Cambial Growth Research Articles

ОСОБЕННОСТИ АДАПТАЦИИ РАЗНЫХ ФОРМ СОСНЫ ОБЫКНОВЕННОЙ В УСЛОВИЯХ ДЛИТЕЛЬНОГО ИЗБЫТОЧНОГО УВЛАЖНЕНИЯ ПОЧВ

Intrapopulation variability of biochemical traits and cambial growth shows the adaptive ability of pine trees in different growth conditions. There is a genetically determined process of activation of defense systems in pine trees under unfavorable environmental conditions. Structural and functional rearrangement of the assimilating apparatus due to seasonal development ensures increased tree resilience and the passage of ontogenesis under the influence of stress factors within the reaction norm. This work aims at the study of adaptive ability of Pinus sylvestris L., which differs in the apophysis form of seed scales under conditions of prolonged excessive soil moistening in northern taiga. Studies were carried out in shrubby-sphagnum pine forests on boggy upland peat soils in the mouth of the Northern Dvina River. Trees with primary apophysis variations (forms) of seed scales were identified on the sample plots. Samples of 1, 2 and 3-year-old needles were taken in order to determine biochemical traits in 10 trees of each pine form isolated by type of apophysis, in different calendar periods (from May to December, 2016). The content of free proline, water-soluble proteins, and ascorbic acid was determined in the needles by the spectrophotometric method. Wood cores were sampled from 52 trees at a height of 1.3 m and width of the annual layer was determined in each selected form. Relative dendrochronological parameters were calculated along with the absolute value of radial growth. Meteorological parameters at the study sites (air temperature and precipitation) were determined from data of the Arkhangelsk Weather Station. The studies show the similarities and differences of trees of various forms in the seasonal dynamics of stress metabolites content in needles of different ages in relation to meteorological factors and phenological phases of pine vegetative organs in the Northern Dvina mouth. Trees with flat form of apophysis inherent more intensive accumulation of ascorbic acid and proline in 2-year-old needles in late October. This indicates increased activation of their protective reactions before overwintering compared to trees with convex form of apophysis. Patterns of variability in cambial growth of trees of different forms in time series were found. It was observed that trees with flat form of apophysis are more strongly affected by maladaptive (stressful) environmental factors.

Relationship between phenology of vegetation canopy and phenology of tree cambium in Helan Mountains, China.

Based on 98 Chinese pine (Pinus tabuliformis) tree-ring width data, normalized diffe-rence vegetation index (NDVI) data and land cover data in the Helan Mountains, we used VS-oscilloscope model to simulate the radial growth process of Chinese pine and to examine the relationship between vegetation canopy phenology and tree cambium phenology. Results showed that the end of season (EOS) of the vegetation canopy was significantly correlated with the EOS of the Chinese pine cambium. Such correlation was stronger than that between grassland and cambium. The start of season (SOS) and EOS of Chinese pine were related to the averaged minimum temperature in May-June and August-September, respectively. When the average minimum temperature in May-June increased by 1 ℃, SOS would be advanced by 4.3 days. The averaged minimum temperature in August-September increased by 1 ℃, EOS would be delayed by 2.6 days. The correlation between the phenology of vegetation canopy and the phenology of the cambium in Chinese pine differed among vegetation types. Simulating tree growth dynamics only through a tree-ring physiology model might lead to biased results. Using remote sensing monitoring data to combine canopy development and cambium growth would help to more accurately understand tree growth dynamics.

