Additive and non‐additive effects of birch genotypic diversity on arthropod herbivory in a long‐term field experiment

Herbivores are important drivers of plant population dynamics and community composition in natural and managed systems. Intraspecific genetic diversity of long‐lived plants like trees might shape patterns of herbivory by different guilds of herbivores that trees experience through time. However, previous studies on plant genetic diversity effects on herbivores have been largely short‐term. We investigated how tree genotypic variation and diversity influence herbivory of silver birch Betula pendula in a long‐term field experiment. Using clones of eight genotypes, we constructed experimental plots consisting of one, two, four or eight genotypes, and measured damage by five guilds of arthropod herbivores twice a year over three different years (four, six and nine years after the experiment was established). Genotypes varied significantly for most types of herbivore damage, but genotype resistance rankings often shifted over time, and none of the clones was more resistant than all others to all types of herbivores. At the plot level, birch genotypic diversity had significant positive additive effect on leaf rollers and negative non‐additive effects on chewing herbivores and gall makers. In contrast, leaf‐mining and leaf‐tying damage was not influenced by birch genotypic diversity. Within diverse plots, the direction of genotypic diversity effects varied depending on birch genotype, some having lower and some having higher herbivory in mixed stands. This research highlights the importance of long‐term studies including different feeding guilds of herbivores to understand the effects of plant genetic diversity on arthropod communities. Different responses of various feeding guilds to genotypic diversity and shifts in resistance of individual genotypes over time indicate that genotypic mixtures are unlikely to result in overall reduction in herbivory over time.     

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.     

The role of foliar microfungi in mountain birch - insect herbivore relationships

We studied the effects of epiphytic and endophytic phyllosphere fungi and pathogenic birch rust fungus infection of mountain birch Betula pubescens ssp czerepanovit trees on the larval performance of leaf beetle Phratora potaris We assessed the effects of epiphytic fungi by growing larvae on leaves from trees with manipulated fungal densities We also monitored larval perfonnance and endophytic fungal densities among tree groups classified by herbivory or rust fungus densities The differences in expenmentally manipulated epiphytic fungal densities did not affect larval relative growth rates (RGR) of the species, instead we found significant tree effects Phratora polaris RGR was higher on trees with high level of herbivory than on trees with low herbivory, nevertheless, endophyte densities between these groupings did not differ In the rust fungus expenment, P polarts performance was lowest on trees with low infection compared to no and high infection trees We also did not find correlations among tree-specific endophyte densities and P polaris performance on high and low herbivory trees and trees classified by rust fungus infection Although antagonism among fungi and induction of tree defences cannot be excluded, we suggest that epiphytic and endophytic fungi of mountain birch have negligible effects on P polaris larval performance under natural conditions, probably due to mountain birch variability and a loose ecological connection between mountain birch and its epi- and endophytes Mountain birch and pathogenic birch rust have a more tightly linked relationship, which may also affect insect herbivores Still, leaf properties may play an important role and the effects will depend on the relative timing of the rust infection, herbivore development and changes in leaf quality     

Genotypic variation in yellow autumn leaf colours explains aphid load in silver birch

? It has been suggested that autumn-migrating insects drive the evolution of autumn leaf colours. However, evidence of genetic variation in autumn leaf colours in natural tree populations and the link between the genetic variation and herbivore abundances has been lacking. ? Here, we measured the size of the whole aphid community and the development of green-yellow leaf colours in six replicate trees of 19 silver birch (Betula pendula) genotypes at the beginning, in the middle and at the end of autumn colouration. We also calculated the difference between green leaf and leaf litter nitrogen (N) and estimated the changes in phloem sap N loading. ? Autumn leaf colouration had significant genetic variation. During the last survey, genotypes that expressed the strongest leaf reflectance 2-4 wk earlier had an abundance of egg-laying Euceraphis betulae females. Surprisingly, the aphid community size during the first surveys explained N loss by the litter of different birch genotypes. ? Our results are the first evidence at the tree intrapopulation genotypic level that autumn-migrating pests have the potential to drive the evolution of autumn leaf colours. They also stress the importance of recognizing the role of late-season tree-insect interactions in the evolution of herbivory resistance.     

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).     

