Interactive effects of elevated ozone and temperature on carbon allocation of silver birch (Betula pendula) genotypes in an open-air field exposure

In the present experiment, the single and combined effects of elevated temperature and ozone (O(3)) on four silver birch genotypes (gt12, gt14, gt15 and gt25) were studied in an open-air field exposure design. Above- and below-ground biomass accumulation, stem growth and soil respiration were measured in 2008. In addition, a (13)C-labelling experiment was conducted with gt15 trees. After the second exposure season, elevated temperature increased silver birch above- and below-ground growth and soil respiration rates. However, some of these variables showed that the temperature effect was modified by tree genotype and prevailing O(3) level. For instance, in gt14 soil respiration was increased in elevated temperature alone (T) and in elevated O(3) and elevated temperature in combination (O(3) + T) treatments, but in other genotypes O(3) either partly (gt12) or totally nullified (gt25) temperature effects on soil respiration, or acted synergistically with temperature (gt15). Before leaf abscission, all genotypes had the largest leaf biomass in T and O(3) + T treatments, whereas at the end of the season temperature effects on leaf biomass depended on the prevailing O(3) level. Temperature increase thus delayed and O(3) accelerated leaf senescence, and in combination treatment O(3) reduced the temperature effect. Photosynthetic : non-photosynthetic tissue ratios (P : nP ratios) showed that elevated temperature increased foliage biomass relative to woody mass, particularly in gt14 and gt12, whereas O(3) and O(3) + T decreased it most clearly in gt25. O(3)-caused stem growth reductions were clearest in the fastest-growing gt14 and gt25, whereas mycorrhizal root growth and sporocarp production increased under O(3) in all genotypes. A labelling experiment showed that temperature increased tree total biomass and hence (13)C fixation in the foliage and roots and also label return was highest under elevated temperature. Ozone seemed to change tree (13)C allocation, as it decreased foliar (13)C excess amount, simultaneously increasing (13)C excess obtained from the soil. The present results suggest that warming has potential to increase silver birch growth and hence carbon (C) accumulation in tree biomass, but the final magnitude of this C sink strength is partly counteracted by temperature-induced increase in soil respiration rates and simultaneous O(3) stress. Silver birch populations' response to climate change will also largely depend on their genotype composition.     

Effects of long-term,elevated ultraviolet-B radiation on phytochemicals in the bark of silver birch (Betula pendula)

Long-term outdoor experiments were conducted to investigate the effects of elevated ultraviolet-B (UV-B, 280-320 nm) radiation on secondary metabolites (phenolics and terpenoids) and the main soluble sugars (sucrose, raffinose and glucose) in the bark of silver birch (Betula pendula Roth) saplings. Saplings were exposed to a constant 50% increase in erythemal UV irradiance (UV-B(CIE); based on the CIE (International Commission on Illumination) erythemal action spectrum) and a small increase in UV-A radiation (320-400 nm) for three growing seasons in an irradiation field in central Finland. Two control groups were used: saplings exposed to ambient radiation and saplings exposed to slightly increased UV-A radiation. Concentrations of sucrose, raffinose and glucose in bark were higher in UV-treated saplings than in saplings grown in ambient radiation, indicating that stem carbohydrate metabolism was changed by long-term elevated UV radiation. Saplings in the elevated UV-A + UV-B radiation treatment and the UV-A radiation control treatment had significantly increased concentrations of certain UV-absorbing phenolics, such as salidroside, 3,4'-dihydroxypropiophenone-3-glucoside, (+)-catechin and (-)-epicatechin compared with saplings in ambient radiation. In contrast, the radiation treatments had no effect on the non-UV-B-absorbing terpenoids, papyriferic acid and deacetylpapyriferic acid. We conclude that plant parts, in addition to leaves, accumulate specific phenolic UV-filters in response to UV radiation exposure.     

