shoots of young conifer trees represent an interesting model to study the development and growth of conifers from meristematic cells in the shoot apex to differentiated tissues at the shoot base. In this work, microarray analysis was used to monitor contrasting patterns of gene expression between the apex and the base ofmaritime pine shoots. A group of differentially expressed genes were selected and validated by examining their relative expression levels in different sections along thestem, from the top to the bottom. After validation of the microarray data, additional geneexpression analyses were also performed in the shoots of young maritime pine treesexposed to different levels of ammonium nutrition. Our results show that the apex ofmaritime pine trees is extremely sensitive to conditions of ammonium excess or deficiency, as revealed by the observed changes in the expression of stress-responsivegenes. This new knowledge may be used to precocious detection of early symptoms of nitrogen nutritional stresses, thereby increasing survival and growth rates of young treesin managed forests. 
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5.
  • Carlsson, Johanna, et al. (författare)
  • Nitrogen utilization during germination of somatic embryos of Norway spruce : revealing the importance of supplied glutamine for nitrogen metabolism
  • 2019
  • Ingår i: Trees. - : SPRINGER HEIDELBERG. - 0931-1890 .- 1432-2285. ; 33:2, s. 383-394
  • Tidskriftsartikel (refereegranskat)abstract
    • Key messageThis paper shows that germinating Norway spruce somatic embryos are dependent on the carbon and nitrogen supplied in the medium, and that supplied glutamine accounts for 50 % of assimilated nitrogen during germination.AbstractThe female megagametophyte, which provides the zygotic embryo with nitrogen (N), carbon (C) and energy during germination, is not present in Norway spruce (Picea abies) mature somatic embryos. Therefore, somatic embryos presumably rely on nutrients supplied in the germination medium in addition to their storage compounds accumulated during maturation. However, to what extent stored versus supplied compounds contribute to a somatic embryo germination is unclear. In this 24-day study, we addressed the above question by monitoring the biomass changes and the N and C budget during somatic embryo germination, under low-intensity red light. We found that the C and N storage reserves, accumulated during the maturation phase, were not sufficient to support the growth of the germinating somatic embryos, rather they were dependent on the medium components. In addition, in a previous study it has been found that glutamine (Gln) supplied in the medium was crucial for maintaining the primary amino acid (AA) metabolism and growth of the proliferating embryogenic cultures of Norway spruce (Carlsson et al., PLoS One 12(8):e0181785, 2017). Therefore, we hypothesised that Gln would be required as a significant source of N also during somatic embryo germination. By tracing the uptake of isotopically labelled N-sources from the medium and further into primary N assimilation, we found that Gln was the preferred source of N for the germinating somatic embryos, accounting for 50% of assimilated N. As the amounts of both arginine (Arg) and Gln were increased in the germinating somatic embryos, it also suggested that germination in low-intensity red light promoted N storage, similar to what has been observed in the zygotic embryo maturation in conifers (King, Gifford, Plant Physiol 113:1125-1135, 1997).
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6.
  • Collins, Emily, et al. (författare)
  • Limited effective gene flow between two interfertile red oak species
  • 2015
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 29:4, s. 1135-1148
  • Tidskriftsartikel (refereegranskat)abstract
    • Highly elevated differentiation in different life stages between two interfertile oak species at a CONSTANS -like gene suggests a role of this gene in pre-zygotic isolation and adaptive divergence between species. Genome-wide differentiation patterns among oak species suggest that divergent selection can maintain species-specific adaptations and morphological integrity by reducing effective interspecific gene flow. While there is evidence for both pre- and post-zygotic isolation mechanisms in oaks (e.g., differences in flowering time, selection against hybrids), these mechanisms are rarely studied at each life stage from acorns to adult trees within the same forest. To assess the reproductive isolation mechanisms between two ecologically divergent species, we (1) quantified the number of hybrids in different life stages in Quercus rubra and Quercus ellipsoidalis, two interfertile red oaks with different adaptations to drought, and (2) assessed the timing of bud burst in both natural populations and in a seedling common garden trial. The low number of hybrids in all life stages suggested pre-zygotic isolation between species or selection in very early life stages that have not been sampled (e.g., early seed abortion). Significant differences in bud burst were found in two consecutive years between species in a common garden seedling trial but not in natural populations of the same provenance. In addition, we found evidence for divergent selection on several gene loci between species in each life stage. In particular, an SSR repeat located within the coding sequence of a CONSTANS-like gene, a locus involved in the photoperiodic regulation of flowering time and development, showed very high interspecific differentiation between species in all life stages (mean F (ST) = 0.83), compared to the average neutral differentiation of 3.7 %.
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7.
  • Drobyshev, Igor (författare)
  • Root connections affect radial growth of balsam poplar trees
  • 2016
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 30, s. 1775-1783
  • Tidskriftsartikel (refereegranskat)abstract
    • Connected root systems reduced the negative impact of August temperatures and insect outbreak on growth.Root connections between trees can be an ecological advantage of clonal plant species in environments with unevenly distributed resources. We investigated the effects of root connectivity in stands of balsam poplar in Quebec (Canada). We evaluated differences in growth response between groups of trees with and without root connections through climate-growth analyses, comparison of the growth dynamics, and analysis of growth response to a severe forest tent caterpillar (FTC) outbreak. Current May temperature had a positive influence on radial growth of both connected and non-connected trees. Growth of non-connected trees was negatively affected by August temperatures (r = -0.3) while connected trees did not reveal a significant relationship for that month. A mixed effect ANOVA showed a significant difference (F (1, 25) = 5.59, p = 0.02) in growth responses to FTC outbreak between connected and non-connected trees. Connected trees grew on average 16 % better than unconnected trees during the outbreak, with bootstrapped 95 % confidence range from 2.28 to 31.36 %. The study suggests a sharing of resources through root connections, affecting radial growth of connected balsam poplar trees under both average and extreme environmental conditions.
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8.
  • Duethorn, Elisabeth, et al. (författare)
  • Influence of micro-site conditions on tree-ring climate signals and trends in central and northern Sweden
  • 2013
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 27:5, s. 1395-1404
  • Tidskriftsartikel (refereegranskat)abstract
    • Tree-ring chronologies are important indicators of pre-instrumental, natural climate variability. Some of the longest chronologies are from northern Fennoscandia, where ring width measurement series from living trees are combined with series from sub-fossil trees, preserved in shallow lakes, to form millennial-length records. We here assess the recent ends of such timeseries by comparing climate signals and growth characteristics in central and northern Sweden, of (1) trees growing at lakeshore micro-sites (representing the source of sub-fossil material of supra-long chronologies), with (2) trees collected in dryer micro-sites several meters inland. Calibration trials reveal a predominating June-September temperature signal in N-Sweden and a weaker but significant May-September precipitation signal in C-Sweden. At the micro-site level, the temperature signal in N-Sweden is stronger in the lakeshore trees compared to the inland trees, whereas the precipitation signal in C-Sweden remains unchanged among the lakeshore and inland trees. Tree-rings at cambial ages > 40 years are also substantially wider in the lakeshore micro-site in C-Sweden, and juvenile rings are more variable (and wider) in the dryer micro-site in N-Sweden (compared to the adjacent micro-sites). By combining the data of the various micro-sites with relict samples spanning the past 1,000 years, we demonstrate that growth rate differences at the micro-site scale can affect the low frequency trends of millennial-length chronologies. For the supra-long chronologies from northern Fennoscandia, that are derived from sub-fossil lake material, it is recommended to combine these data with measurement series from only lakeshore trees.
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9.
  • Eklund, Leif, et al. (författare)
  • Enhanced growth and ethylene increases spiral grain formationin Picea abies and Abies balsamea trees
  • 2003
  • Ingår i: Trees. - : Springer. - 0931-1890 .- 1432-2285. ; 17:1, s. 81-86
  • Tidskriftsartikel (refereegranskat)abstract
    • Spiral grain angle in Norway spruce (Piceaabies) trees and balsam fir (Abies balsamea) seedlingswas investigated in relation to growth rate, endogenousand applied ethylene. Trees from stands of Norwayspruce, which were irrigated and fertilised in order to enhancegrowth, and trees having different growth rates innon-treated stands were studied. Stem growth rate at thestand level (m3 ha–1 year–1) was measured annually, orby means of microscopy on stem sections as the numberand size of tracheids produced. Enhanced growth increasedethylene evolution and maintained a high levelof left-handed spiral grain angle in comparison to slower-growing trees. An increased number of earlywoodtracheids in fast growing trees was correlated to a moreleft-handed spiral grain angle. Ethrel, applied to stems ofbalsam fir seedlings, increased the internal ethylene levelsin parallel with increased left-handed spiral grain angle.The results indicate that ethylene regulates the extentof spiral grain angle.