Structural organization in palm stems of Roystonea regia and Archontophoenix alexandrae

Abstract Having a high stature subjects palms to the same constraints as trees, but the lack of cambial growth urges them to adopt a different strategy. We aimed to characterize the spatial organization of xylem tissues and their potential functions in two palm stems: a 30 cm diameter at breast height (DBH) royal palm (Roystonea regia) and a 12 cm DBH Alexandra king palm (Archontophoenix alexandrae). Macroscopic and microscopic anatomical characteristics were assessed at five vertical locations and 5–6 radial locations at each height. Over 9600 vessels across the two stems were drawn manually and measured based on histological sections. Vertically, a hydraulic bottleneck was identified at the first meter, and both stems showed conduit tapering from 4 m to the top. Radially, most water transport and mechanical support were achieved within 2–5 cm below the bark. The larger stem diameter of royal palm may have improved its water transport, storage, and potential for mechanical support compared to king palm. There was a strong trade-off between ground parenchyma and the fiber fraction. However, the correlation between theoretical hydraulic conductivity (Kt) and the ground parenchyma fraction, and between Kt and the fiber fraction, shifted from positive or non-significant below the bark, to strongly negative close to the center. These changes reflect the functional sectoriality of the palm stems, which may reduce the constraint of trade-offs between water transport, storage, and mechanical support. To conclude, functional sectoriality may have helped both palm species to withstand the hydraulic and mechanical constraints due to high stature.

Winter-spring temperature pattern is closely related to the onset of cambial reactivation in stems of the evergreen conifer Chamaecyparis pisifera

Temperature is an important factor for the cambial growth in temperate trees. We investigated the way daily temperatures patterns (maximum, average and minimum) from late winter to early spring affected the timing of cambial reactivation and xylem differentiation in stems of the conifer Chamaecyparis pisifera. When the daily temperatures started to increase earlier from late winter to early spring, cambial reactivation occurred earlier. Cambium became active when it achieves the desired accumulated temperature above the threshold (cambial reactivation index; CRI) of 13 °C in 11 days in 2013 whereas 18 days in 2014. This difference in duration required for achieving accumulated temperature can be explained with the variations in the daily temperature patterns in 2013 and 2014. Our formula for calculation of CRI predicted the cambial reactivation in 2015. A hypothetical increase of 1–4 °C to the actual daily maximum temperatures of 2013 and 2014 shifted the timing of cambial reactivation and had different effects on cambial reactivation in the two consecutive years because of variations in the actual daily temperatures patterns. Thus, the specific annual pattern of accumulation of temperature from late winter to early spring is a critical factor in determining the timing of cambial reactivation in trees.

Peculiarities of cambial growth of some woody plants introduced in Kakheti region

The paper deals with the study of cambial growth of 32 species of woody plants, carried out in Kakheti region during six years. We have studied several plants and found out that they begin their cambial growth (with the exception of some oak species) after bud opening. According to calendar time, two groups of plants were distinguished: the first group of the plants began cambial growth in late March and at the beginning of April. These plants are as follows: Larix decidua Mill and Larix leptolepis Gord., Acer negundo L., Aesculus carnea Haine., Aesculus hippocastanum L. and 20 other species. The second group of the plants began cambium activity in May. These are plant species like Picea orientalis (L.) Link., Pinus griffithii Mc Cleland, Quercus occidentalis J. Gay., Magnolia grandiflora L. and others. The earliest completion of cambial growth was observed in the lateral branches of spruce, fir and other trees. The latest accomplishment (the first half of October) of cambial growth occurred in case of Cedrus atlantica Mannetti. and Cedrus deodara Loud., Pinus griffithii Mc Clel., Magnolia grandiflora L., Firmiana platanifolia Schott., etc. The endogenous rhythm of the investigated plants (with few exceptions) is in synchronous connection with the climate of Kakheti region, so we consider these plants to be interesting species for the decorative gardening and forestry of Telavi district, and deserve widespread distribution.

Peculiarities of cambial growth of some woody plants introduced in Kakheti region

Peculiarities of cambial growth of some woody plants introduced in Kakheti region

Stem emissions of monoterpenes, acetaldehyde and methanol from Scots pine (Pinus sylvestris L.) affected by tree-water relations and cambial growth.

