Mechanism of freeze-induced embolism in Fagus sylvatica L.

 The mechanism of freeze stress-induced embolism in Fagus sylvatica L. branches was analyzed under controlled conditions. Excised branches were exposed to successive freeze-thaw cycles in temperature controlled chambers. Thermocouples were placed on the bark to detect sap freezing exotherms. The degree of xylem embolism was estimated after each cycle by the loss of hydraulic conductivity. After one freeze-thaw cycle the degree of embolism was found to decrease with xylem specific hydraulic conductivity, small apical shoots being more susceptible to embolism. Exotherms revealed that distal shoots were freezing first and exuded sap as a result of water expansion. The lower water content in apical shoots upon freezing probably induced higher sap tensions which promoted air bubble expansion and vessel cavitation preferentially near the apices. When the decrease in water content was experimentally prevented, embolism developed to a lesser extent. The higher vulnerability of shoot apices may protect the rest of the branch from winter damage. Received: 29 May 1998 / Accepted: 15 August 1998     

The effect of shoot architecture on hydraulic conductance in beech (Fagus sylvatica L.)

 Shoot hydraulic conductance was measured in beech (Fagus sylvatica L.) that had previously been exposed to high levels of nitrogen input. Whole-shoot hydraulic conductance, conductance per unit pressure gradient and leaf specific conductance were negatively correlated with the number of bud scars per unit length, a morphological parameter of tree decline. We propose a negative feedback mechanism by which stress induced alterations in shoot morphology can cause a lasting reduction of tree vigour. Received: 2 July 1997 / Accepted: 25 June 1998     

欧洲水青冈(Fagus sylvatical L.)构筑型与形态多样性研究

通过对植物构件和构筑型的分析,可以了解植物的整体结构与系统演化关系。高等植物构筑型的研究以树木最为深入,植物学家对全球的树木进行了构筑模式的分类,并确定了２３个基本的构筑类型。植物的构筑型和其形态的多样性是密不可分的。构筑奕型确定了植物所属的整体形态类型,而对每种植物具体的形态多样性分析可以深入了解每种构筑型的数量特征及其形成过程。在概述了树木树筑型研究的基础上,系统说明了欧洲水青冈构筑才形态多样性分析的步骤和步骤和分析的意义。水青冈属（Fagus)为Ｔroll型构筑模式,处于不同生态条件下的同一种的不同种群之间,在形态、解剖、生理和遗传多样性方面都存在着差异。树木的形态多样性虽然主要受遗传因素的控制,但生态条件对其形态和遗传多样性也有非常显著的影响。在对树木进行构筑型分析时,道德要根据构筑要素（主要是形态与生长特性）确定它所属的构筑类型,其次是分析它的形态特征与环境条件的关系,进行进一步分析其遗传多样性。     

An assessment of genetic relationships within the genus Digitalis based on PCR-generated RAPD markers

RAPD markers were used to study inter-specific variation among six species of the genus Digitalis: D. obscura, D. lanata, D. grandiflora, D. purpurea, D. thapsi and D. dubia, and the hybrid D. excelsior (D. purpurea×D. grandiflora). A total of 91 highly reproducible bands amplified with four arbitrarily chosen decamer primers were obtained. Homology of the co-emigrating RAPD markers was tested by blot hybridisation and sequencing of selected bands. The application of a range of statistical approaches for RAPD data analysis, including distance and parsimony methods, family clustering and the analysis of molecular variance (AMOVA), indicated that these molecular markers were taxonomically informative in Digitalis. The species relationships revealed were fully consistent with those previously obtained using morphological affinities. The hybrid D. excelsior seems to have stronger affinity to the section Digitalis than to Grandiflorae. This is the first known report of the application of RAPD markers for the study of genetic relationships among species of the genus Digitalis. Received: 20 October 1999 / Accepted: 9 November 1999     

The influence of mycorrhizal colonization on growth in the greenhouse and on catechin, epicatechin and procyanidin in roots of Fagus sylvatica L.

