Silver birch shows nonlinear responses to moisture availability and temperature in the eastern Baltic Sea region

Silver birch (Betula pendula Roth.) is a widespread species with a high potential for aiding sustainability and multifunctionality of European forests, as evidenced in Finland and the Baltics. However, under increasing relevance of climate change for tree growth, the meteorological sensitivity of the species is largely unknown, presuming it to be weather tolerant (low sensitivity). Considering local adaptations of populations of widespread species, climatic changes are subjecting trees to extreme conditions, thus testing their adaptability. Accordingly, information on the plasticity (variability) of responses across a gradient of meteorological conditions is crucial for reliable predictions of tree growth. Tree-ring width network was established to assess the plasticity of growth responses of silver birch to meteorological conditions across the eastern Baltic climatic gradient. Time series analysis in combination with generalized additive modelling were applied to assess responses of birch from 21 naturally regenerated conventionally managed stands scattered from southern Finland to northern Germany. Despite the presumed tolerance, explicit meteorological sensitivity of silver birch was estimated. A gradient of local linear weather-growth relationships was estimated, as growth limitation shifted from temperature during the dormancy to water availability during vegetation period in southern Finland and northern Germany, respectively. However, these relationships were nonstationary, as the effect of summer water shortage was intensifying and sensitivity to it has likely been subjected to local adaptation. The regional generalization revealed presence of stationary, yet nonlinear and plastic growth responses, implying disproportional effects of climatic changes. Such responses also explained the nonstationarities, as the local climates shifted along the regional gradient. At the regional scale, summer water shortage was the main driver of increment, while winter conditions had a secondary role; temperature of the preceding vegetation season also had an effect on increment. Accordingly, increased variability of increment of silver birch is expected under changing climate; still, sensitivity and plasticity of increment can be considered as an adaptation to shifting environments.     

Cold acclimation in silver birch (Betula pendula). Development of freezing tolerance in different tissues and climatic ecotypes

A number of environmental cues including short day photoperiod (SD) and low temperature (LT) are known to interact in triggering growth cessation, cold acclimation and other adaptive responses in temperate-zone tree species. Proper timing of these responses is particularly important for survival of trees in the boreal and subarctic regions. Therefore, we used a northern tree species, silver birch ( Betula pendula Roth) as an experimental model to investigate the effect of SD and LT on development of freezing tolerance and on levels of endogenous abscisic acid (ABA) in short-term experiments under controlled conditions. We characterized differences in SD and LT-induced cold acclimation between three different climatic ecotypes from southern, central and northern habitats. The results demonstrated that cold acclimation was rapidly triggered by exposing the plants to SD or LT, and that a combination of the different treatments had an additive effect on freezing tolerance. Freezing tolerance induction was not uniform in the different tissues, the buds and leaves developed freezing tolerance more rapidly than the stem, and the young leaves had a higher freezing tolerance than the old leaves. The ability of the leaves to respond to SD and LT and similarity of the bud and leaf responses indicate that birch leaves provide a rapid and convenient system for studies on molecular mechanisms of cold acclimation. Development of freezing tolerance was dependent on the climatic ecotype, the northern ecotype was clearly more responsive to both SD and LT than the two more southern ecotypes. Development of freezing tolerance induced by SD and LT was accompanied by transient changes in ABA levels. These alterations in ABA levels were ecotype-dependent, the northern ecotype reacting more strongly to the environmental cues.     

Reddish spring colouring of deciduous leaves: a sign of ecotype?