Tree stems are an overlooked source of volatile organic compounds (VOCs). Their contribution to ecosystem processes and total VOC fluxes is not well studied, and assessing it requires better understanding of stem emission dynamics and their driving processes. To gain more mechanistic insight into stem emission patterns, we measured monoterpene, methanol and acetaldehyde emissions from the stems of mature Scots pines (Pinus sylvestris L.) in a boreal forest over three summers. We analysed the effects of temperature, soil water content, tree water status, transpiration and growth on the VOC emissions and used generalized linear models to test their relative importance in explaining the emissions. We show that Scots pine stems are considerable sources of monoterpenes, methanol and acetaldehyde, and their emissions are strongly regulated by temperature. However, even small changes in water availability affected the emission potentials: increased soil water content increased the monoterpene emissions within a day, whereas acetaldehyde and methanol emissions responded within 2-4 days. This lag corresponded to their transport time in the xylem sap from the roots to the stem. Moreover, the emissions of monoterpenes, methanol and acetaldehyde were influenced by the cambial growth rate of the stem with 6-10-day lags.

Root secondary growth: an unexplored component of soil resource acquisition.

Despite recent progress in elucidating the molecular basis of secondary growth (cambial growth), the functional implications of this developmental process remain poorly understood. Targeted studies exploring how abiotic and biotic factors affect this process, as well as the relevance of secondary growth to fitness of annual dicotyledonous crop species under stress, are almost entirely absent from the literature. Specifically, the physiological role of secondary growth in roots has been completely neglected yet entails a unique array of implications for plant performance that are distinct from secondary growth in shoot tissue. Since roots are directly responsible for soil resource capture, understanding of the fitness landscape of root phenotypes is important in both basic and applied plant biology. Interactions between root secondary growth, edaphic conditions and soil resource acquisition may have significant effects on plant fitness. Our intention here is not to provide a comprehensive review of a sparse and disparate literature, but rather to highlight knowledge gaps, propose hypotheses and identify opportunities for novel and agriculturally relevant research pertaining to secondary growth of roots. This viewpoint: (1) summarizes evidence from our own studies and other published work; (2) proposes hypotheses regarding the fitness landscape of secondary growth of roots in annual dicotyledonous species for abiotic and biotic stress; and (3) highlights the importance of directing research efforts to this topic within an agricultural context. Secondary growth of the roots of annual dicots has functional significance with regards to soil resource acquisition and transport, interactions with soil organisms and carbon sequestration. Research on these topics would contribute significantly toward understanding the agronomic value of secondary growth of roots for crop improvement.

An interpreted language implementation of the Vaganov–Shashkin tree-ring proxy system model

We describe the implementation of the Vaganov–Shashkin tree-ring growth model (VSM) in MATLAB. VSM, originally written in Fortran, mimics subdaily and daily resolution processes of cambial growth as a function of soil moisture, air temperature, and insolation, with environmental forcing modeled as the principle of limiting factors. The re-implementation in a high level interpreted language, while sacrificing speed, provides opportunities to systematically evaluate model parameters, generate large ensembles of simulated tree-ring chronologies, and embed proxy system modeling within data assimilation approaches to climate reconstruction. We provide a versioned code repository and examples of model applications which permit process-level understanding of tree ring width variations in response to environmental variations and boundary conditions.

ELIMÄKI Locus Is Required for Vertical Proprioceptive Response in Birch Trees.

Tree architecture has evolved to support a top-heavy above-ground biomass, but this integral feature poses a weight-induced challenge to trunk stability. Maintaining an upright stem is expected to require vertical proprioception through feedback between sensing stem weight and responding with radial growth. Despite its apparent importance, the principle by which plant stems respond to vertical loading forces remains largely unknown. Here, by manipulating the stem weight of downy birch (Betula pubescens) trees, we show that cambial development is modulated systemically along the stem. We carried out a genetic study on the underlying regulation bycombining an accelerated birch flowering program with a recessive mutation at the ELIMÄKI locus(EKI), which causes a mechanically defective response to weight stimulus resulting in stem collapse after just 3months. We observed delayed wood morphogenesis in eki compared with WT, along with a more mechanically elastic cambial zone and radial compression of xylem cell size, indicating that rapid tissue differentiation is critical for cambial growth under mechanical stress. Furthermore, the touch-induced mechanosensory pathway was transcriptionally misregulated in eki, indicating that the ELIMÄKI locus is required to integrate the weight-growth feedback regulation. By studying this birch mutant, we were able to dissect vertical proprioception from the gravitropic response associated with reaction wood formation. Our study provides evidence for both local and systemic responses to mechanical stimuli during secondary plant development.