 The influence of mycorrhizal colonization on beech (Fagus sylvatica L.) root tannin (procyanidin polymer) and its putative precursors catechin and epicatechin was investigated by high performance liquid chromatography. Seedlings planted in a sterile mixture of litter, compost, soil and sand were inoculated with brown beech ectomycorrhizas collected from a woodland (Lactarius subdulcis Bull ex Fr. ×  F. sylvatica). The seedlings were not fertilized during the first year of growth. Nonmycorrhizal control plants showed severe nutrient-deficiency symptoms on their leaves and grew less well than mycorrhizal plants. Mycorrhizal roots contained significantly less catechin, epicatechin and procyanidin polymer than nonmycorrhizal roots. In the second year of growth, the plants were fertilized and procyanidin formation in roots was investigated. None of the fertilized plants showed mineral-deficiency symptoms. Fertilized mycorrhizal roots consistently contained significantly less catechin and epicatechin than nonmycorrhizal controls, but procyanidin polymer content varied between replicate experiments. The possible function of catechin and epicatechin in ectomycorrhizal formation is discussed. Accepted: 11 July 1997     

Acclimation to changing light conditions of long-term shade-grown beech (Fagus sylvatica L.) seedlings of different geographic origins

 Effects of changing light conditions on the ecophysiological condition behind survival were examined on beech from two different populations. Plants were grown in a greenhouse under simulated understorey and canopy gap light conditions. Upon exposure to high light maximum photosynthesis of shade-acclimated leaves increased followed by a reduction over several days to between high- and low-light control rates. In the reciprocal transfer, the decrease in maximum photosynthesis was rapid during the first 2–3 days and then levelled off to values comparable to low-light controls. Seedlings from Sicily (Madonie) showed generally higher maximum photosynthetic rates than those from Abetone. Leaf conductance varied in the same direction as photosynthesis in high- to low-light seedlings but to a lesser degree. Leaves grown under low light and exposed to high light experienced photoinhibition. The Abetone population was more susceptible to photoinhibitory damage than the seedlings from Sicily. Exposure to high light of shade-acclimated seedlings resulted in intermediate chlorophyll concentrations between levels of the high-light and low-light seedlings. Carotenoid concentration was unaffected by treatments. Seedlings grew more in high light, but had a lower leaf area ratio. Light-limited seedlings showed a shift in carbon allocation to foliage. Leaves formed in the new light regime maintained the same anatomy that had been developed before transfer. Seedlings from Sicily had thicker leaves than those of seedlings from Abetone. Seedlings from Abetone were found to be more susceptible to changing light conditions than seedlings from Sicily. We conclude that small forest gaps may represent a favorable environment for photosynthesis and growth of beech regeneration as a result of the limited ability of seedlings to acclimate to sudden increases in high irradiance and because of the moderate levels of light stress in small gaps. Received: 11 April 1997 / Accepted: 11 December 1997     

RAPD markers on seed bulks efficiently assess the genetic diversity of a Brassica oleracea L. collection

 The concept of a core collection was elaborated to fit the necessity of optimizing the management, for both conservation and use, of genetic resources in sizeable collections. This approach requires an analysis of how the genetic variability is structured among the accessions. The large number of heterogeneous populations in our collection of Brassica oleracea makes genetic diversity studies based on plant-to-plant analysis impracticable. To overcome this limitation, the variability analysis by RAPD on seed bulks was investigated for its efficiency in assessing the structure of the genetic diversity of this collection. The optimal bulk size and the bulking or sampling variation were evaluated with bulks of different size and with replicated samples. A mixture of known genotypes was also used to characterise the band detection in bulks, and to compare the plant-to-plant and the bulk methods. Forty seeds were chosen to represent each population. In such a bulk, the detection of bands depended on the proportion of the genotype they were derived from in the mixture. Intense and frequent bands were detected in the bulk with a 15% detection limit. The observed bulking or sampling variation within populations was smaller than the variation between populations, leading to an efficient separation of populations with a clustering of all samples of the same population. The distances calculated from bulk data were highly correlated with the distances based on the plant-to-plant analysis. We demonstrated that RAPD on seed bulks can be used to describe the genetic diversity between populations. Received: 27 August 1998 / Accepted: 29 September 1998     

The effects of acclimation to sunlight on the xylem vulnerability to embolism in Fagus sylvatica L.

