Genetic variation and differentiation in populations of Japanese emperor oak <Emphasis Type="Italic">Quercus dentata</Emphasis> Thunb. and Mongolian oak <Emphasis Type="Italic">Quercus mongolica</Emphasis> Fisch. ex Ledeb.) in the south of the Russian Far East

Allozyme variation of Japanese emperor oak Quercus dentata Thunb. and Mongolian oak Quercus mongolica Fisch. ex Ledeb.) was examined in 11 populations of these species from southern Primorye. Analysis of 18 loci showed that in these populations, 66.7% of genes of Mongolian oak are polymorphic, the number of alleles per locus being 2.28. In Japanese emperor oak, these parameters were respectively 59.8 and 2.36%. The observed heterozygosity in both species did not differ from the expected values, constituting 0.198 in Japanese emperor oak and 0.161 in Mongolian oak. The Nei’s distance between Quercus mongolica and Q. dentata was 0.053. The main contribution to the species differentiation is made by loci Lap-1, Idh-1, Pgm-1, and Ndh-1, although none of them is diagnostic. The Japanese emperor oak and Mongolian oak populations formed separate clusters in an UPGMA dendrogram. Taking into account morphological and ecological isolation of the species, we suggest that the differences in gene frequencies may reflect selection acting in favor of adaptation to different growth conditions and counteracting between-species hybridization.     

Allozyme variation in cork oak (Quercus suber L.): the role of phylogeography and genetic introgression by other Mediterranean oak species and human activities

 Genetic variation in the cork oak (Quercus suber L.) was investigated using 11 loci from seven enzyme systems in 40 populations sampled over the entire distribution of this species in the western Mediterranean Basin. Mean heterozygosity values over the polymorphic loci (Ho=0.283), the percentage of polymorphic populations (M=0.76), and the total genetic diversity (Ht=0.31) from which 11% was accounted for among-population variation, are among the highest recorded in oak species. In contrast to previous results in holm oak (Q. ilex L.), another evergreen species in the same area, cork oak possessed a smaller allele pool and a lower average number of alleles per locus and per population (A=2.0). More particularly, very few low-frequency alleles were observed in cork oak except for eight populations in which allozyme polymorphism at locus Pgi 1, diagnostic between both species, indicates that these low-frequency alleles are introgressed from holm oak. On the basis of the genetic distance estimated from allozyme frequencies, 32 of the 40 cork oak populations studied were classified into two very distinct sets which also corresponded to distinct geographic areas. One set gathered together the 18 populations from the Iberian peninsula and two adjacent areas in France, i.e. the centre of origin of cork oak, according to paleobotanical data. This set was characterized by a larger allele pool, a higher within-population genetic diversity and a lower differentiation between populations than was observed in the other set, which comprised the populations from North Africa, Sicily, Sardinia, Corsica, continental Italy and the region of Provence (southeastern France). In these more southern and eastern disjunct areas, cork oak migration from Iberia may have occurred at different periods since the end of the Tertiary. The possible effect of human activity on cork oak genetic structure, i.e. the selection of good-quality cork, acorn over-use for animal food, and even human nutrition, is discussed. Received: 3 March 1998 / Accepted: 19 March 1998     

Phylogeographic structure and late Quaternary population history of the Japanese oak Quercus mongolica var. crispula and related species revealed by chloroplast DNA variation

