Browsing by Subject "Norway spruce"

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  • Hu, Man; Lehtonen, Aleksi; Minunno, Francesco; Mäkelä, Annikki (2020)
    Tree structure equations derived from pipe model theory (PMT) are well-suited to estimate biomass allocation in Scots pine (Pinus sylvestrisL.) and Norway spruce (Picea abies[L.] Karst.). However, age dependence of parameters should be accounted for when applying the equations.
  • Zhao, Lei (Helsingfors universitet, 2016)
    In Norway spruce (Picea abies L. Karst.) lignin forms a major part of the xylem cell walls and renders the tracheids water resistant while giving support to the cell walls and the whole tree trunk. In Norway spruce lignin is polymerized mainly from coniferyl alcohol but the origins of this monolignol are not known. In our study, we employed laser capture microdissection (LCMD) system to isolate ray parenchyma cells and xylem tracheids from thin (30-40 μm), tangential cryomicrotome sections of developing xylem of the spruce trunk. We wanted to analyse the monolignol biosynthesis pathway gene expression separately in these cell types. Our aim was to examine the possibility that coniferyl alcohol is produced in the tracheid cells, or whether also the neighboring cells (ray cells) contribute to the biosynthesis of monolignols during the lignification as has been confirmed in angiosperms before. Total RNA extracted from the collected material was used to perform low mRNA input sequencing on the Illumina HiSeq platform to identify transcripts potentially involved in monolignol biosynthesis and secretion. As a control material we used whole cryomicrotome sections containing both xylem tracheids and rays. Deep sequencing was performed to generate quantitative expression data within a particular cell type. Differential gene expression was conducted with a Chipster analysis software by using DESeq2. Altogether, 936 genes were differentially expressed between whole sections and ray cells, and 424 transcripts were more abundant in ray cells, while 512 transcripts were less abundant. Comparison between whole sections and xylem tracheids illustrated that 18 transcripts were more abundant in xylem tracheids and 275 transcripts were less abundant. Our study demonstrated the usefulness of LCMD combined with RNA-Seq to characterize gene expression in specific cell types.
  • Metsämuuronen, Sari; Sirén, Heli (2019)
    Phenolics and extracted phenolic compounds of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) show antibacterial activity against several bacteria. The majority of phenolic compounds are stilbenes, flavonoids, proanthocyanidins, phenolic acids, and lignans that are biosynthesized in the wood through the phenylpropanoid pathway. In Scots pine (P. sylvestris), the most abundant phenolic and antibacterial compounds are pinosylvin-type stilbenes and flavonol- and dihydroflavonol-type flavonoids, such as kaempferol, quercetin, and taxifolin and their derivatives. In Norway spruce (P. abies) on the other hand, the main stilbene is resveratrol and the major flavonoids are quercetin and myricetin. In general, when the results from the literature regarding the activities of flavonoid glycosides and their aglycones against a total of twenty-one microorganisms are summarized, it was found that phenolic glycosides are less active than the corresponding aglycones, although a number of exceptions are also known. The aglycones in plants respond to various kinds of biotic stress. Synergistic effects between aglycones and their glycosides have been observed. Minimum inhibition concentrations of below 10 mg L−1 against bacteria have been reported for gallic acid, apigenin, and several methylated and acylated flavonols present in these industrially important trees. In general, the phenolic compounds are more active against Gram-positive bacteria, but apigenin is reported to exhibit strong activity against Gram-negative bacteria. The present review lists some of the biosynthesis pathways for the antibacterial phenolic metabolites found in Scots pine (P. sylvestris) and Norway spruce (P. abies). The antimicrobial activity of the compounds is collected and compared to gather information about the most effective secondary metabolites.