We assessed the effects of irradiance received during growth on the vulnerability of Fagus sylvatica L. xylem vessels to water-stress-induced embolism. The measurements were conducted on (1) potted saplings acclimated for 2 years under 100% and 12% incident global radiation and (2) branches collected from sun-exposed and shaded sides of adult trees. Both experiments yielded similar results. Light-acclimated shoots were less vulnerable to embolism. Xylem water potential levels producing 50% loss of hydraulic conductivity were lower in sun-exposed branches and seedlings than in shade-grown ones (–3·0 versus –2·3 MPa on average). The differences in vulnerability were not correlated with differences in xylem hydraulic conductivity nor vessel diameter. Resistance to cavitation was correlated with transpiration rates, midday xylem and leaf water potentials in adult trees. We concluded that vulnerability to cavitation in Fagus sylvatica may acclimate to contrasting ambient light conditions.     

Winter North Atlantic oscillation effects on the tree rings of the Italian beech (Fagus sylvatica L.)

Climatic signals in beech tree-ring width series from Central Italy have been studied over different periods of time. Prewhitened tree-ring chronologies respond mainly to summer precipitation and they do not correlate in a significant manner with the winter North Atlantic oscillation (NAO) index. In this high-frequency pattern the NAO signs are only found on a small number of rings characterized by being very narrow or wide. By contrast, tree-ring width chronologies in which all the frequency components are conserved were significantly related to the NAO. The significant inverse correlation between actual measurements of ring width and NAO is a consequence of the availability of water in the soil at the beginning of the growing season. In fact, in the Mediterranean area the recharging of soil moisture depends on the amount of winter precipitation, which is inversely correlated with the NAO. Strong signals of winter precipitation and NAO are found in the low-frequency components of tree-ring growth. Received: 18 March 1999 / Revised: 29 February 2000 / Accepted: 1 March 2000     

Water relations and gas exchange in Fagus sylvatica L. and Quercus petraea (Mattuschka) Liebl. in a mixed stand at their southern limit of distribution in Europe

Water status and gas exchange of beech (Fagus sylvatica L.) and sessile oak [Quercus petraea (Mattuschka) Liebl.] were studied in a mixed stand in the Montejo de la Sierra forest (central Iberian Peninsula), one of the southernmost locations of both species in Europe. Gas exchange and water potential were measured in leaves at different canopy levels over several days in two growing seasons. The daily variation pattern was established with the measurements of three selected dates per year, representative of the soil moisture content situations in early, mid- and late summer. A similar daily time course of leaf water potential was found for the two species. Nevertheless, beech showed a most noticeable decrease of water potential at midmorning and maintained lower leaf water potential than oak in the early afternoon. In 1994 the sessile oak saplings showed higher values of predawn water potential (Ψ_pd) than beech at the end of summer, when soil moisture content was lowest (20 cm depth). Beech showed a significantly lower net assimilation rate (A) than sessile oak for leaves under the same PPFD. Maximum net photosynthesis values (A _max) for beech and sessile oak on sunny leaves were 10.1±0.4 μmol m^–2 s^–1 and 17.8±1.7 μmol m^–2 s^–1 respectively, and those for water vapour stomatal conductance (g _wv) were 265±31 mmol m^–2 s^–1 and 438±74 mmol m^–2 s^–1. Differences in A and g _wv between the two species were maintained throughout the day on all measurement dates. No clear relationship was found between water status of saplings and stomata performance; there was only a negative correlation between Ψ_pd and g _wvmid in beech. Nevertheless, a significant response to the air vapour pressure gradient between leaf and air was translated into stomata closure on an hourly basis, more intensively in beech. Received: 4 March 1999 / Accepted: 21 December 1999     

