Optimization of sucrose and inorganic nitrogen concentrations for somatic embryogenesis of birch (Betula pendula Roth.) callus cultures: A statistical approach

The effects of different concentrations of sucrose and inorganic nitrogen on somatic embryogenesis of birch (Betula pendula Roth.) callus cultures were studied using Box-Wilson statistical experimental design. The experimental results were processed by regression analysis, and mathermatical models describing the effects of the selected variables were derived. On the basis of the modeling, maximum embryo production can be achieved with 35 mM total inorganic nitrogen and 20.8 g 1^-1 sucrose in the medium.     

Light quality affects photosynthesis and leaf anatomy of birch plantlets in vitro

Cultures in vitro of Betula pendula Roth were subjected to light of different spectral qualities. Photosynthetic capacity was highest when the plantlets were exposed to blue light (max recorded photosynthesis, 82 mol CO₂ dm^–2 h^–1) and lowest when irradiated with light high in red and/or far-red wave lengths (max recorded photosynthesis, 40 mol CO₂ dm^–2 h^–1). Highest chlorophyll content (2.2 mg dm^–2 leaf area) was found in cultures irradiated with blue light, which also enhanced the leaf area. Morphometric analysis of light micrographs showed that the epidermal cell areas were largest in plantlets subjected to blue light and smallest in those subjected to red light. Morphometric analysis of electron micrographs of palisade cells, showed that the functional chloroplast area was largest in chloroplasts of leaves subjected to blue light and smallest in those exposed to red light. We suggest that light quality affects photosynthesis both through effects on the composition of the photosynthetic apparatus and on translocation of carbohydrates from chloroplasts.     

Effects of constant and fluctuating temperature on time to budburst in Betula pubescens and its relation to bud respiration

 Effects of fluctuating and constant temperatures on budburst time, and respiration in winter buds were studied in Betula pubescens Ehrh. Dormant seedlings were chilled at 0°C for 4 months and then allowed to sprout in long days (LD, 24 h) at constant temperatures of 6, 9, 12, 15, 18 and 21°C, and at diurnally fluctuating temperatures (12/12 h, LD 24 h) with means of 9, 12, 15 and 18°C. No difference in thermal time requirements for budburst was found between plants receiving constant and fluctuating temperatures. The base temperature for thermal time accumulation was estimated to 1°C. Respiration in post-dormant (dormancy fully released) excised winter buds from an adult tree increased exponentially with temperature and was 20 times as high at 30°C than at 0°C. However, respiration in buds without scales was 30% higher at 0°C, and it was 2.7 times higher at 24°C than in intact buds. Thus, the tight bud scales probably constrain respiration and growth and are likely to delay budburst in spring. Arrhenius plots of the respiration data were biphasic with breaks at 13–15°C. However, this phase transition is unlikely to be associated with chilling sensitivity since the present species is hardy and adapted to a boreal climate. Received: 10 January 1997 / Accepted: 23 June 1997     

Chemical composition of five deciduous tree species in four-year-old,closely spaced plantations

Summary Contents of N, P, K, Ca, Mg, and Mn in aboveground tree components of five deciduous species were determined in closely-spaced (0.9×0.6 m) 4-year-old plantations growing on a river terrace site in the Ohio Valley region of western Kentucky (USA). Species evaluated were: a hybrid poplar, American sycamore, European alder, river birch and green ash. The only significant difference in dry weight of tree components was greater bolebark biomass of the hybrid poplar. Total aboveground elemental content of N, K, Ca, and Mn varied significantly for some species. N content of green ash was significantly lower and K content of the hybrid poplar and Mn content of European alder were significantly greater compared with the other species. Ca contents of the hybrid poplar, American sycamore and European alder were significantly greater than those of other species. Based on the relationship between biomass production and nutrient content of the harvested biomass, it seems that on this and comparable sites, river birch is a preferred species in view of the lower potential nutrient removals in the harvested biomass.The investigation reported in this paper (79-8-129) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director.     

Elevated CO2 ameliorates birch response to high temperature and frost stress: implications for modeling climate-induced geographic range shifts

Despite predictions that both atmospheric CO₂ concentrations and air temperature will rise together, very limited data are currently available to assess the possible interactive effects of these two global change factors on temperate forest tree species. Using yellow birch (Betula alleghaniensis) as a model species, we studied how elevated CO₂ (800 vs. 400 μl l⁻¹) influences seedling growth and physiological responses to a 5°C increase in summer air temperatures (31/26 vs. 26/21°C day/night), and how both elevated CO₂ and air temperature during the growing season influence seedling ability to survive freezing stress during the winter dormant season. Our results show that while increased temperature decreases seedling growth, temperature-induced growth reductions are significantly lower at elevated CO₂ concentrations (43% vs. 73%). The amelioration of high-temperature stress was related to CO₂-induced reductions in both whole-shoot dark respiration and transpiration. Our results also show that increased summer air temperature, and to a lesser degree CO₂ concentration, make dormant winter buds less susceptible to freezing stress. We show the relevance of these results to models used to predict how climate change will influence future forest species distribution and productivity, without considering the direct or interactive effects of CO_2. Received: 5 June 1997 / Accepted: 16 December 1997     

Onset of freezing tolerance in birch (Betula pubescens Ehrh.) involves LEA proteins and osmoregulation and is impaired in an ABA-deficient genotype