Generally, oaks dominate the broadleaf deciduous forests in Japan. The genetic variation in 6 cpDNA regions (trnT-trnL, trnL-trnF, atpB-rbcL, and trnH-psbA speacers, trnL intron, and matK gene) with regard to the Japanese oak (Quercus mongolica var. crispula) and 3 related species in the section Prinus (Q. serrata, Q. dentata and Q. aliena) was investigated in 598 trees belonging to 44 populations distributed throughout the Japanese archipelago. Additional samples were collected from Korea, China, and Russia (Sakhalin). Thirteen haplotypes (I to XIII) were identified on the bases of 15 nucleotide substitutions and 3 indels. Haplotypes I and II were discovered in northeastern Japan, whereas haplotypes III to IX were distributed in southwestern Japan. The boundary distinguishing these 2 groups was located in central Japan coincident with the Itoigawa-Shzuoka tectonic line. Haplotype I was also found in Sakhalin, whereas haplotypes VI, VII, VIII, X, XI, XII, and XIII were found in Korea and China. Four oak species in the same location shared identical haplotypes, suggesting cpDNA introgression by occasional hybridization. Both the values of total haplotype diversity (HT) and haplotype diversity within populations (HS) in Q. mongolica var. crispula were higher in the southwestern populations than in the northeastern populations. A haplotype network indicated that haplotype VI is the ancestral haplotype. The presence of identical haplotypes in Korea, China, and Japan suggested that the haplotypes diversified on the Eurasian continent before the last glacial period. The difference in genetic structure between the northeastern and southwestern regions indicates a difference in the history of migration and recolonization in Japan during the last glacial period.     

中国北方蒙古栎林起源和发展的初步探讨

古生态学的研究显示 ,栎林 (包括蒙古栎林 )在华北地区和东北地区的分布在地质历史时期不是一成不变的 ,其优势度也呈现上下波动 ,栎树优势度的增减是由于地质历史时期气候的变化造成的 ;蒙古栎的起源时间可能不早于上新世中期 ,蒙古栎林的起源也应不早于上新世中期。蒙古栎林的起源原因有 2种 ,即火与人类的反复砍伐。火是原生性质蒙古栎林在地质历史时期存在和扩散的根本原因 ,过度的人类活动 (主要是反复砍伐 )是促成现在蒙古栎次生林占优势地位的主要原因 ,这是由蒙古栎这个树种的生物学特性决定的 ,在没有外界因素的干扰和火减少的情况下 ,蒙古栎在演替过程中逐渐被耐荫的树种所取代 ,但是在中国北方 ,由于人类活动的加剧 ,蒙古栎林的优势度有增加的趋势。     

啮齿动物捕食和搬运蒙古栎种子对种群更新的影响

2010-2011年,在东北林业大学城市林业示范基地研究了啮齿动物对蒙古栎种子的捕食和搬运。结果表明,蒙古栎种子捕食率在年际间无显著差异,但2010年的蒙古栎种子搬运率显著高于2011年,存留率显著低于2011年。啮齿动物在胡桃楸林、樟子松林、水曲柳林和白桦林内对蒙古栎种子的总捕食率和总搬运率分别达到(5.7±13.5)%和(27.1±37.1)%。蒙古栎种子在樟子松林内的捕食率和搬运率均最高,胡桃楸林内蒙古栎种子存留率最高;2010年蒙古栎种子在与蒙古栎林边缘距离0,10,20,30,40,50m组间的捕食率无显著差异,搬运率和存留率有显著差异,但2011年蒙古栎种子在不同距离组间的捕食率呈显著差异,搬运率和存留率无显著差异。与蒙古栎林边缘距离20m处蒙古栎种子的捕食率最高。2010年和2011年,分别有(37.8±49.7)%和(27.7±49.8)%的蒙古栎种子被啮齿动物利用,这表明啮齿动物是林业示范基地内蒙古栎地表种子的主要捕食者。冬季食物匮乏秋季贮藏种子是造成啮齿动物对蒙古栎种子有较大捕食、扩散压力的主要原因。因此,啮齿动物对蒙古栎种子的捕食和搬运影响了蒙古栎林的种群更新。     

Tree-ring element analysis of Korean pine (Pinus koraiensis Sieb. et Zucc.) and Mongolian oak (Quercus mongolica Fisch. ex Turcz.) from Changbai Mountain,north-east China

Summary Tree-ring analysis of 17 elements (Pb, Cd, Cu, Zn, As, Cr, Ti, Ni, V, Mn, Fe, Al, Ca, Mg, K, Na and P) was performed on Korean pine (Pinus koraiensis Sieb. et Zucc.) and Mongolian oak (Quercus mongolica Fisch. ex Turcz.) specimens from Changbai Mountain, a remote nature reserve in north-east China. The radial distribution patterns of Pb, Cu, Cr, Ti, Ni, V, As and Fe for both Korean pine and Mongolian oak were similar: concentrations remained generally constant in tree-ring intervals spanning approximately 200 years. These temporal patterns were in accordance with the known stability of the local ecological environment during this period. However, the other elements showed characteristic distribution patterns that differed between Korean pine and Mongolian oak. These patterns can only be interpreted in terms of physiological results; specifically they appeared to be related to the sapwood-heartwood conversion.     

