Wound-induced changes in the palatability of Betula pubescens and B. pendula

Summary Leaves of Betula were damaged artificially in April, June and August 1982. Palatability of damaged and adjacent undamaged leaves was assessed against controls in bioassays using the polyphagous Lepidoptera Spodoptera littoralis and Orgyia antiqua. Assessments were carried out at intervals from six hours to five months following each damage date. Palatability (relative proportions of leaves consumed) was significantly lower than controls in damaged and adjacent leaves after six hours and remained detectable for up to two months but this was less clear in the June-damaged samples and undetectable in the August group. Adjacent leaves were significantly affected whether distal or proximal to the damaged leaves. Marked and significant changes occurred in levels of soluble tannins in the damaged and adjacent leaves but the relationship between crude tannin levels and changed palatability was not simple cause and effect. No significant effects of damage on aphid (Euceraphis punctipennis) reproduction could be detected among birches in a growth room experiment in which half the trees were artificially damaged and half were controls. The results are discussed in the light of earlier work on induced defence in birch and five areas of significant new information represented by the results in this paper are identified.Spodoptera was reared under M.A.F.F. licence PHF 121/57     

Freezing exposure releases bud dormancy in Betula pubescens and B. pendula

Bud dormancy in woody plants is released by long-term exposure to non-freezing chilling temperatures, whereas freezing temperatures have been considered to have little or no effect. However, the present results demonstrate that short-term exposure to freezing can release bud dormancy in Betula pubescens (Ehrh.) and B. pendula (Roth). Short-term freezing during the dormancy induction phase improved the release of bud dormancy only if an adequate level of dormancy had been reached. In fully dormant or chilled plants both the percentage and the speed of bud-burst increased, the more so the lower the temperature. Our results rule out the possibility that endogenous abscisic acid could be directly involved in the physiological control of bud dormancy release. The fast, easily applicable method presented here for bud dormancy release could further investigations into the biochemical and biophysical background to the process. The mechanisms of bud dormancy release and its relationship to cold acclimation are discussed in the light of these results, as also are the implications of the findings for modelling of bud dormancy.     

Sun and shade leaves in Betula pubescens and Betula pendula

Summary

Measurements of the net photosynthesis and dark respiration rates of excised twigs from Betula pubescens Ehrh. subsp. odorata (Bechst.) Warburg and B. pendula Roth, at different light intensities were made using infra-red gas analysis. B. pubescens appears to possess leaves which on the basis of physiological responses can be described as sun and shade leaves. In the more open canopy of B. pendula differences between leaf types are less pronounced. The presence of sun and shade leaves is suggested as a means whereby the net assimilation rate of the shrubby growth form of B. pubescens can be increased. This type of mechanism becomes increasingly important at high altitudes and latitudes.     

Leaf-shape as an indicator of introgression between Betula pendula and B. pubescens

Summary

Leaf-shape comparisons were made between individual trees in a mixed wood containing B. pendula and B. pubescens, and two relatively pure stands. Data sets were subjected to analysis of variance, principal components and discriminant analyses in order to study within-tree variation, variation within each species and the relationships between them. Within-tree variation was found to be much less than that between trees and principal component analysis provided a separation of the material into species groups and indicated extensive variation within them. The employment of a discriminant function sharpened the separation of the pure woods and pointed to the occurrence of possible hybrids and back-crossed individuals within the mixed wood. The findings indicate that gene flow probably proceeds from the diploid to the tetraploid level.     

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.     