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10.
  • Eklund, Leif, et al. (författare)
  • The influence of wind on spiral grain formation in conifer trees
  • 2000
  • Ingår i: Trees. - : Springer. - 0931-1890 .- 1432-2285. ; 14, s. 324-328
  • Tidskriftsartikel (refereegranskat)abstract
    • The correlation between spiral grain formationand crown asymmetry was investigated in 18 Scots pine(Pinus sylvestris L.) and 17 Norway spruce [Picea abies(L.) Karst.] trees selected from clones of each speciesgrowing in the south of Sweden. The angle between thelongitudinal direction of the tracheids in the outermostyear ring compared to the longitudinal direction of thestem was measured by scribing lines which followed thedirection of the tracheids. The crown asymmetry wasmeasured by taking photographs of the trees followed bya simple picture analysis of the tree. Wind data for thegrowing seasons of 1997 and 1998 were obtained fromthe Swedish Meteorological and Hydrological Institute.The results showed a significant correlation between theangle of the tracheids compared to the stem longitudinaldirection going from a left-handed angle if the trees hada crown projected to the north towards a right-handedangle the more the crown projects to the south.
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11.
  • Esper, Jan, et al. (författare)
  • Site-specific climatic signals in stable isotope records from Swedish pine forests
  • 2018
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 32:3, s. 855-869
  • Tidskriftsartikel (refereegranskat)abstract
    • Pinus sylvestris tree-ring delta C-13 and delta O-18 records from locally moist sites in central and northern Sweden contain consistently stronger climate signals than their dry site counterparts. We produced twentieth century stable isotope data from Pinus sylvestris trees near lakeshores and inland sites in northern Sweden (near Kiruna) and central Sweden (near Stockholm) to evaluate the influence of changing microsite conditions on the climate sensitivity of tree-ring delta C-13 and delta O-18. The data reveal a latitudinal trend towards lower C and O isotope values near the Arctic tree line (-0.8 parts per thousand for delta C-13 and - 2.4 parts per thousand for delta O-18 relative to central Sweden) reflecting widely recognized atmospheric changes. At the microsite scale, delta C-13 decreases from the dry inland to the moist lakeshore sites (- 0.7 parts per thousand in Kiruna and - 1.2 parts per thousand in Stockholm), evidence of the importance of groundwater access to this proxy. While all isotope records from northern and central Sweden correlate significantly against temperature, precipitation, cloud cover and/or drought data, climate signals in the records from moist microsites are consistently stronger, which emphasizes the importance of site selection when producing stable isotope chronologies. Overall strongest correlations are found with summer temperature, except for delta O-18 from Stockholm correlating best with instrumental drought indices. These findings are complemented by significant positive correlations with temperature-sensitive ring width data in Kiruna, and inverse (or absent) correlations with precipitation-sensitive ring width data in Stockholm. A conclusive differentiation between leading and co-varying forcings is challenging based on only the calibration against often defective instrumental climate data, and would require an improved understanding of the physiological processes that control isotope fractionation at varying microsites and joined application of forward modelling.
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12.
  • Fuentes, Mauricio, et al. (författare)
  • Assessing the dendroclimatic potential of Nothofagus betuloides (Magellan's beech) forests in the southernmost Chilean Patagonia
  • 2019
  • Ingår i: Trees-Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890. ; 33:2, s. 557-575
  • Tidskriftsartikel (refereegranskat)abstract
    • Key messageTree growth of Nothofagus betuloides forests south of 50 degrees S is affected by local temperature and precipitation together with large-scale high-latitude climate patterns, but also significant influences from the Tropical Pacific were found.The characterization of past climate dynamics in southern South America is difficult due to the shortness of instrumental data. However, abundant forests in the southernmost part of the continent makes it an ideal place to assess the dendroclimatological potential for developing high-resolution climate proxy time series to extend the observations back in time. Whereas the majority of dendroclimatological studies have focused on latitudes north of 50 degrees S, we present six new Magellan's beech (Nothofagus betuloides (Mirb.) Oerst.) tree-ring width (TRW) chronologies, spanning between 202 and 500years, developed from southernmost Patagonia (>50 degrees S), Chile. The climate signal in the trees was analyzed using local station data, regional sea surface temperature (SST) and large-scale atmospheric indices: the Southern Oscillation Index (SOI) and the southern annual mode (SAM). The correlations between individual site chronologies and observed summer temperatures and precipitation varied, reflecting diverse microsite conditions and local scale geographic patterns. An influence of southern Pacific SST was evident at two of the northern sites. Although the associations with SOI and SAM were weak, the influence of regional sea level pressure on tree growth in the region was evident.
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13.
  • Ghasemkhani, Marjan, et al. (författare)
  • Real-time PCR for detection and quantification, and histological characterization of Neonectria ditissima in apple trees
  • 2016
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 30, s. 1111-1125
  • Tidskriftsartikel (refereegranskat)abstract
    • Neonectria ditissima, the causal pathogen of fruit tree canker, is a sordariomycete fungus that affects apple orchards, especially in north-western Europe. To prevent serious disease epidemics, an accurate, rapid, and sensitive method for detection of N. ditissima is needed for pathogen identification. A quantitative real-time PCR (qPCR) assay was developed for both detection and quantification of this pathogen in infected apple cultivars. Several primer sets were designed from regions of the β-tubulin gene. One primer set passed several validation tests, and the melting curve confirmed species-specific amplification of the correct product. In addition, the N. ditissima biomass could be detected at variable amounts in samples from the infection sites of six different cultivars, with ‘Aroma' having the lowest amount of N. ditissima biomass and ‘Elise' the highest. To complement the qPCR results, tissue from detached shoots and 1-year-old trees of ‘Cox's Orange Pippin' (susceptible) and ‘Santana' (partially resistant) was used in a histopathology study. In both detached shoots and trees, fungal hyphae were found in cells of all tissues. No qualitative differences in the anatomy of the infected samples were observed between the cultivars. In the detached shoot experiment, both cultivars were affected but differences in the rate of disease progression suggest that the partially resistant cultivar could resist the fungus longer. The qPCR assay developed in our study produced reproducible results and can be used for detection of N. ditissima in infected trees.
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14.
  • Greaves, Ciara, et al. (författare)
  • Remarkably high blue ring occurrence in Estonian Scots pines in 1976 reveals wood anatomical evidence of extreme autumnal cooling
  • 2023
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 37:2, s. 511-522
  • Tidskriftsartikel (refereegranskat)abstract
    • ‘Blue rings’ (BRs) are visual indicators of less lignified cell walls typically formed towards the end of a tree’s growing season. Though BRs have been associated with ephemeral surface cooling, often following large volcanic eruptions, the intensity of cold spells necessary to produce BRs, as well as the consistency of their formation within and between trees still remains uncertain. Here, we report an exceptionally high BR occurrence within and between Scots pine (Pinus sylvestris L.) trees at two sites in Estonia, including the first published whole-stem analysis for BRs. Daily meteorological measurements from a nearby station allowed us to investigate the role temperature has played in BR formation since the beginning of the twentieth century. The single year in which BRs were consistently formed within and amongst most trees was 1976. While the summer of 1976 is well known for an exceptional heatwave in Northwest Europe, mean September and October temperatures were remarkably low over Eastern Europe, and 3.8 °C below the 1961–1990 mean at our sites. Our findings contribute to a better eco-physiological interpretation of BRs, and further demonstrate their ability to reveal ephemeral cooling not captured by dendrochronological ring width and latewood density measurements. 
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15.
  • Göransson, Hans, et al. (författare)
  • Nutrient acquisition from different soil depths by pedunculate oak
  • 2006
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 1432-2285 .- 0931-1890. ; 20:3, s. 292-298
  • Tidskriftsartikel (refereegranskat)abstract
    • Eight oak trees (Quercus robur L.) received P-32 at a soil depth of 50 cm and P-33 at a soil depth of 15 cm at the end of June 2002 through plastic tubes inserted into the mineral soil. The phosphorus uptake from different soil depths was estimated by analysing the concentration of P-32 and P-33 in the foliage of oak growing in a mixed stand in southern Sweden. P-32 and P-33 were recovered in the leaves/needles after 21 and 39 days. The recovery of labelled P in oak was higher from 15 cm soil depth than from 50 cm, however, more than 4% of the total amount of labelled P was taken up from 50 cm. This indicates that oak can utilize deep soil layers for nutrient uptake. A study on the uptake of Cs (as an analogue to K) and N-15 into the leaves was performed on the same trees and detectable amounts of N-15 and Cs were recovered in leaves and buds. This indicates that N-15 and Cs can be used to study nutrient uptake of mature trees from the mineral soil.