Biochemical acclimation patterns of Betula pendula and Pinus sylvestris seedlings to elevated carbon dioxide concentrations

Acclimation of photosynthesis to increasing atmospheric carbon dioxide concentration ([CO2]; 350 to 2,000 micromol mol-1) was followed in silver birch (Betula pendula Roth.) and Scots pine (Pinus sylvestris L.) seedlings for two years. Chlorophyll fluorescence and concentrations of Rubisco, chlorophyll, total soluble protein and nitrogen were monitored together with steady-state gas exchange at three CO2 concentrations (ambient [CO2] (345 +/- 20 micromol mol-1), the growth [CO2] and 1950 +/- 55 micromol mol-1). Rubisco and chlorophyll concentrations decreased in birch and Scots pine with increasing growth [CO2]. A nonlinear response was recorded for Rubisco and chlorophyll concentrations in birch, which was correlated with a significant decrease in specific leaf area. Nitrogen concentration decreased in birch leaves, but was unchanged in Scots pine needles. The species differed substantially in their steady-state CO2 exchange response to increasing growth [CO2]. The principal effect in birch was a significant nonlinear decrease in the steady-state gas exchange rate at the ambient [CO2], whereas in Scots pine the main effect was a significant increase in the steady-state gas exchange rate at the growth [CO2].     

Genetic transformation of silver birch (Betula pendula) by particle bombardment

We used in vitro callus and shoot cultures as target material for genetic transformation of silver birch (Betula pendula Roth) by particle bombardment. Cultivation of in vitro shoot cultures before particle bombardment and a long selection period, combined with a high concentration of selective agent after bombardment, led to the production of transformed plantlets that were stable, and no escapes were found among the tree lines produced. Clonal variation in transformation efficiency was found in transient expression of the beta-glucuronidase gene in callus cultures and in plantlets transformed by stable integration of the ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit (RbcS) and neomycin phosphotransferase (npt2) genes.     

Variations in phenology and growth of European white birch (Betula pendula) clones

Phenology can have a profound effect on growth and climatic adaptability of northern tree species. Although the large interannual variations in dates of bud burst and growth termination have been widely discussed, little is known about the genotypic and spatial variations in phenology and how these sources of variation are related to temporal variation. We measured bud burst of eight white birch (Betula pendula Roth) clones in two field experiments daily over 6 years, and determined the termination of growth for the same clones over 2 years. We also measured yearly height growth. We found considerable genetic variation in phenological characteristics among the birch clones. There was large interannual variation in the date of bud burst and especially in the termination of growth, indicating that, in addition to genetic effects, environmental factors have a strong influence on both bud burst and growth termination. Height growth was correlated with timing of growth termination, length of growth period and bud burst, but the relationships were weak and varied among years. We accurately predicted the date of bud burst from the temperature accumulation after January 1, and base temperatures between +2 and -1 degrees C. There was large clonal variation in the duration of bud burst. Interannual variation in bud burst may have important consequences for insect herbivory of birches.     

Analysis of EST-SSRs in silver birch(Betula pendula Roth.)

Simple sequence repeats(SSRs) defined as sequence repeat units between 1 and 6 bp occur abundantly in both coding and non-coding regions in eukaryotic genomes and these repeats can affect gene expression. In this study, ESTs(expressed sequence tags) of Betula pendula(silver birch) were analyzed for in silico mining of ESTSSRs, protein annotation, open reading frames(ORFs),designing primers, and identifying codon repetitions. In B.pendula, the frequency of ESTs containing SSRs was 7.8 %with an average of 1SSR/4. 78 kb of EST sequences. A total of 188 SSRs was identified by using MISA software and dinucleotide SSR motifs(65.9 %) were found to be the most abundant type of repeat motif followed by tri-(27.1 %),tetra-(4.8 %), and penta-(2.2 %) motifs. Based on ORF analysis, 175 of 178 sequences were predicted as ORFs and the most frequent SSRs were detected in 50 UTR(58.43 %),followed by in ORF(31.46 %) and in 30UTR(8.43 %). 102 of 178 ESTs were annotated as ribosomal protein, transport protein, membrane protein, carrier protein, binding protein,and transferase protein. For a total of 102 SSRs(57.3 %)with significant matches, a set of 102 primers(100 %) with forward and reverse strands was designed by using Primer 3 software. Serine(Ser, 19.6 %) was predominant in putative encoded amino acids and most of amino acids showed nonpolar(35.3 %) nature. Our data provide resources for B.pendula and can be useful for in silico comparative analyses of Betulaceae species, including SSR mining.     

