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     

Foraging by moose on two species of birch when these occur in different proportions

The two tree-like birch species Betula pendula and B. pubescens are of medium preference to moose during winter in northern Sweden. Because these birches are abundant in many biotopes, they form a major part of the moose diet. The two birches are very similar in appearance and often occur in mixed stands. Twenty-one birch stands where B. pendula formed from 2 to 97% of the birches were investigated to determine how the relative composition of the stands affected browsing of the two species by moose. In stands composed of 60% or less of B. pendula , there was a preference for this species when regarding 1.5–3.0 m high birches, which carry the largest amount of available browse per tree. At higher proportions B. pendula was still preferred, but use was closer to availability. However, in all stands there were significantly more moose bites per tree of B. pendula than of B. pubescens . In four birch stands browsing on 1.0–1.5 m high birches was also investigated. For this height class there was still a preference for B. pendula , but the difference between the two species was less pronounced than for the 1.5–3.0 m height class.     

Extensive sharing of chloroplast haplotypes among European birches indicates hybridization among Betula pendula, B. pubescens and B. nana

Extensive sharing of chloroplast haplotypes among the silver birch, Betula pendula Roth., the downy birch, B. pubescens Ehrh., and the dwarf birch, B. nana L., was discovered using polymerase chain reaction-restriction fragment length polymporphism markers. The geographical component of the genetic variation was stronger than the species component: the species were not significantly different while 11% of the variation could be attributed to differentiation between the two main regions studied, Scandinavia and western Russia. All haplotypes occurring in more than 2% of the individuals were shared among the species and the introgression ratios were quite large: 0.79 between B. pubescens and B. pendula and 0.67 between B. pubescens and B. nana. The data also indicate that B. pendula individuals are more similar to sympatric B. pubescens than to B. pendula individuals from nearby forests. However, this trend is not as pronounced when B. pubescens is considered, suggesting that introgression is not symmetrical. The haplotype sharing among the three Betula species is most likely caused by hybridization and subsequent cytoplasmic introgression.     

HPLC analysis of leaf surface flavonoids for the preliminary classification of birch species

Flavonoid aglycones found on the surfaces of birch (Betula spp.) leaves may constitute up to 10% of the dry weight of the leaf. A facile extraction and HPLC procedure has been developed that can be used for the preliminary classification of birch species according to the patterns of their leaf surface flavonoids. The procedure involves no complex sample preparation steps, and is able to provide HPLC chromatograms from fresh leaves in less than 30 min. If necessary, leaves do not even need to be removed from the tree. Since the genus Betula is taxonomically complex and separation of different birch species can be problematic, the developed method was applied to 15 Betula species and four sub-species of Betula pendula Seven of the studied species were classified as B. pubescens and eight as B. pendula-type birches. The remaining four species did not belong to either of these two classes on account of their unique pattern of external flavonoids. The difference between the leaf surface flavonoid composition of B. pubescens and B. pendula type birch species was unambiguously clear, and the developed method could reliably distinguish between the two species. Whilst leaf surface flavonoids can be valuable chemotaxonomic markers, they classify birch species differently from morphological markers. Birch species with diploid chromosome sets did not contain any of the flavanones that were present in the leaves of other species. The close relationship between the occurrence of some flavonoid aglycones and the ploidy level of Betula species suggests that these chemotaxonomic markers may be useful both in taxonomic and phylogenetic analyses.     

Comparative analysis of leaf trichome structure and composition of epicuticular flavonoids in Finnish birch species

The morphology, ultrastructure, density and distribution of trichomes on leaves of Betula pendula, B. pubescens ssp. pubescens, B. pubescens ssp. czerepanovii and B. nana were examined by means of light, scanning and transmission electron microscopy. The composition of flavonoids in ethanolic leaf surface extracts was analysed by high pressure liquid chromatography. All taxa examined contained both glandular and non-glandular trichomes (short and/or long hairs) but differed from each other in trichome ultrastructure, density and location on the leaf. Leaves of B. pubescens were more hairy than those of B. pendula, but the latter species had a higher density of glandular trichomes. Of the two subspecies of B. pubescens, leaves of ssp. pubescens had more short hairs on the leaf surface and four times the density of glandular trichomes of leaves of ssp. czerepanovii, whereas, in the latter subspecies, short hairs occurred largely on leaf veins, as in B. nana. The glandular trichomes were peltate glands, consisting of medullar and cortical cells, which differed structurally. Cortical cells possessed numerous small, poorly developed plastids and small vacuoles, whereas medullar cells had several large plastids with well-developed thylakoid systems and fewer vacuoles. In B. pubescens subspecies, vacuoles of the glandular cells contained osmiophilic deposits, which were probably phenolic, whereas in B. pendula, vacuoles of glandular trichomes were characterized by the presence of numerous myelin-like membranes. The composition of epicuticular flavonoids also differed among species. The two subspecies of B. pubescens and B. nana shared the same 12 compounds, but five of these occurred only in trace amounts in B. nana. Leaf surface extracts of B. pendula contained just six flavonoids, three of which occurred only in this species. In summary, the structure, density and distribution of leaf trichomes and the composition of epicuticular flavonoids represent good taxonomic markers for Finnish birch species.     