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16.
  • Hagen-Thorn, Anna, et al. (författare)
  • Micronutrient levels in some temperate European tree species: a comparative field study
  • 2005
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 1432-2285 .- 0931-1890. ; 19:5, s. 572-579
  • Tidskriftsartikel (refereegranskat)abstract
    • Micronutrient concentrations in foliage and stemwood (including bark) of six European tree species (Betula pendula Roth., Quercus robur L., Fraxinus excelsior L., Fagus sylvatica L., Tilia cordata Mill. and Picea abies (L.) Karst.) planted on the same type of soil at six sites in three different countries were studied. Micronutrient concentrations in foliage were considerably higher than in stemwood for all elements and species studied, except for Fe in spruce. Interspecies comparisons revealed significant differences in concentrations both in foliar and stemwood biomass, as well as in stemwood:foliage nutrient ratios. Lime foliage showed a considerably higher concentration of B than all other species, while the stemwood concentration of this element was highest in ash. Mn concentration in both foliar and stemwood biomass of ash was extremely low compared with concentrations in other species. Birch stemwood showed nearly double the level of Zn in other species at all sites. Zn concentrations in the birch foliage were also higher than in other species, with the exception of the Lithuanian sites, which showed lower EDTA-extractable Zn concentrations in the soils. The concentration of Cu was lowest in spruce foliage, while Cu concentrations in stemwood were similar in all species. It was concluded that species-related differences in microelement nutrition must be taken into account when evaluating the nutrient status of common European forest tree species, and when using them as bio-indicators of the effects of environmental pollution.
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17.
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18.
  • Hjelm, Ulrika, et al. (författare)
  • Photosynthetic responses to short-term and long-term light variation in Pinus sylvestris and Salix dasyclados
  • 2004
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 18, s. 622-629
  • Tidskriftsartikel (refereegranskat)abstract
    • Trees-Structure and Function: 2004 18:622-629 Pinus sylvestris and Salix dasyclados, which differ in leaf longevity, were compared with respect to four aspects of photosynthetic light use and response: high light acclimation, photoinhibition resistance and recovery, lightfleck exposure and use and chloroplast acclimation across leaves. The first two aspects were examined using seedlings under controlled conditions and the other two were tested using trees in the field. When exposed to high light, shade leaves of Pinus acclimated completely, achieving the same photosynthetic capacities as sun leaves, whereas shade leaves of Salix did not reach sun leaf capacities although the absolute magnitude of their acclimation was larger. Shade leaves of Pinus were also more resistant to photoinhibition than those of Salix. Much of the direct light supplied within the canopy was in the form of rapid fluctuations, lightflecks, for Pinus and Salix alike. They exploited short lightflecks with similar efficiency. The greater proportion of diffuse light in the canopy for Pinus than Salix seems to lead to a lesser degree of differential intra-leaf acclimation of chloroplasts, in turn leading to lower efficiency of photosynthesis under unilateral light as reflected by a lower convexity, rate of bending, of the light-response curve. The differences in light use and responses are discussed in relation to possible differences in characteristics of the long and short-lived leaf.
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19.
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20.
  • Jönsson, Anna Maria, et al. (författare)
  • Frost hardiness in bark and needles of Norway spruce in southern Sweden
  • 2001
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 1432-2285 .- 0931-1890. ; 15:3, s. 171-176
  • Tidskriftsartikel (refereegranskat)abstract
    • Bark necrosis and resin flows in Norway spruce have increased in southern Sweden over the last few decades. Frost damage late in spring has been suggested as a possible cause, but other factors besides the climate may have contributed to the damage. The nutrient status influences the hardening processes and plants with poor nutritional conditions have an increased sensitivity to frost. In this study the sensitivity to frost of bark and the hardiness status of needles of Norway spruce were compared with the nutrient status at two sites with different soil fertility. The trees were 30-40 years old. The hardiness status of the bark and needles was negatively affected by low concentrations of P and Mg.
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21.
  • Kim, Jongsik, et al. (författare)
  • Heterogeneous distribution of pectin and hemicellulose epitopes in the phloem of four hardwood species
  • 2018
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 32, s. 393-414
  • Tidskriftsartikel (refereegranskat)abstract
    • Distributional patterns of pectin and hemicellulose epitopes in the phloem of four hardwoods vary between cell types including sieve tube elements, companion cells, parenchyma and sclerenchyma and between tree species.Using immunolocalization methods combined with monoclonal antibodies, the distribution of pectin and hemicellulose epitopes was examined in the secondary phloem of two diffuse porous (birch, aspen)- and two ring porous (oak, ash) hardwoods with a focus on sieve tube elements (SEs), companion cells (CCs), axial/ray parenchyma cells, and sclerenchyma cells (sclereids and phloem fibers). In all tree species, rhamnogalacturonan-I (RG-I), homogalacturonan (HG), and xyloglucan epitopes were common in cell walls of SEs, CCs, and axial/ray parenchyma cells. However, the amount of these epitopes varied greatly between cell types and between hardwood species. Apart from aspen, heteroxylan or/and heteromannan epitopes were detected in SEs, but were not detected in CCs and parenchyma cells. With sclerenchyma cells, RG-I, HG, and xyloglucan epitopes were common in compound middle lamellae (CML) of sclereids and phloem fibers. Except for oak, heteromannan epitopes were also detected in CML of sclereids. Distributional patterns of epitopes in CML of birch and ash sclereids varied greatly depending on anatomical structure of CML. Secondary cell walls of sclereids and phloem fibers revealed abundant heteroxylan epitopes, but showed no heteromannan epitopes. Some phloem fibers also showed sparse xyloglucan epitopes in secondary cell walls. Together, results suggest that there are great variations in distributional patterns of pectin and hemicellulose epitopes in hardwood phloem between cell types and between tree species.
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22.
  • Kim, Jongsik, et al. (författare)
  • Immunolocalization of pectin and hemicellulose epitopes in the phloem of Norway spruce and Scots pine
  • 2017
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 31, s. 1335-1353
  • Tidskriftsartikel (refereegranskat)abstract
    • Although there is considerable information on the gross chemistry of conifer bark, little is known on the chemistry of secondary phloem at the individual cell level. This study investigated distribution of pectins and hemicelluloses in the phloem of two conifer species (Norway spruce and Scots pine) at an individual cell wall level using nine monoclonal antibodies specific for pectin and hemicellulose epitopes combined with immunofluorescence and TEM immunogold labeling. Differences in phloem cell wall chemistry between juvenile (seedlings) and mature conifer trees were also examined. The two conifer species showed qualitatively similar distribution patterns of epitopes in sieve- and (axial/ray) parenchyma cells, irrespective of seedlings and mature trees. Sieve- and parenchyma cell walls showed the presence of rhamnogalacturonan-I (RG-I), homogalacturonan (HG) and xyloglucan epitopes, but revealed the absence of heteroxylan epitopes. Heteromannan epitopes were only detected in sieve cell walls, showing a chemical difference between sieve- and parenchyma cells. In contrast to qualitative similarity, there were several quantitative differences of epitope localization in sieve- and parenchyma cells between the two conifer species, indicating variations in the chemical structure and/or the amount of pectins and hemicelluloses between the two conifer species. These differences were more significant in seedlings than mature trees. Immunogold labeling of Norway spruce seedlings further indicated the possibility of chemical variations between cell wall regions within a single sieve cell wall. Phloem stone cells detected in mature Norway spruce showed the presence of heteromannans/heteroxylans and RG-I/HG/xyloglucans in secondary cell wall and middle lamellae, respectively.
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23.