Comparative sectoriality in temperate hardwoods: hydraulics and xylem anatomy

In wood, lateral transport of water and minerals occurs readily in 'integrated' trees but is more restricted in 'sectored species'. Dye distribution and a novel hydraulic technique are used to quantify species-specific differences in sectoriality in three temperate hardwoods, Betula papyrifera , Acer saccharum and Quercus rubra. Sectoriality was related to key elements of xylem structure: intervascular pitting, vessel diameter and vessel grouping. Perfusion of 0.5% safranin through isolated roots showed root-to-branch dye transport was most extensive in B. papyrifera and least extensive in Q. rubra . To test sectorialty using hydraulics, 20 m m KCl solution was pushed at 0.1 MPa through 5-cm wood segments, before and after occluding the direct axial outlet with glue, with flow rate measured in grams of solution expelled over time. Direct (axial) conductance (g MPa⁻¹ s⁻¹) through unglued outlets was compared with indirect (tangential) conductance around occluded outlets. Species with high indirect/direct conductance ratios (Integration Index) are the most integrated. Integration Index ranged from 0.26 in B. papyrifera to 0.02 in Q. rubra . Macerates showed that B. papyrifera has much greater percentage of cell wall area covered with intervascular pits than does A. saccharum or Q. rubra . Vessel grouping was closest in B. papyrifera and vessels were most isolated in Q. rubra . Widest diameter vessels occurred in Q. rubra , where they concentrated in springwood. Intervascular pitting, vessel diameter and grouping are wood traits that contribute to the continuum of sectoriality in trees, and may influence the ability of tree species to dominate in homogeneous or in patchy environments.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 150 , 61–71.     

Delayed induced responses of birch glandular trichomes and leaf surface lipophilic compounds to mechanical defoliation and simulated winter browsing

Changes in morphology and chemistry of leaf surface in response to herbivore damage may increase plant resistance to subsequent herbivore attack; however, there is lack of studies on induced responses of glandular trichomes and their exudates in woody plants and on effects of these changes on herbivores. We studied delayed induced responses in leaf surface traits of five clones of silver birch (Betula pendula Roth) subjected to various types of mechanical defoliation and simulated winter browsing. Glandular trichome density and concentrations of the majority of surface lipophilic compounds increased in trees defoliated during the previous summer. This induced response was systemic, since control branches in branch defoliated trees responded to the treatments similarly to defoliated branches, but differently from control trees. In contrast to defoliation treatments, simulated winter browsing reduced glandular trichome density on the following summer and had fewer effects on individual surface lipophilic compounds. Moreover, constitutive density of glandular trichomes was negatively correlated with induced total amount of lipophilic compounds per trichome, indicating a trade-off between constitutive and induced resistance in silver birch. Induced changes in leaf surface traits had no significant effect on leaf damage by chewers, miners and gall mites, but increased susceptibility of birch trees to aphids. However, leaf damage by chewers, miners and gall mites in defoliated (but not in control) trees was correlated with concentrations of some fatty acids and triterpenoids, although the direction of relationships varied among herbivore species. This indicates that induction of surface lipophilic compounds may influence birch resistance to herbivores. Our study thus demonstrated both specificity of elicitation of induced responses of birch leaf surface traits by different types of damage and specificity of the effects of these responses on different types of herbivores.Electronic Supplementary Material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Genotypic variation in growth and resistance to insect herbivory in silver birch (<Emphasis Type="Italic">Betula pendula</Emphasis>) seedlings

If herbivory is unevenly distributed among different types of plants, or if individual plants differ in their response to herbivory, herbivores may affect seedling growth and survival, and consequently plant population structure. In this study we examined variation in resistance to insect herbivory and in growth responses to feeding among 20 silver birch (Betula pendula Roth) genotypes representing variation within a natural population. Birch seedlings were grown in dense stands in random arrangement so that seedlings of different genotypes competed with each other. On insect exposure plots natural colonization of insects was allowed, and insect removal plots were sprayed with insecticide. Resistance to insect herbivory was measured as the inverse of leaf damage, and growth responses of seedlings to feeding were determined as the change in seedling height relative to the amount of damage. Resistance varied significantly among genotypes, but growth responses to feeding did not. In fertilized seedlings, resistance correlated negatively with height, indicating a trade-off between resistance and growth. The absence of such a correlation in non-fertilized seedlings is a sign of environmental effects on the cost of resistance. Growth responses to feeding did not correlate with either resistance or growth. Nevertheless, different effects of the actual damage on height increase changed the positions of the genotypes in the size hierarchy of the experimental populations. Thus, even moderate levels of insect herbivory can change the outcome of competitive interactions between birch genotypes.Due to an error in the citation line, this revised PDF (published in December 2003) deviates from the printed version, and is the correct and authoritative version of the paper.     