Dendrochronology of a Rare, Long-Lived Mediterranean Shrub

Ceanothus verrucosus (CEVE) is a globally rare, long-lived, chaparral shrub endemic to coastal southern California (CA) and northern Mexico. There is concern for CEVE persistence because of habitat loss, fire, and climate change, yet little is known about basic features of the plant, including whether it contains annual rings, plant age, and climate–growth response. Growth-ring analysis was challenging because of semi-ring-porous structure, false, and missing rings. We successfully crossdated CEVE annual rings, primarily from Cabrillo National Monument, CA, using a nearby Pinus torreyana chronology. The oldest living individual had 116 rings; the oldest inner-ring date was 1873; and most of the plants established between 1894 and 1905, all older than previous estimates. CEVE mortality occurred during a dry period from the late 1940s through the early 1960s. Correlations between age and stem measurements were weak to moderate (r = 0.10 to 0.56) posing challenges for field-based estimates of plant ages, which are important for population modeling. Variability in CEVE ring width had a strong positive correlation with prior cool-season (October–April) precipitation, yet 2- to 7-day warm-season precipitation events were recorded as rare false rings in multiple years, indicating extreme plasticity in cambial phenology and growth response to moisture.

INFLUENCE OF EXOGENOUS GIBBERELLIN AND ITS MIXTURE WITH SUCROSE ON THE FORMATION OF XYLEM INCREMENT OF SILVER BIRCH

We studied the effect of gibberellin on cambial activity towards the xylem formation in adult birch trees (Betula pendula Roth var. pendula, common birch). The injection of exogenous solutions was used as a methodological technique. To do this, “chambers” were made on tree trunks by cutting out the outer layers of the bark up to the inner parts of the non-conductive phloem, leaving the conductive phloem and cambial zone intact. GA3 gibberellin solutions (0.005%, 0.01%, 0.02%, 0.05%, 0.1%, 0.2 %) and a mixture of gibberellin with sucrose (GA3 0.01% + sucrose 1% - 20%) were injected into the chambers using a syringe. A strong stimulating effect of the hormone on the formation of xylem increment has been established. It was not possible to identify the dependence of the growth increment on the concentrations used, since their values obviously exceeded the level at which the maximum possible response of the cambial zone to the action of gibberellin was achieved with a given metabolic status of cells and tissues. This is confirmed by the effect of the residual action of exogenous solutions, which manifested itself after the termination of their administration: in variants with higher concentrations of the hormone, the final increase in xylem was greater. It was demonstrated for the first time that high sucrose concentrations (10% and 20%) reduce the stimulating effect of gibberellin. It has been suggested that in this case, sucrose can act through an increase in the level of UDP-glucose, the interaction of which with gibberellin leads to its conjugation (inactivation). The reaction of UDP-glucose with auxin cannot also be excluded, as a result of which it’s the conjugate IAA-glucose is formed, since gibberellin provides acceleration of cambial growth only in the presence of physiologically active (free) auxin in the tissue.