Geographic variation in the structure of oak hybrid zones provides insights into the dynamics of speciation

Studying geographic variation in the rate of hybridization between closely related species could provide a useful window on the evolution of reproductive isolation. Reinforcement theory predicts greater prezygotic isolation in areas of prolonged contact between recently diverged species than in areas of recent contact, which implies that old contact zones would be dominated by parental phenotypes with few hybrids (bimodal hybrid zones), whereas recent contact zones would be characterized by hybrid swarms (unimodal hybrid zones). Here, we investigate how the hybrid zones of two closely related Chinese oaks, Quercus mongolica and Q. liaotungensis, are structured geographically using both nuclear and chloroplast markers. We found that populations of Q. liaotungensis located around the Changbai Mountains in Northeast China, an inferred glacial refugium, were introgressed by genes from Q. mongolica, suggesting historical contact between the two species in this region. However, these introgressed populations form sharp bimodal hybrid zones with Q. mongolica. In contrast, populations of Q. liaotungensis located in North China, which show no sign of ancient introgression with Q. mongolica, form unimodal hybrid zones with Q. mongolica. These results are consistent with the hypothesis that selection against hybrids has had sufficient time to reinforce the reproductive barriers between Q. liaotungensis and Q. mongolica in Northeast China but not in North China.     

三种温带树种非结构性碳水化合物的分配

树体中的非结构性碳水化合物(NSC)浓度、含量及其分配反映了树木整体的碳供应状况, 是决定树木生长和存活的关键因子, 也是构建树木碳平衡模型的关键参数。温带树种的NSC尚缺乏系统研究。该文测定了特性各异的3种温带树种在生长盛期的NSC及其组分的浓度和含量以及分配格局的种间种内变异。结果表明, NSC及其组分的浓度在树种和组织之间差异显著, 可溶性糖、淀粉和总NSC浓度分别在0.65-8.45、1.96-5.95和3.00-13.90 g·100 g^-1 DM之间波动。NSC及其组分含量的大小依次为: 兴安落叶松(Larix gmelinii) >蒙古栎( Quercus mongolica) >红松( Pinus koraiensis), 其中叶和根中的浓度较高。树干中的NSC及其组分浓度的纵向变化不显著, 但其心材与边材之间的浓度差异却随树种和NSC组分而异, 表现为心边材的可溶性糖浓度差异不显著, 但其淀粉和总NSC浓度差异显著。不同直径根系的NSC及其组分浓度在2种针叶树种中差异不显著, 但在蒙古栎中差异显著。蒙古栎将可溶性糖主要投资到地上生长, 而2种针叶树将更多的可溶性糖投资到根系生长。淀粉的主要储存库为树干, 其在树体内的分布格局与可溶性糖正相反, 因而使总NSC在树根和树枝中的分配趋于较平衡状态。在树干中, 除了2种针叶树的可溶性糖库以边材为主外, 心材是淀粉和总NSC的主要储存库。在树根中, 粗根是NSC及其组分的优势储存库。该研究中3种温带树种的NSC及其组分的浓度和含量的种间和种内变化, 反映了这些树种的生长对策和体内碳源汇强度的差异。     

Frequent cytoplasmic exchanges between oak species that are not closely related: Quercus suber and Q. ilex in Morocco