Effect of defoliation on concentrations of allelochemicals and soluble sugars in leaves of weeping birch (<Emphasis Type="Italic">Betula pendula</Emphasis> roth)

Effect of strong (75%) and complete (100%) artificial defoliation of weeping birch Betula pendula Roth on the dynamics of soluble sugars and phenols—flavonols, catechins, and tannins in leaves of damaged plants was investigated. Within the first 15 days after strong defoliation of birch, no changes were found in leaf contents of flavonol, catechin, and tannin. The concentration of sugars first increased but, on the 10th day after defoliation, it returned to the normal level. One year after strong defoliation, the lead concentrations of catechins and tannins in damaged trees increased, while the concentrations of flavonols and sugars did not differ from that in leaves of control trees. In two years after strong damage, the increased concentration of tannins was retained, while catechins and sugars remained at the control level. One year after complete (100%) artificial defoliation, the leaf concentrations of flavonols and sugars in damaged plants did not differ from that in control plants, while the leaf concentrations of catechins and tannins exceeded those in control plants. Two years after complete damage, the leaves contained an increased amount of tannins, whereas the amounts of catechins, flavonols, and sugars did not differ from the control levels.     

Selective ultrasound-assisted extractions of lipophilic constituents from Betula alleghaniensis and B. papyrifera wood at low temperatures

Betula alleghaniensis and B. papyrifera are widely distributed in the province of Québec (Canada) and, since these trees are valuable exports for the local lumber industry, large amounts of their residual ligneous biomass are available for further exploitation. Betula species are well known for their significant concentrations of triterpenes, some of which were recently discovered to present promising bioactivity. The secondary transformation of birch biomass could therefore become important for many industries, particularly the pharmaceutical industry. In the present study, extracts from birch sawdust were obtained using an optimised ultrasound-assisted extraction in which the careful choice of temperature permitted a selective extraction of the targeted triterpenes. Moreover, compared with the classical Soxhlet method, higher extraction yields were obtained in a shorter time. The lipophilic extracts obtained using dichloromethane as a solvent were analysed by GC-MS and the major compounds identified as lupane-type cyclic triterpenoids accompanied by the non-cyclic triterpene squalene. Numerous aliphatic long-chain fatty acids were also found in the extracts together with phytosterols. Betulonic acid and squalene, the major extract constituents for both B. alleghaniensis and B. papyrifera, are both bioactive molecules.     

Oviposition and mining by Phytobia betulae (Diptera: Agromyzidae) in genotypes of European white birch (Betula pendula)

Abstract 1 The colonization success of herbivorous insects depends partly on the ability of females to choose suitable host plants. Phytobia betulae Kangas (Diptera: Agromyzidae), a miner of differentiating xylem, infests birch (Betula pendula Roth and Betula pubescens Ehrh.) trees. 2 In a field experiment we measured successful ovipositions in the long shoots of eight 5‐year‐old‐birch genotypes. Later in the growing season, in the same experiment, we counted the number of larvae from the same birch genotypes (different replicates). 3 We attempted to determine where Phytobia females lay their eggs in the birch canopy, what kind of shoots Phytobia utilize, whether birch genotypes differ in their susceptibility to Phytobia, and which tree characteristics correlate with successful utilization of birch for oviposition and larval development. 4 The ovipositions were concentrated in fast growing shoots and only 5% of the available shoots were utilized. Usually a shoot contained only one oviposition (80% of the cases). However, oviposition pattern resulted in significant aggregations (two to four ovipositions per shoot): 11% of shoots selected for oviposition contained more than one Phytobia and 22% of larvae shared their shoot with at least one other larva. Although birch shoots were much more abundant than Phytobia, there may be intraspecific competition for host resources among Phytobia. 5 Birch genotypes differed in the number of ovipositions but not in the number of larvae, although in general the number of larvae was correlated positively with the number of ovipositions. There were more ovipositions in the faster growing genotypes.     

