Effects of aluminium on growth and nutrient uptake of Betula pendula seedlings

The response to aluminium concentrations was evaluated for birch seedlings ( Betula pendula Roth, formerly Betula verrucosa Ehrh.) by using a growth technique that provides stable internal concentrations of nutrients in plants. Aluminium was added as aluminium nitrate and aluminium chloride and pH was kept at 3.8±0.2 by adding HCl or NaOH. The seedlings were grown in two different series of nutrient treatments, either with near-optimum conditions (relative addition rate 25% day⁻¹) or with constant nutrient stress (relative addition rate 10% day⁻¹) before the aluminium addition. Growth reduction occurred at aluminium concentrations greater than 3 m M , and lethal effects at aluminium concentrations greater than 15 m M . In plants subjected to near-optimum conditions before aluminium addition, the internal nutrient concentrations decreased with increasing aluminium concentration for all macronutrients. The concentration of the macronutrients N, K and P decreased gradually with increasing aluminium concentration, while the concentration of Ca and Mg decreased fairly abruptly when aluminium concentrations exceeded 1 m M . The same tendency was observed in nutrient stressed birch seedlings, but the pattern was more scattered. Relative growth rate of the seedlings was not affected by a low Ca/Al ratio. In all treatments, the molar Ca/Al ratio in/on the roots was below 0.2 at the end of the experiments. As decrease in growth occurs only at high aluminium concentrations, there is no reason to suggest that aluminium in acid soils is growth limiting for natural birch stands.     

Effects of aluminium on growth and root reactions of phosphorus stressed Betula pendula seedlings

The impact of two constant non-toxic levels of Al stress (0.2 and 0.4 mM) on growth and ³²P uptake capacity on sub-optimal (P-limited) Betula pendula seedlings grown in sand culture was examined.Seedling growth was under optimum controlled conditions in a growth chamber where nutrient additions were made at a predetermined relative addition rate (R_A) of 10% day^-1. Three treatment groups of seedlings 0, 0.2 and 0.4 mM Al were harvested at 15, 29 and 42 days. The excised roots were exposed to a ³²P-labelled solution for 15 minutes to measure their capacity for P uptake. Growth was determined by weighing the roots, stems and leaves of the seedlings.Growth data showed that relative growth rate (R_G) should equal the R_A of P the most limiting nutrient, which was supplied at P/N 3% instead of an optimal 15%. Therefore, Ingestad's theory can also be used succesfully in sand culture and this may be particularly important for future studies of root and rhizosphere exudates. Low levels of Al (< 0.2 mM) in combination with low P supply significantly lowered the R_G of the birch seedlings by further reducing P supply. However, previous studies of birch seedling growth and nutrient uptake using Ingestad's solution culture technique with optimumal P supply did not show any effect of Al on growth untill the Al was in excess of 3 mM. Aluminium was not directly toxic to the plants and therefore roots could respond to the ³²P bioassay.     

The influence of root-zone temperature on growth of Betula pendula Roth.

We have examined shoot and root growth and the concentration of carbohydrates in seedlings of a northern (67°N) and a southern (61°N) ecotype of Betula pendula Roth. cultivated at root-zone temperatures of 2, 6, 12 and 17°C. Three hydroponic experiments were conducted in controlled environments. We used three different pretreatments before seedlings were subjected to the experimental temperature treatments. Actively growing seedlings that were acclimated to the hydroponic solution for 3 weeks at a root temperature of 17°C, continued to grow at all the experimental temperatures, with an expected increase in growth from 2 to 17°C. However, if we started with ecodormant cold stored plants or used seedlings grown actively in perlite, no growth was observed at 2°C and only minor growth was found at 6°C. The highest root temperature always produced the best growth. The concentration of nonstructural carbohydrates was higher in seedlings grown at 2°C than at 17°C, and this is probably due to extensive incorporation of carbohydrates into cell walls and other structural elements at 17°C. We found no evidence for differences between the two ecotypes in root growth, in timing of bud burst, but shoot growth terminated in the northern ecotype in the first experiment because the natural photoperiod was below the critical value. Our study highlights the importance of post-transplantation stress (planting check) related to root growth, and that root threshold temperatures may change according to the way plants are pretreated.     