In many woody plants a short photoperiod triggers the onset of cold acclimation, but the nature of this process has remained obscure. We aimed to establish which physiological and genetic factors have a role in short-day-induced acclimation by comparing two types of birch, Betula pubescens Ehrh. and B. pubescens f. hibernifolia Ulv., the latter being unable to increase its abscisic acid (ABA) levels. In the wild type, short-day or natural autumn conditions in the field appeared to elevate the ABA levels before acclimation, which was accompanied by tissue desiccation, osmotic adjustments and accumulation of Group 2 LEA proteins [responsive to ABA (RAB) 16-like; 24, 30 and 33 kDa] and Group 4 LEA proteins [late embryogenesis abundant (LEA) 14-like; 19 kDa]. Under similar conditions the ABA-deficient birch showed reduced water loss, defective osmoregulation, absence of inducible Group 2 LEA proteins, and delayed or reduced tolerance to freezing. In contrast, both birch genotypes showed similar seasonal production patterns of Group 4 LEA proteins. Our results demonstrate that onset of cold acclimation in birch is based on multiple mechanisms, including molecular pathways that are typical of stress responses. ABA may be important for the accurate timing of cold acclimation in trees that are sensitive to photoperiod.     

Physiological, stomatal and ultrastructural ozone responses in birch (Betula pendula Roth.) are modified by water stress

The physiological, stomatal and ultrastructural responses to ozone and drought of ozone-sensitive and more ozone-tolerant birch ( Betula pendula Roth.) clones were studied singly and in combination, in a high-stress chamber experiment and in a low-stress open-field experiment. In the chamber experiment, well watered (WW), moderately watered (MW) or drought-stressed (DS) saplings were exposed for 36 d to 0 or 130 nmol mol^∠1 ozone. In the open-field experiment, well watered or drought-stressed saplings were grown for one growing season in ambient air or exposed to 1·8 × ambient ozone. Drought stress reduced growth rate, stomatal conductance, stomatal density and the proportion of starch and thylakoids in chloroplasts, but stimulated net photosynthesis, Rubisco and chlorophyll quantity at the end of the growing season, and increased the size and density of plastoglobuli. Ozone fumigations caused more variable, clone- and exposure-dependent responses in growth, decreased stomatal conductance and net photosynthesis, an increased number of stomata, visible and ultrastructural chloroplast injuries, and enhanced autumn yellowing of the leaves. Ozone-induced changes in plastoglobuli, starch and thylakoids resembled drought responses. The two experiments revealed that, depending on the experimental conditions and the variable, the response to drought and ozone stress can be independent, additive or interactive. Drought protected the plants from ozone injuries under high-stress conditions in the chamber experiment. In the low-stress, open-field experiment, however, enhanced ozone damage was observed in birch saplings grown under restricted water supply.     

Element content in leaves of birch (Betula verrucosa Ehrh.) in an air polluted area

 The content of natural (S, N, P, Ca, Mg, K, Mn, Zn, Cu) and extraneous elements (Pb, Cd, Al) in leaves of birch growing in the Krusne hory Mts. (Czech Republic), a territory affected by air pollution (SO₂), was evaluated with regard to the altitude and age of birch stands, and in relation to stand nutrition. The contents of S, Ca, Mg, Zn and Pb culminated at the highest points of the altitudinal transect (elevation 900–1000 m). In contrast, at high altitudes the content of Cd, Al and Mn decreased. The content of elements in leaves was mostly not dependent on tree age. In terms of nutrition and growth of birch, the content of Cu was insufficient, the content of Ca, Mg, N, P and K was optimum, and the content of S, Zn and primarily Mn was higher. The content of Pb and Al was at natural background levels, that of Cd higher. Received: 3 July 1997 / Accepted: 19 May 1998     

Structure of a pristine Picea abies forest in northeastern Europe

Abstract. The forest structure in a large, relatively homogeneous area of pristine Picea abies taiga in the southern boreal region west of the Ural mountains was studied along four 500-m long transects. P. abies dominated the forest in association with Abies sibirica and Betula spp. The mean volume of living trees was 216 m³/ha. This value varied among the four transects, from 138 - 252 m³/ha. Mean density of trees (DBH > 1 cm) (and variation over the transects) was 2 064/ha (1670 - 2710). Living trees classified as dying or seriously damaged made up 2.9 (2.5 - 3.5) % of the living tree volume. Betula was an important canopy component and made up 16% of the living tree volume. The number of dead standing trees varied from 195 - 325/ha, corresponding to a volume of 10.8 - 70.7 m³/ha. The density of trees with a broken stem was 90 - 170/ha and their estimated volume 7.6 - 41.3 m³/ha. Standing dead trees and trees with broken stems represented 10.4 and 8.9% of the total standing tree volume (living + dead), respectively. The mean volume of decaying logs on the forest floor was 117 (84.4–156.2) m³/ha, corresponding to 54 (35 - 113) % of the living tree volume. The canopy-forming trees were present in the understory as abundant saplings and suppressed individuals. The size distribution of the dominant tree species resembled the inverse J-shape. Generally, the forest was characterized by a high small-scale structural variation and a larger-scale relative homogeneity. This pattern is consistent with forest dynamics where the forest consists of a small-scale mosaic of patches in different stages of recovery following disturbance. Our results suggest that the ecology and dynamics of extensive areas of natural boreal forests can be driven by small-scale disturbance.