  • Kännaste, Astrid, et al. (författare)
  • Odors of Norway spruce (Picea abies L.) seedlings : differences due to age and chemotype
  • 2013
  • Ingår i: Trees. - : Springer. - 0931-1890 .- 1432-2285. ; 27, s. 149-159
  • Tidskriftsartikel (refereegranskat)abstract
    • Small conifer seedlings (mini-seedlings) are less damaged by the large pine weevil Hylobius abietis (L.) (Coleoptera: Curculionidae) compared to conventional seedlings. Chemical difference between the seedling types is one possible explanation for this phenomenon. In the present paper, the emissions of volatile organic compounds (VOC) of 7- to 43-week-old Norway spruce [Picea abies (L.) Karst.] seedlings were analyzed. Collection and identification of the volatiles was made by solid phase micro-extraction and gas chromatography mass spectrometry (SPME–GC–MS). The enantiomers of α-pinene and limonene were separated in a two-dimensional GC (2D-GC). Most of the seedlings represented either a limonene- or a bornyl acetate-chemotype. Only minor changes in the volatile composition of the two types of seedlings were found during the first year. Age-related changes, however, were found in the volatiles released by wounded phloem where green leaf volatiles (GLVs) and borneol were the dominated VOC for young seedling. The attractive compound for the pine weevil, α-pinene, was first detected in the phloem emissions of 18- to 22-week-old seedlings. Different storage conditions of the seedlings during the winter/early spring-phase influenced the volatile composition in the phloem. High amount of GLVs was characteristic for the 43-week-old seedlings stored in naturally changing outdoor temperature, but not present in the seedlings winter-stored at a constant temperature of −4 °C. The possible role of these observed differences in odor emissions between seedlings of different age and physiological status for the feeding preferences of the large pine weevil is discussed.
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24.
  • Lagergren, Fredrik, et al. (författare)
  • Time shift between net and gross CO2 uptake and growth derived from tree rings in pine and spruce
  • 2019
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890. ; 3:33, s. 765-776
  • Tidskriftsartikel (refereegranskat)abstract
    • Key message: A 6–9 month backward time shift of the carbon uptake gave the highest correlation between annual biomass increment and carbon uptake in this old even aged forest. Abstract: Plants’ carbon uptake and allocation to different biomass compartments is an important process for both wood production and climate mitigation. Measurements of the net ecosystem carbon dioxide exchange between ecosystems and the atmosphere provide insights into the processes of photosynthesis, respiration and accumulation of carbon over time, and the increase in woody biomass can be assessed by allometric functions based on stem diameter measurements. The fraction of carbon allocated to radial stem growth varies over time, and a lag between carbon uptake and growth can be expected. The dynamics of non-structural carbohydrates and autotrophic and heterotrophic respiration are key mechanisms for understanding this lag effect. In this study, a 9-year record of carbon flux and tree-ring data from Norunda, Sweden was used to investigate the relationship between net and gross carbon uptake and carbon allocated to growth. The flux data were aggregated to monthly sums. When full 12-month periods of accumulated carbon exchange were successively shifted backwards in time, the highest correlation was found with a 6–9 month shift, showing that a large part of the previous growing season was important for explaining the biomass increment of the following year.
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25.
  • Lai, Huayan, et al. (författare)
  • Does phosphorus deficiency induce formation of root cortical aerenchyma maintaining growth of Cunninghamia lanceolata?
  • 2018
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 32, s. 1633-1642
  • Tidskriftsartikel (refereegranskat)abstract
    • Key messagePhosphorous (P) deficiency induces root cortical aerenchyma (RCA) formation in Chinese fir seedlings with marked genotypic variation, and the adaptive role of RCA is mainly related to root P reduction.AbstractRoot cortical aerenchyma (RCA) formation in response to phosphorus (P) deficiency and its adaptive role are largely unexplored in trees. We hypothesized that RCA formation in response to P deficiency varies with its severity and genotype, and that P-stressed seedlings maintain similar seedling growth to non-stressed seedlings by reducing the P requirements of roots and metabolic cost of soil exploration. Seedlings of two half-sib families (nos. 25 and 36) of Cunninghamia lanceolata (Chinese fir) were grown in pots with three levels of P supply for 3months. Significant differences in RCA formation in 40-45mm root segments from the root tip were observed between families and P supply levels. Severe P deficiency induced more RCA formation in family no. 36 than in family no. 25, whereas moderate P deficiency induced RCA formation in family no. 36 only. Family no. 36 had significantly higher height increment, needle biomass, and P concentration in stems and needles, but lower root biomass and root P concentration, than family 25. A significantly negative relationship was found between RCA and root P concentration, increments in average root diameter, and root surface area, whereas significantly positive correlations were observed between some root morphological traits and biomass and P concentration in the organs of P-stressed seedlings of family 36. In conclusion, severe P deficiency induces formation of RCA in Chinese fir seedlings with marked genotypic variation, and the adaptive role of RCA formation during P deficiency is mainly related to the reduction of root P concentration.
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26.
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27.
  • Malmqvist, Cecilia, 1965-, et al. (författare)
  • Differences in bud burst timing and bud freezing tolerance among interior and coastal seed sources of Douglas fir
  • 2017
  • Ingår i: Trees. - : Springer. - 0931-1890 .- 1432-2285. ; 31:6, s. 1987-1998
  • Tidskriftsartikel (refereegranskat)abstract
    • The need for species that will grow well through ongoing climate change has increased the interest in Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] in Sweden. One of the most common problems seen in plantations of Douglas fir seedlings is damage caused by late spring frost, known to be highly correlated with the timing of bud burst. The objective of this study was to investigate spring-related bud development under Nordic conditions of seven Douglas fir provenances and to compare data with a local provenance of Norway spruce (Picea abies (L.) Karst). Results from a field trial and a greenhouse-based study were compared. The interior Douglas fir provenances exhibited an earlier bud burst than coastal provenances, both in the greenhouse and in the field trial. When comparing differences within the groups of interior and coastal Douglas fir provenances, no differences could be found. The local Norway spruce, only grown in the greenhouse, showed an intermediate bud development profile similar to the interior Douglas fir provenance Three Valley. We therefore suggest that Three Valley could be planted at the same locations as the investigated local provenance of Norway spruce in mid-Sweden. To avoid spring frost damage the Douglas fir seedlings need to be frozen stored and planted late in spring. Planting under shelterwood can also help protect the seedlings from spring frost damages. As similar results for bud development patterns of Douglas fir and Norway spruce provenances were obtained from the greenhouse and field trials, greenhouse tests could facilitate selection of provenances.
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28.
  • Marshall, John (författare)
  • Thermal imaging of increment cores: a new method to estimate sapwood depth in trees
  • 2023
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 37, s. 349-359
  • Tidskriftsartikel (refereegranskat)abstract
    • The cells in tree sapwood form a network of interconnected conduits which enables the transport of water and nutrients from the tree roots to the canopy. Sapwood depth must be assessed when tree water use is estimated from sap flow velocities. However, current approaches to assess sapwood depth are either not applicable universally, or require expensive instruments, the application of chemicals or laborious field efforts. Here, we present a new method, which estimates sapwood depth by thermal imaging of increment cores. Using a low-cost thermal camera for mobile devices, we show that the sapwood-heartwood boundary is detectable by a sharp increase in temperature. Estimated sapwood depths agree with dye estimates (R-2 = 0.84). We tested our approach on a broad range of temperate and tropical tree species: Quercus robur, Pinus sylvestris, Swietenia macrophylla, Guazuma ulmifolia, Hymenaea courbaril, Sideroxylon capiri and Astronium graveolens. In nearly all species, the methods agreed within 0.6 cm. Thermal imaging of increment cores provides a straightforward, low-cost, easy-to-use, and species-independent tool to identify sapwood depth. It has further potential to reveal radial differences in sapwood conductivity, to improve water balance estimations on larger scales and to quickly develop allometric relationships.
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29.
  • Marshall, John (författare)
  • Tree-ring isotopic composition reveals intraspecific variation in water use efficiency of Ait. provenances grown in common gardens
  • 2023
  • Ingår i: Trees - Structure and Function. - 0931-1890 .- 1432-2285. ; 37, s. 1767-1780
  • Tidskriftsartikel (refereegranskat)abstract
    • Given the impacts of climate change on forest resources and considering the slowness of evolutionary processes in trees, a need arises to understand the interplay between tree species adaptation to climate, genetic variation, and their impact on tree growth and productivity. Broadening knowledge of the capacity of tree populations to respond to climate-related disturbances is a prerequisite for the development of resilience strategies, including assisted migration and climate-smart forestry. This study tests the physiological ability of different maritime pine provenances, comparing Mediterranean (Corsica, Sardinia, and Tuscany) and Atlantic (Portugal) provenances, to adapt to progressively drier conditions that have occurred in the last thirty years. Four provenance trials with randomized blocks of the five maritime pine provenances were used as test sites in Sardinia (Italy). Wood cores were collected from the 40-year-old plants. Cores were split into five-year segments to determine provenance-related variations in carbon and oxygen stable isotopes and provide information on long-term patterns in intrinsic water use efficiency (iWUE). The provenance x site interaction was the most important source of variation, meaning that the genotypes responded differently to the planting sites. Considering the main effects, both genotype and environmental conditions at the planting sites influenced stable isotope composition in tree rings. This suggests that iWUE was determined by phenotypic plasticity that differed among genotypes. In contrast, provenance responses were stable with time, and the provenance x site interaction was stable across time periods. These findings suggest that provenance selection to improve iWUE in maritime pine may need to consider site conditions but point more to soil conditions than to climate. In any case, they limit our ability to recommend maritime pine provenances based on iWUE until the missing site factors can be identified.
