1,721,006 research outputs found
Suitability of Illumina deep mRNA sequencing for reliable gene expression profiling in a non-model conifer species (Pseudotsuga menziesii)
No full textTranscriptome responses to temperature, water availability and photoperiod are conserved among mature trees of two divergent Douglas-fir provenances from a coastal and an interior habitat
No full textBackgroundLocal adaptation and phenotypic plasticity are important components of plant responses to variations in environmental conditions. While local adaptation has been widely studied in trees, little is known about plasticity of gene expression in adult trees in response to ever changing environmental conditions in natural habitats. Here we investigate plasticity of gene expression in needle tissue between two Douglas-fir provenances represented by 25 adult trees using deep RNA sequencing (RNA-Seq).ResultsUsing linear mixed models we investigated the effect of temperature, soil water availability and photoperiod on the abundance of 59189 detected transcripts. Expression of more than 80 % of all identified transcripts revealed a response to variations in environmental conditions in the field. GO term overrepresentation analysis revealed gene expression responses to temperature, soil water availability and photoperiod that are highly conserved among many plant taxa. However, expression differences between the two Douglas-fir provenances were rather small compared to the expression differences observed between individual trees. Although the effect of environment on global transcript expression was high, the observed genotype by environment (GxE) interaction of gene expression was surprisingly low, since only 21 of all detected transcripts showed a GxE interaction.ConclusionsThe majority of the transcriptome responses in plant leaf tissue is driven by variations in environmental conditions. The small variation between individuals and populations suggests strong conservation of this response within Douglas-fir. Therefore we conclude that plastic transcriptome responses to variations in environmental conditions are only weakly affected by local adaptation in Douglas-fir
Assessing the relationship between height growth and molecular genetic variation in Douglas-fir (Pseudotsuga menziesii) provenances
No full textDouglas-fir (Pseudotsuga menziesii) is a conifer tree native to western North America. In central Europe, it shows superior growth performance and is considered a suitable substitute for tree species impaired in vitality due to climate change. Maintenance and improvement of growth performance in a changing environment is a main challenge for forest tree breeders. In this context, genetic variation as a factor underlying phenotypic variation, but also as the basis for future adaptation, is of particular interest. The aims of this study were to analyse (1) genetic diversity of selected Douglas-fir provenances, (2) variation in height growth among provenances, and (3) to assess the link between genetic and phenotypic variation in height growth. Genotyping was done on microsatellite loci. Effects of 'provenance', 'genotype', and 'site' on height growth were assessed by fitting mixed linear models. The most significant genetic differentiation was observed between provenances of the coastal variety, versus a provenance of the interior variety originating from British Columbia. Although genetic differentiation among provenances of the coastal variety was lower, genetic structures within this variety were identified. Moreover, genetic diversity showed a latitudinal gradient with the southernmost provenances being more diverse, probably reflecting the species' evolutionary history. The modelling approach revealed that height growth differed significantly by 'provenance', 'site', and the interaction between 'site' and 'provenance'. Additionally, this analysis showed that genetic variation captured by the genotyped microsatellite loci was significantly related to variation in height growth, providing statistical evidence for a genetic component in the observed phenotypic variation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Intraspecific Variation in Regulation of Water Status and Cold Acclimation in Interior and Coastal Douglas-fir in Response to Simulated Warmer and Drier Climate
Full text linkClimate change in northern forests is causing increased water stress during summer droughts and potentially increased frost vulnerability following warmer autumns. Physiological responses to changing climate may vary among populations of tree species with broad ranges, such as Douglas-fir (Pseudotsuga menziesii). We aimed to characterize intraspecific variation in the responses of interior and coastal Douglas-fir to summer drought and autumn warming. We assessed photosynthesis, water use efficiency, xylem function, and freezing tolerance in seedlings under controlled conditions. Interior populations exhibited hydraulically safer but less efficient xylem whereas coastal populations exhibited more hydraulically efficient but less safe xylem. Differences in photosynthesis were minimal but suggested lower drought tolerance in the most coastal population. Autumn warming delayed downregulation of photosynthesis, however this did not impair development of freezing tolerance. This research will help determine which tree populations are best adapted to future warmer and dryer climates and thus improve forest regeneration efforts.M.Sc
Effects of Warming on the Phenology of Photosynthesis of Eastern White Pine and Implications for the use of Remote Sensing in a Changing Climate
Full text linkIn northern trees, temperature and photoperiod control the beginning and end of the photosynthetically active season. Climate warming could extend the length of the photosynthetically active season, while photoperiod could potentially prevent trees from benefitting from warmer temperatures. Changes in the length of the photosynthetically active season can be estimated with the photochemical reflectance index (PRI), which detects xanthophyll cycle pigments involved in non-photochemical quenching (NPQ), a process affecting photosynthetic efficiency. In overwintering conifers, sustained NPQ replaces xanthophyll cycle-mediated NPQ, likely causing seasonal variations in the relationship between PRI and photosynthetic efficiency.
To better understand the impacts of climate warming on the spring and autumn photosynthesis of conifer forests, we investigated 1) the potential for enhanced photosynthesis during warmer springs and autumns in Pinus strobus L. and 2) seasonal variations in the relationship between PRI and the photosynthetic efficiency of needles.
During simulated summer-autumn and winter-spring transitions, PRI variation mainly reflected constitutive carotenoid pigment pool adjustments. During spring, differences in the timing of pigment pool adjustments and photosynthetic recovery impaired the relationship between PRI and photosynthesis. NPQ mechanisms and energy sinks undetected by PRI, such as electron transport around photosystem I, also impaired the relationship between PRI and photosynthesis.