Effects of ultraviolet-B radiation on growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula Roth) seedlings grown in low-nutrient conditions

The effects of increased ultraviolet‐B (UV‐B) radiation on the growth, mycorrhizas and mineral nutrition of silver birch (Betula pendula Roth) seedlings were studied in greenhouse conditions. Seedlings—planted in a birch‐forest top soil and sand substrate—were grown without additional nutrient supply. Ultraviolet treatment started immediately after the seedlings emerged and the daily integrated biologically effective UV‐B irradiance on the UV‐B‐treated plants was equivalent to a 25% depletion of stratospheric ozone under clear sky conditions. Visible symptoms of UV‐B damage or nutrient deficiency were not observed throughout the experiment. Seedling height and dry weight (DW) (measured after 58 days and 76 days of treatment) were not affected by increased UV‐B. However, a significant shift in DW allocation toward roots resulted in a lower shoot/root ratio and leaf area ratio in UV‐B‐treated plants compared to control plants. At the first harvest (after 58 days of treatment), the percentage of various mycorrhizal morphotypes and the number of short roots per unit of root length or weight were not affected by increased UV‐B despite significantly increased DW allocation toward roots. Subtle reduction in the allocation of nitrogen (N) to leaves and increased allocation of phosphorus (P) to roots may suggest cumulative effects that could affect the plant performance over the long‐term.     

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.     

Investigation of daily mitotic activity of the birch, Betula pendula Roth

A study was made of the daily mitotic activity in the seedling root meristem of birch trees growing in an ecologically clear area--the biological station of Voronezh State University "Venevitinovo". The peak of mitotic activity was exposed at 9 a. m. (according to winter time). The rise of mitotic index was noted at 9 and 12 p. m. due to an increase in the share of cells being in the prophase stage, and to a high number of dividing cells with persistent nucleoli. A possibility of prolongation of the mitotic cycle time is supposed to be due to cell delay in prophase stage, which may be associated with anthropogenic and nature-climatic influences on the original trees themselves and on their seed progeny. This makes it possible to consider the investigated region as only conventionally clear, because of the availability of a high recreative pressure upon the trees.     

Vitrification, a complementary cryopreservation method for Betula pendula Roth

Cryopreservation--the storage of plant germplasm in liquid nitrogen--provides a modern tool for the conservation of forest genetic resources. It is especially applicable for species in which their micropropagation can be initiated from mature tree buds, e.g., silver birch (Betula pendula Roth), thus enabling the conservation of specific genotypes: endangered elite trees and trees expressing rare, valuable or interesting characteristics. The aim of the present study was to develop a vitrification protocol applicable for the cryostorage of silver birch that avoids the use of expensive sophisticated freezers. The average recovery of vitrified axillary silver birch buds was 71% using a protocol that started with four-week cold hardening of bud-bearing in vitro donor shoots on modified medium under short day conditions. After cold hardening, the excised axillary buds were precultivated on medium containing 0.7 M sucrose for 24 h under the same conditions as during the cold hardening period. Following preculture, the buds were treated with loading solution containing 2M glycerol and 0.4 M sucrose for 20 min at room temperature. Finally, the buds were dehydrated with PVS2 cryoprotectant for 120 min followed by direct immersion in liquid nitrogen. According to the morphology and the RAPD profiles of regenerated plants in the greenhouse, the genetic fidelity of the vitrified birch material seems to have remained unchanged.     

Influence of elevated CO2 and O3 on Betula pendula Roth crown structure

Elevated CO(2) and ozone effects were studied singly and in combination on the crown structure of two Betula pendula clones. Measurements were made at the end of the second fumigation period in an open-top-chamber experiment with 9-year-old trees. Shoot ramification (number of long and short daughter shoots), shoot length, and number of metamers, leaves and buds were measured at four positions in every tree. As a result of increased temperature, trees in chambers had longer shoots and more frequent shoot ramification than control trees not enclosed in chambers. Ozone treatment decreased shoot ramification significantly. Additionally, ozone treatment resulted in an increased number of metamers in one clone. There was no statistically significant interaction between ozone effect and crown position; however, there was a slight tendency for the lower crown to be more affected by ozone. Elevated CO(2) caused a significant increase in the number of long-shoot metamers. Therefore, 2x ambient CO(2) concentration partly ameliorated the negative effect of ozone because the increased number of leaves per shoot counteracted the decreased branching. Although the main effects of elevated ozone and CO(2) were similar in the two clones, slight, statistically insignificant, differences appeared in their responses when interactions with crown position were considered.     