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30.
  • Nybom, Hilde, et al. (författare)
  • Assessment of fire blight tolerance in apple based on plant inoculations with Erwinia amylovora and DNA markers
  • 2012
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 26, s. 199-213
  • Tidskriftsartikel (refereegranskat)abstract
    • Fire blight (Erwinia amylovora) causes serious damage to pome fruit orchards, and identification of germplasm with heritable disease resistance is therefore crucial. Two dominant SCAR (sequence characterised amplified region) marker alleles (AE10-375 and GE-8019), flanking a previously identified QTL (quantitative trait locus) for resistance to fire blight on ‘Fiesta’ linkage group 7 in apple cultivars related to ‘Cox’s Orange Pippin’, were screened on 205 apple cultivars. Both marker alleles were present in 22% of the cultivars, indicating presence of the QTL allele for tolerance, and both were lacking in 25%, indicating homozygosity for absence of the QTL tolerance allele. However, 33% had only the marker allele AE10-375, while 20% had only GE-8019, suggesting that some cultivars with the dominant alleles for both of the flanking markers can carry these on separate chromosomes and may lack the QTL allele for tolerance. In 2009 and 2010, terminal shoots of greenhouse-grown grafted trees of 21 cultivars (only 20 in 2010) were inoculated with Erwinia amylovora. ‘Idared’ (susceptible) and ‘Enterprise’ (tolerant) were included as controls. Disease severity for each cultivar was expressed as percentage of necrosis in relation to entire length of shoot, and the ranking of cultivars in 2009 and 2010 was compared with a Spearman rank correlation test,P<0.01. A relationship between presence of both flanking marker alleles for tolerance and level of fire blight tolerance was confirmed with a Mann–Whitney U-test,P<0.01 in 2009, andP<0.05 in 2010. A PCO (principal coordinate) analysis based on band profiles obtained with 12 SSR (simple sequence repeat) loci produced three loose clusters, two of which contained known offspring of ‘Cox’s Orange Pippin’, and one with cultivars that were either unrelated or had an unknown origin. Cases where DNA markers did not predict level of fire blight damage as expected, were, however, as common among descendants of ‘Cox’s Orange Pippin’ as among apparently unrelated cultivars. Obviously the ‘Fiesta’ LG 7 QTL has some predictive value, both for known ‘Cox’ relatives and others, but more efficient markers would be desirable for marker-assisted selection.
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31.
  • Nybom, Hilde, et al. (författare)
  • European pome fruit genetic resources evaluated for disease resistance
  • 2012
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 26, s. 179-189
  • Forskningsöversikt (refereegranskat)abstract
    • Pome fruit genetic resources collections constitute a highly valuable resource not only for fruit breeding but also for direct use by nurseries, growers, and home gardeners. In order to use these resources efficiently and sustainably, reliable evaluation data on fruit and tree characteristics must be generated. Here we focus on pome fruit genetic resources evaluated phenotypically and genotypically for susceptibility to apple scab (Venturiainaequalis), powdery mildew (Podosphaeraleucotricha), fire blight (Erwiniaamylovora), pear rust (Gymnosporangiumsabinae) and storage diseases (e.g.,Penicilliumexpansum). Examples are presented of several ongoing projects throughout Europe, with the aim to evaluate fruit genetic resources for disease susceptibility and potential use in breeding and for commercial use. The COST action 864 has fostered international cooperation in the evaluation of pome fruit genetic resources, and some of these evaluations therefore involve research groups from several of the participating countries.
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32.
  • Ogana, Friday Nwabueze (författare)
  • Vessel characterization and ring-width of a multipurpose agroforestry tree species (Garcinia kola.(Heckel)) and its relationship with climate in Nigeria
  • 2024
  • Ingår i: Trees - Structure and Function. - 0931-1890 .- 1432-2285. ; 38, s. 139-150
  • Tidskriftsartikel (refereegranskat)abstract
    • Tropical agroforestry species are characterized by irregular growth and fruiting pattern, this is because of seasonal differences in the region and unanticipated environmental changes. Tree-ring width features and vessel variables could have a direct relationship with environmental conditions and factors such as precipitation and temperature could impact the growth of the species. This is because, during stressful environmental conditions, tree species record environmental changes through their physiological adjustment. Therefore, wood anatomical and tree-ring width time series was developed for Garcinia kola, a multipurpose tropical species, from a humid forest zone and derived savannah, along two vegetation zones in Nigeria. The species forms rings characterized by marginal parenchyma. The mean tree-ring width (TRW) ranges from 2.63 and 2.30 mm in the humid forest zone and derived savannah, respectively while the vessel number (VN) and vessel density (VD) are 95, 93, and 9.46, and 10.28 N/mm(2) respectively. The results revealed that the radial growth of G. kola showed a positive relationship with the precipitation and the minimum temperature during the peak of the rainy season in derived savannah areas. The VN, RW, and TVA show a significant relationship with the mean annual maximum temperature in the Rainforest and derived savannah area. The vessels are more abundant in samples from the rainforest area than in the derived savannah area, the results revealed that the wood anatomical variables and TRW were sensitive to climatic variables. Hence, they could be good indicators for evaluating tropical tree responses to environmental changes in tropical agroforestry species.
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33.
  • Ormarsson, Sigurdur, et al. (författare)
  • Numerical study of how creep and progressive stiffening affect the growth stress formation in trees
  • 2010
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 1432-2285 .- 0931-1890. ; 24:1, s. 105-115
  • Tidskriftsartikel (refereegranskat)abstract
    • It is not fully understood how much growth stresses affect the final quality of solid timber products in terms of, e.g. shape stability. It is, for example, difficult to predict the internal growth stress field within the tree stem. Growth stresses are progressively generated during the tree growth and they are highly influenced by climate, biologic and material-related factors. To increase the knowledge of the stress formation, a finite element model was created to study how the growth stresses develop during the tree growth. The model is an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The material model used is based on the theory of small strains (where strains refer to the undeformed configuration which is good approximation for strains less than 4%) where so-called biological maturation strains (growth-related strains that form in the wood fibres during their maturation) are used as a driver for the stress generation. It is formulated as an incremental material model that takes into account elastic strain, maturation strain, viscoelastic strain and progressive stiffening of the wood material. The results clearly show how the growth stresses are progressively generated during the tree growth. The inner core becomes more and more compressed, whereas the outer sapwood is subjected to slightly increased tension. The parametric study shows that the growth stresses are highly influenced by the creep behaviour and evolution of parameters such as modulus of elasticity, micro-fibril angle and maturation strain.
  •  
34.
  • Ormarsson, Sigurdur, et al. (författare)
  • Numerical study of how creep and stiffness evolution affect the growth stress formation in trees
  • 2010
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 24:1, s. 105-115
  • Tidskriftsartikel (refereegranskat)abstract
    • It is not fully understood how much growth stresses affect the final quality of solid timber products in terms of e.g. shape stability. It is for example difficult to predict the internal growth stress field within the tree stem. Growth stresses are progressively generated during the tree growth and they are highly influenced by climate, biologic and material related factors. To increase the knowledge of the stress formation a finite element model was created to study how the growth stresses develop during the tree growth. The model is an axisymmetric general plane strain model where material for all new annual rings is progressively added to the tree during the analysis. The material model used is based on the theory of small strains (where strains refer to the undeformed configuration which is good approximation for strains less than 4%) where so-called biological maturation strains (growth-related strains that form in the wood fibres during their maturation) are used as a driver for the stress generation. It is formulated as an incremental material model that takes into account elastic strain, maturation strain, viscoelastic strain and progressive stiffening of the wood material. The results clearly show how the growth stresses are progressively generated during the tree growth. The inner core becomes more and more compressed whereas the outer sapwood is subjected to slightly increased tension. The parametric study shows that the growth stresses are highly influenced by the creep behaviour and evolution of parameters such as modulus of elasticity, micro fibril angle and maturation strain.