In P. strobus seedlings from provenances located along a 1000 km latitudinal gradient, we observed differences in the phenology of photosynthesis, suggesting genetic controls of photosynthesis by photoperiod, with stronger controls during autumn than spring. The PRI could effectively track seasonal variations in energy partitioning, as well as carotenoid pigment pool sizes indicative of cold stress.
Photosynthesis in P. strobus might be enhanced during warmer springs and autumns, however, photoperiodic regulation of photosynthesis is to be expected during autumn. The interpretation of the PRI in evergreens should take into account alternative energy sinks, especially under cold spring and autumn conditions.Ph.D.2020-03-21 00:00:0
Photoprotective Isoprenoids as Indicators for Stress Responses in Forest Trees
No full textFor long-lived forest tree species, intraspecific variation among populations in their response to environmental conditions can reveal their ability to cope with and adapt to climate change. Plants constantly adjust the pigment composition of the photosynthetic apparatus to environmental conditions. Under abiotic stress conditions (e.g. drought), plants induce isoprenoid-mediated photoprotective mechanisms such as non-photochemical quenching (NPQ) and increased biosynthesis of antioxidants to minimize photooxidative stress. This thesis investigated the intraspecific variation in the isoprenoid metabolism in Douglas-fir (Pseudotsuga menziesii) comparing Douglas-fir provenances, which represent populations from locations with contrasting environmental conditions. Furthermore, the influence of foliar photosynthetic pigments on leaf optical properties was studied using senescing sugar maple (Acer saccharum) leaves. First, I established a simple and cost-effective protocol for the rapid analysis of isoprenoids using high-performance liquid chromatography (HPLC) (Chapter 2). Three experiments were conducted to evaluate 1) the adjustments of the isoprenoid metabolism when photosynthesis is limited in response to environmental conditions (Chapter 3 and 4); 2) provenance-specific adjustments of photoprotective isoprenoids in response to drought (Chapter 3 and 4); and 3) the influence of senescence-associated changes in isoprenoid levels on leaf optical properties in sugar maple (Chapter 5). In chapter 3, photosynthesis and photosynthetic pigments in seedlings of two Douglas-fir provenances were compared under controlled drought conditions. In chapter 4, intraspecific variation in photosynthesis and photosynthetic pigments in response to changing environmental conditions were studied in mature trees of four provenances over the course of two years. Both experiments revealed that the more drought-tolerant interior provenances exhibit enhanced carotenoid-chlorophyll ratios, and larger pools of xanthophyll cycle pigments and β-carotene compared to coastal provenances from mesic habitats. This provenance-specific variation demonstrated the importance of the isoprenoid metabolism for the adaptation of provenances to drought. In chapter 5, the leaf optical properties of senescing sugar maple leaves were studied. The degradation of photosynthetic pigments as indicator for the progress of senescence was reflected by spectral reflectance measurements and digital image analysis. Isoprenoid metabolism may thus be a potential trait for selection of provenances for future forest management and indicator for remote-sensing of the plant physiological status.Ph.D
Impacts of Short Photoperiod, Elevated Temperature, and Elevated CO2 on Cold Hardening in Eastern White Pine
No full textCold hardening in evergreen conifers is induced during autumn by decreasing temperature and photoperiod, and may be delayed or impaired by climate warming. This work aimed to 1) characterize the control of photoperiod versus temperature over the downregulation of photosynthesis, changes in carbohydrate metabolism and development of freezing tolerance that occur during cold hardening in Eastern white pine (Pinus strobus L.) seedlings; and 2) assess the impact of elevated temperature and elevated CO2 on the timing and extent of cold hardening in P. strobus seedlings under controlled and field conditions.
Under controlled conditions, short photoperiod rapidly induced adjustments of leaf starch and sucrose, while low temperature rapidly induced adjustments of leaf pigments, photosynthesis and accumulation of glucose. Prolonged exposure to short photoperiod and low temperature induced downregulation of photosynthesis, accumulation of cryoprotective carbohydrates, and development of freezing tolerance. A novel 16-kD dehydrin protein was induced by short photoperiod and maximally expressed with the addition of low temperature; expression of this dehydrin strongly correlated with freezing tolerance.
Under controlled conditions, elevated temperature suppressed the downregulation of photosynthesis and accumulation of cryoprotective compounds; freezing tolerance was impaired, but provided sufficient protection against average historical winter temperatures at the seedlingsâ native origin. The combination of elevated temperature and elevated CO2 enhanced photosynthesis and, under long photoperiod, enhanced accumulation of starch. Elevated CO2 did not further impair development of freezing tolerance.
Under field conditions, development of freezing tolerance was initiated during early autumn by decreasing photoperiod. Frost exposure in mid-late autumn induced the downregulation of photosynthesis, accumulation of soluble sugars, and strongly enhanced freezing tolerance. However, the projected temperature increase for the year 2050 did not perceptibly delay downregulation of photosynthesis or impair freezing tolerance.
These findings indicate crucial roles for short photoperiod and low temperature during cold hardening. Warmer climates with elevated CO2 levels may allow P. strobus seedlings to benefit from increased carbon uptake and extend photosynthetic activity during the autumn. Elevated temperature and CO2 may impair the development of freezing tolerance, but is unlikely to increase risk of damage incurred by winter exposure for P. strobus seedlings grown in southern Ontario.Ph.D
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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