Distribution of hydrolysable tannins in the foliage of Finnish birch species

On the basis of qualitative and quantitative analysis with liquid chromatography--electrospray ionisation mass spectrometry, the foliage of dwarf birch (Betula nana L.), silver birch (B. pendula Roth) and mountain birch (B. pubescens ssp. czerepanovii (Orlova) H?met-Ahti) were found, for the first time, to contain the same individual HTs that were described earlier for white birch (B. pubescens Ehrh.). In addition, one previously unidentified ellagitannin was preliminarily identified from the leaves of white and mountain birches, being totally absent from the foliage of the other two species. There were large variations in the contents of HTs between species. Seasonal variation affected significantly the contents of some individual HTs within species, and these changes were mainly in accordance with the biosynthetic pathway of HTs. All species converted galloylglucoses (GGs) into ellagitannins (ETs), dwarf birch being the only one that's efficient ET synthesis resulted in seasonally increased contents of ETs and thereof total HTs as well. The presence of insoluble ETs as well as the absence of insoluble GGs was confirmed in all four birch species for the first time. Furthermore, the amounts of insoluble ETs per one birch leaf were found to accumulate during the growing season. These findings complemented our knowledge of the biosynthetic pathway of birch leaf HTs: from soluble GGs via soluble ETs into insoluble ETs. The possible role of HTs in the herbivore defence of these species is discussed.     

Changes in leaf trichomes and epicuticular flavonoids during leaf development in three birch taxa

BACKGROUND AND AIMS: Changes in number of trichomes and in composition and concentrations of their exudates throughout leaf development may have important consequences for plant adaptation to abiotic and biotic factors. In the present study, seasonal changes in leaf trichomes and epicuticular flavonoid aglycones in three Finnish birch taxa (Betula pendula, B. pubescens ssp. pubescens, and B. pubescens ssp. czerepanovii) were followed. METHODS: Trichome number and ultrastructure were studied by means of light, scanning and transmission electron microscopy, while flavonoid aglycones in ethanolic leaf surface extracts were analysed by high-pressure liquid chromatography. KEY RESULTS: Density of both glandular and non-glandular trichomes decreased drastically with leaf expansion while the total number of trichomes per leaf remained constant, indicating that the final number of trichomes is established early in leaf development. Cells of glandular trichomes differentiate before those of the epidermis and produce secreted material only during the relatively short period (around 1-2 weeks) of leaf unfolding and expansion. In fully expanded leaves, glandular trichomes appeared to be at the post-secretory phase and function mainly as storage organs; they contained lipid droplets and osmiophilic material (probably phenolics). Concentrations (mg g(-1) d. wt) of surface flavonoids decreased with leaf age in all taxa. However, the changes in total amount ( microg per leaf) of flavonoids during leaf development were taxon-specific: no changes in B. pubescens ssp. czerepanovii, increase in B. pendula and in B. pubescens ssp. pubescens followed by the decline in the latter taxon. Concentrations of most of the individual leaf surface flavonoids correlated positively with the density of glandular trichomes within species, suggesting the participation of glandular trichomes in production of surface flavonoids. CONCLUSIONS: Rapid decline in the density of leaf trichomes and in the concentrations of flavonoid aglycones with leaf age suggests that the functional role of trichomes is likely to be most important at the early stages of birch leaf development.     

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),...     

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.     

Photosynthetic responses to low temperature in Betula pubescens and Betula tortuosa

The acclimation of the net flux density of CO₂ to temperature, and the effects of freezing-stress on the functional integrity of photosynthesis were compared for Betula tortuosa and Betula pubescens . Single expanded leaves of B. tortuosa had a higher rate of net photosynthesis and a greater capacity to acclimate to a low growth temperature regime than had leaves of B. pubescens . At low temperatures, stomatal conductances were higher for B. tortuosa than for B. pubescens . In neither species were the stomatal conductances determining the decrease of the rate of net photosynthesis at low temperatures. There was a marked difference between leaves of the two species in their ability to withstand freezing, as revealed by measurements of changes in temperature-induced variable fluorescence. The chloroplast thylakoids of B. tortuosa were better able to maintain their functional integrity at sub-zero temperatures than were those of B. pubescens .     