Twilight far-red treatment advances leaf bud burst of silver birch (Betula pendula)

Bud development of boreal trees in spring, once initiated, is driven by ambient air temperature, but the mechanism triggering bud development remains unclear. We determined if some aspect of the diurnal or seasonal light regime influences initiation of bud burst once the chilling requirement is met. We grew 3-year-old birch plantlets cloned from a mature tree of boreal origin in light conditions realistically simulating the lengthening days of spring at 60 degrees N. To emulate the reduction in red to far-red light (R:FR) ratio between daylight and twilight, one group of plantlets was subjected to reduced R:FR ratio in the morning and evening in addition to progressively lengthening days, whereas the other group was subjected to the same R:FR ratio throughout the day. The reduced R:FR ratio of twilight advanced bud burst by 4 days compared with the reference group (P = 0.04). To assess the interplay between the fulfillment of the chilling requirement and the subsequent response to warming, we fitted a thermal time model to the data with separate parameterizations for the starting dates of heat sum accumulation in each treatment. Least-squares fitting suggested that bud development started in light regimes corresponding to late March, almost two months after the chilling requirement for dormancy release was satisfied. Therefore, shortening night length or increasing day length, or both, appears to be the cue enabling bud development in spring, with twilight quality having an effect on the photoperiodic response. If twilight alone were the cue, the difference in bud burst dates between the experimental groups would have been greater than 4 days. The result gives experimental support for the use of thermal-time models in phenological modeling.     

Genotypic variation in drought response of silver birch (Betula pendula): leaf water status and carbon gain

To assess genotypic variation in drought response of silver birch (Betula pendula Roth), we studied the plasticity of 16 physiological traits in response to a 12-14-week summer drought imposed on four clones in two consecutive years. In a common garden experiment, 1-year-old clonal trees from regions with low (550 mm year(-1)) to high rainfall (1270 mm year(-1)) were grown in 45-l pots, and leaf gas exchange parameters, leaf water potentials, leaf osmotic potentials and leaf carbon isotope signatures were repeatedly measured. There were no clonal differences in leaf water potential, but stomatal conductance (gs), net photosynthesis at ambient carbon dioxide concentration, photosynthetic water-use efficiency, leaf carbon isotope composition (delta13C) and leaf osmotic potentials at saturation (Pi0) and at incipient plasmolysis (Pip) were markedly influenced by genotype, especially gs and osmotic adjustment. Genotypes of low-rainfall origin displayed larger osmotic adjustment than genotypes of high-rainfall origin, although their Pi0 and Pip values were similar or higher with ample water supply. Genotypes of low-rainfall origin had higher gs than genotypes of high-rainfall origin under both ample and limited water supply, indicating a higher water consumption that might increase competitiveness in drought-prone habitats. Although most parameters tested were significantly influenced by genotype and treatment, the genotype x treatment interactions were not significant. The genotypes differed in plasticity of the tested parameters and in their apparent adaptation to drought; however, among genotypes, physiological plasticity and drought adaptation were not related to each other. Reduction of gs was the first and most plastic response to drought in all genotypes, and allowed the maintenance of high predawn leaf water potentials during the drought. None of the clones exhibited non-stomatal limitation of photosynthesis. Leaf gs, photosynthetic capacity, magnitude of osmotic adjustment and delta13C were all markedly lower in 2000 than in 1999, indicating root limitation in the containers in the second year.     