Effects of elevated carbon dioxide concentration on photosynthesis and growth of small birch plants (Betula pendula Roth.) at optimal nutrition

Small birch plants (Betula pendula Roth.) were grown from seed for periods of up to 70d in a climate chamber at optimal nutrition and at present (350 μmol mol^?1) or elevated (700 μmol mol^?1) concentrations of atmospheric CO₂. Nutrients were sprayed over the roots in Ingestad-type units. Relative growth rate and net assimilation rate were slightly higher at elevated CO₂, whereas leaf area ratio was slightly lower. Smaller leaf area ratio was associated with lower values of specific leaf area. Leaves grown at elevated CO₂ had higher starch concentrations (dry weight basis) than leaves grown at present levels of CO₂. Biomass allocation showed no change with CO₂, and no large effects on stem height, number of side shoots and number of leaves were found. However, the specific root length of fine roots was higher at elevated CO₂. No large difference in the response of carbon assimilation to intercellular CO₂ concentration (A/C_i curves) were found between CO₂ treatments. When measured at the growth environments, the rates of photosynthesis were higher in plants grown at elevated CO₂ than in plants grown at present CO₂. Water use efficiency of single leaves was higher in the elevated treatment. This was mainly attributable to higher carbon assimilation rate at elevated CO₂. The difference in water use efficiency diminished with leaf age. The small treatment difference in relative growth rate was maintained throughout the experiment, which meant that the difference in plant size became progressively greater. Thus, where plant nutrition is sufficient to maintain maximum growth, small birch plants may potentially increase in size more rapidly at elevated CO₂.     

Within-stand variation in silver birch (Betula pendula Roth) phenology

Key message

Within a local population genotypes differ in the timing of bud burst, but genotypes with early bud burst unfold their leaves slower, resulting in an equal period of carbon gain.

Abstract

The ability of local populations to cope with disturbances like adverse weather events or a changing climate depends on the genotypic richness of such populations, emphasising the importance of differences between genotypes in traits related to growth and survival at this scale. Due to their longevity, these differences are of special importance in trees, yet for trees, differences between genotypes within local populations remain unexplored. The phenological cycle is important in this respect, since a correct timing of phenological events is critical for growth and survival of trees, especially in environments with strong seasonality and changes in the timing of phenological events has consequences for, among others, net ecosystem productivity and the climate system as a whole. In this light accounting for differences in the timing of phenological events within species is currently identified as a research challenge. This study contributes to the knowledge of differences between genotypes on the small spatial scale of a local population. We examined the timing of phenological events of 15 micropropagated silver birch (Betula pendula Roth) genotypes representing a natural population. Measurements covered bud burst (7 years) and leaf unfolding in spring and chlorophyll degradation in autumn (2 years for both). These data were used to estimate the period of carbon gain. Differences between genotypes in the temperature sum required for bud burst were present, with genotypes showing ‘early’ (i.e. a low temperature sum requirement for bud burst) and ‘late’ bud burst across the 7-year study period. Differences were small in most years (i.e. 3 days), but differences of 16 days were recorded within the 7-year study period as well. Genotypes with ‘early’ bud burst were less sensitive to variations in environmental conditions in spring compared to genotypes with ‘late’ bud burst. Differences in bud burst were not carried over to the estimated period of carbon gain. Due to faster leaf expansion in genotypes with ‘late’ bud burst and the lack of differences between genotypes in autumn senescence the estimated period of carbon gain was similar among genotypes.     

Somatic embryogenesis in cell cultures of birch (Betula pendula Roth.)

Somatic embryogenesis was induced in cell cultures of birch (Betula pendula Roth.) derived from juvenile tissue of seed embryos and from mature leaf tissue. Embryos were formed in liquid and on solidified medium containing 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-furfurylaminopurine (kinetin). Sometimes somatic embryos formed only after transfer to medium devoid of growth regulators. The embryos germinated on hormone-free medium and were potted in soil and grown in the greenhouse.Finnish Forest Research InstituteUniversity of Helsinki, School of Pharmacy;     

Ozone exposure over two growing seasons alters root-to-shoot ratio and chemical composition of birch (Betula pendula Roth)