Reproductive variability and pollen limitation in three Betula taxa in northern Sweden

This 3-yr study documents large variation in pollination and seed quality in birches (Betula) in northern Sweden between taxa, high and low altitude populations, and among years Seed quality was positively correlated with pollination degree and improved by pollen supplementation in B pubescens ssp pubescens in the mountain area, indicating pollen limitation Betula pendula showed the same tendency, but less pronounced Reduced sexual reproduction of B pendula in the mountain area might more often be due to limited resources for seed maturation and defense of the seeds against predispersal seed predation In contrast, coastal populations of both species display relatively high pollination rates and supplemental pollination had no effect on seed quality, suggesting that pollen limitation is rare or absent here The mountain birch Betula pubescens ssp tortuosa showed generally lower pollination and seed quality compared with B pubescens ssp pubescens , but not compared with mountain populations of B pendula It is concluded that pollen limitation may occur in Betula , but to what extent varies with taxon, altitude and year The seed quality is also strongly affected by other factors such as infections of gall midges (Semudobia spp, Diptera Cecidomyndae) and incomplete seed maturation     

Content and Composition of Fatty Acids in Total Lipids from the Buds of Betula pubescens,B. pendula,and B. pendula var. carelica

Russian Journal of Plant Physiology - Absolute content and composition of fatty acids (FAs) in total lipids from the buds of white birch (Betula pubescens Ehrh.), silver birch (B. pendula Roth),...     

Structure,composition and regeneration of riparian forest along an altitudinal gradient in northern Iran

In order to protect and understand the regeneration of riparian forests, it is important to understand the environmental conditions that lead to their vegetation differentiation. We evaluated the structure, composition, density and regeneration of woody species in forests along the river Safaroud in Ramsar forest in northern Iran in relation to elevation, soil properties and distance from the river. Using 60 transects located perpendicularly to river and 300 quadrats, we examined forests 0, 50, 100, 150 and 200 m from the stream along an elevation gradient spanning from 350 to 2,400 m a.s.l. We found that total density, regeneration, diameter and basal area of trees were significantly higher in the interior of the forest whereas shrub density was higher close to the river. The uneven-aged forest structure showed no significant differences among gradient from the river to the forest interior. Hydro-geomorphic processes, flooding, the elevation gradient, distance from the river and soil properties were the most important factors that influenced plant community distribution in relation to the river.     

Regional and local patterns of ectomycorrhizal fungal diversity and community structure along an altitudinal gradient in the Hyrcanian forests of northern Iran

? Altitudinal gradients strongly affect the diversity of plants and animals, yet little is known about the altitudinal effects on the distribution of microorganisms, including ectomycorrhizal fungi. ? By combining morphological and molecular identification methods, we addressed the relative effects of altitude, temperature, precipitation, host community and soil nutrient concentrations on species richness and community composition of ectomycorrhizal fungi in one of the last remaining temperate old-growth forests in Eurasia. ? Molecular analyses revealed 367 species of ectomycorrhizal fungi along three altitudinal transects. Species richness declined monotonically with increasing altitude. Host species and altitude were the main drivers of the ectomycorrhizal fungal community composition at both the local and regional scales. The mean annual temperature and precipitation were strongly correlated with altitude and accounted for the observed patterns of richness and community. ? The decline of ectomycorrhizal fungal richness with increasing altitude is consistent with the general altitudinal richness patterns of macroorganisms. Low environmental energy reduces the competitive ability of rare species and thus has a negative effect on the richness of ectomycorrhizal fungi. Because of multicollinearity with altitude, the direct effects of climatic variables and their seasonality warrant further investigation at the regional and continental scales.     

Comparison of soil seed banks of habitats distributed along an altitudinal gradient in northern Iran

In this study we investigated the variations in soil seed banks along an altitudinal gradient in the Alborz mountains, Iran, covering three habitats from lower to upper altitudes: forest, forest-subalpine grassland ecotone and subalpine meadow. In each habitat from 1850 to 2400 m, 20 quadrats were established along four transects, and the above-ground vegetation and the germinable seed banks were determined. Results show that the similarity between seed bank and vegetation was lowest in the ecotone located at intermediate altitudes. Together with the contrasting highest density and species diversity of seeds at these altitudes, the ecotonal role of this habitat was confirmed.We found evidence that lower altitudes could act as storage for seeds of some species growing at higher altitudes; the role of the ecotone was more prominent as a reserve for the meadow plant seeds than the role of the forest as a reserve for seeds of the meadow and ecotone habitats. Soil seed banks, particularly from the ecotone, can be used for restoring vegetation in some degraded sites.     