Chloroplast (cp) and mitochondrial (mt) DNA variation were studied in 97 populations of cork oak (Quercus suber) in Morocco; in 31 of these populations, holm oak (Quercus ilex), a clearly distinct species, also occurred and was compared with Q. suber. Three cpDNA and one mtDNA primer pairs were used in the survey, each in combination with one restriction enzyme. Six haplotypes belonging to two very divergent lineages were detected; one lineage predominates in each species, and is probably ancestral, as inferred from comparisons with other oak species. In the mixed-species populations, cytoplasmic genomes were frequently shared across species, as indicated by an introgression ratio of 0.63. This index is a new measure of the propensity of species to share locally genetic markers, varying from zero (complete differentiation) to one (no differentiation). By contrast, more closely related deciduous oak species (Q. robur, Q. petraea and Q. pubescens) have introgression ratios varying from 0.82 to 0.97. The introgression events appear to have been more frequent in the direction Q. ilex (female) x Q. suber (male), a finding which seems attributable to the flowering phenology of these two species. This asymmetry may have favoured immigration of Q. suber beyond its main range, in regions already colonized by Q. ilex. There, rare hybridization and further introgression through long distance pollen flow have established populations that are morphologically indistinguishable from Q. suber but that have cytoplasmic genomes originating from the local Q. ilex populations.     

两种温带落叶阔叶林降雨再分配格局及其影响因子

林冠对降雨的再分配是森林生态系统的重要生态水文过程,影响着生态系统生物地球化学循环。于2012年5—10月连续测定帽儿山森林生态站的两种温带天然次生林型——蒙古栎林和杂木林的林外降雨、穿透雨及树干径流,旨在量化其降雨再分配过程及其影响因素。结果表明:蒙古栎林的平均穿透雨、树干径流、林冠截留分别占同期林外降雨的76%、7%和17%;杂木林分别占85%、5%和10%。根据模型估算,当降雨量分别超过1.0mm和0.7mm时蒙古栎和杂木林开始出现穿透雨;当降雨量超过3.0mm开始出现树干径流。当降雨量超过5.6mm,树干径流体积会随着树木胸径的增加而显著增加;而当降雨量低于5.6mm则出现相反趋势。穿透雨、树干径流及林冠截留的绝对量均随降雨量的增大而显著增加,但其占降雨量的比例却表现出不同的变化趋势。穿透雨量的空间变异随降雨量和降雨强度的增大显著减小。两种林型的降雨再分配格局因受降雨量、降雨强度等降雨特征和林冠结构的影响而产生差异。     

Gas composition and respiration of water oak (Quercus nigra L.) and green ash (Fraxinus pennsylvanica Marsh.) roots after prolonged flooding

Summary We compared the effects of 9.5 months of a continuous flooding treatment with a drained control treatment on one year-old seedlings of green ash (Fraxinus pennsylvanica Marsh.) and water oak (Quercus nigra L.), two tree species common to the bottomland-hardwood forests of eastern North America. The internal root gas composition of the more flood tolerant species, green ash, maintained higher oxygen and lower carbon dioxide concentrations under the flooding treatment than water oak. This apparently resulted in differences in rhizosphere oxidation. The amounts of Fe and Mn and the Fe/Mn ratio of the root coating extracted from trees in reduced soil conditions were much higher for the green ash than the water oak. It is argued that this reflects differences in the ability of these two species to maintain rhizosphere oxidation under prolonged periods of flooding and to prevent the accumulation of reduced potentially phytotoxic compounds. Alcohol dehydrogenase activity increased in the green ash and decreased in the water oak in the flooded treatment. This indicated that the better adapted species was able to rely upon increased anaerobic respiration in order to compensate for the decreased root oxygen supply, but the water oak was unable to maintain previous levels of respiration, probably as the result of sulfide toxicity.     

Phylogeographical variation of chloroplast DNA in holm oak (Quercus ilex L.)