Quantitative analysis of polymeric proanthocyanidins in birch leaves with normal-phase HPLC

The proanthocyanidin composition and content in the leaves of nine birch species (Betula albosinensis, B. ermanii B. maximowicziana, B. nana, B. papyrifera, B. pendula, B. platyphylla, B. pubescens, and B. pubescens ssp. czerepanovii) were studied with different methods including colorimetric assay, HPLC coupled with PAD or ESI/MS and NMR. Total proanthocyanidin content was determined using the acid butanol assay. A normal phase-HPLC method was applied for the analysis of polymeric proanthocyanidins. The content of polymeric proanthocyanidins was estimated from a late eluting peak in the chromatogram. With this HPLC method, quantitative analysis of polymeric proanthocyanidins could be performed directly from leaf extracts: no additional purification or preparation steps were required. It was shown that birch leaves contained mainly polymeric proanthocyanidins with a degree of polymerisation greater than 10. Total proanthocyanidin content (expressed as dry weight) was found to vary from 44mg/g (B. papyrifera) to 145mg/g (B. nana), and polymeric proanthocyanidin content from 39mg/g (B. pendula) to 119 mg/g (B. nana).     

Recent invasion of the mountain birch Betula pubescens ssp. tortuosa above the treeline due to climate change: genetic and ecological study in northern Sweden

Mountain birch, Betula pubescens ssp. tortuosa, forms the treeline in northern Sweden. A recent shift in the range of the species associated with an elevation of the treeline is commonly attributed to climate warming. Using microsatellite markers, we explored the genetic structure of populations along an altitudinal gradient close to the treeline. Low genetic differentiation was found between populations, whereas high genetic diversity was maintained within populations. High level of gene flow compensated for possible losses of genetic diversity at higher elevations and dissipated the founding effect of newly established populations above the treeline. Spatial autocorrelation analysis showed low spatial genetic structure within populations because of extensive gene flow. At the treeline, significant genetic structure within the juvenile age class at small distances did not persist in the adult age class, indicating recent expansion of young recruits due to the warming of the climate. Finally, seedling performance above the treeline was positively correlated with parameters related to temperature. These data confirm the high migration potential of the species in response to fluctuating environmental conditions and indicate that it is now invading higher altitudes due to the recent warming of the climate.     

Oncopsis flavicollis (L.) associated with tree birches (Betula): a complex of biological species or a host plant utilization polymorphism?

The closely related species of leafhoppers, Oncopsis flavicollis (L.) and 0. subangulata (Sahl.), are restricted to birches, Betula pendula Roth and B. pubescens Ehrh., as host plants. Morphometric discriminant analyses of adult insects from S Wales showed O. flavicollis populations from the two Betula species to be significantly different. The best discrimination was provided by characters of the male dorsal abdominal apodemes. Analyses of such apodeme morphology in populations more widely from S Britain showed three distinct types: in western localities type 1 dominantly on B. pubescens , type 2 dominantly on B. pendula and type 3 absent; in eastern localities type 3 only on B. pendula , type 2 on both species of Betula and type 1 only on B. pubescens. Acoustic calling and courtship signals of males showed clear differences between the three apodeme types of 0. flavicollis. It is concluded that the three 0. flavicollis types, together with 0. subangulata , are distinct but very closely related biological species. Contrary to earlier suggestions, this example provides no evidence for host plant utilization polymorphisms.     

Interspecific variation in resistance of Asian, European, and North American birches (Betula spp.) to bronze birch borer (Coleoptera: Buprestidae)