Seasonal and within-stem variations of neutral lipids in silver birch (Betula pendula) wood

Neutral lipids were analyzed in stem wood of a 7-year-old clone and in five 35-70-year-old mature trees of silver birch (Betula pendula Roth). In young trees and in mature wood of old trees, the free fatty acid fraction comprised less than 5% of the concentration of triacylglycerols (TG). The concentration of free linoleic acid was lowest in March when the young trees were dormant and highest during midsummer and September. In mature trees, the TG concentration increased toward the pith, indicating that living parenchyma cells close to the pith have a large TG storage capacity. The TG concentration (mean 0.51 +/- 0.02% of wood dry mass) remained constant throughout the year in young trees, whereas the concentration of beta-sitosterol, the dominant free sterol (mean 82.5 +/- 0.4% of total free sterols), decreased during spring and early summer when the temperature gradually increased, and increased during autumn when the trees became dormant. In young trees, we detected a seasonal interconversion between the free and esterified forms of beta-sitosterol and campesterol, and within the steryl ester fraction between squalene and betulaprenol-7. The concentration of esterified sterols/isoprenoids was exceptionally high, especially in the inner regions of mature stem wood (mean 0.6 +/- 0.03% of wood dry mass). No heartwood formation was detected.     

Photosynthesis and canopy characteristics in genetically defined families of silver birch (Betula pendula)

Net photosynthetic rates (A) of leaves in upper and lower crown layers (A(upper) and A(lower)), leaf area index (LAI), mean tilt angle (MTA), several leaf characteristics, and volume growth were observed in fast- and slow-growing families of a 14-year-old full-sib and half-sib family progeny test of Betula pendula Roth. Each measure of net photosynthetic rate was calculated after correcting measured net photosynthesis for the effects of environmental variables. The differences in A(upper) and LAI among families were significant. The proportions of the total variance assigned to family for A(upper), A(lower) and LAI were 33.64, 28.93 and 54.99%, respectively. The mean A(upper) and LAI of the fast-growing families were significantly higher than those of the slow-growing families, whereas the mean A(lower) of the fast-growing families was significantly lower than that of the slow-growing families. There were also significant differences among families in leaf size, leaf shape, and the ratios leaf fresh weight/area and leaf dry weight/area. Between 27.55 and 54.55% of the total variance in these characteristics could be assigned to the family effect. Volume growth was positively correlated with A(upper) and LAI, but it was most strongly correlated with A(upper) x LAI.     

Differential responses of silver birch (Betula pendula) ecotypes to short-day photoperiod and low temperature

We investigated interrelations of dormancy and freezing tolerance and the role of endogenous abscisic acid (ABA) in the development of silver birch (Betula pendula Roth) ecotypes in controlled environments. Short-day treatment induced growth cessation, bud set and dormancy development, as well as initiation of cold acclimation and an increase in freezing tolerance. Subsequent low temperature and short days (12-h photoperiod) resulted in a significant increase in freezing tolerance, whereas bud dormancy was gradually released. The concentration of ABA increased in response to short days and then remained high, but ABA concentrations fluctuated irregularly when the dormant plants were subsequently exposed to low temperature during short days. Although there was a parallel development of freezing tolerance and bud dormancy in response to short days, subsequent exposure to low temperature had opposite effects on these processes, enhancing freezing tolerance and releasing dormancy. Compared with the southern ecotype, the northern ecotype was more responsive to short days and low temperature, exhibiting earlier initiation of cold acclimation, growth cessation and an increase in ABA concentrations in short days, and higher freezing tolerance, faster dormancy release and greater alteration in ABA concentrations when subsequently exposed to low temperature during short days. The rates and extent of the increases in ABA concentration may be related to increases in freezing tolerance and dormancy development during short days, whereas the extent of the fluctuations in ABA concentration may play an important role in enhancing freezing tolerance and releasing dormancy during a subsequent exposure to low temperature during short days.     