Variation in the lengths of restriction fragments (RFLPs) of the whole chloroplast DNA molecule was studied in 174 populations of Quercus ilex L. sampled over the entire distribution of this evergreen and mainly Mediterranean oak species. By using five endonucleases, 323 distinct fragments were obtained. From the 29 and 17 cpDNA changes identified as site and length mutations, respectively, 25 distinct chlorotypes were distinguished, mapped and treated cladistically with a parsimony analysis, using as an outgroup Q. alnifolia Poech, a closely related evergreen oak species endemic to Cyprus where Q. ilex does not grow. The predominant role of Q. ilex as maternal parent in hybridization with other species was reflected by the occurrence of a single very specific lineage of related chlorotypes, the most ancestral and recent ones being located in the southeastern and in the northwestern parts of the species’ geographical distribution, respectively. The lineage was constituted of two clusters of chlorotypes observed in the ‘ilex’ morphotyped populations of the Balkan and Italian Peninsulas (including the contiguous French Riviera), respectively. A third cluster was divided into two subclusters identified in the ‘rotundifolia’ morphotyped populations of North Africa, and of Iberia and the adjacent French regions, respectively. Postglacial colonization probably started from three distinct southerly refugia located in each of the three European peninsulas, and a contact area between the Italian and the Iberian migration routes was identified in the Rhône valley (France). Chlorotypes identical or related to those of the Iberian cluster were identified in the populations from Catalonia and the French Languedoc region, which showed intermediate morphotypes, and in the French Atlantic populations which possessed the ‘ilex’ morphotype, suggesting the occurrence of adaptive morphological changes in the northern part of the species’ distribution.     

Extent of nuclear genome sharing among white oak species (Quercus L. subgen. Lepidobalanus (Endl.) Oerst.) in Slovakia estimated by allozymes

European white oak species (Quercus subg. Lepidobalanus) are known to share a substantial part of the nuclear and cytoplasmic genome. In spite of this fact, they have preserved their integrity. We analyzed genetic variation at thirteen isozyme loci in nine Quercus robur, ten Q. petraea, two Q. pubescens and two mixed (two-species) populations in Slovakia to assess the extent of allele sharing. Moreover, a detailed morphometric study based on thirteen leaf traits was done in the mixed stands. A Bayesian analysis of population structure in the set of pure populations revealed the existence of three clusters, which coincided with the supposed taxonomical identity of populations. However, the distribution of posterior probabilities of data was bimodal with a second peak at six groups, what indicates a possible substructure in the gene pools of the investigated oak species. Moreover, gene admixture was close to 50% in all investigated populations. Morphometric analysis of the two mixed stands revealed a clear morphological separation of the studied oak species, sharply contrasting with a high degree of gene admixture. Differentiation is not uniformly distributed over the genome. High levels of differentiation (F _ST > 0.10) were observed at only three out of thirteen loci. The hypotheses explaining extensive allele sharing (shared ancestral polymorphisms vs. high levels of interspecific gene flow) are briefly discussed.     

Contrasting patterns of historical colonization in white oaks (Quercus spp.) in California and Europe

Phylogeography allows the inference of evolutionary processes that have shaped the current distribution of genealogical lineages across a landscape. In this perspective, comparative phylogeographical analyses are useful in detecting common historical patterns by either comparing different species within the same area within a continent or by comparing similar species in different areas. Here, we analyse one taxon (the white oak, genus Quercus, subgenus Quercus, section Quercus) that is widespread worldwide, and we evaluate its phylogeographical pattern on two different continents: western North America and Western Europe. The goals of the present study are: (i) to compare the chloroplast genetic diversity found in one California oak species vs. that found in the extensively studied European oak species (in France and the Iberian Peninsula); (ii) to contrast the geographical structure of haplotypes between these two taxa and test for a phylogeographical structure for the California species. For this purpose, we used the same six maternally inherited chloroplast microsatellite markers and a similar sampling strategy. The haplotype diversity within site as well as the differentiation among sites was alike in both taxa, but the Californian species has higher allelic richness with a greater number of haplotypes (39 vs. 11 in the European white oak complex). Furthermore, in California these 39 haplotypes are distributed locally in patches while in the European oaks haplotypes are distributed into lineages partitioned longitudinally. These contrasted patterns could indicate that gene movement in California oak populations have been more stable in response to past climatic and geological events, in contrast to their European counterparts.     