  • Lintunen, Anna; Lindfors, Lauri; Kolari, Pasi; Juurola, Eija; Nikinmaa, Eero; Hölttä, Tuomo (2014)
  • Kaarakka, Lilli; Hyvönen, Riitta; Strömgren, Monika; Palviainen, Marjo; Persson, Tryggve; Olsson, Bengt A; Launonen, Erno; Vegerfors, Birgitta; Helmisaari, Heljä-Sisko (2016)
    The use of forest-derived biomass has steadily increased in Finland and Sweden during the past decades leading to more intensive forest management practices in the region, such as whole-tree harvesting, both above- and belowground. Stump harvesting results in a direct removal of stump and coarse-root carbon (C) from the stand and can cause extensive soil disturbance, which has been suggested to increase C mineralization. In this study, the effects of stump harvesting on soil C and nitrogen (N) mineralization, and soil surface disturbance were studied in two different clear-felled Norway spruce (Picea abies) sites in Central Finland. The treatments were whole-tree harvesting (WTH, removal of stems and logging residues), and WTH and stump harvesting (WTH + S). Both sites, Honkola (2 stands) and Haukilahti (6 stands) were mounded. In both treatments, soil samples were taken from different soil layers down to a total depth of 20 cm in the mineral soil from (i) mounds, (ii) undisturbed soil and (iii) pits. The sampling was performed 11-12 years after treatments. Soil C and N mineralization rates were determined in laboratory incubation experiments. In addition, total C and N pools (g m(2)) were estimated for each disturbance class and soil layer. Soil C and N pools had a tendency to be lower following stump harvesting, but no statistically significant treatment effect was detected. Stump harvesting increased soil mixing as indicated by a significant decrease in C concentration in the mound disturbance class. There was no significant effect of stump harvesting on soil C mineralization rates. A combination of mineralization rates and soil pool data showed that field C mineralization (g CO2-C m(-2) yr(-1)) did not significantly differ between stands where stumps were removed or were retained. Further, stump harvesting did not seem to have any stimulating effect on soil CO2 efflux 11-12 years after treatment. (C) 2016 Elsevier B.V. All rights reserved.
  • Stewart, Erik (Helsingfors universitet, 2016)
    Heterobasidion annosum s.l. is a devastating forest pathogen species complex which causes extensive damage to timber products in northern Europe. This study examined resistance of Norway spruce (Picea abies) in two field sites in Finland to annosum root rot (Heterobasidion parviporum) utilizing non-clonal stocks of P. abies. The northern field site in Rovaniemi does not have a historical presence of the pathogen, whereas the southern field site in Lapinjärvi has extensive historical presence of the pathogen. The goals of the study were to assess potential difference in susceptibility between the sites, as well as to examine the differences in susceptibility between tissue types and organs in the trees examined. The study inoculated treatment trees with H. parviporum, as well as mock inoculations without the pathogen for control trees. Six inoculations of one treatment type were placed into each of thirty randomly selected trees at both field sites. Three inoculations were done in the stem, and three in the roots, for a total of 360 inoculations. After being left in situ for three months, the trees were harvested, and resulting lesions in the phloem and xylem tissues in both the roots and stem were measured to determine the extent of visible lesion extensions from the inoculation point. Data collected from the experiment was analyzed in the context of three mixed effects models, with the assumption that larger lesions indicated lower resistance to the pathogen. The measurements considered as response variables for the models were the total length of the lesion, total width of the lesion, and total area of the lesion. Results indicated minor overall differences in the lesion sizes between site in the lesion width and lesion area models. Significant differences were found between tissue types in the lesion width, and lesion area models. Additionally, interactions between treatment and organ, as well as treatment and tissue were significant across all models. Several other interactions were significant across some, but not all models The results indicate that further research into the potential effects of historical or geographic isolation on the resistance of P. abies to H. parviporum should include strict genetic controls with crossing of genotypes across sites, and should also consider the differences due to abiotic factors which may influence resistance in field trials.
