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.     

Effects of elevated atmospheric CO2 and/or O3 on intra- and interspecific competitive ability of aspen

Three model communities of trembling aspen (monoculture, and mixed with either paper birch or sugar maple) were grown for seven years in elevated atmospheric CO(2) and O(3) using Free Air CO(2) Enrichment (FACE) technology. We utilized trends in species' importance, calculated as an index of volume growth and survival, as indications of shifting community composition. For the pure aspen communities, different clones emerged as having the highest change in relative importance values depending on the pollutant exposure. In the control and elevated CO(2) treatments, clone 42E was rapidly becoming the most successful clone while under elevated O(3), clone 8 L emerged as the dominant clone. In fact, growth of clone 8 L was greater in the elevated O(3) treatment compared to controls. For the mixed aspen-birch community, importance of aspen and birch changed by - 16 % and + 62 %, respectively, in the controls. In the treatments, however, importance of aspen and birch changed by - 27 % and + 87 %, respectively, in elevated O(3), and by - 10 % and + 45 %, respectively, in elevated CO(2). Thus, the presence of elevated O(3) hastened conversion of stands to paper birch, whereas the presence of elevated CO(2) delayed it. Relative importance of aspen and maple changed by - 2 % and + 3 %, respectively, after seven years in the control treatments. But in elevated O(3), relative importance of aspen and maple changed by - 2 % and + 5 %, respectively, and in elevated CO(2) by + 9 and - 20 %, respectively. Thus, elevated O(3) slightly increases the rate of conversion of aspen stands to sugar maple, but maple is placed at a competitive disadvantage to aspen under elevated CO(2).     

光皮桦组织培养离体再生研究

采用正交试验等设计,系统开展了光皮桦组织培养高效再生体系研究。结果表明:光皮桦茎段外植体最佳诱导培养基及激素组合为MS+0.50mg.L-1 6-BA+0.10mg.L-1 TDZ+30mg.L-1蔗糖+5.50g.L-1琼脂,丛生芽最佳生根培养基为1/2MS+1mg.L-1 IBA+20g.L-1蔗糖+5.50g.L-1琼脂;丛生芽在最佳生根培养基上培养15d后获健壮生根苗,移栽成活率达90%。该实验结果为光皮桦的优良品种快繁以及遗传转化体系建立奠定了良好的基础。     

Interactive effect of elevated temperature and O<Subscript>3</Subscript> on antioxidant capacity and gas exchange in <Emphasis Type="Italic">Betula pendula</Emphasis> saplings

We studied the effects of slightly elevated temperature (T), O₃ concentration (O₃) and their combination (T + O₃) on the antioxidant defense, gas exchange and total leaf area of Betula pendula saplings in field conditions. During the second year of the experiment, T enhanced the total leaf area, net photosynthesis (P _n) and maximum capacity of carboxylation, redox state of ascorbate and total antioxidant capacity in the apoplast. O₃ did not affect the total leaf area, but P _n was slightly and g _s significantly reduced. The saplings responded to elevated O₃ level by closing the stomata and by developing leaves with a lower leaf area per mass, rather than by accumulating ascorbate in the apoplast. The effects of T and O₃ on total leaf area and P _n were counteractive. Elevated O₃ reduced the saplings’ ability to utilize the warmer growth environment by increasing the stomatal limitation for photosynthesis and by reducing the redox state of ascorbate in the apoplast in the combination treatment as compared to T alone.     

Annual and spatial variation in shoot demography associated with masting in Betula grossa: comparison between mature trees and saplings

Backgrounds and Aims

Shoot demography affects the growth of the tree crown and the number of leaves on a tree. Masting may cause inter-annual and spatial variation in shoot demography of mature trees, which may in turn affect the resource budget of the tree. The aim of this study was to evaluate the effect of masting on the temporal and spatial variations in shoot demography of mature Betula grossa.

Methods

The shoot demography was analysed in the upper and lower parts of the tree crown in mature trees and saplings over 7 years. Mature trees and saplings were compared to differentiate the effect of masting from the effect of exogenous environment on shoot demography. The fate of different shoot types (reproductive, vegetative, short, long), shoot length and leaf area were investigated by monitoring and by retrospective survey using morphological markers on branches. The effects of year and branch position on demographic parameters were evaluated.

Key Results

Shoot increase rate, production of long shoots, bud mortality, length of long shoots and leaf area of a branch fluctuated periodically from year to year in mature trees over 7 years, in which two masting events occurred. Branches within a crown showed synchronized annual variation, and the extent of fluctuation was larger in the upper branches than the lower branches. Vegetative shoots varied in their bud differentiation each year and contributed to the dynamic shoot demography as much as did reproductive shoots, suggesting physiological integration in shoot demography through hormonal regulation and resource allocation.