Physiological and chemical responses of 17 birch (Betula pendula Roth) clones to 1.5–1.7 × ambient ozone were studied in an open‐field experiment over two growing seasons. The saplings were studied for growth, foliar visible injuries, net photosynthesis, stomatal conductance, and chlorophyll, carotenoid, Rubisco, total soluble protein, macronutrient and phenolic concentrations in leaves. Elevated ozone resulted in growth enhancement, changes in shoot‐to‐root (s/r) ratio, visible foliar injuries, reduced stomatal conductance, lower late‐season net photosynthesis, foliar nutrient imbalance, changes in phenolic composition, and reductions in pigment, Rubisco and soluble protein contents indicating accelerated leaf senescence. Majority of clones responded to ozone by changing C allocation towards roots, by stomatal closure (reduced ozone uptake), and by investment in low‐cost foliar antioxidants to avoid and tolerate ozone stress. A third of clones, showing increased s/r ratio, relied on inducible efficient high‐cost antioxidants, and enhanced leaf production to compensate ozone‐caused decline in leaf‐level net photosynthesis. However, the best ozone tolerance was found in two s/r ratio‐unaffected clones showing a high constitutive amount of total phenolics, investment in low‐cost antioxidants and N distribution to leaves, and lower stomatal conductance under ozone stress. The results highlight the importance of phenolic compounds in ozone defence mechanisms in the birch population. Depending on the genotype, ozone detoxification was improved by an increase in either efficient high‐cost or less efficient low‐cost antioxidative phenolics, with close connections to whole‐plant physiology.     

Growth performance of hybrid families by crossing selfed lines of Betula pendula Roth

Hybrid breeding is an effective approach in many agricultural crops. In allogamous tree species severe inbreeding depression and long reproductive cycles generally prohibit its use. However, three generations of selfing in silver birch (Betula pendula Roth) were obtained by forcing trees to flowering under greenhouse conditions. Hybrids were produced by crossing first-, second and third-generation selfed lines. The effects of different levels of parental inbreeding on the growth performance of hybrid families were observed in a 9-year-old field progeny test. Also, provenance crosses were carried out between selfed lines from different parts of Finland and several other European countries. Observations of growth performance of the provenance hybrids were made in the same trial. The results indicated that the mean stem volumes were significantly different between classes of parental in breeding coefficients (F_P) (P<0.0001), and were positively correlated with F_P (r=0.9106, P<0.05). Within-family variation of the hybrid families decreased with an increase of F_P. The performance of the provenance crosses between parents at a relatively close distance did not depart significantly from the standard controls. However, when the cross distance was extended far to the south, hybrids grew faster, indicating either higher heterozygosity or an extended growth period.     

Variation of non-structural carbohydrates in silver birch (Betula pendula Roth) wood

Non-structural carbohydrates in silver birch (Betula pendula Roth) wood were analysed in a 7-year-old clone and in five mature stems. The analysis was conducted to obtain more detailed information on seasonal fluctuation of these components and of the tree-to-tree variation and within stem variation. The sugars were analysed by GLC-MS. The smallest total soluble sugar amounts (consisting of sucrose, fructose, glucose, raffinose and myo-inositol) in young trees were measured during mid-summer (ca. 0.3%) and the largest while in dormancy (ca. 1.6% on wood dry weight basis). Raffinose was detected in autumn as a minor component. The proportion of monosaccharides and the amount of myo-inositol were largest during growth. Compared to other studies silver birch showed more evident seasonal fluctuation in soluble sugars than evergreen tree species. The sugar amount in mature stems was approximately at the same level as in young trees that had the same felling time. Tree-to-tree variation in the non-structural carbohydrates in the mature wood was fairly large. However, the amount of total soluble sugars, sucrose and glucose showed significant variation within the stem. The amount of these sugars was largest in samples that were taken close to the cambium. Starch was also detected close to pith. According to the heartwood definition and starch measurement results in this paper, it could be stated that silver birch does not form heartwood.     

An overview of long-term effects of elevated atmospheric CO2 concentration on the growth and physiology of birch (Betula pendula Roth.)

Summary

An extensive number of biochemical and physiological measurements were made over the third and fourth years of the growth of birch (Betula pendula Roth.) in elevated CO₂. Trees in elevated CO₂ had 58% more biomass than trees grown in ambient CO₂ although relative growth rate was not affected in the last year of the study. No changes in biomass allocation were observed. Elevated CO₂ caused an increase in starch accumulation in the leaves that resulted in a series of feedback mechanisms to re-establish the source-sink balance of the trees. A decrease in Rubisco activity and to a lesser extent in chlorophyll and soluble proteins led to a decrease in the photosynthetic activity. Although the positive CO ₂effect on photosynthetic activity was maintained in the field over the whole experiment, the photosynthetic capacity of the trees was reduced by long-term exposure to elevated CO₂. Both maximum electron transport capacity (J _max) and maximum carboxylation capacity (V _emax) were reduced to a similar extent, so the ratio of J _max:V _cmax was not altered. Root biomass, fine root density and mycorrhizal infection were increased in elevated CO ₂. The mycorrhizal species of fungi associated with the trees grown in elevated CO₂ were late-successional species whereas the species associated with trees grown in ambient CO₂ were early successional species. This lends support to the hypothesis of a CO₂ effect on the ontogeny of the trees.     