Random amplified polymorphic DNA (RAPD) analysis reveals genetic relationships among the annual Cicer species

 Random amplified polymorphic DNA markers were used to distinguish between nine different Cicer taxa representing the cultivated chickpea and eight other related annual wild species. Of the 75 random10-mer primers tested, only 8 amplified genomic DNA across all the species. A total of 115 reproducibly scorable RAPD markers were generated, all except 1 polymorphic, and these were utilized to deduce genetic relationships among the annual Cicer species. Four distinct clusters were observed and represented C. arietinum, C. reticulatum and C. echinospermum in first cluster followed by C. chorassanicum and C. yamashitae in the second cluster, while C. pinnatifidum, C. judaicum and C. bijugum formed the third cluster. Cicer cuneatum did not cluster with any of the species and was most distantly placed from the cultivated species. Except for the placement of C. chorassanicum and C. yamashitae, deduced species’ relationships agreed with previous studies. In addition, species-diagnostic amplification products specific to all the nine species were identified. The results clearly demonstrate a methodology based on random-primed DNA amplification that can be used for studying Cicer phylogeny and chickpea improvement. Received: 27 July 1998 / Accepted: 5 August 1998     

Storage and mobilization of nonstructural carbohydrates and biomass development of beech seedlings (Fagus sylvatica L .) under different light regimes

 Beech seedlings were grown under 8%, 13%, 23% and 100% relative light intensity for 2 years after germination. Starch, sucrose and monosaccharides from the bark and wood parenchyma of shoots and roots were analyzed during the course of the second year. The annual allocation pattern of starch revealed five successive phases: starch disintegration in November (1) was paralleled by high monosaccharide concentrations in the shoot cortex (≤ 33.4 mg/g DW). Seedlings of all light variants reached maximum sucrose concentrations (≤ 82.8 mg/g DW) during starch disintegration in January (2) that coincided with decreased monosaccharide contents. Up to mid-April, resynthesis of starch (3) occurred in most shaded and unshaded seedlings. In May, starch was converted into monosaccharides in all storage tissues (4). Seedlings grown under 13% light intensity showed de novo synthesis of starch (5) 4 weeks after bud burst. These seedlings reached 98% maximum starch storage capacity of the shoot and 89% of the root in July. In mid-October, the maximum starch concentration of the roots increased with light intensity, and this corresponded with an increase of lateral root growth. The variation of shoot and root dry weight was closely related to the content of nonstructural carbohydrates during the second year. The shift of shoot growth to the first half of the growing season and the suppression of lateral root growth during the second half is assumed to be a strategy of young beech to survive under light limiting conditions. Received: 22 May 1997 / Accepted: 10 October 1997     

Gene Flow in European Beech (Fagus sylvatica L.)

Three relatively isolated stands were used to study gene flow in European beech (Fagus sylvatica L.) in Northern Germany. Nine allozyme loci (Got-B, Idh-A, Lap-A, Mdh-B, Mdh-C, Mnr-A, 6-pgdh-A, Pgi-B and Pgm-A) were utilized for multilocus-genotyping adult trees and seeds. Expected heterozygosity (He) ranged from 0.325 to 0.351 for the three stands. F(ST) revealed that there was small differentiation among stands (mean F(ST) = 0.013). The indirect estimates of gene flow (Nm) based on the mean F(ST) were high and the average Nm was 19.14. External gene flow by pollen ranged from 0.7 to 1.2% inferred from new alleles in seed samples. Moreover, paternity analysis was used to assess effective pollen dispersal by inferring paternity of offspring. The weighted mean distances of pollen dispersal for these three stands were 36.8 and 37.1 m based on simple exclusion procedure and most-likely method, respectively. Two of the trees in one stand had rare allozyme alleles (Lap-A1 and Idh-A4, respectively), which were used to directly measure pollen movement away from those trees. The frequency of the rare Lap and Idh alleles in seeds declines as the distance from the source tree increases. The weighted mean distance of pollen dispersal with rare allele Lap-A1 or Idh-A4 was 26.3 m.     