Conclusions

Masting caused periodic annual variation in shoot demography of the mature trees and the effect was spatially variable within a tree crown. Since masting is a common phenomenon among tree species, annual variation in shoot demography and leaf area should be incorporated into resource allocation models of mature masting trees.     

光皮桦花粉离体萌发试验

设置若干温度的培养环境以及各种浓度蔗糖、蔗糖+硼酸、蔗糖+硝酸钙、蔗糖+硼酸+硝酸钙培养基,研究温度以及蔗糖、硼、钙对光皮桦花粉离体萌发的影响,探明光皮桦花粉萌发的适宜温度和最佳培养基。结果表明:合适浓度的蔗糖、硼酸和硝酸钙均能显著促进光皮桦花粉萌发,而高浓度的蔗糖、硼和钙均抑制其花粉萌发;光皮桦花粉离体萌发的合适培养基为10%蔗糖+200mg.L-1硼酸+200mg.L-1硝酸钙,适宜培养温度为30℃;在此条件下培养4h后花粉萌发率基本稳定,培养6h后花粉管长度亦趋于稳定。     

7个光响应曲线模型对不同植物种的实用性

光响应曲线研究方法被广泛应用在植物生理的研究中,但是在应用光响应模型拟合光响应数据时,往往只考虑到研究的目的,很少考虑到模型是否适用于所研究的植物。本文通过采用7个不同的光响应模型对白桦叶片和兴安落叶松针叶光响应曲线数据拟合的比较,发现不同模型对同一种植物光响应曲线的拟合结果存在着差异,同一模型对同种植物不同部位叶片光响应曲线的拟合效果也不同,所以在研究植物的光响应时,应考虑到所选光响应模型对该种植物的光响应情况的描述是否恰当。根据具体情况选择最佳模型,以最大限度地保证估测生理指标结果的精确性。     

Life-history strategies affect aphid preference for yellowing leaves

According to the nutrient-translocation hypothesis, yellowing tree leaves are colonized by aphids at the end of the growing season owing to improved availability of nutrients in the phloem sap after chlorophyll degradation. We measured aphid densities on potted Betula pendula seedlings in a field site where a small proportion of foliage rapidly turned yellow before normal autumn coloration as a consequence of root anoxia. The number of adults and nymphs of the birch-feeding specialist aphids Euceraphis betulae, Betulaphis brevipilosa and Callipterinella tuberculata were counted from leaves on each of the 222 plants. Aphids were detected on 19 per cent of green leaves and on 41 per cent of yellow leaves. There was no indication of aphid avoidance of yellow leaves, and the number of winged (alate) viviparous E. betulae adults and their nymphs were significantly higher on yellow leaves than on green leaves, while the numbers of apterous B. brevipilosa and C. tuberculata did not differ between the leaf colour types. Our result suggests that only aphid species with alate generation during colour change can take advantage of yellowing leaves. This may explain the exceptional abundance of E. betulae compared with other aphid species on birches.     

Herbivores inhibit climate-driven shrub expansion on the tundra

Recent Pan-Arctic shrub expansion has been interpreted as a response to a warmer climate. However, herbivores can also influence the abundance of shrubs in arctic ecosystems. We addressed these alternative explanations by following the changes in plant community composition during the last 10 years in permanent plots inside and outside exclosures with different mesh sizes that exclude either only reindeer or all mammalian herbivores including voles and lemmings. The exclosures were replicated at three forest and tundra sites at four different locations along a climatic gradient (oceanic to continental) in northern Fennoscandia. Since the last 10 years have been exceptionally warm, we could study how warming has influenced the vegetation in different grazing treatments. Our results show that the abundance of the dominant shrub, Betula nana , has increased during the last decade, but that the increase was more pronounced when herbivores were excluded. Reindeer have the largest effect on shrubs in tundra, while voles and lemmings have a larger effect in the forest. The positive relationship between annual mean temperature and shrub growth in the absence of herbivores and the lack of relationships in grazed controls is another indication that shrub abundance is controlled by an interaction between herbivores and climate. In addition to their effects on taller shrubs (>0.3 m), reindeer reduced the abundance of lichens, whereas microtine rodents reduced the abundance of dwarf shrubs (<0.3 m) and mosses. In contrast to short-term responses, competitive interactions between dwarf shrubs and lichens were evident in the long term. These results show that herbivores have to be considered in order to understand how a changing climate will influence tundra ecosystems.