  • Kovalchuk, Andriy; Zeng, Zhen; Ghimire, Rajendra P; Kivimäenpää, Minna; Raffaello, Tommaso; Liu, Mengxia; Mukrimin, Mukrimin; Kasanen, Risto; Sun, Hui; Julkunen-Tiitto, Riitta; Holopainen, Jarmo K; Asiegbu, Fred O (BioMed Central, 2019)
    Abstract Background Root and butt rot of conifer trees caused by fungi belonging to the Heterobasidion annosum species complex is one of the most economically important fungal diseases in commercial conifer plantations throughout the Northern hemisphere. We investigated the interactions between Heterobasidion fungi and their host by conducting dual RNA-seq and chemical analysis on Norway spruce trees naturally infected by Heterobasidion spp. We analyzed host and pathogen transcriptome and phenolic and terpenoid contents of the spruce trees. Results Presented results emphasize the role of the phenylpropanoid and flavonoid pathways in the chemical defense of Norway spruce trees. Accumulation of lignans was observed in trees displaying symptoms of wood decay. A number of candidate genes with a predicted role in the higher level regulation of spruce defense responses were identified. Our data indicate a possible role of abscisic acid (ABA) signaling in the spruce defense against Heterobasidion infection. Fungal transcripts corresponding to genes encoding carbohydrate- and lignin-degrading enzymes, secondary metabolism genes and effector-like genes were expressed during the host colonization. Conclusions Our results provide additional insight into defense strategies employed by Norway spruce trees against Heterobasidion infection. The potential applications of the identified candidate genes as markers for higher resistance against root and butt rot deserve further evaluation.
  • Kovalchuk, Andriy; Zeng, Zhen; Ghimire, Rajendra P.; Kivimäenpää, Minna; Raffaello, Tommaso; Liu, Mengxia; Mukrimin, Mukrimin; Kasanen, Risto Aarne Olavi; Sun, Hui; Julkunen-Tiitto, Riitta; Holopainen, Jarmo K.; Asiegbu, Frederick Obioma (2019)
    BackgroundRoot and butt rot of conifer trees caused by fungi belonging to the Heterobasidion annosum species complex is one of the most economically important fungal diseases in commercial conifer plantations throughout the Northern hemisphere. We investigated the interactions between Heterobasidion fungi and their host by conducting dual RNA-seq and chemical analysis on Norway spruce trees naturally infected by Heterobasidion spp. We analyzed host and pathogen transcriptome and phenolic and terpenoid contents of the spruce trees.ResultsPresented results emphasize the role of the phenylpropanoid and flavonoid pathways in the chemical defense of Norway spruce trees. Accumulation of lignans was observed in trees displaying symptoms of wood decay. A number of candidate genes with a predicted role in the higher level regulation of spruce defense responses were identified. Our data indicate a possible role of abscisic acid (ABA) signaling in the spruce defense against Heterobasidion infection. Fungal transcripts corresponding to genes encoding carbohydrate- and lignin-degrading enzymes, secondary metabolism genes and effector-like genes were expressed during the host colonization.ConclusionsOur results provide additional insight into defense strategies employed by Norway spruce trees against Heterobasidion infection. The potential applications of the identified candidate genes as markers for higher resistance against root and butt rot deserve further evaluation.
  • Nikinmaa, Laura (Helsingin yliopisto, 2017)
    The physiological effects of drought on trees has been studied excessively but many of them remain unclear. In this thesis I studied tree sugar dynamics under drying-wetting cycle as well as the role of soil hydraulic conductivity on how trees experience drought. I experimented with five Norway spruce seedlings in October and November 2016. The seedlings were in water after which they were put in to PEG solution of -0.5 MPa for 24 h and then transferred back to water. Sugar samples were taken from liquids, needles and roots once for every phase. Osmolality samples were taken from current year needles and water potential samples were taken from current year needles and roots every half an hour during day time. Continuous gas exchange measurements were done with Walz GFS-3000. There was no change in osmolality and no significant change in photosynthesis or transpiration rate. For sugar concentrations there was significant increase of non-structural carbohydrates in needles and significant decrease in roots. There was no change in sugar concentration in liquid. Overall impression was that trees did not suffer much from the PEG treatment. The results supported my hypothesis that changes in soil hydraulic conductivity are more important to effects of drought than changes in soil water potential.