Genetic Differentiation of Quercus mongolica and Q. liaotungensis Based on Morphological Observation,Isozyme and DNA Analysis

The Liaodong oak ( Quercus liaotungensis Koidz. ) is a close relative of the Mongolia oak ( Q. mongolica Fisch. ) which were separated by some morphological characters, such as the number of leaf lobes and the squamate form of cupula. Recently some authors observed that morphological diversity made the Liaodong oak unable to separate clearly from the Mongolia one, therefore, plant materials have been collected from Maoer Mountain of Heilongjiang province as a typical Q. mongolica population, and from Guandi Mountain of Shanxi Province which represented the typical Liaodong oak population to compare isozyme and DNA diversity between both species. The winter bud samples were also analysed from Dongling Mountain near Beijing City since Dongling population is an intermediate form between the Maoer population and the Guandi population morphologically. Statistics of 13 putative loci belonging to 5 enzymes showed a high level of diversity within all populations. The value of genetic distance among populations was low, and showed that the Dongling population genetically located at the middle of both typical species. DNA data also showed that both typical oak populations shared similar variation with the Dongling population. Among 172 polymorphic RAPD and DAF loci, no population-specific band has been found. A significant difference in frequency of amplified products existed in 26 loci. Except for 3 irregular ones, frequency distribution of 23 loci seems clinal. The Dongling population also genetically located at the middle of both flanking populations. It was worth to note that the OPD-08434 was probably unique to the Dongling oak since its frequency in the Guandi population has been estimated up to 100% and decreased to 0 in the Maeer population. The Dongling population received this unique DNA from the Guandi population probably by introgression. The strong gene flow in both directions implied a long history of distributive continuity for both oak species. High levels of morphological, isozymatic and DNA diversity supplied enough genetic basis for reconstruction of degraded oak ecosystems.     

Field study of beech (t Fagus sylvatica L.) and melojo oak (t Quercus pyrenaica Willd) leaf litter decomposition in the centre of the Iberian Peninsula

The effect of the canopy on leaf decomposition of beech (t Fagus sylvatica) and melojo oak (t Quercus pyrenaica) was studied during a period of 660 days in a mountain forest of central Spain; response of leaves to leaching was also studied to determine the effects of rainfall after leaf fall. Beech leaves lost 5.8% of their weight by leaching, whereas melojo oak leaves lost 13%. Under both types of canopy, beech leaves showed almost no difference in their decomposition patterns, with decay constants of 0.31 and 0.32 respectively. Melojo oak leaves showed quite a different behaviour under both canopies; decay constant was 0.47 under t Quercus pyrenaica and 0.77 under beech canopy. Total immobilization of nitrogen was less in the melojo oak forest. Effects of summer dryness were sharper in the melojo oak forest, where decomposition stopped during the summer. This delay in the decomposition might have been due to the lower canopy density in the melojo oak forest. The decomposition patterns of the leaves of both species, under the canopy of the other species, suggests what might happen in mixed stands. Thus, the presence of melojo oaks in beech forest would increase decay and decrease nitrogen immobilization. The presence of beech trees in melojo oak forests would improve microclimatic conditions and increase decay, whereas beech litter on the soil would immobilizate more nitrogen.     

Attack pattern of Platypus koryoensis (Coleoptera: Curculionidae: Platypodinae) in relation to crown dieback of Mongolian oak in Korea

The ambrosia beetle, Platypus koryoensis (Murayama), vectors the Korean oak wilt (KOW) pathogen, Raffaelea quercus-mongolicae K.H. Kim, Y.J. Choi, & H.D. Shin, in Korea, which is highly lethal to Mongolian oak, Quercus mongolica Fisch., and is considered a major threat to forest ecosystem health. We characterized the attack pattern of P. koryoensis along the lower trunk of 240 Mongolian oaks in relation to tree decline symptoms on Mt. Uam in Gyeonggi-Do Province, Korea during June-July 2009. For each tree, we recorded diameter at breast height (dbh) (DBH) and P. koryoensis entrance hole density at two heights along the lower trunk (near groundline and at 1.5 m above groundline) and on opposite sides (downslope side and upslope side). Trees were assigned to one of three dieback classes: 1) apparently healthy, no or practically no wilted foliage, and no obvious platypodine frass near the base of the tree; 2) no or only partial wilting with obvious frass near the base of the tree; and 3) apparently recently killed by KOW with all foliage wilted and mostly retained with obvious frass near the base of the tree. As dieback class increased from 1 to 3, P. koryoensis entrance hole density increased at all four trunk locations. Attack density was highest on the downslope side of the trunk near groundline, and principal component analysis indicated that this trunk location was the best indicator of tree dieback. In addition, DBH tended to increase with dieback class suggesting that larger trees were infested first.     