Silver birch telomeres shorten in tissue culture

Shortening of telomeres has been connected with ageing and loss of cell replication or regeneration capacity. The aim of the present study was to examine potential variation in the length of telomeric repeats in silver birch (Betula pendula Roth) using clonal materials consisting of different-aged outdoor trees and tissue cultures of seven genotypes. The overall average length of telomeres was 13.6 kb (±0.3), the minimum length of repeats in the different genotypes varied from 5.9 kb (±0.5) to 9.6 kb (±0.6), and the maximum length varied from 15.3 kb (±1.1) to 22.8 kb (±0.4). When germinated seeds and leaf and cambium samples from 15- and 80-year-old trees were compared, no correlation of ageing and the length of telomeric repeats was found. Positional variation in the telomere length was, however, observed in the cambium of mature trees, the stem base having longer repeats than the upper parts of the tree. Tissue cultures were found to have shorter telomeres than outdoor trees: prolonged culture, callus culture and stressful conditions were all observed to shorten telomeric repeats and should thus be avoided in birch micropropagation. There were significant differences among the studied silver birch genotypes in their telomere length, and these differences were consistent over the sample types. This is the first report on variation of telomeric repeats in a long-living organism studied with clonal materials.     

Host tree resistance against the polyphagous wood-boring beetle Anoplophora glabripennis

Anoplophora glabripennis (Motschulsky) (Coleoptera: Cerambycidae: Lamiini) is an invasive wood‐boring beetle with an unusually broad host range and a proven ability to increase its host range as it colonizes new areas and encounters new tree species. The beetle is native to eastern Asia and has become an invasive pest in North America and Europe, stimulating interest in delineating host and non‐host tree species more clearly. When offered a choice among four species of living trees in a greenhouse, adult A. glabripennis fed more on golden‐rain tree (Koelreuteria paniculata Laxmann) and river birch (Betula nigra L.) than on London planetree (Platanus × acerifolia (Aiton) Willdenow) or callery pear (Pyrus calleryana Decaisne). Oviposition rate was highest in golden‐rain tree, but larval mortality was also high and larval growth was slowest in this tree species. Oviposition rate was lowest in callery pear, and larvae failed to survive in this tree species, whether they eclosed from eggs laid in the trees or were manually inserted into the trees. Adult beetles feeding on callery pear had a reduced longevity and females feeding only on callery pear failed to develop any eggs. The resistance of golden‐rain tree against the larvae appears to operate primarily through the physical mechanism of abundant sap flow. The resistance of callery pear against both larvae and adults appears to operate through the chemical composition of the tree, which may include compounds that are toxic or which otherwise interfere with normal growth and development of the beetle. Unlike river birch or London planetree, both golden‐rain tree and callery pear are present in the native range of A. glabripennis and may therefore have developed resistance to the beetle by virtue of exposure to attack during their evolutionary history.     

Processing and macroinvertebrate colonization of detritus in an Alaskan subarctic stream

Monument Creek, a second-order Alaskan subarctic stream, experiences a severe thermal regime, with water temperatures of 0°C for six months. Leaching, long-term decomposition and macroinvertebrate colonization of 5 g leaf packs were studied using leaves of the major riparian tree species, alder Alnus tenuifolia Nutt., birch Betula papyrifera Marsh. and willow Salix alaxensis (Anderss.) Cov. subsp. alaxensis and Salix arbucolides Anders. var. glabra Anderss. The processing rates of birch (k = 0.0080) and willow (k = 0.0063) were moderate while alder was processed very rapidly (k = 0.0513). Leaching rates did not differ significantly among the three leaf species, and accounted for 10–15% of total weight loss. Densities and biovolume of colonizing insects increased from fall to winter. Shredders dominated insect biovolume by midwinter, but were a small fraction of total biovolume in leaf packs that had frozen over winter and were sampled following spring thaw. This may be a function of low food quality in spring and/or the timing of shredder life histories. Limited allochthonous input and constriction of the stream channel due to freezing, with resultant high shredder densities, may explain the relatively rapid detritus processing rates in Monument Creek, despite cold stream temperatures.     