Allozyme variation in populations, full-sib families and selfed lines in Betula pendula Roth

Changes in genetic variability in populations (stand origins), full-sib (FS) families and three generations of selfed lines of Betula pendula were observed based on 15 allozyme loci. Growth vigour, measured as stem volume, and its relationship with heterozygosity was studied to determine the effect of inbreeding. Pooled FS families showed a higher percentage of polymorphic loci (P) and allelic numbers per locus (A) than those of natural populations, but no difference in heterozygosity. There was no difference in allozyme variability between fast-and slow-growing family groups, and heterozygosity was not correlated with stem volume among FS families. Allozyme variability was significantly decreased in advancing generations of selfing, and the further the selfing generation, the lower the heterozygosity and the slower the growth. Observed heterozygosity after advancing generations of inbreeding was increasingly higher than expected, indicating overdominance effects or, alternatively, selection against deleterious homozygotes.     

The Role of Sucrose in Regulation of Trunk Tissue Development in Betula pendula Roth

Comparative ultrastructural analysis of the conducting and non-conducting phloem cells in the common straight-grained silver birch (Betula pendula var. pendula) and the Karelian birch (B. pendula var. carelica) with abnormal patterned wood was carried out, leading to the conclusion that there is an elevated sucrose content in the conducting phloem of the Karelian birch. A connection between sucrose levels and formation of abnormalities in the development of conducting tissues in the Karelian birch trunk was surmised. Experiments in which exogenous sucrose was applied to the silver birch trunk tissues have demonstrated the effects of different sucrose concentrations (0 g L⁻¹, 10 g L⁻¹, 25 g L⁻¹, 50 g L⁻¹, 100 g L⁻¹) on the formation of xylem and phloem structural elements, and they yielded the types of tissue development that correspond to the abnormal tissue development in the Karelian birch trunk.     

The seasonal activity and the effect of mechanical bending and wounding on the PtCOMT promoter in Betula pendula Roth

In this study, 900-bp (signed as p including nucleotides –1 to –886) and partly deleted (signed as dp including nucleotides –1 to –414) COMT (caffeate/5-hydroxyferulate O-methyltransferase) promoters from Populus tremuloides Michx. were fused to the GUS reporter gene, and the tissue-specific expression patterns of the promoters were determined in Betula pendula Roth along the growing season, and as a response to mechanical bending and wounding. The main activity of the PtCOMTp- and PtCOMTdp-promoters, determined by the histochemical GUS assay, was found in the developing xylem of stems during the 8th–13th week and in the developing xylem of roots in the 13th week of the growing season. The GUS expression patterns did not differ among the xylem cell types. The PtCOMT promoter-induced GUS expression observed in phloem fibres suggests a need for PtCOMT expression and thus syringyl (S) lignin synthesis in fibre lignification. However, the PtCOMTdp-promoter induced GUS expression in stem trichomes, which may contribute to the biosynthesis of phenylpropanoid pathway-derived compounds other than lignin. Finally, a strong GUS expression was induced by the PtCOMT promoters in response to mechanical stem bending but not to wounding. The lack of major differences between the PtCOMTp- and PtCOMTdp-promoters suggests that the deleted promoter sequence (including nucleotides −415 to −886) did not contain a significant regulatory element contributing to the GUS expression in young B. pendula trees.     

Characterization of a birch (Betula pendula Roth.) embryogenic gene,BP8

We have isolated the birch homologue (BP8) for the carrot embryogenic gene DC8 by heterologous hybridization. The birch BP8 gene encodes a putative protein of 53 kDa, showing 52% sequence identity with the DC8 gene at the amino acid level. The putative BP8 protein contains 20 repeats of 11 amino acids and thus belongs to the group of LEA proteins isolated from such plants as carrot, cotton and wheat. Northern hybridization of mRNA isolated from birch cells representing different stages of somatic embryogenesis and non-embryogenetic material with a PB8 probe gave no signals, suggesting a low expression level of the BP8 gene.