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35.
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36.
  • Ramesh, Vetukuri (författare)
  • Exogenous melatonin-stimulated transcriptomic alterations of Davidia involucrata seedlings under drought stress
  • 2021
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285.
  • Tidskriftsartikel (refereegranskat)abstract
    • Key message This study shows mitigating effects achieved by exogenously applied melatonin in drought-stressed Davidia involucrata seedlings and demonstrates the reprogramming of gene networks related to melatonin-mediated drought stress response. Drought stress can have adverse effects on endangered plant species such as the dove tree (Davidia involucrata Baill.). Despite significant advances in uncovering the roles of melatonin in abiotic stress tolerance, the function of melatonin in the dove tree during drought stress is unknown. Here, we show the effects of exogenously applied melatonin on drought damage to D. involucrata seedlings. Melatonin pretreatment of dove tree seedlings was correlated with reduced membrane lipid peroxidation, suppressed production of drought-induced reactive oxygen species (ROS), and improved antioxidant capacity. Comparative RNA-Seq-based transcriptome profiling was employed to dissect the mechanistic basis of melatonin in drought response. We found that melatonin pretreatment resulted in differential expression of 2737 genes (1849 up-regulated and 888 down-regulated) under drought stress. Further detailed analysis suggested that melatonin modulates D. involucrata response to drought through fine-tuning of multiple phytohormone signaling and synthesis pathways, including transcriptional stimulation of auxin signaling-related genes and brassinosteroid biosynthetic genes. Moreover, phenylpropanoid biosynthesis and glutathione metabolism pathways were activated by melatonin, which could be linked to the observed enhancement of ROS scavenging capacity in melatonin-pretreated D. involucrata seedlings under drought condition. Additionally, melatonin-mediated drought stress response may involve activation of calcium signaling via up-regulating gene expressions of CNGC, CaM/CML, and CDPK family members. Collectively, this study yields insights into transcriptionally regulatory mechanisms of melatonin action under drought stress and provides a potential strategy for ex situ cultivation and landscape application of endangered ornamental tree species particularly in the context of global climate change.
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37.
  • Redondo, Miguel Angel (författare)
  • Histology of Quercus ilex roots during infection by Phytophthora cinnamomi
  • 2015
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 29, s. 1943-1957
  • Tidskriftsartikel (refereegranskat)abstract
    • The speed of infection of Quercus ilex by Phytophthora cinnamomi is influenced by the method of inoculation used, and structural changes in the host do not differ depending on whether primary or secondary roots are infected.This study aimed to elucidate the infection process of the invasive pathogen Phytophthora cinnamomi on primary and secondary roots of 2-month-old Quercus ilex seedlings. To test if different methods of inoculation lead to different changes in the host caused by the pathogen, the root system of plants was either immersed into a suspension of P. cinnamomi zoospores, or placed in direct contact with agar plugs colonized by P. cinnamomi mycelium. Histology of root sections obtained every 24 h for 10 days revealed similar changes in the structure of cells and tissues of the host irrespective of the inoculation method used. However, the immersion method resulted in a delay in the colonization of the host, different aerial symptoms, and the formation of different reproductive structures of the pathogen. Emerging secondary and tertiary roots and sites where secondary or tertiary roots were about to emerge were identified as main entry points. Hyphae in the xylem tissues were more frequently found in secondary than in primary roots, but in both types of roots the phloem was the most important pathway of colonization. For the first time in the interaction between Q. ilex and P. cinnamomi, transmission electron microscopy was used to describe degradation of the host cell walls, pit penetration and extrahaustorial matrix. Haustoria development during intracellular growth and hyphal aggregations (stromata) caused no damage to the host cell walls indicating hemibiotrophic parasitism.
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38.
  • Reinap, Ausra, et al. (författare)
  • Oak leaves as aerosol collectors: relationships with wind velocity and particle size distribution. Experimental results and their implications
  • 2009
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 23:6, s. 1263-1274
  • Tidskriftsartikel (refereegranskat)abstract
    • Advancing the understanding of the aerosol-capture efficiencies of forest components such as leaves and needles, and of the mechanisms that underpin these efficiencies, is essential to the many related issues of forest turnover of nutrients and pollutants. For idealized collectors (such as artificial plates or cylinders) aerosol-mechanics offers a means for calculating capture efficiencies. For living collectors, in particular deciduous leaves, experimental investigations become necessary to assist in formulating the sub-models of capture efficiency that are fundamental to the modelling of fluxes of aerosol-borne substances to forests. We here present wind-tunnel based methods and results for leaves of Quercus robur L. exposed to an aerosol whose mass versus aerodynamic particle size distribution is characterised by a geometric mean aerodynamic particle diameter around 1.2 mu m and a geometric standard deviation around 1.8. With respect to that distribution, and founded on a specially designed leaf wash-off method, we obtained average oak-leaf capture efficiencies ranging from 0.006% of the approaching aerosol mass flux at wind-speed 2 ms(-1) to 0.012% of the flux at wind-speeds 10 ms(-1), respectively. These values can be translated into deposition velocities (V (d) ) for a leaf ensemble with a given leaf area index (LAI). With LAI in the range 2-5 (commonly found in the field) and for wind-speeds 2, 5 and 10 ms(-1), resulting V (d) -values would be 0.02-0.05, 0.05-0.13, and 0.2-0.6 cm/s, respectively. To the extent comparisons are possible, our capture efficiency values are at the low end of the range of values reported by other researchers. The strong wind-speed sensitivity of V (d) has implications for the deposition of aerosol-borne substances to forests for which wind regimes may shift as a result of climatic and land-use changes.
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39.
  • Rocha, Eva, et al. (författare)
  • Assessing urban climate effects on Pinus sylvestris with point dendrometers : a case study from Stockholm, Sweden
  • 2023
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 37:1, s. 31-40
  • Tidskriftsartikel (refereegranskat)abstract
    • Changes in surface properties of the urban environments significantly impact the local microclimate. While urban trees are known for providing important thermal regulation, the impact of urban climate on tree growth remains relatively unexplored. The present study focuses on the climate response and growth dynamics of urban Scots pine trees (P. sylvestris) in comparison to their rural counterparts. High-resolution monitoring of stem-radius variations using automatic point dendrometers was performed during the growing seasons (April–October) of 2017 and 2018 in Stockholm, Sweden. In 2018, the region experienced a severe and long-lasting summer drought. In May and July, temperatures were up to 5 °C higher relative to the reference period (1981–2010), and precipitation sums were below the reference period for the entire growing season. Our results show that the urban climate primarily impacts the daily water storage dynamics by decreasing the radius change amplitudes and delaying the time of maximum stem-water replenishment and depletion. Under standard climatic conditions, the warmer climate (1.3 °C) at the urban sites had a positive impact on radial growth increment. Drought periods significantly impact the climate–growth relationships. Stem shrinkage intensifies during the day, and lower growth rates were registered, resulting in reduced annual growth. The high-resolution monitoring provided valuable insights into daily and seasonal patterns of Scots pine stem-radius variations, showing that growth responses to increasing temperature are mainly controlled by moisture availability and site-specific conditions. 
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40.
  • Seim, Andrea, et al. (författare)
  • Dendroclimatological potential of three juniper species from the Turkestan range, northwestern Pamir-Alay Mountains, Uzbekistan
  • 2016
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 30:3, s. 733-748
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a detailed dendroclimatological study of three juniper species, Juniperus seravschanica Kom., Juniperus semiglobosa Regel and Juniperus turkistanica Kom., sampled at six sites of different elevation (2100–2700 m a.s.l.), exposition (west and south) and steepness (10°–30°) in the Zaamin National Park, Turkestan range, Pamir-Alay mountain system in eastern Uzbekistan. Simple correlation statistics and redundancy analyses were applied to detect species- and site-specific climate responses during the twentieth century, which were additionally investigated in the high-frequency domain by identifying extreme growth years. Our results show that tree-ring formation of J. seravschanica at our low-elevation site is strongly limited by April to September drought conditions, while J. semiglobosa inherits a weak and variable climate response with respect to elevation. J. turkistanica growth at high altitudes is positively associated with warm spring and summer temperatures. Species-specific growth extremes are triggered by incoming air masses from the Atlantic and Arctic, highlighting the connection of synoptic climate regimes across Eurasia. From a dendroclimatic perspective, J. seravschanica exhibits a high potential for reconstructing past drought and pluvials, but under sustained temperature rise also J. semiglobosa will likely increase its sensitivity to drought. Moreover, J. turkistanica at its distribution limit at the tree line is a suitable proxy of summer temperature. Our findings clearly demonstrate that a careful selection of the site, overall topography and elevation as well as the different juniper species are important for successfully reconstructing past climate in Uzbekistan.