Bronze birch borer (Agrilus anxius Gory) is the key pest of birches (Betula spp.) in North America, several of which have been recommended for ornamental landscapes based on anecdotal reports of borer resistance that had not been confirmed experimentally. In a 20-yr common garden experiment initiated in 1979 in Ohio, North American birch species, including paper birch (Betula papyrifera Marshall), 'Whitespire' gray birch (Betula populifolia Marshall), and river birch (Betula nigra L.), were much more resistant to bronze birch borer than species indigenous to Europe and Asia, including European white birch (Betula pendula Roth), downy birch (Betula pubescens Ehrh.), monarch birch (Betula maximowicziana Regel), and Szechuan white birch (Betula szechuanica Jansson). Within 8 yr of planting, every European white, downy, and Szechuan birch had been colonized and killed, although 100% of monarch birch had been colonized and 88% of these plants were killed after nine years. Conversely, 97% of river birch, 76% of paper birch, and 73% Whitespire gray birch were alive 20 yr after planting, and river birch showed no evidence of colonization. This pattern is consistent with biogeographic theory of plant defense: North American birch species that share a coevolutionary history with bronze birch borer were much more resistant than na?ve hosts endemic to Europe and Asia, possibly by virtue of evolution of targeted defenses. This information suggests that if bronze birch borer were introduced to Europe or Asia, it could threaten its hosts there on a continental scale. This study also exposed limitations of anecdotal observation as evidence of host plant resistance.     

Consequences of defoliation on phenological interaction between Epirrita autumnata and its host plant, Mountain Birch

1. Defoliation-induced changes in the budbreak phenology of Mountain Birches ( Betula pubescens ssp. tortuosa (Ledeb.) Nyman), and their effects on herbivore performance, were investigated during an outbreak of the spring-feeding geometrid, Epirrita autumnata (Bkh.).
2. Total defoliation (followed by refoliation) by E. autumnata larvae was required to achieve significant delaying of budbreak of Mountain Birch one year after damage.
3. Delayed budbreak has potentially deleterious effects on herbivore performance. However, E. autumnata larvae show phenotypic responses that increase the synchrony between larvae and leaves: high larval density, a prerequisite for severe defoliation, delays egg hatch in the following year.
4. Late hatching larvae performed as well on birches with delayed budbreak due to the previous year's total defoliation as did early hatching larvae on birches with earlier budbreak.     

Genotype-environment interactions in pollen competitive ability in an anemophilous tree,Betula pendula Roth

This study describes genotype-environment interactions in pollen competitive ability expressed as pollen-tube growth rate and seed-siring success in Betula pendula Roth. A factorial crossing design was applied using the same maternal and paternal clones in two different environmental conditions, in a B. pendula seed orchard established in a greenhouse and at an outdoor clone collection. Both single donor and two-donor pollinations were employed. Female inflorescences were collected after a fixed time of germination, pollen-tube lengths were measured for each cross, and paternity of the seeds sired by two-donor pollen mixtures was analyzed using isozyme markers. The pollination site had a significant influence on pollen-tube growth rate and seed-siring success. Significant interactions between pollination site and pollen donor indicated genotype-environment interactions in pollen-tube growth rate and seed-siring success. A highly significant positive correlation between pollen-tube growth rate and seed-siring success was found in the greenhouse but not at the outdoor clone collection. These results suggest that the pollen-tube growth rate can be a predictor of seed-siring success in controlled greenhouse conditions, where differences among maternal plants are mainly of genetic origin, but not in more heterogeneous outdoor conditions. In natural birch stands, environmental maternal effects probably diminish the significance of pollen competition for sexual selection in Betula pendula. At seed orchards, the effects of environmental conditions on pollen competitive ability can have important consequences for the genetic composition of the seed crop.     

Variation in Betula pubescens Ehrh. (Betulaceae) in Scotland: its nature and association with environmental factors

A classification, based on climatological, topographical and geological attributes and developed by Bunce, Barr & Whittaker (1981: Annual Report of the Institute of Terrestrial Ecology, U.K. 1980) for stratifying the U.K. into 32 land classes, was used to ensure objectivity when sampling the range of variation within Betula spp. in northern Britain.
Seeds of Betula spp. were collected, wherever possible, from each of ten woodland trees in three geographically distinct locations of each of 12 land classes known to 'carry' Betula species. Trees in a thirteenth land class, restricted to the west of Scotland, were inaccessible.
Seedlings from 170 of 196 trees were attributed to B. pubescens which occurred in all 12 land classes: the remaining 26 trees were identified as B. pendula which is restricted to five land classes in southern and eastern Scotland.
Detailed analyses of plant morphological and phenological features using principal component analyses, cluster analyses and canonical variance analyses showed that leaf size, shape and hairiness were good discriminators of variation, as was the occurrence of fruitbodies of Laccaria proxima , a sheathing (ecto-)mycorrhizal fungus. These discriminators enabled the seedlings to be arranged in a nuniber of distinctive groups: sredlings with drooping branclirs and small laves, chararteristirs of B. pubescens subspecies tortuosa , originating from westerly and wet locations to seedlings with upright branches arid large leaves originating from easterly and dry locations.
Leaf lengths and the increasing frequency of petiolar hairs were related to maximum July trmperaturcs and mcasurrs of oceanicity (at the sites of origin).     