Several deciduous woody plant species produce anthocyanins during leaf development in spring and again during leaf senescence in autumn. The leaves of Betula pendula Roth (silver birch) commonly exhibit transient reddening in juvenile leaves under northern growing conditions, with the intensity of the red colour varying among individual trees. The objective of our study was to test the hypothesis that the accumulation of foliar anthocyanins during spring in leaves of B. pendula is an ecotypic response. Chlorophyll fluorescence ratio (Fv/Fm), leaf reflectance and anthocyanin concentrations were measured, in relation to phenology in spring, summer and autumn from birches used for landscaping with either red or green-emergent leaves. The results suggest that (1) the trees with green- or red-emergent juvenile leaves represent different populations, and (2) that the red-emergent leaves senesced earlier, indicating that (3) trees with red-emerging leaves belong to a more northern ecotype than the trees with green-emerging leaves. The role of anthocyanin synthesis in a northern radiation environment is discussed.     

Field performance of chitinase transgenic silver birches (<Emphasis Type="Italic">Betula pendula</Emphasis>): resistance to fungal diseases

A field trial of 15 transgenic birch lines expressing a sugar beet chitinase IV gene and the corresponding controls was established in southern Finland to study the effects of the level of sugar beet chitinase IV expression on birch resistance to fungal diseases. The symptoms caused by natural infections of two fungal pathogens, Pyrenopeziza betulicola (leaf spot disease) and Melampsoridium betulinum (birch rust), were analysed in the field during a period of 3 years. The lines that had shown a high level of sugar beet chitinase IV mRNA accumulation in the greenhouse also showed high sugar beet chitinase IV expression after 3 years in the field. The level of sugar beet chitinase IV expression did not significantly improve the resistance of transgenic birches to leaf spot disease. Instead, some transgenic lines were significantly more susceptible to leaf spot than the controls. The level of sugar beet chitinase IV expression did have an improving effect on most parameters of birch rust; the groups of lines showing high or intermediate transgene expression were more resistant to birch rust than those showing low expression. This result indicates that the tested transformation may provide a tool for increasing the resistance of silver birch to birch rust.     

The dynamics of phenolic compounds and soluble sugars in the leaves of the silver birch (<Emphasis Type="Italic">Betula pendula</Emphasis> Roth) after defoliation and their significance in entomological plant resistance

The dynamics of phenolic compounds, flavonols, catechines, tannins, and soluble sugars in the leaves of the silver birch Betula pendula Roth after strong (75%) and total (100%) artificial defoliation was studied. It was shown that the flavonol content in the leaves did not change after strong and total defoliation, while the amount of tannins did not change during the first 15 days but increased later on 1 and 2 years after 75% and 100% defoliation. The catechine content did not change during the first 15 days and increased later on 1 year after strong and total defoliation; however, it returned to the level of control plants 2 years after both types of defoliations. The amount of soluble sugars in the leaves increased 2 days after 75% defoliation; however, their content conformed to that in control plants after 10 days and it remained later 1 and 2 years after the damage. The amount of soluble sugars in the leaves also did not change 1 year after 100% defoliation.     

Red : far-red light ratio and UV-B radiation: their effects on leaf phenolics and growth of silver birch seedlings

The natural variation in quantity and quality of light modifies plant morphology, growth rate and concentration of biochemicals. The aim of two growth‐room experiments was to study the combined effects of red (R) and far‐red (FR) light and ultraviolet‐B (UV‐B) radiation on the concentrations of leaf phenolics and growth and morphology of silver birch (Betula pendula Roth) seedlings. Analysis by high‐performance liquid chromatography showed that the leaves exposed to supplemental FR relative to R contained higher concentrations of total chlorogenic acids and a cinnamic acid derivative than the leaves treated with supplemental R relative to FR. In contrast, concentration of a flavonoid, quercetin 3‐galactoside, was higher in the R + UV‐B leaves than in the FR + UV‐B leaves. The UV‐B induced production of kaempferols, chlorogenic acids and most quercetins were not modified by the R : FR ratio. Growth measurements showed that the leaf petioles and stems of FR seedlings were clearly longer than those of R seedlings, but leaf area was reduced by UV‐B radiation. Results of these experiments show that exposure of silver birch seedlings to supplemental FR compared to R leads to fast elongation growth and accumulation of phenolic acids in the leaves.     