  • Virkkunen, Eero (Helsingin yliopisto, 2017)
    This study aimed at conducting a baseline for optimal harvesting schedules with economic criteria for Scots pine, Norway spruce and silver birch in Estonia. Additionally, this study aimed at providing comparison to previous findings about optimal schedules in boreal forests and recommendation for practitioners. Faustmann’s (1849) forest rotation theory provides the theoretical foundation for the thesis. The study was performed by including Estonian whole-stand forest growth models and local timber prices and forest regeneration costs in the optimization, which was based on the Hooke and Jeeves’ (1961) direct optimization method. Scots pine was found to be the optimal species in most site classes, silver birch being the optimum in the most fertile site. The schedules for silver birch were found to be less sensitive to changes in the rate of interest, site fertility and timber price than the conifers. The current legal restrictions lead to longer rotations, more thinnings and economic losses when compared to the unrestricted optimal scenarios. The optimal number of thinnings in most scenarios for all species turned out to be three, if the legal restrictions are followed. In general, the optimal rotation periods were found to be shorter and the timing of the first thinning earlier in many scenarios than in Finland. Also the optimal number of thinnings was found to be more stable in Estonia than in Finland. It was found that if the initial stand stocking for the main tree species falls below a certain threshold in mid-rotation mixed-species stands including less valuable broadleaves, it is optimal to clear fell the stand immediately and regenerate the stand according to the optimal stocking recommendations. From the practical point of view, given the current limitations regarding the timing of clear fell, forestry practitioners have the most value creation potential in improving the forest regeneration methods and thinning schedule. In comparison to Finnish studies, it was found that there exists many similarities regarding the schedules and the suitability of species for different forest sites between the findings of this study and previous Finnish studies and the Finnish silvicultural recommendations. Thus, the extensive Finnish recommendations and findings provide a good basis for practitioners also in Estonia. However, given also the found differences, harvesting schedules in Estonia should be developed in more detail for more sophisticated recommendations for local practices.
  • Parkatti, Vesa-Pekka (Helsingfors universitet, 2017)
    This study optimizes the management regime of boreal Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestric L.) stands. The aim is to compare the economic profitability of continuous cover management and clearcut management and to study the hypothesis that continuous cover forestry is more favorable in the case of Norway spruce, compared to Scots pine. Additionally, the study analyses the outcomes of two different growth models for these tree species and compares the results with the requirements of the Finnish Forest Act of 2014. Earlier studies comparing the suitability of Norway spruce and Scots pine to continuous cover forestry have applied unclear model specifications and unnecessary limitations in the optimization methods. In this study, the optimization is carried out using a theoretically sound economic optimization model that determines the choice of the management regime as an outcome of the optimization. The model uses empirically estimated ecological growth models and includes both fixed and variable harvesting costs. Two different empirically estimated ecological growth models are used and compared. The optimization model is solved as a bi-level problem where harvest timing is the upper-level problem and harvesting intensity the lower-level problem. The optimization is solved using gradient-based methods for the lower-level problems and genetic and hill-climbing algorithms for the upper-level problems. This is the first study using this method to solve optimal continuous cover solutions for Scots pine. The results show that the main differences in optimal solutions between the two species are independent of the ecological two growth models used. According to both ecological models, continuous cover forestry is less favorable for Scots pine compared to Norway spruce, in both low and average fertility sites. However, the magnitude of this favorability and the characteristics of the optimal solutions strongly depend on the ecological model. Optimal continuous cover solutions for Scots pine are also found to have very low stand densities. Almost all economically optimal solutions are illegal because of their low number of trees or basal area per hectare.