Sacrificing growth and maintaining a dynamic carbohydrate storage are key processes for promoting beech survival under prolonged drought conditions

In case of a prolonged drought, the stored carbohydrates in trees were remobilized to fuel survival functions until their nearly depletion at death stage. Dynamic global vegetation models project forest tree mortality in response to the recurrent severe droughts likely in the future. However, these models should better take into account the physiological processes involved in tree mortality. Faced with severe drought, the Fagus sylvatica L. tree strongly limits its cambial growth. This suggests that readjustments in carbon (C) allocation among sink functions are taking place in response to the lack of water and this could allow tree’s survival. For 3 years, we induced a water shortage on 8-year-old beech trees in a rain exclusion system. During this period, we analysed the consequences of severe drought on survival rate, growth, and non-structural carbohydrate (NSC) dynamics in the aboveground and belowground compartments of control, water-stressed living, and dead trees. The survival rate after 3 years of drought was 87%, while primary and secondary growth was strongly reduced. The first 2 years, NSC concentrations increased in all tree compartments (stem, branches, and roots) in response to drought. However, during the third year, starch dropped markedly in water-stressed trees, while soluble sugar concentrations remained similar to control trees. All the compartments in dead trees were virtually empty of starch and soluble sugars. Maintaining an active C storage function at the expense of growth was certainly key to F. sylvatica survival under prolonged extreme drought conditions. Process-based models predicting mortality should better take into account C storage and remobilization processes in forest trees.

Оцінка посухостійкості Ailanthus Altissima (Mill.) в умовах Правобережного Лісостепу і Степу України

Досліджено посухостійкість A. altissima упродовж вегетаційного періоду за п'ятибальною шкалою С. С. П'ятницького в умовах Правобережного Лісостепу і Степу України. Встановлено, що рослини роду Ailanthus добре переносять посуху й часто ростуть у місцях з обмеженим доступом води. За результатами аналізу середньомісячних та середніх багаторічних даних метеостанції м. Умань упродовж травня – серпня, надано порівняльну характеристику гідротермічного режиму років досліджень. Визначено, що водний і термічний режими деревних і кущових видів у Степу є головним фізіологічним аспектом успішності степового лісорозведення, з огляду на що очевидною є актуальність вивчення стійкості та адаптації інтродукованого виду A. altissima до несприятливих умов степової зони. Доведено, що рослини A. altissima, що зростають в умовах Правобережного Лісостепу і Степу України, реагували на посуху без значних пошкоджень, зберігаючи високий тургор листків і молодих пагонів. Дерева досліджуваного виду мали близькі до найвищих і найвищі бали посухостійкості (4,8-5,0 бала). Встановлено, що за період досліджень 2014-2017 рр. істотних ознак в'янення листків у дорослих дерев A. altissima в умовах Правобережного Лісостепу та Степу України не виявлено. Високі літні температури (до +38°С) і тривалі бездощові періоди (55-60 діб) всі досліджувані дерева A. altissima перенесли добре. Наведено результати дослідження водного режиму листків A. altissima за показниками загального вмісту води, водного дефіциту та інтенсивності втрати вологості, що свідчить про високий рівень адаптації досліджуваних рослин до посушливих періодів в умовах Правобережного Лісостепу та Степу України.

Ethylene Signaling Is Required for Fully Functional Tension Wood in Hybrid Aspen.

Tension wood (TW) in hybrid aspen trees forms on the upper side of displaced stems to generate a strain that leads to uplifting of the stem. TW is characterized by increased cambial growth, reduced vessel frequency and diameter, and the presence of gelatinous, cellulose-rich (G-)fibers with its microfibrils oriented parallel to the fiber cell axis. Knowledge remains limited about the molecular regulators required for the development of this special xylem tissue with its characteristic morphological, anatomical, and chemical features. In this study, we use transgenic, ethylene-insensitive (ETI) hybrid aspen trees together with time-lapse imaging to show that functional ethylene signaling is required for full uplifting of inclined stems. X-ray diffraction and Raman microspectroscopy of TW in ETI trees indicate that, although G-fibers form, the cellulose microfibril angle in the G-fiber S-layer is decreased, and the chemical composition of S- and G-layers is altered than in wild-type TW. The characteristic asymmetric growth and reduction of vessel density is suppressed during TW formation in ETI trees. A genome-wide transcriptome profiling reveals ethylene-dependent genes in TW, related to cell division, cell wall composition, vessel differentiation, microtubule orientation, and hormone crosstalk. Our results demonstrate that ethylene regulates transcriptional responses related to the amount of G-fiber formation and their properties (chemistry and cellulose microfibril angle) during TW formation. The quantitative and qualitative changes in G-fibers are likely to contribute to uplifting of stems that are displaced from their original position.