水分、氮肥及MeJA处理对白桦三萜积累特性的影响

以一年半生白桦幼树为试材,研究水分、氮肥和茉莉酸甲酯(MeJA)处理对白桦三萜物质积累的影响,并对白桦植株中三萜积累规律进行了探讨。结果表明:(1)白桦幼树植株中总三萜主要分布在茎皮和叶片,根皮中最低,平均含量分别为71.94、81.60和25.45mg.g-1;叶片中总三萜积累高峰出现在6、7月份,茎皮和根皮中总三萜积累高峰分别出现在8月份和7月份。(2)干旱胁迫早期(6月)中度和重度干旱胁迫显著促进了叶中总三萜积累,分别是对照的1.24和1.27倍。茎皮中,除7月水分胁迫处理显著高于对照外,其它各月份水分胁迫不利于茎皮中总三萜含量积累,干旱胁迫不利根皮中三萜积累。(3)施氮早期(6月)不利于三萜在叶片和根皮中积累,中后期(7～10月),氮肥处理对三萜积累有显著促进作用;而施氮早期(6～7月)促进茎皮中三萜积累作用。(4)MeJA喷施处理对叶片和根皮中三萜积累(7月～10月)均具有显著的促进作用,在积累高峰期分别是对照的1.42倍和1.52倍。(5)轻度干旱、氮肥均促进了白桦幼树株高的增长和生物量的积累,而MeJA处理对整株生物量的积累不利。     

Leaf features of silver birch (Betula pendula Roth). Variability within and between two populations (uncontaminated vs Pb-contaminated and Zn-contaminated site)

Fourteen morphometric variables of silver birch (Betula pendula Roth) leaves from two sites in the Upper Silesia province were analyzed to establish the pattern of intrapopulational and interpopulational relations. The leaves were collected from ten trees growing on a zinc–lead dump as well as from ten trees in the unpolluted area of Mirów within the same bioclimatic region. Leaf samples were collected from the trees during the vegetative seasons 1999 and 2000. The size and shape of leaves were studied using standard biometric methods. Cluster analysis indicated overall differences between the populations. Both populations differed with respect to almost all the morphometric variables (P<0.05). Most variables of the leaves, collected from single trees (or combined as a total) on the zinc–lead dump showed more variability than those from the unpolluted site. Discriminant function analysis confirmed the angle of the leaf base as the most important variable in the evaluation of interpopulational variability of leaves.     

Vocal Diversity and Taxonomy of <Emphasis Type="Italic">Nomascus</Emphasis> in Central Vietnam and Southern Laos

Previous researchers suggested that gibbon song repertoire is genetically determined and song characteristics are useful for assessing systematic relationships. The southern white-cheeked crested gibbon is regarded as either a subspecies of Nomascus leucogenys or its own species (Nomascus siki). I studied vocal diversity among different wild populations of Nomascus in central Vietnam and southern Laos to assess their taxonomic relationships and to examine whether their vocal patterns correspond to forms previously described for Nomascus siki. I examined the songs of 7 Nomascus populations in Vietnam and Laos. I analyzed 192 song bouts from different gibbon groups including 173 phrases of 42 females and 192 phrases of 42 males. Linear discriminant analysis, classification trees, and multidimensional scaling revealed marked separation of groups in the northern and southern populations. Within the 2 geographic populations, there is little variability and the vocal characteristics exhibited no apparent cline. I conclude that the northern and southern geographic populations may represent 2 distinct taxa. I postulate that a taxonal boundary such as large rivers existing between southern Quang Binh province and northern Thua-Thien Hue province in Vietnam and northern Phou Xang He NBCA and southern Dong Phou Vieng NBCA in Laos has limited gene flow between the populations. Differing topographic features could also serve as a selective force for improved sound transmission in a highly territorial species, driving the divergence between the 2 populations.     