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41.
  • Shah, Syed Rehmat Ullah, et al. (författare)
  • Shoot organogenesis from roots of seabuckthorn (Hippophaë rhamnoides L.): structure, initiation and effects of phosphorus and auxin
  • 2015
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 29, s. 1989-2001
  • Tidskriftsartikel (refereegranskat)abstract
    • Shoots from roots formed on seedlings in vitro in the groove of lateral roots as on plants growing in a natural habitat. The finding has ecological and applied relevance.Shoot organogenesis from roots (root suckers, shoots from roots, SfRs) allows vegetative propagation of the small tree seabuckthorn (HippophaA << rhamnoides L.) in addition to sexual propagation and is an important trait associated with the root system. Using an in vitro system, we studied initiation, localization and development of SfRs and interacting roles of phosphorus (P) and indole-3-acetic acid (IAA). After transfer of seedlings to the W4 medium (WPM medium with added IAA, benzyl adenine and giberellic acid), SfRs protruded after 2 weeks from the primary root initially at the groove of lateral roots (LR) as seen by scanning electron microscopy and light microscopy. This is also the location of SfRs on plants growing in natural conditions, which suggests a similar developmental pathway. To localize SfR initiation, staining by the DNA-binding fluorochrome 4',6-diamidino-2-phenylindole in root cross sections revealed a high density of small cells as in meristems in the pericycle area between endodermis and vascular tissue. During 8-10 weeks, SfRs emerged also in other positions on the primary root, concomitantly with senescence of existing LRs and suppression of new LR formation. Since SfR formed in relation to LRs, we hypothesized that P and IAA play a role in SfR formation. Highest production of SfRs occurred in W4 medium after pre-treatment with high P in the presence of IAA while LR production in WPM was stimulated by IAA in low and middle P. SfRs developed in vitro on seedlings originating from three subspecies of H. rhamnoides showing this trait to be common. This experimental system allowed studies of organogenesis of SfRs and LRs in response to plant growth regulators, P and IAA and may be further implemented in basic studies and in applied clonal propagation of seabuckthorn.
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42.
  • Sierra, Carlos (författare)
  • Intra-annual isotope variations in tree rings reveal growth rhythms within the least rainy season of an ever-wet tropical forest
  • 2022
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 36, s. 1039-1052
  • Tidskriftsartikel (refereegranskat)abstract
    • Key message Isotope variation (delta O-18) in wood suggests new insights on growth rhythms in trees growing in tropical forest with extremely high precipitation, without seasonal droughts or flooding. It is well known that growth-limiting factors such as seasonal droughts can induce periodicities in woody tissue formation of tropical trees. In regions without seasonal droughts or flooding but sufficient water for photosynthesis (ever-wet tropical forests), rhythmic growth has been previously reported; however, triggering factors remain little explored. Our objective was to establish tree-ring frequency and probable growing season by analysis of the intra-annual variability of isotopic ratios in cellulose (delta O-18(cellulose) and delta C-13(cellulose)) and relationships with environmental variables in two tree species (Humiriastrum procerum and Virola dixonii) growing in an ever-wet tropical forest (Choco region of Colombia, precipitation 7200 mm year(-1), mean annual temperature 25.9 degrees C), located close to the Pacific Ocean at ca 3 degrees 57 ' 12.54 '' N-76 degrees 59 ' 27.96 '' W. Here, we report annual rhythmic growth evidenced by radiocarbon analysis, leaf phenology, dendrometer records, and stable-isotope variation in cellulose. All evidence points to the probable growing season occurring during the least rainy months for both species. While intra-annual delta O-18(cellulose) values follow a rhythmic variation, delta C-13(cellulose) variations show a less clear pattern, probably due to deciduity and remobilization of non-structural carbon stored in previous growing stages. Furthermore, delta O-18(cellulose) covary with relative humidity, vapor pressure deficit, short-wave solar radiation, and temperature during the least rainy months. In contrast, delta C-13(cellulose) values were not significantly correlated with environmental variables. Our results show that stable-isotope variations in tree rings, even under ever-wet conditions, are valuable for understanding drivers of tropical tree growth in such conditions.
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43.
  • Tigabu, Mulualem (författare)
  • Calcium-mediated adaptive responses to low phosphorus stress in Chinese fir
  • 2020
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 34, s. 825-834
  • Tidskriftsartikel (refereegranskat)abstract
    • Key message Ca2+ induces adaptive response to low P stress through increased root growth and expansion, but plays minor or no role in remobilization of P in leaf tissues or in maintaining membrane integrity. The role of calcium (Ca2+) in signaling environmental stress has been demonstrated; however, its role in signaling low phosphorus (P) stress and subsequent adaptive responses in trees are largely unexplored. The aim of this study was to examine the effects of Ca2+ application on root growth and expansion, seedling growth, remobilization of P, and maintaining membrane integrity in leaf tissues. Thus, a sand culture experiment was set up with five Ca2+ concentrations (0, 1, 3, 5, and 10 mmol/L Ca(NO3)(2)center dot 4H(2)O) under two P treatments (0.0 and 1.0 mmol/L KH2PO4). After 4 months, growth attributes, P and Ca2+ accumulations, and biochemical responses were determined. Results showed that (1) low P seedlings supplied with 5 mmol/L Ca2+ produced longer roots, larger root surface area, higher root diameter, and larger root volume than the control; (2) seedling height and root collar diameter were positively affected by addition of 3 and 5 mmol/L Ca2+ into the growing media, and whole plant biomass of low P seedlings supplied with 5 mmol/L Ca2+ was significantly higher than the control; (3) whole plant P accumulation was higher in 3 and 5 mmol/L Ca2+ treatments in low P seedlings, whereas whole plant Ca2+ accumulation increased linearly with increasing Ca2+ concentration; and (4) the effects of Ca2+ on malondialdehyde and soluble protein contents and acid phosphatase activity did not show consistent trend with increasing or decreasing Ca2+ concentration. In conclusion, Ca2+ induces adaptive response to low P stress through increased root growth and expansion, but plays minor or no role in remobilization of P in leaf tissues or in maintaining membrane integrity.
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44.
  • Tigabu, Mulualem (författare)
  • Genetic diversity and population structure of Pinus halepensis Mill. in Jordan revealed by simple sequence repeats
  • 2022
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 36, s. 977-989
  • Tidskriftsartikel (refereegranskat)abstract
    • Key message Pinus halepensis populations in Jordan maintained a moderate level of genetic diversity with considerable intra-population than inter-population differentiation due to long-distance zygotic and gametic gene flows among populations. The genetic diversity and structure of 156 germplasm samples collected from four natural and five planted Pinus halepensis Mill. populations in Jordan were investigated using simple sequence repeat markers. These fragmented stands represent the easternmost edge of the species natural range of distribution in the Mediterranean basin. Our study revealed relatively high expected heterozygosity and Shannon's diversity index (He = 0.574, I = 1.124). Genetic diversity parameters, Na, Ne, He, and I slightly increased in planted populations compared to natural populations. The AMOVA and population genetic differentiation index (Fst) analysis revealed higher level of intra-population differentiation than inter-population differentiation. The UPGMA cluster analysis and genetic structure analysis revealed two sub-groups, which were not consistent with the geographic distribution pattern. Furthermore, the population genetic distance was not correlated with geographic distance (rxy = - 0.507; p = 0.197; R-2 = 0.2568; y = 60.323x + 8.7366). It can be concluded that Jordan's Aleppo pine populations maintained a moderate level of genetic diversity with marked intra-population than inter-population differentiation. The low genetic differentiation among natural populations can be attributed to an effective gene flow among populations.
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45.