Different responses of Korean pine (Pinus koraiensis) and Mongolia oak (Quercus mongolica) growth to recent climate warming in northeast China

Different tree species growing in the same area may have different, or even contrasting growth responses to climate change. Korean pine (Pinus koraiensis) and Mongolia oak (Quercus mongolica) are two crucial tree species in temperate forest ecosystems. Six tree-ring chronologies for Korean pine and Mongolia oak were developed by using the zero-signal method to explore their growth response to the recent climate warming in northeast China. Results showed that Mongolia oak radial growth was mainly limited by precipitation in the growing season, while Korean pine growth depended on temperature condition, especially monthly minimum temperature. With the latitude decrease, the relationships between Korean pine growth and monthly precipitation changed from negative to positive correlation, while the positive correlation with monthly temperature gradually weakened. In the contrary, Mongolia oak growth at the three sampling sites was significantly and positively correlated with precipitation in the growing season, while it was negatively correlated with temperature and this relationship decreased with the latitude decrease. The radial growth of Korean pine at different sites showed a clearly discrepant responses to the recent warming since 1980. Korean pine growth in the north site increased with the temperature increase, decreased in the midwest site, and almost unchanged in the southeast site. Conversely, Mongolia oak growth was less affected by the recent climate warming. Our finding suggested that tree species trait and sites are both key factors that affect the response of tree growth to climate change. In addition, the suitable distribution area of Korean pine may be moved northward with the continued global warming in the future, but Mongolia oak may not shift in the same way.     

Strength, diversity and plasticity of postmating reproductive barriers between two hybridizing oak species (Quercus robur L. and Quercus petraea (Matt) Liebl.)

Very little is known about the nature and strength of reproductive isolation (RI) in Quercus species, despite extensive research on the estimation and evolutionary significance of hybridization rates. We characterized postmating pre- and postzygotic RI between two hybridizing oak species, Quercus robur and Quercus petraea, using a large set of controlled crosses between different genotypes. Various traits potentially associated with reproductive barriers were quantified at several life history stages, from pollen-pistil interactions to seed set and progeny fitness-related traits. Results indicate strong intrinsic postmating prezygotic barriers, with significant barriers also at the postzygotic level, but relatively weaker extrinsic barriers on early hybrid fitness measures assessed in controlled conditions. Using general linear modelling of common garden data with clonal replicates, we showed that most traits exhibited important genotypic differences, as well as different levels of sensitivity to micro-environmental heterogeneity. These new findings suggest a large potential genetic diversity and plasticity of reproductive barriers and are confronted with hybridization evidence in these oak species.     

Genetic differentiation of pedunculate oak Quercus robur L. in the European part of Russia based on RAPD markers

Using randomly amplified polymorphic DNA markers (RAPD), genetic variation and differentiation in four populations of pedunculate oak Quercus robur L. were examined. The populations occupy a large part of the Quercus robur range in the European Russia (Voronezh and Novgorod oblasts; Republics of Mordovia and Bashkortostan). With each of six random primers (A02, A09, A17, B01, B08, B11), 96 DNA samples were analyzed by PCR. In all, 48 putative polymorphic RAPD loci were detected. We failed to reveal population-specific DNA fragments for any primer although the frequencies of 14 fragments were significantly different among populations. The oak populations studied exhibited high variability: 73-90% of genes were polymorphic and the effective allele number was about 1.4. The total genetic variation varied from 0.202 (Vor) to 0.245 (Nov), which corresponded to the estimates for populations of this species from Central and Western Europe. The populations examined showed low among-population differentiation (GST = 0.098); gene flow Nem was 4.61. The proportion of among-population variation of the RAPD loci studied accounted for 7% of the total variability; more than 93% of the total variability was explained by individual and within--population variation.