Extending a RFLP-based genetic map of rye using random amplified polymorphic DNA (RAPD) and isozyme markers

RFLP-based genetic map of rye, developed previously using a cross of lines DS2×RXL10 (F₂ generation), was extended with 69 RAPD and 12 isozyme markers. The actual map contains 282 markers dispersed on all seven chromosomes and spans a distance of 1,140 cM. The efficiency of mapping RAPD markers was close to ten loci per 100-screened arbitrary primers. A strong selection of polymorphic, intensive and reproducible fragments was necessary to reveal individual marker loci that could be assigned to rye chromosomes. Newly mapped markers cover a substantial part of the rye genome and constitute a valuable tool suitable for map saturation, marker-aided selection and phenetic studies. A specific nomenclature for the RAPD loci mapped on individual rye chromosomes, which could be helpful in managing of accumulating data, is proposed. Received: 8 May 2000 / Accepted: 17 October 2000     

Evaluation of the extent of genetic variability among Theobroma cacao accessions using RAPD and RFLP markers

 Random amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) markers were used to evaluate genetic relationships within the Theobroma cacao species and to assess the organization of its genetic diversity. Genetic variability was estimated with 18 primers and 43 RFLP probes on 155 cocoa trees belonging to different morphological groups and coming from various geographic origins. The majority of the RFLP probes issued from low-copy DNA sequences. On the basis of on the genetic distance matrices, the two molecular methods gave related estimates of the genetic relationship between genotypes. Although an influence of cocoa morphological groups and geographical origins of trees was observed, a lack of gene differentiation characterized the T. cacao accessions studied. The continuous RFLP variability observed within the species may reflect the hybridization and introgressions between trees of different origins. Nevertheless, the Nacional type was detected to be genetically specific and different from well-known types such as Forastero, Criollo and Trinitario. Some of those genotypes were characterized by a low heterozygosity rate and may constitute the original Nacional pool. These results also provide information for the constitution of a cocoa tree core collection. Received: 10 June 1996/Accepted: 11 October 1996     

Is the spatial distribution of European beech (Fagus sylvatica L.) limited by its potential height growth?

Aim To improve our understanding of species range limits by studying how height growth, a trait related to plant survival, varies throughout the geographic range of Fagus sylvatica L. in France. Location The geographic range of beech in France, representing the western area of its European distribution, within which this species exhibits range distribution limits in both plains and mountainous areas. Methods A generalized linear regression model was used to link beech growth performance to environmental variables using data from 819 plots of the French National Forest Inventory (IFN) database. This model was applied to predict potential growth on 97,281 IFN plots covering the geographic range of beech in France. A kriging technique was used to interpolate estimated growth potential. Finally, the performance of plot‐based predictions of potential growth from the map (i.e. map quality) was evaluated against an independent data set. Results The beech growth performance model highlighted the major impact of climate on potential tree growth at a broad spatial scale. The relevant climatic factors were related mainly to spring cold, summer heat, and winter temperatures and rainfall. The study also revealed the predictive power of soil parameters, which explained a large proportion of the variation in potential beech growth (c. 30%). Analyses of height growth patterns near the boundary of the species range in France showed that the limit only partly coincides with the growth decline caused by climatic and soil factors. Along parts of the range limit, the predicted potential for growth was high, suggesting that in these areas the limit of the range could be explained by other factors, such as competition or constraints on reproduction. Main conclusions The spatial variation in the potential height growth of Fagus sylvatica can be explained by environmental factors and is partly correlated with its regional range limits. By identifying areas where growth potential constrains the geographic range of species, environmental growth models can help to improve our knowledge of the spatial drivers of species geographic range limits and shed light on their response to future environmental changes.     