Development of a Technique for Obtaining Polysaccharides from Leaves of the Birch (Betula pendula Roth. and Betula pubescens Ehrh.)

Russian Journal of Bioorganic Chemistry - The goal of the study was to develop a complex technique for the extraction and purification of polysaccharides from the leaves of birch (Betula pendula...     

Shifts in patterns of microhabitat occupation by six closely related species of mosses along a complex altitudinal gradient

Summary Changes in patterns of microhabitat occupation were examined for six closely related moss species (family Polytrichaceae) found growing together along a complex altitudinal gradient on the northeast face of Mount Washington, New Hampshire. Little evidence could be found to support the hypothesis that the relative distributions of these six moss species were determined by competitive interactions occurring among them. Instead, the data support the hypothesis that changing patterns in the relative distributions of these six moss species result from differences in microhabitat availability among sites. The moss species appear to behave in an opportunistic manner, occupying a wide array of microhabitats as these microhabitats become available to them.     

Phenolic compounds in seedlings of Betula pubescens and B. pendula are affected by enhanced UVB radiation and different nitrogen regimens during early ontogeny

We studied the ability of tree seedlings to respond to two environmental factors, elevated ultraviolet B (UVB) radiation and availability of nitrogen (N), at the beginning of their development. Seeds of two birch species, Betula pubescens Ehrh. (common white birch) and B. pendula Roth (silver birch), were germinated and the seedlings grown in an experimental field in eastern Finland. The experimental design consisted of a constant 50% increase in UVB radiation (including a slight increase in UVA), a UVA control (a slight increase in UVA) and a control. The seedlings were fertilized with three levels of N. The experiment lasted for 2 months; aboveground biomass was measured and the most mature leaf of each seedling was taken for the analyses of phenolics. Growth of the seedlings was not significantly affected by enhanced UVB, but was increased by increasing N. Elevated UVB induced significant changes in phenolic compounds. Quercetin glycosides were accumulated in the leaves of both species in response to UVB; this is considered to be a protective response. However, the direction of the responses of individual phenolics to different N regimens differed. In addition, concentration of soluble condensed tannins was lower at moderate N than that at lower levels of N in both species; on the contrary, in B. pubescens the concentration of insoluble condensed tannins was highest at moderate N. No significant interaction between UV and N was detected, and the responses of the two species were highly similar to UVB, while the responses to N regimens varied slightly more between species.     

Mating patterns of Minshan's toad (Bufo minshanicus) from three populations along an altitudinal gradient

The large-male mating advantage and size-assortative mating are two different size-based patterns, which deviate from random mating in toads. These two pairing patterns may arise due to female choice, male-male competition, male choice, or a combination of these. This study investigated the mating system of Minshan's toad (Bufo minshanicus) from three populations along an altitudinal gradient during two breeding reasons in the northeastern Tibetan plateau. Our study shows that males found in amplexus with females were larger on average than non-amplectant males in two sites with higher operational sex ratios. Similarly, in those sites, males and females found in amplexus maintained an optimal size ratio. These data suggest that male-male competition leads to size-assortative mating in the lack of mate choice (female and male mate choice) by Minshan's toad, as larger males performed higher frequencies for taking-over other low quality ones with amplectant females.     

Transplantation experiments with saplings of Betula pubescens ssp. tortuosa near the tree-limit in Central Sweden

Saplings of mountain birch Betula pubescens Ehrh. ssp. tortuosa (Ledeb.) Nyman, three years old, were transplanted into three contrasting habitats, viz. moderate and extreme snow-bed and windswept crest. The experimental sites were situated just below the present local tree-limit of birch. During 1978–1983 mortality and height increment were monitored. High initial mortality was succeeded by lower mortality at all three sites. The height increment was significantly higher in moderate snow-bed compared with the two extreme habitats (winswept crest and extreme snow-bed). The main conclusions are that after the first seedling stage the mountain birch survives broad climatic variation. However, normal completion of the life-cycle is only possible within more narrow limits. A minimum amount of the snow-free preriod is needed, e.g. to satisfy the requirements of nitrogen nutrition. The results Stress the opportunistic nature of the mountain birch which gives it a selective advantage in the extremely unpredictable climate in mountainous areas in Scandinavia. The reproductive strategy of mountain birch apparently includes having a bank of persistent saplings.     