Distribution and expression characteristics of triterpenoids and OSC genes in white birch (<Emphasis Type="Italic">Betula platyphylla</Emphasis> suk.)

Betulin and oleanolic acids (pentacyclic triterpenoid secondary metabolites) have broad pharmacological activities and can be potentially used for the development of anti-cancer and anti-AIDS drugs. In this study, we detected the accumulation and the distribution characteristics of betulin and oleanolic acid in various organs of white birch at different ages. We also determined the expression of 4 OSC genes (LUS, β-AS, CAS1 and CAS2) involved in the triterpenoid synthesis pathways by real time RT-PCR. The result showed that the 1-year old birch can synthesize betulin and oleanolic acid. In addition, betulin and oleanolic acids were mainly distributed in the bark, while the content in the root skin and leaf was very low. The content of betulin and oleanolic acid in birch varied in different seasons. The content of betulin and oleanolic acid and their corresponding LUS and β-AS gene expression were very low in 1-year old birch. With increasing age of birch, betulin content was increased, while oleanolic acid was decreased. Similar changes were also observed for their corresponding synthesis genes LUS and β-AS. In the leaf of 1-year old plant, the highest expression of CAS1 and CAS2 occurred at end of September, while expression of LUS and the β-AS was low from June to October. In the stem skin,high expression of β-AS and the LUS genes occurred from the end of July to September. In the root, high expression of the β-AS gene was observed at the end of October. These results indicated that triterpenoid gene expression was similar to the triterpene accumulation. Expression of LUS gene and β-AS gene in birch with different ages were corresponding to the betulinic and oleanolic acid accumulation. Expression of CAS1 and CAS2 genes were elevated with increasing age of birch. This study provides molecular mechanisms of triterpenes synthesis in birch plants.     

Effects of natural and artificial defoliation on the content and composition of extractive substances in birch leaves

Qualitative and quantitative compositions of extracts of birch (Betula pendula Roth.) leaves after natural and artificial defoliation were studied. Composition of the fraction of total lipids was determined. Over-all, 11 fatty acids were identified. Differences between the fatty acid compositions of total lipids in the trees subjected to defoliation, consisting in the increase in quantities of short-chain saturated fatty acids and trienoic acids, were detected. Nine individual compounds—six flavones, two flavanones, and one flavanonol—were isolated from the flavonoid fraction by column chromatography. It was found that the total content of extractive substances in birch leaves as well as amounts of free sterols, triterpene compounds, and flavones decreased 1 year after artificial defoliation and 1 month after depredation of 75% of birch stands by gypsy moths. On the contrary, the contents of flavanones and flavanonol increased. The assay method proposed may be used for studying the compositions of plant extracts.Translated from Prikladnaya Biokhimiya i Mikrobiologiya, Vol. 41, No. 1, 2005, pp. 107–112.Original Russian Text Copyright © 2005 by Shults, Bakhvalov, Martemyanov, Petrova, Syromyatnikova, Shakirov, Tolstikov.     

Potassium nutrition and free polyamines of Betula pendula Roth and Betula pubescens Ehrh.

Potassium and free polyamine concentrations in the leaves of silver birch (Betula pendula Roth) and downy birch (Betula pubescens Ehrh) were followed during three successive growing seasons 1996, 1997 and 1998 in order to define K deficiency levels.The highest foliar K concentrations were found in June. In August, the K concentrations were lower and remained quite stable in Betula pendula but varied in Betula pubescens. In addition to a common diamine, putrescine, and the polyamines, spermidine and spermine, also a less common diamine and polyamine, 1,3-diaminopropane and norspermidine were found in the birch leaves. The accumulation of both diamines, putrescine and 1,3-diaminopropane, was used to define the critical levels of K nutrition in birch leaves. Foliar K concentrations below 7–8 mg g ^–1 DW were found to correlate with the accumulation of diamines at most sampling dates.     