Simulated and predicted responses of tree stem radial growth to climate change—A case study in semi-arid north central China

Precise knowledge how tree growth will respond to future climate change is essential for the adapted management of forest ecosystems. By conducting sensitivity tests, tree-ring process-based cambial growth models can provide an innovative way to better understand wood formation under different climate change scenarios. As a case study in semi-arid north central China, we used artificially increased or decreased daily climatic data as input to the Vaganov-Shashkin dynamic growth model to investigate the response of wood formation to climatic change. By calibrating the tree-ring model using daily climate data over the period 1951–2010, we found that 81% of radial growth was driven by soil moisture, while 13% of growth was controlled by temperature. During the main growing season June–August, significant differences in the integral growth rate occurred after changing precipitation by ± 30% or by decreasing temperature by 3.0 °C (p < 0.05). However, increasing temperature showed only modest effects on tree radial growth rate. During the past 60 years, a significant advancement of the starting dates of growth was detected, whereby non-significant variability was found for the ending dates of growth. Contemporaneously, the effect of previous winter temperature (previous December to current January) on cambial growth initiation declined after 1980. Significant differences in the growth onset dates only occurred when temperature was reduced by 4.5 °C or increased by 5.5 °C. Moreover, both the onset and ending dates of growth in the study region were more sensitive to cooling rather than to warming. If temperature will increase by 2°C and precipitation will increase by 30% at the end of this century as predicted by some Earth system models, tree radial growth might increase by 19% in the study region, compared to the average during the period 1952–2010. Consequently, tree stem radial growth is expected to increase under a warming and wetting climatic scenario, but will decrease under drying conditions.

Differential gene expression in non-transgenic and transgenic \u201cM.26\u201d apple overexpressing a peach CBF gene during the transition from eco-dormancy to bud break

The CBF signal pathway is responsible for a significant portion of plant responses to low temperature and freezing. Overexpression of CBF genes in model organisms such as Arabidopsis thaliana enhances abiotic stress tolerance but also reduces growth. In addition to these effects, overexpression of the peach (Prunus persica [L.] Batsch) CBF1 gene in transgenic apple (Malus x domestica Borkh.) line T166 also results in early entry into and late exit from dormancy. Although the regulation of dormancy-induction and dormancy-release occur while the CBF regulon is operative in perennial, woody plants, how overexpression of CBF1 affects these dormancy-related changes in gene expression is incompletely understood. The objective of the present study was to characterize global changes in gene expression in peach CBF1-overexpressing and non-transformed apple bark tissues at different states of dormancy via RNA-seq. RNA-seq bioinformatics data was confirmed by RT-qPCR on a number of genes. Results indicate that the greatest number of significantly differentially expressed genes (DEGs) occurred in April when dormancy release and bud break normally occur but are delayed in Line T166. Genes involved in storage and inactivation of auxin, GA, and cytokinin were generally upregulated in T166 in April, while those for biosynthesis, uptake or signal transduction were generally downregulated in T166. Genes for cell division and cambial growth were also downregulated in T166 relative to the non-transformed line. These data suggest that overexpression of the peach CBF1 gene impacts growth hormone homeostasis and as a result the activation of growth in the spring, and most likely growth cessation in the fall as well.