  • Hänninen, Heikki; Pelkonen, Paavo (Suomen metsätieteellinen seura, 1988)
  • Pyörälä, Jiri (Helsingfors universitet, 2013)
    This study is a part of the research project of uneven-aged forest stands ERIKA by Finnish Institute for Forest Research. The aim of this study was to identify the growth and quality of Norway spruce wood and sawn wood products from uneven-aged forest stands in South Finland. The properties ex-amined were fiber length, wood density, modulus of elasticity and visual grade according to Nordic standards of visual grading. 64 trees were measured for fiber length and sawn wood of 40 trees (355 pc.) was measured for density, modulus of elasticity and visual grading. The variation of fiber length was modeled in respect to distance from pith and ring width using a mixed model. The variation of density, modulus of elasticity and visual grade was analyzed in respect to the within-tree location with two-sided variance analysis. In respect to cambial age and ring width the properties were analyzed by means of regression modeling. According to the results fiber length, density and MOE did not differ significantly from those characteristic to spruce in even-aged stands: most variation was among-tree which gives a reason to think that the changes in within-tree growth rhythm do not affect these proper-ties within an individual tree. Visual grading for sawn wood gave that there was a good amount of class A (~ 20 %) but class C (> 33 %) was more common than class B (> 25 %): Timber was knotty especially near pith and loose knots were dense on lumber boards. Twisting was high near pith in timber boards but did not differ from the usual. There was remarkable amount of compression wood and decay in the material. The within-tree variation of visual grade was equal to the among-tree varia-tion. Due to the small sample size the results are not yet applicable to uneven-aged forests in general, but they give an impression that there might not be any major differences between the quality of even-aged and uneven-aged wood. First of all, the results give light to the characteristics of uneven-aged spruce wood properties that might be of interest for further research.
  • Taniwan, Steven (Helsingin yliopisto, 2020)
    Norway spruce is commonly cultivated throughout Europe, Russia, and Japan. Cultivation of Norway spruce often faces the issue of fungal diseases, one of which is cherry rust disease caused by Thekopsora areolata. The gene model MA_10g0010 encoding an uncharacterized peroxidase (PabPrx86) has previously been associated with the presence of this pathogen. The aim of this study was to describe and assay the protein produced from this gene model, observe its localization in the cell, and determine its relative expression level in different tissues of Norway spruce. Experiments were performed by isolating the full length cDNA for PabPrx86 and cloning the cDNA into destination vectors pEAQ-HT-DEST1 and pK7FWG2 leading to a hypertranslatable transcript and a C-terminal GFP fusion, respectively. The plasmid constructs were transformed to Agrobacterium tumefaciens and agro-infiltrated to Nicotiana benthamiana. In addition, the relative expression level of this gene in different spruce tissues at different times of the year was determined using the qRT-PCR method. Sequencing showed that there were two allelic variants of this gene in the spruce individual sampled for RNA. Results showed that both alleles code for a peroxidase with basic pI. Subcellular localization with the GFP tag detected that PabPrx86 protein was located out of cytoplasm, indicating that the protein was translated in the ER-ribosomes, whereas relative expression level analysis revealed that PabPrx86 was highest expressed in the bud and lateral bud in June. Peroxidases are known to relate with plant defense, but further experiments are required to determine the role of PabPrx86 in Norway spruce and what the association with T. areolata means.
  • Mukrimin, Mukrimin; Conrad, Anna O.; Kovalchuk, Andriy; Julkunen-Tiitto, Riitta; Bonello, Pierluigi; Asiegbu, Fred O. (2019)
    Conifer trees, including Norway spruce, are threatened by fungi of the Heterobasidion annosum species complex, which severely affect timber quality and cause economic losses to forest owners. The timely detection of infected trees is complicated, as the pathogen resides within the heartwood and sapwood of infected trees. The presence of the disease and the extent of the wood decay often becomes evident only after tree felling. Fourier-transform infrared (FT-IR) spectroscopy is a potential method for non-destructive sample analysis that may be useful for identifying infected trees in this pathosystem. We performed FT-IR analysis of 18 phloem, 18 xylem, and 18 needle samples from asymptomatic and symptomatic Norway spruce trees. FT-IR spectra from 1066 – 912 cm−1 could be used to distinguish phloem, xylem, and needle tissue extracts. FT-IR spectra collected from xylem and needle extracts could also be used to discriminate between asymptomatic and symptomatic trees using spectral bands from 1657 – 994 cm−1 and 1104 – 994 cm−1, respectively. A partial least squares regression model predicted the concentration of condensed tannins, a defense-related compound, in phloem of asymptomatic and symptomatic trees. This work is the first to show that FT-IR spectroscopy can be used for the identification of Norway spruce trees naturally infected with Heterobasidion spp.