Does lignin modification affect feeding preference or growth performance of insect herbivores in transgenic silver birch (<Emphasis Type="Italic">Betula pendula</Emphasis> Roth)?

Transgenic silver birch (Betula pendula Roth) lines were produced in order to modify lignin biosynthesis. These lines carry COMT (caffeate/5-hydroxyferulate O-methyltransferase) gene from Populus tremuloides driven by constitutive promoter 35S CaMV (cauliflower mosaic virus) or UbB1 (ubiquitin promoter from sunflower). The decreased syringyl/guaiacyl (S/G) ratio was found in stem and leaf lignin of 35S CaMV-PtCOMT transgenic silver birch lines when compared to non-transformed control or UbB1–PtCOMT lines. In controlled feeding experiments the leaves of transgenic birch lines as well as controls were fed to insect herbivores common in boreal environment, i.e., larvae of Aethalura punctulata, Cleora cinctaria and Trichopteryx carpinata (Lepidoptera: Geometridae) as well as the adults of birch leaf-feeding beetles Agelastica alni (Coleoptera: Chrysomelidae) and Phyllobius spp. (Coleoptera: Curculionidae). The feeding preferences of these herbivores differed in some cases among the tested birch lines, but these differences could not be directly associated to lignin modification. They could as well be explained by other characteristics of leaves, either natural or caused by transgene site effects. Growth performance of lepidopteran larvae fed on transgenic or control leaves did not differ significantly.     

Leaf Surface Lipophilic Compounds as One of the Factors of Silver Birch Chemical Defense against Larvae of Gypsy Moth

Plant chemical defense against herbivores is a complex process which involves a number of secondary compounds. It is known that the concentration of leaf surface lipophilic compounds (SLCs), particularly those of flavonoid aglycones are increased with the defoliation treatment of silver birch Betula pendula. In this study we investigated how the alteration of SLCs concentration in the food affects the fitness and innate immunity of the gypsy moth Lymantria dispar. We found that a low SLCs concentrations in consumed leaves led to a rapid larval development and increased females’ pupae weight (= fecundity) compared to larvae fed with leaves with high SLCs content. Inversely, increasing the compounds concentration in an artificial diet produced the reverse effects: decreases in both larval weight and larval survival. Low SLCs concentrations in tree leaves differently affected larval innate immunity parameters. For both sexes, total hemocytes count in the hemolymph increased, while the activity of plasma phenoloxidase decreased when larvae consume leaves with reduced content of SLCs. Our results clearly demonstrate that the concentration of SLCs in silver birch leaves affects not only gypsy moth fitness but also their innate immune status which might alter the potential resistance of insects against infections and/or parasitoids.     

A proposed role for the anaerobic pathway during low-temperature sweetening in tubers of Solanum tuberosum

Survival and growth of temperate zone woody plants under changing seasonal conditions is dependent on proper timing of cold acclimation and development of vegetative dormancy, shortening photoperiod being an important primary signal to induce these adaptive responses. To elucidate the physiological basis for climatic adaptation in trees, we have characterized photoperiodic responses in the latitudinal ecotypes of silver birch ( Betula pendula Roth) exposed to gradually shortening photoperiod under controlled conditions. In all ecotypes, shortening photoperiod triggered growth cessation, cold acclimation and dormancy development, that was accompanied by increases in endogenous abscisic acid (ABA) and decreases in indole-3-acetic acid (IAA). There were distinct differences between the ecotypes in the rates and degrees of these responses. The critical photoperiod and the photoperiodic sensitivity for growth cessation varied with latitudinal origin of the ecotype. The northern ecotype had a longer critical photoperiod and a greater photoperiodic sensitivity than the southern ecotype. Compared with the southern ecotypes, the northern ecotype was more responsive to shortening photoperiod, resulting in earlier cold acclimation, dormancy development, increase in ABA content and decrease in IAA content. However, at the termination of the experiment, all the ecotypes had reached approximately the same level of cold hardiness (−12 to −14°C), ABA content (2.1–2.3 µg g⁻¹ FW) and IAA content (17.2–20.3 ng g⁻¹ FW). In all ecotypes, increase in ABA levels preceded development of bud dormancy and maximum cold hardiness. IAA levels decreased more or less parallel with increasing cold hardiness and dormancy, suggesting a role of IAA in the photoperiodic control of growth, cold acclimation and dormancy development in birch.     