Annual wood formation of tropical pioneer species related to stem diameters

Annual wood increment and cambial activity in Macaranga gigantea and Endospermum diadenum growing in tropical rainforest were monitored to examine their relationship with stem sizes and climatic factors. The monitoring period was done from March 2013 to February 2014. Wood blocks containing phloem, cambium and outer sapwood were collected monthly from the main trunk of selected trees. Results showed that M. gigantea with smaller stem diameter showed higher annual diameter increment (16.63 ± 7.2 mm) than those with larger stem diameters (3.30 ± 0.1 mm) The total amount of wood formed in E. diadenum with larger stem diameter (9.17 ± 0.3 mm) was higher than the trees with smaller stem size (3.33 ± 0.3 mm). The rhythm of cambial activity were found different among tree species and stem diameters within the same species. M. gigantea with smaller stem diameter had longer active cambial growth period and produced higher number of cell layers than trees with larger stem diameter. In contrast, E. diadenum with larger stem diameter showed longer active growth period and higher number of cell layers than trees with smaller stem diameter. This study showed no significant correlation between mean number of cambial and enlarging cell layers with monthly total rainfall, monthly mean relative humidity, vapor pressure deficit and day length. Significant negative correlations were detected between maximum temperature and number of cambial and enlarging cell layers in M. gigantea with smaller stem size. For E. diadenum with smaller stem size, monthly mean temperature had significant negative correlation with the number of cambial cell layer. This study concluded that the intra-annual wood formation patterns of this two pioneer species are species specific and stem sizes specific.

Changes in Spruce Growth and Biomass Allocation Following Thinning and Guying Treatments

When forest stands are thinned, the retained trees are exposed to increased light and greater mechanical strain from the wind. The consequent greater availability of photosynthate and localised mechanical strain in stems and roots are both known to increase cambial growth in conifers, but their relative importance has not previously been quantified. Light availability and wind movement were manipulated in a 10-year-old stand of Sitka spruce trees on an exposed upland site. Treatments were “Control”—no change in spacing or wind loading; “Thinned”—light availability and wind loading increased by removing neighbouring trees; “Thinned and guyed”—light increased and wind loading reduced by removing neighbouring trees and guying stems with wires. Twelve trees per treatment were maintained and monitored for four years before harvesting and removal of cross-sectional stem samples from four heights for measurement of radial growth response. Root systems were excavated from each treatment for observations of associated root growth responses. The “Thinned” treatment and “Thinned and guyed” treatment showed no significant stem growth response in the first year after treatment, but very large increases in the second and subsequent years. There were much larger growth responses in the “Thinned” treatment than in the “Thinned and guyed” treatment, especially in the lower stem. Similar growth responses were observed in the structural roots, close to the stem base. These increases in stem and root growth in response to wind movement corresponded with a reduction of branch growth. Such changes in allocation have implications for the hydraulic and biomechanical requirements of trees, and should be incorporated into tree growth and stability models.

Source–Sink Relations in the Organs and Tissues of Silver Birch during Different Scenarios of Xylogenesis

Source–sink relations in the “leaf–stem–root” system at the time of cambial growth were studied in two forms of silver birch: common birch (Betula pendula Roth var. pendula) and Karelian birch (B.pendula var. carelica (Merckl.) Hamet-Ahti). As compared with common birch, reduced sucrose content in the leaves of elongated (auxiblasts) and short (brachyblasts) twigs of Karelian birch is associated with the accumulation of starch. In common birch, a pronounced sucrose gradient between the phloem (responsible for sucrose delivery to sink tissues) and xylem (the main acceptor of sucrose flowing from the leaves) points to an active consumption of the disaccharide in the production of structural elements of wood. As compared with common birch, in the phloem of Karelian birch where apoplast invertase activity is high, the content of sucrose decreases and the level of starch rises. Formation of anomalous patterned wood is associated with a suppression of sucrose synthase pathway and activation of the apoplastic pathway of sucrose utilization. At the same time, the content of cellulose in the tissues decreases and the level of starch increases. Sucrose gradient between the phloem and xylem in the anomalous areas is less pronounced. We suppose that, as a result of metabolism transformation in Karelian birch, the sink power of trunk tissues increases, which shows itself in structural and functional peculiarities of the source of photoassimilates—the leaves of brachyblasts that are larger in size in Karelian birch.