  • Baison, John; Vidalis, Amaryllis; Zhou, Linghua; Chen, Zhi-Qiang; Li, Zitong; Sillanpää, Mikko J.; Bernhardsson, Carolina; Scofield, Douglas; Forsberg, Nils; Grahn, Thomas; Olsson, Lars; Karlsson, Bo; Wu, Harry; Ingvarsson, Pär K.; Lundqvist, Sven-Olof; Niittylae, Totte; Garcia-Gil, M. Rosario (2019)
    Norway spruce is a boreal forest tree species of significant ecological and economic importance. Hence there is a strong imperative to dissect the genetics underlying important wood quality traits in the species. We performed a functional genome-wide association study (GWAS) of 17 wood traits in Norway spruce using 178 101 single nucleotide polymorphisms (SNPs) generated from exome genotyping of 517 mother trees. The wood traits were defined using functional modelling of wood properties across annual growth rings. We applied a Least Absolute Shrinkage and Selection Operator (LASSO-based) association mapping method using a functional multilocus mapping approach that utilizes latent traits, with a stability selection probability method as the hypothesis testing approach to determine a significant quantitative trait locus. The analysis provided 52 significant SNPs from 39 candidate genes, including genes previously implicated in wood formation and tree growth in spruce and other species. Our study represents a multilocus GWAS for complex wood traits in Norway spruce. The results advance our understanding of the genetics influencing wood traits and identifies candidate genes for future functional studies.
  • Zeng, Zhen; Wu, Jiayao; Kovalchuk, Andriy; Raffaello, Tommaso; Wen, Zilan; Liu, Mengxia; Asiegbu, Fred O. (2019)
    Heterobasidion parviporum is the most devastating fungal pathogen of conifer forests in Northern Europe. The fungus has dual life strategies, necrotrophy on living trees and saprotrophy on dead woods. DNA cytosine methylation is an important epigenetic modification in eukaryotic organisms. Our presumption is that the lifestyle transition and asexual development in H. parviporum could be driven by epigenetic effects. Involvements of DNA methylation in the regulation of aforementioned processes have never been studied thus far. RNA-seq identified lists of highly induced genes enriched in carbohydrate-active enzymes during necrotrophic interaction with host trees and saprotrophic sawdust growth. It also highlighted signaling- and transcription factor-related genes potentially associated with the transition of saprotrophic to necrotrophic lifestyle and groups of primary cellular activities throughout asexual development. Whole-genome bisulfite sequencing revealed that DNA methylation displayed pronounced preference in CpG dinucleotide context across the genome and mostly targeted transposable element (TE)-rich regions. TE methylation level demonstrated a strong negative correlation with TE expression, reinforcing the protective function of DNA methylation in fungal genome stability. Small groups of genes putatively subject to methylation transcriptional regulation in response to saprotrophic and necrotrophic growth in comparison with free-living mycelia were also explored. Our study reported on the first methylome map of a forest pathogen. Analysis of transcriptome and methylome variations associated with asexual development and different lifestyle strategies provided further understanding of basic biological processes in H. parviporum. More importantly, our work raised additional potential roles of DNA methylation in fungi apart from controlling the proliferation of TEs.