SEASONAL AND INDIVIDUAL VARIATION IN LEAF QUALITY OF TWO NORTHERN HARDWOODS TREE SPECIES

Seasonal trends in five traits of sugar maple (Acer saccharum Marsh.) and yellow birch (Betula allegheniensis Britt.) leaves thought to influence feeding by herbivores were measured from 17 May through 19 September, 1979. Total nitrogen and water contents declined and toughness increased through the growth season. These seasonal changes were more pronounced in sugar maple than in yellow birch. Total polyphenol contents and tanning coefficients of leaf extracts from both species reached a season high by the end of May and changed very little after that date; these patterns differ from those reported by several other investigators. Sugar maple leaf extracts exhibited much higher tanning coefficients than did those of yellow birch, a finding which is consistent with current plant defense theory. Significant differences in total polyphenol content and tanning coefficients were found between individual trees in yellow birch, but not sugar maple. The relationship between successional status, leaf quality traits, and variability in these traits in forest trees is discussed.     

Flowering of allergenically important plant species in relation to the North Atlantic Oscillation system and thermal time in the Czech Republic

This paper analyses long-term (1960–2015) onset of flowering in 16 native terrestrial plants (11 of them produce important allergens) recorded in different parts of the Czech Republic (southern, central and northern part) in relation to the North Atlantic Oscillation (NAO) index of the preceding winter and thermal data—growing degree-days (GDD) and soil temperature. Flowering occurred significantly earlier following positive winter NAO phases (causing spring to be warmer than normal in Central Europe) in nearly all early-flowering (February, March, April) species; high Pearson correlation values were recorded in, e.g. wood anemone, common snowdrop, goat willow, common hazel and common alder. There was found a difference between the southern and northern part of the country, e.g. in silver birch and pedunculate oak. Out of the later-flowering (May–July) plant species, black elder and meadow foxtail also significantly correlated with the winter NAO index, lime tree correlated less markedly. The best results of a threshold for calculation of GDD to onset of beginning of flowering were found in lime tree—it was 5 °C at all three stations. Results of other taxa were more variable (e.g. 4–7 °C in goat willow; 6–10 °C in silver birch). Pearson correlation coefficients between NAO index and GDD were negative in lime tree at all thresholds (5, 6, 7, 8, 9, 10 °C), while goat willow and silver birch were not so uniform (both positive and negative values). Correlation coefficients between phenophase onset and soil temperature (10 cm depth) had the highest values in silver birch, European larch and wood anemone. Stations situated at higher elevation showed negative correlation coefficient with soil temperature in common snowdrop, pedunculate oak, meadow foxtail and lime tree; other values were positive.     

Homeostatic responses of plants to modern climate change: Spatial and phenological aspects

A series of dates of unfolding of the first leaves and duration of the season of vegetation in the silver birch (Betula pendula Roth. (B. verrucosa Ehrh.)), as well as the duration of flowering of the bird cherry (Padus avium), mountain ash (Sórbus aucupária), and small-leaved lime (Tilia cordata Mill.) for the period 1970–2010 in the central part of European Russia were studied in order to assess the trends. Differences in phenological responses to homogeneous climate changes in the trees of the same species from the northern and southern parts of the range were revealed. If spring events occur 3–7 days earlier in the northern part, no such effect is observed in the south. This fact can be interpreted as a manifestation of the different mechanisms of homeostasis in different populations determined by their biological characteristics (in particular, by the need to pass successfully the periods of organic rest and vegetation).