Microbial activity during leaf decomposition in an Alaskan subarctic stream

Fungal biomass and growth and microbial respiration were studied for two field seasons in a second-order subarctic stream where water temperature is 0°C for approximately 6 months. Leaf packs (5-g) of alder Alnus tenuifolia , birch Betula papyrifera and willows Salix alaxensis and Salix arbusculoides immersed in autumn of 1979 and 1980 were sampled until June 1980 and January 1981, respectively. Fungal growth and microbial respiration occurred in submerged detritus at 0°C. Total and FDA-active hyphal lengths were measured, the active proportion averaging 25% of the total (all leaf species, both years). Generally, microbial respiration peaked in all leaf species after two weeks in the stream. As water approached 0°C, respiration declined by 20–50% depending on leaf species, but often increased later in decomposition (at 0°C). Seasonal trends in microbial respiration and FDA-active hyphal lengths were not similar although maximal respiration usually occurred as FDA-active hyphae were growing most rapidly. The calculated leaf weight loss due to microbial respiration was small (7–10%) in all leaf species, compared with total weight loss over 98 d. Scanning electron microscopy provided a visual record of leaf surface microorganisms and apparent leaf cuticle dissolution by fungi and bacteria.     

The effects of geographic origin and genotype on fungal diversity of silver birch (Betula pendula)

Soil microbes, especially root symbiotic fungi, often have drastic effects on the successful growth and establishment of plants. While plant intraspecific genetic variation is known to affect many ecosystem processes and functions, the effect it has on root fungal communities has received less attention. To determine the effect plant origin and genotype have on root fungal communities, we used high-throughput amplicon sequencing of ITS-regions to detect fungi from the roots of 64 clonally propagated silver birch (Betula pendula) trees representing four different geographical origins and 16 genotypes, all grown together in a common garden. We found that fungal alpha and beta-diversity but not community composition differ by silver birch genotype. Some birch genotypes are potentially more plastic in terms of their fungal interactions, which could make them more robust against environmental changes and provide a competitive advantage especially in disturbed habitats.     

First report of an attractant for a tumbling flower beetle (Coleoptera: Mordellidae)

In 2004 and 2005, large numbers of the tumbling flower beetle, Falsomordellistena bihamata (Melsheimer), were found on traps baited with sweet birch oil, whereas significantly fewer individuals were found on control traps. In both years, peak captures were at 680 DD10 degrees C. Trapping was conducted in Naugatuck State Forest in Naugatuck, CT. Little is known about the ecology and biology of the tumbling flower beetles (Coleoptera: Mordellidae), and the larval food plant for this species is not known. Thus, we cannot say why the beetle is attracted to sweet birch oil. Sweet birch oil is approximately 99.8% methyl salicylate (MeSA). MeSA is found constitutively in large quantities in some plants, but it is also an important signal in, and product of, plant stress-response pathways. MeSA has been found to attract both herbivores that need stressed plants as food and natural enemies of herbivores in stressed plants. To our knowledge, this is the first report of mass trapping of a tumbling flower beetle. Fuller understanding of the phenomenon awaits further study.     

Quantification of Trends in Wood Production Within Trees of Silver Birch (Betula pendula Roth.)

Trends in rate and duration of wood production are analysedalong and between branches, and along main stems of silver birch(Betula pendula Roth.) trees (at early canopy closure and closedcanopy stages of growth). These data are discussed in relationto the control of knot size, log diameter and taper. To providea field guide to cambial reactivation, progress of vessel productionhas been related to stages of leaf expansion.Copyright 1994,1999 Academic Press Betula pendula (Roth.), silver birch, cambial activity, wood production, wood quality, vessel production     

以叶盘为外植体的白桦的再生

从不同的激素组成(BA, K T, 2, 4~D, NAA, GA₃)、基本培养基(MS, WP)、外植体放置的方向性进行了实验, 建立了以白桦叶盘为外植体的再生系统。当叶盘向轴面朝下放置在培养基上时, 三周后, 从叶盘边缘生出不定芽。不定芽的诱导率为64%, 平均每片叶盘可生出6 个不定芽。叶盘再生系统的建立为白桦的遗传转化提供了前提。