  • Uddling, Johan, 1972, et al. (författare)
  • Measuring and modelling leaf diffusive conductance in juvenile silver birch, Betula pendula
  • 2004
  • Ingår i: Trees-Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890. ; 18:6, s. 686-695
  • Tidskriftsartikel (refereegranskat)abstract
    • Leaf diffusive conductance for water (g(l)) and twig xylem pressure (psi(xt)) was measured in juvenile silver birch, Betula pendula, under field conditions in southern Sweden. Data from one site were used to parameterise two different multiplicative models for g(l) (dependent data), and measurements from another site were used to validate these models (independent data). In addition, experiments were performed in controlled environments to validate the g(l) response functions used in the models. The driving variables in the D-model were photosynthetic photon flux density, air temperature and water vapour pressure deficit of the air (D-a), while the DH-model also included the accumulated hours after sunrise each day with D-a above a certain threshold (H). Both models satisfactorily predicted the variation in g(l) in dependent as well as in independent data, and the g(l) response functions used were supported by the experiments in controlled environments. The DH-model was more successful in predicting g(l) than the D-model by accounting for the observation that g(l) was lower at higher H under similar weather conditions. There was a considerable variation in maximum g(l) during the season, as well as between the two sites. On relatively warm and dry days psi(xt) rapidly declined during the morning and then stabilized around a constant value until the late afternoon, with the stomatal regulation effectively preventing psi(xt) from decreasing below this value. We suggest that these models could be used to simulate the g(l) in juvenile birch if maximum g(l) is locally estimated and if the response functions are not extrapolated beyond the climate range for this study.
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46.
  • Vasaitis, Rimvydas (författare)
  • Long-term pathological consequences of resin tapping wounds on stems of Scots pine (Pinus sylvestris L.)
  • 2022
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 36, s. 1507-1514
  • Tidskriftsartikel (refereegranskat)abstract
    • Key message After 5-6 decades since inflicting resin tapping wounds, overmature (> 120 years old) Pinus sylvestris stems remain undecayed and vigorous. Overmature trees of Pinus sylvestris bearing large wounds made by resin tapping decades ago are still present in woodlands of south-eastern Baltic Sea region. The aim of the present study was to investigate health condition of those trees focusing on fungal infections and to estimate impact of the injury on radial stem growth. The study was conducted in Latvia in three overmature stands of P. sylvestris, resin-tapped in 1950-1970 s. On the studied ninety 120-167-year-old trees, exposed sapwood constituted from 1140 to 7755 cm(2) per individual stem. Of the 127 wounds sampled, 52 (41%) showed wood discoloration. The discoloration in its extent was limited, expanding beyond wound margins approx. 1 (max 3) cm in radial, and 6-7 cm in longitudinal directions. Of the 127 wood samples/wounds subjected to fungal isolations, 96% resulted in fungal growth, yielding 236 fungal isolates that represented 47 fungal taxa. The most common among macro-fungi was basidiomycete Porodaedalea pini, which was isolated from 9% of stems. The fungus is currently classed not as a tree pathogen, but instead as an indicator species for woodland sites to be considered for nature conservation. Data from tree ring widths have revealed that tree reacted to the resin tapping injury by increasing radial increment of the un-affected part of the circumference of the stem. Current study demonstrated that even on the long term, resin tapping has little influence on health condition and vitality of P. sylvestris, even at the very old age. This should be considered as a supporting message in case resin taping practices in the region are to be revived.
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47.
  • Wagner, Leopold, et al. (författare)
  • Key parameters controlling stiffness variability within trees : a multiscale experimental–numerical approach
  • 2012
  • Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 27:1, s. 321-336
  • Tidskriftsartikel (refereegranskat)abstract
    • Microstructural properties of wood vary considerably within a tree. Knowledge of these properties and a better understanding of their relationship to the macroscopic mechanical performance of wood are crucial to optimize the yield and economic value of forest stocks. This holds particularly for the end-use requirements in engineering applications. In this study the microstructure–stiffness relationships of Scots pine are examined with a focus on the effects of the microstructural variability on the elastic properties of wood at different length scales. For this purpose, we have augmented microstructural data acquired using SilviScan-3™ (namely wood density, cell dimensions, earlywood and latewood proportion, microfibril angle) with local measurements of these quantities and of the chemical composition derived from wide-angle X-ray scattering, light microscopy, and thermogravimetric analysis, respectively. The stiffness properties were determined by means of ultrasonic tests at the clear wood scale and by means of nanoindentation at the cell wall scale. In addition, micro-mechanical modeling was applied to assess the causal relations between structural and mechanical properties and to complement the experimental investigations. Typical variability profiles of microstructural and mechanical properties are shown from pith to bark, across a single growth ring and from earlywood to latewood. The clear increase of the longitudinal stiffness as well as the rather constant transverse stiffness from pith to bark could be explained by the variation in microfibril angle and wood density over the entire radial distance. The dependence of local cell wall stiffness on the local microfibril angle was also demonstrated. However, the local properties did not necessarily follow the trends observed at the macroscopic scale and exhibited only a weak relationship with the macroscopic mechanical properties. While the relationship between silvicultural practice and wood microstructure remains to be modeled using statistical techniques, the influence of microstructural properties on the macroscopic mechanical behavior of wood can now be described by a physical model. The knowledge gained by these investigations and the availability of a new micromechanical model, which allows transferring these findings to non-tested material, will be valuable for wood quality assessment and optimization in timber engineering.
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48.
  •  
49.
  • Wiström, Björn, et al. (författare)
  • Intraspecific drought tolerance of Betula pendula genotypes: an evaluation using leaf turgor loss in a botanical collection
  • 2021
  • Ingår i: Trees - Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 35, s. 569-581
  • Tidskriftsartikel (refereegranskat)abstract
    • Key message The results showed a significant relationship between the potential evapotranspiration of the provenance collection site and the leaf turgor loss point and significant positive differences in drought tolerance between provenances and subspecies of B. pendula. The ecosystem services provided by urban trees make substantial contributions to the quality of urban living and securing resilience towards the challenges posed by a changing climate. Water deficits are a major abiotic stress for trees in urban environments and, in many regions, this stress is likely to be amplified under future climate scenarios. Although wide variation in drought tolerance exists at the species level, many species also show substantial intraspecific variation in drought tolerance. The aim of this study is to evaluate how drought tolerance, inferred from the water potential at leaf turgor loss point (psi(P0)), varies in Betula pendula from different geographical origins and determine if the observed drought tolerance can be related to the local climate and seasonal water balance from the provenance of origin, despite the trees now being established in similar soil and climatic conditions within a single botanical collection. Six subsp. betula, five subsp. mandshurica and two subsp. szechuanica were evaluated, giving a total of 12 different provenances. The results showed a significant relationship between the potential evapotranspiration of the provenance collection site and the leaf turgor loss point and significant positive differences in drought tolerance between provenances and subspecies of B. pendula. By directing efforts towards identifying more drought-tolerant genotypes, it will be possible to diversify the palette of trees that could confidently be integrated by urban tree planners and landscape architects into the urban landscape. The results of this study on different ecotypes of B. pendula clearly show that it is possible to find more drought-tolerant plant material.
  •  
50.
  • Zhang, Peng, et al. (författare)
  • The influence of elevational differences in absolute maximum density values on regional climate reconstructions
  • 2015
  • Ingår i: Trees-Structure and Function. - : Springer Science and Business Media LLC. - 0931-1890. ; 29:4, s. 1259-1271
  • Tidskriftsartikel (refereegranskat)abstract
    • We found that indiscriminately using tree-ring MXD data with inhomogeneous temporal distribution from different elevations might cause biased chronologies. A mean-adjusting method was developed to overcome this bias. Here we analyse maximum latewood density (MXD) of Pinus sylvestris L. (Scots pine), from deadwood (dry) and subfossil wood (from lakes) collected along an elevation gradient in and close to the central Scandinavian Mountains, in the province of Jamtland, Sweden. Focusing on two common time periods (900-1150 CE and 1300-1550 CE), the mean absolute MXD of deadwood samples showed an inverse relationship with elevation, i.e. the absolute MXD decreases with elevation. However, the MXD values of the subfossil samples did not show such a consistent relationship with elevation. It was also noted that the differences in mean absolute MXD values among sites of different elevations in a given period were larger than among sites of similar elevation between the two time periods, where the former was assumed to be warmer than the latter. Using a theoretical model and a real example, it was shown that indiscriminately using MXD data with inhomogeneous temporal distribution from different elevations may cause biased chronologies, which can have significant effects on subsequent interpretations of past climate variability. A mean-adjusting method was developed to overcome this bias, and its usefulness was demonstrated by comparing two chronologies built on mean-adjusted and unadjusted MXD samples. It was concluded that unadjusted samples from different elevations with inhomogeneous temporal distribution can distort the long-term trend in a final chronology, while this bias can be alleviated if mean-adjusted samples are used.
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