Genetic relationships among Stylosanthes species revealed by RFLP and STS analyses

Genetic relationships between 6 unclassified taxa and 24 known species of the genus Stylosanthes were investigated by RFLP and STS analyses. This allowed the diploid taxa used in this study to be classified into nine basal (genome) groups. Representative species in these groups included ’S. seabrana’/S. hamata (Group A), S. viscosa (Group B), S. humilis (Group C), S. macrocephala/S. bracteata (Group D), S. pilosa (Group E), S. leiocarpa (Group F), S. guianensis (Group G), S. tomentosa (Group H) and S. calcicola (Group I). Polyploid taxa used were grouped into five classes based on their putative genomic structures. These are AABB for S. scabra, S. aff. scabra, S. sericeiceps, S. aff. hamata and S. tuberculata; AACC for S. mexicana, S. subsericea, S. sundaica and S. sp.A; DDEE for S. capitata; AAFF for S. sympodialis; and AABBXX for S. erecta, with XX representing an unknown genome. Of the 6 unclassified taxa, three were diploids and 3 tetraploids. Of the 3 diploids, the genome of S. sp. was markedly distinct from those of all other diploids analysed in this study, with that of S. leiocarpa being the closest. The genome of S. sp.B was similar to that of S. humilis, with an average dissimilarity value of 15% between them. The genome of S. aff. viscosa was very similar to that of S. viscosa. Genetic variation between these 2 taxa was not larger than that within each of the 2 taxa. Of the 3 tetraploids, the genomic structure of S. sp.A was similar to those of S. mexicana, S. sundaica and S. subsericea, and the genomic structures of S. aff. scabra and S. aff. hamata were similar to those of S. scabra and S. sericeiceps. Received: 18 September 1998 / Accepted: 23 March 1999     

Variation among and within Capsicum species revealed by RAPD markers

 Germplasm characterization is an important link between the conservation and utilization of plant genetic resources. A total of 134 accessions from six Capsicumspecies maintained at the Asian Vegetable Research and Development Center were characterized using 110 randomly amplified polymorphic DNA (RAPD) markers. Ten pairs of potentially duplicated accessions were identified. Multidimensional scaling analysis of the genetic distances among accessions resulted in clustering corresponding to a previous species assignment except for six accessions. Diagnostic RAPDs were identified which discriminate among the Capsicumspecies. The diagnostic markers were employed for improved taxonomic identification of accessions since many morphological traits used in the identification of Capsicumare difficult to score. Three Capsicumaccessions, misclassified based on morphological traits, were reassigned species status based on diagnostic RAPDs. Three accessions, not previously classified, were assigned to a species based on diagnostic RAPDs. Definitive conclusions about the species assignment of three other accessions were not possible. The level of diversity between Capsicum annuumaccessions from the genebank and the breeding program were compared and no differences were observed either for RAPD variation or diversity. The utilization of genetic resources as a source of variance for useful traits in the breeding program may be the reason for the similarity of these two groups. Received: 1 September 1998 / Accepted: 28 December 1998     

Direct comparison of levels of genetic variation among barley accessions detected by RFLPs, AFLPs, SSRs and RAPDs

 RFLPs, AFLPs, RAPDs and SSRs were used to determine the genetic relationships among 18 cultivated barley accessions and the results compared to pedigree relationships where these were available. All of the approaches were able to uniquely fingerprint each of the accessions. The four assays differed in the amount of polymorphism detected. For example, all 13 SSR primers were polymorphic, with an average of 5.7 alleles per primer set, while nearly 54% of the fragments generated using AFLPs were monomorphic. The highest diversity index was observed for AFLPs (0.937) and the lowest for RFLP (0.322). Principal co-ordinate analysis (PCoA) clearly separated the spring types from the winter types using RFLP and AFLP data with the two-row winter types forming an intermediate group. Only a small group of spring types clustered together using SSR data with the two-row and six-row winter varieties more widely dispersed. Direct comparisons between genetic similarity (GS) estimates revealed by each of the assays were measured by a number of approaches. Spearman rank correlation ranked over 70% of the pairwise comparisons between AFLPs and RFLPs in the same order. SSRs had the lowest values when compared to the other three assays. These results are discussed in terms of the choice of appropriate technology for different aspects of germplasm evaluation.