Silver birch and climate change: variable growth and carbon allocation responses to elevated concentrations of carbon dioxide and ozone

We studied the effects of elevated concentrations of carbon dioxide ([CO2]) and ozone ([O3]) on growth, biomass allocation and leaf area of field-grown O3-tolerant (Clone 4) and O3-sensitive clones (Clone 80) of European silver birch (Betula pendula Roth) trees during 1999-2001. Seven-year-old trees of Clones 4 and 80 growing outside in open-top chambers were exposed for 3 years to the following treatments: outside control (OC); chamber control (CC); 2 x ambient [CO2] (EC); 2 x ambient [O3] (EO); and 2 x ambient [CO2] + 2 x ambient [O3] (EC+EO). When the results for the two clones were analyzed together, elevated [CO2] increased tree growth and biomass, but had no effect on biomass allocation. Total leaf area increased and leaf abscission was delayed in response to elevated [CO2]. Elevated [O3] decreased dry mass of roots and branches and mean leaf size and induced earlier leaf abscission in the autumn; otherwise, the effects of elevated [O3] were small across the clones. However, there were significant interactions between elevated [CO2] and elevated [O3]. When results for the clones were analyzed separately, stem diameter, volume growth and total biomass of Clone 80 were increased by elevated [CO2] and the stimulatory effects of elevated [CO2] on stem volume growth and total leaf area increased during the 3-year study. Clone 80 was unaffected by elevated [O3]. In Clone 4, elevated [O3] decreased root and branch biomass by 38 and 29%, respectively, whereas this clone showed few responses to elevated [CO2]. Elevated [CO2] significantly increased total leaf area in Clone 80 only, which may partly explain the smaller growth responses to elevated [CO2] of Clone 4 compared with Clone 80. Although we observed responses to elevated [O3], the responses to the EC+EO and EC treatments were similar, indicating that the trees only responded to elevated [O3] under ambient [CO2] conditions, perhaps reflecting a greater quantity of carbohydrates available for detoxification and repair in elevated [CO2].     

The effects of heavy thinning on stem quality and timber properties of silver birch (Betula pendula Roth)

A study was carried out into the effects of heavy thinning onstem quality and timber properties of silver birch (Betula pendulaRoth). Comparisons were made with lightly thinned and unthinnedbirch stands. Birch stands from the UK were also compared withsimilarly managed stands from Germany and Denmark. In general,trees from lightly thinned and unthinned stands had similarcharacteristics. Heavy thinning enhanced diameter incrementthrough greater ring width in comparison with the other treatments.The timber properties of basic density, grain angle and shrinkagecoefficients in the radial, tangential and longitudinal directions,however, were largely unaffected. More and bigger branches andgreater stem taper were found on trees from heavily thinnedstands, but these stems still met the current Finnish veneerbirch quality and dimension standards. Comparisons between birchstands, managed by heavy and light thinning, from the UK andGermany and Denmark revealed no meaningful differences in timberproperties. The results suggest that veneer dimension and qualitylogs could be produced in the UK in rotations as short as 40years on good sites if heavy thinning is adopted.     

Growth responses and related biochemical and ultrastructural changes of the photosynthetic apparatus in birch (Betula pendula) saplings exposed to low concentrations of ozone

Saplings of ozone-sensitive and ozone-tolerant birch (Betula pendula Roth.), clones B and C, respectively, were exposed to ozone concentrations that were 1.7-fold higher than ambient for one growing season under open-field conditions. Ambient air was used as the control treatment. In the ozone-sensitive clone B, there was an initial stimulation of leaf area growth in response to the ozone treatment, but further ozone exposure caused reductions in leaf and stem biomass growth, Rubisco and chlorophyll a contents, net photosynthesis, water use efficiency and chloroplast size. It also caused an alteration in chloroplast shape and injury to thylakoid membranes. In the ozone-tolerant clone C, ozone fumigation did not affect growth rate, and there were no consistent changes in chlorophyll content, photosynthesis or water use efficiency. There were also fewer ultrastructural abnormalities in the chloroplasts of clone C than of clone B. Based on the observed biochemical, physiological and structural changes in chloroplasts of clone B in response to low concentrations of ozone, we conclude that the increasing concentration of tropospheric ozone represents a risk to natural birch populations.     