Disturbances, elevation, topography and spatial proximity drive vegetation patterns along an altitudinal gradient of a top biodiversity hotspot

The correlation between vegetation patterns (species distribution and richness) and altitudinal variation has been widely reported for tropical forests, thereby providing theoretical basis for biodiversity conservation. However, this relationship may have been oversimplified, as many other factors may influence vegetation patterns, such as disturbances, topography and geographic distance. Considering these other factors, our primary question was: is there a vegetation pattern associated with substantial altitudinal variation (10–1,093 m a.s.l.) in the Atlantic Rainforest—a top hotspot for biodiversity conservation—and, if so, what are the main factors driving this pattern? We addressed this question by sampling 11 1-ha plots, applying multivariate methods, correlations and variance partitioning. The Restinga (forest on sandbanks along the coastal plains of Brazil) and a lowland area that was selectively logged 40 years ago were floristically isolated from the other plots. The maximum species richness (>200 spp. per hectare) occurred at approximately 350 m a.s.l. (submontane forest). Gaps, multiple stemmed trees, average elevation and the standard deviation of the slope significantly affected the vegetation pattern. Spatial proximity also influenced the vegetation pattern as a structuring environmental variable or via dispersal constraints. Our results clarify, for the first time, the key variables that drive species distribution and richness across a large altitudinal range within the Atlantic Rainforest.     

Climate change and frog calls: long-term correlations along a tropical altitudinal gradient

Temperature affects nearly all biological processes, including acoustic signal production and reception. Here, we report on advertisement calls of the Puerto Rican coqui frog (Eleutherodactylus coqui) that were recorded along an altitudinal gradient and compared these with similar recordings along the same altitudinal gradient obtained 23 years earlier. We found that over this period, at any given elevation, calls exhibited both significant increases in pitch and shortening of their duration. All of the observed differences are consistent with a shift to higher elevations for the population, a well-known strategy for adapting to a rise in ambient temperature. Using independent temperature data over the same time period, we confirm a significant increase in temperature, the magnitude of which closely predicts the observed changes in the frogs’ calls. Physiological responses to long-term temperature rises include reduction in individual body size and concomitantly, population biomass. These can have potentially dire consequences, as coqui frogs form an integral component of the food web in the Puerto Rican rainforest.     

Relationships between aquatic plants and environmental factors along a steep Himalayan altitudinal gradient

We examined the relationships of aquatic plants with physical–chemical characteristics among 28 lakes within a steep altitudinal gradient ranging from tropical (77 m) to high alpine (4750 m) in the Himalayas of Nepal. Species richness and diversity showed an approximately linear decrease with increasing altitude. The study region exhibits a relatively high proportion of monocotyledonous helophytes, as is typical of aquatic plants on the Indian subcontinent. A canonical correspondence analysis of the entire altitudinal gradient (CCA-1) suggested that the strongest abiotic influences on the distribution of aquatic plants are associated with water temperature, substrate quality, altitude, pH, transparency and conductivity. Two more-restricted CCA analyses examined a shorter altitudinal gradient of 70–1500 m. The CCA-2 analysis (all aquatic plants) and CCA-3 (only euhydrophytes) found that the most important abiotic influences were associated with temperature, lake surface area, suspended solids, bicarbonate and dissolved phosphorus. These results suggest that relatively local influences are different from those that have a regional basis, but that climate-related influences are key along altitudinal gradients. The temperature gradient in the CCA distinguished montane and alpine Arcto-tertiary floristic elements of the highest altitudinal regions from the more widely distributed temperate and tropical species of the lower regions.