  • Mukrimin, Mukrimin; Kovalchuk, Andriy; Neves, Leandro G.; Jaber, Emad H. A.; Haapanen, Matti; Kirst, Matias; Asiegbu, Fred O. (2018)
    Root and butt rot caused by members of the Heterobasidion annosum species complex is the most economically important disease of conifer trees in boreal forests. Wood decay in the infected trees dramatically decreases their value and causes considerable losses to forest owners. Trees vary in their susceptibility to Heterobasidion infection, but the genetic determinants underlying the variation in the susceptibility are not well-understood. We performed the identification of Norway spruce genes associated with the resistance to Heterobasidion parviporum infection using genome-wide exon-capture approach. Sixty-four clonal Norway spruce lines were phenotyped, and their responses to H. parviporum inoculation were determined by lesion length measurements. Afterwards, the spruce lines were genotyped by targeted resequencing and identification of genetic variants (SNPs). Genome-wide association analysis identified 10 SNPs located within 8 genes as significantly associated with the larger necrotic lesions in response to H. parviporum inoculation. The genetic variants identified in our analysis are potential marker candidates for future screening programs aiming at the differentiation of disease-susceptible and resistant trees.
  • Lopez, Jose Gutierrez; Tor-Ngern, Pantana; Oren, Ram; Kozii, Nataliia; Laudon, Hjalmar; Hasselquist, Niles J. (2021)
    Trees in northern latitude ecosystems are projected to experience increasing drought stress as a result of rising air temperatures and changes in precipitation patterns in northern latitude ecosystems. However, most drought-related studies on high-latitude boreal forests (>50 degrees N) have been conducted in North America, with few studies quantifying the response in European and Eurasian boreal forests. Here, we tested how daily whole-tree transpiration (Q, Liters day(-1)) and Q normalized for mean daytime vapor pressure deficit (Q(DZ), Liters day(-1) kPa(-1)) were affected by the historic 2018 drought in Europe. More specifically, we examined how tree species, size, and topographic position affected drought response in high-latitude mature boreal forest trees. We monitored 30 Pinus sylvestris (pine) and 30 Picea abies (spruce) trees distributed across a topographic gradient in northern Sweden. In general, pine showed a greater Q(DZ) control compared to spruce during periods of severe drought (standardized precipitation-evapotranspiration index: SPEI <-1.5), suggesting that the latter are more sensitive to drought. Overall, Q(DZ) reductions (using non-drought Q(DZ) as reference) were less pronounced in larger trees during severe drought, but there was a species-specific pattern: Q(DZ) reductions were greater in pine trees at high elevations and greater in spruce trees at lower elevations. Despite lower Q(DZ) during severe drought, drought spells were interspersed with small precipitation events and overcast conditions, and Q(DZ) returned to pre-drought conditions relatively quickly. This study highlights unique species-specific responses to drought, which are additionally driven by a codependent interaction among tree size, relative topographic position, and unique regional climate conditions.
  • Guo, Siying (Helsingin yliopisto, 2018)
    This thesis represents a thorough study on association between tree height and phloem anatomy of a tree. Phloem is one of the major components of the vascular system of a plant as it facilitates the transportation of products of photosynthesis from source to sink. In this research, a coniferous tree species, Picea abies (L.) Karst, which is commonly known as Norway spruce, was carefully examined as a model plant. Specifically, the correlation between tree height and the anatomical features of cells that constitute each compartment of a tree stem (i.e., outer bark, phloem, cambium, and xylem, which is composed of sapwood and heartwood) was investigated, aiming to help understand the phloem anatomy and elucidate the underlying mechanisms that govern the secondary tree growth. In particular, the variations of an array of anatomical properties of wood, such as cell number, cell size, structural dimensions, were measured at different height levels to establish the axial profiles for these anatomical features. Notably, the number of tracheid and sieve cells in the stem of Norway spruce was found to increase with tree height and water stress gradient. While the size of tracheid cell in radial direction exhibited no distinct axial pattern, a decrease in sieve cell size from the middle part of the living crown towards the top of the crown in both radial and tangential direction was observed. Also, the widths of wood layer, phloem and periderm exhibited dependence on tree height. This dissertation consists of a literature review relevant to this study, the detailed experimental methods involved in this work, a summary of the results and discussion, and a conclusion chapter.