Environmental conditions and host genotype direct genetic diversity of Venturia ditricha,a fungal endophyte of birch trees

We investigated whether genetic variation of a common foliar endophyte of birch trees, Venturia ditricha, is affected by environmental conditions or host genotype. Fungal samples were collected from 10 half-sibling families of mountain birch (Betula pubescens ssp. czerepanovii) grown in two environmental conditions with different daily average temperatures: a forested river valley and an adjacent open tundra (altitudinal difference 180 m). Genetic analysis of V. ditricha isolates was done using random amplified microsatellite polymerase chain reaction. We found that host genotypes, along with prevailing environmental conditions, influence the probability of infection by particular endophyte genotypes. The most susceptible host genotypes were highly infected with genetically similar endophyte genotypes, whereas the most resistant trees were poorly infected and they were infected by genetically dissimilar endophytes. Our results also showed environment-host genotype interactions, suggesting that the susceptibility of the host to a particular endophyte genotype may change in natural environments when environmental conditions are changed. It appears that a particular endophyte genotype needs to find the right host genotype for a successful infection. There are many host genotypes in natural stands; this means, from the point of view of the fungus, the environment is heterogeneous. Thus, under the influence of birch tree genotypes, genetically differentiated subgroups of the endophytic fungus may be formed in different environments.     

Climate-driven synchrony in seed production of masting deciduous and conifer tree species

Aims Understanding fluctuations in plant reproductive investment can constitute a key challenge in ecology, conservation and management. Masting events of trees (i.e. the intermittent and synchronous production of abundant seeding material) is an extreme example of such fluctuations. Our objective was to establish the degree of spatial and temporal synchrony in common four masting tree species in boreal Finland and account for potential causal drivers of these patterns.Methods We investigated the spatial intraspecific and temporal interspecific fluctuations in annual seed production of four tree species in Finland, silver birch Betula pendula Roth, downy birch Betula pubescens Ehrh., Norway spruce Picea abies (L.) H.Karst. and rowanberry Sorbus aucuparia L. We also tested to see whether variations in seed production were linked to annual weather conditions. Seeding abundance data were derived from tens of stands per species across large spatial scales within Finland during 1979 to 2014 (for rowanberries only 1986 to 2014).Important findings All species showed spatial synchrony in seed production at scales up to 1000 km. Annual estimates of seed production were strongly correlated between species. Spring and summer temperatures explained most variation in crop sizes of tree species with 0-to 2-year time lags, whereas rainfall had relatively little influence. Warm weather during flowering (May temperature) in the flowering year (Year t) and 2 years before (t ?2) were correlated with seed production. However, high May temperatures during the previous year (t^-1) adversely affected seed production. Summer temperatures in Year t^-1 was positively correlated with seed production, likely because this parameter enhances the development of flower primordials, but the effect was negative with a time lag of 2 years. The negative feedback in temperature coefficients is also likely due to patterns of resource allocation, as abundant flowering and seed production in these species is thought to reduce the subsequent initiation of potential new flower buds. Since the most important weather variables also showed spatial correlation up to 1000 km, weather parameters likely explain much of the spatial and temporal synchrony in seed production of these four studied tree species.     

Variation in quality of mountain birch and tea-leaved willow for mammal and insect herbivores: differences among trees, among sites and between tree species

We evaluated palatability of winter dormant tree twigs to the mountain hare Lepus tunidus and the grey-sided vote Clethrionomys rufocanus with captive animals We tested differences among trees within sites, among sites, and between two tree species (the mountain birch Betula pubescens ssp czerepanovii and the tea-leaved willow Salix phylicifolia ) In one of the sites, we also measured growth rates of autumnal moth Epirrita autumnata larvae on the same trees that were used m preference trials with the hares and voles The differences m palatability to hares and voles were greatest at the level of tree Species, both hares and voles preferred birches over willows, but with the hare there was some overlap in palatability between the tree species There were also large and significant differences among sites and among trees within sites Within sites, variation in tree palatability seemed to be larger among willows than among birches Hares and voles may select willows at least partly on the same basis, but there was no correlation between palatability of the trees to the mammals and the growth rate of the larvae of the autumnal moth on the same trees Variation in twig palatability to the hares and voles was so large at all levels (among trees within sites, among sites and between tree species) that we suggest it also has implications for food selection of these mammalian herbivores under natural conditions