Monolignol oxidation by xylem peroxidase isoforms of Norway spruce (Picea abies) and silver birch (Betula pendula)

We partially purified peroxidase isoform fractions from xylem extracts of a gymnosperm, Norway spruce (Picea abies (L.) Karst.), and an angiosperm, silver birch (Betula pendula Roth.), to determine the participation of xylem-localized peroxidases in polymerization of different types of lignin in vivo. Several peroxidase fractions varying in isoelectric point values from acidic to basic were tested for their ability to catalyze the oxidation of the monolignols coniferyl alcohol, sinapyl alcohol and p-coumaryl alcohol in vitro. All of the xylem peroxidases extracted from Norway spruce and most of those from silver birch showed the highest rate of oxidation with coniferyl alcohol in the presence of hydrogen peroxide. The exception was an acidic peroxidase fraction (pI 3.60-3.65) from silver birch that exhibited higher oxidation activity for sinapyl alcohol than for coniferyl alcohol. For the xylem enzyme fractions extracted from silver birch, the ability to oxidize the artificial phenolic substrate syringaldazine coincided with high specific activity for sinapyl alcohol. Therefore, we conclude that the acidic, neutral and basic xylem peroxidases of Norway spruce all function in the synthesis of guaiacyl-type lignin, whereas in silver birch the acidic peroxidases preferentially oxidize sinapyl subunits. The latter provides a mechanism for synthesis of guaiacyl-syringyl lignin typical of tracheid cell walls in angiosperm trees.     

Effects of acid rain treatments on the birch rust,Melampsoridium betulinum and birch,Betula pendula

Effects of acidic rain on birch rust and on the growth of Betula pendula seedlings were studied by irrigating with acidic water at pH 3, 4 and 5.6. The seedlings were inoculated with uredospores of Melampsoridium betulinum and the development of rust and the severity of rust infection was examined. The increasing acidity of the irrigation water did not affect on the development of the rust, but the nitrogen in the acidified water resulted in an extension of seedling growth, and hence the leaves became senescent at a later date in autumn and the rust grew for a longer time.     

Discoloration and associated fungi in stems of silver birch (Betula pendula Roth.) following logging damage

Study aim was to investigate discoloration and associated fungi in 50‐ to 70‐year‐old stems of Betula pendula damaged by logging. Investigated wounds (on 70 stems) were inflicted 4–18 years previously, and all of them had discoloration with mean radial spread (±SD) 2.9 ± 2.9 cm and longitudinal spread 50.3 ± 24.0 cm. Both wound area and length had a strong impact on a total length of discoloration (r = 0.665 and r = 0.745, respectively; p < 0.001), but had no influence on its spread beyond wound margins (r = ?0.035 and r = ?0.079). There was no correlation between the age of an injury and spread of the discoloration neither in vertical (r = ?0.110) nor in radial (r = ?0.280) direction. Average wound closure rate was 1.2 ± 0.5 cm year ^?1. The difference between discoloration length in stems with open and occluded injuries was insignificant (t‐test, p = 0.769). The principal fungi isolated from the wounds were ascomycetes (Epicoccum, Cadophora, Neonectria, Alternaria spp.) that were able to cause discoloration of wood with little effect on its mechanical properties and capable only for limited spread inside a stem of a living tree. In conclusion, results of the present study demonstrate that the amount of discoloured wood beyond logging wounds in B. pendula is mainly restricted to the damaged portion of a stem and that the associated loss of wood production remains low during about 10 years since the damage.