干旱和湿润生境下辽东栎群体遗传结构及其适应意义的初步研究

应用同工酶分析方法,测定北京市东灵山区两个分别代表干旱和湿润生境的辽东栋（ＱｕｅｒｃｕｓｌｉａｏｔｕｎｇｅｎｓｉｓＫｏｉｚ．）群体的遗传结构。共分析统计了１３ 个酶系统３０ 个位点。结果表明：辽东栎群体内部存在丰富的遗传变异（多态位点百分率为８６．６％ ,等位基因平均数为２．２５）。两群体遗传结构的相似性程度很高（Ｄ＝ ０．０２９, ＧＳＴ＝ ０．０４８）;但在个别位点上仍存在较大差异,这些差异的产生可能与对小生境的适应有关。对不同年龄段的初步分析结果显示,基因频率的动态变化可能有其适应意义     

Comparative structural study ofQuercus serrata andQ. acutissima formed byPisolithus tinctorius andHebeloma cylindrosporum

Ectomycorrhizas were synthesized in pots and growth pouches betweenQuercus serrata, Q. acutissima, and two ectomycorrhizal fungi,Pisolithus tinctorius andHebeloma cylindrosporum. Root morphology and the structure of the mantle and Hartig net were compared using light, fluorescence, scanning and transmission electron microscopy.P. tinctorius initially colonized root cap cells, and eventually produced a highly branched lateral root system with a complete mantle, whereasH. cylindrosporum promoted root elongation with few hyphae on the root apex surface indicating that interaction between roots differs with fungal species. Hartig net structure and hyphal inclusions varied between all the combinations tested. There were structural differences between mycorrhizas ofH. cylindrosporum/Q. acutissima grown in soil and growth pouches, which indicate that the growth pouch environment can induce artefacts in roots. Fruit bodies ofH. cylindrosporum developed in pots withQ. acutissima. AlthoughP. tinctorius has been used to inoculate oak seedlings in the nursery, results of this study indicate thatH. cylindrosporum may also be an effective ectomycorrhizal fungus forQ. serrata andQ. acutissima.     

Anatomical studies of branchlet abscission related to crown modification in Quercus cerris L.

The basic anatomy of lateral twig insertion onto the main branch in both healthy and damaged Quercus cerris L. trees was studied. An abscission zone is always present: in healthy trees it is formed by a smaller number of cell layers than in damaged ones, where it is more evident with many layers of cells. Cells of the abscission zone are roundish, with many intercellular spaces between them; cell walls are thin, non-lignified and without secondary walls. No starch was found in cells of the abscission zone, where, instead, a few scattered calcium oxalate druses are seen.     

Structure and identification of root bark of Quercus robur L.

The root bark structure of Quercus robur L. was analysed at different stages of root development and compared to the structure of stem bark. Root bark thickness varied considerably between different roots. Sclereid quantity decreased with increasing distance from the stem, which means it increased with age. Visible growth increments diminished with increasing distance from the stem. In lateral roots crystal quantity decreased with increasing distance from the stem. In lateral roots secondary phloem fibre length, sieve tube member length, and sieve tube diameter showed no regular trend. There were only a few basic structural differences between root and stem bark. The zone of cell differentiation (cell expansion, lignification) was wider in root bark; sieve tube collapse was delayed. In lateral root bark fewer sclereids were formed. The first-formed periderm often originated from deeper cell layers. Thus, primary elements were lacking after periderm formation. In root bark the phellem cell walls were of equal thickness. Thus, phellem lacked visible growth increments. Root bark phellem cells were slightly larger. The root phelloderm was more distinct. The secondary phloem fibres were slightly shorter than those in stem bark. Sieve tube members of stem and root bark were of similar length and diameter. The qualitative bark anatomical characters of oak root bark are suitable for root identifications. Due to minor structural differences between root and stem bark the characters must be used with care.     

峨嵋山冷杉森林衰退状况研究

报道和分析了峨嵋山冷杉森林的衰退状况。对冷杉种群的受害程度、分布规律、症状特点及其与海拔、特定生境、立木径级和林型的关系进行了研究分析。指出峨嵋山冷杉森林衰退是全球森林衰退的组成部份,而不是个别的或偶然的现象;肯定了当地冷杉林衰退具有某些个性特征。由此认为,导致当地冷杉衰退的主要原因可能是某种或某些作用范围广、持续时间长、发生频率高、对全球森林系统构成威胁的因素所致。     

Changes in the floristic composition of a Quercus coccifera L. garrigue in relation to different fire regimes

Plant Ecology - To analyse the impact of fire on plants, an experiment has been set up in a Quercus coccifera L. garrigue near Montpellier. The objectives of the study were to follow the changes of...     

Natural convection from leaves at realistic Grashof numbers

Abstract. The boundary layer resistance of model leaves was measured in still air, at a range of leaf-to-air temperature differences. The results were compared to those calculated from standard formulae for natural convection. The agreement between observed and calculated was only satisfactory when Grashof numbers exceeded about 105. At the lower Grashof numbers, which often prevail in nature, the observed rates of heat transfer considerably exceeded those calculated.     

What are the consequences of being a downy oak (quercus pubescens) or a holm oak (Q. ilex) for breeding blue tits (Parus caeruleus)?

By comparison with deciduous oaks, the lower yearly production of new leaves in sclerophyllous oaks is hypothesized to have several consequences on animal communities. In particular, the production of arthropod communities that feed upon the leaves should be lower in sclerophyllous than in deciduous oaks, this causing changes in breeding patterns and the demographic balance in insectivorous birds. Studies in both deciduous and sclerophyllous habitats in southern France have shown that: 1) the spring development of new leaves occurs later and more slowly in sclerophyllous than in deciduous oaks, 2) the biomass of caterpillars is much lower in sclerophyllous oak forests, and 3) there is a large variation in life history traits of the Blue Tit depending in which type of habitat they breed. Laying date occurs later and clutch size is lower in sclerophyllous habitats than in deciduous habitats. The evolution of life history traits is discussed according to whether poor sclerophyllous habitats are isolated (e.g. on Corsica) or are parts of landscapes including both habitat types.     

Evaluation of actual evapotranspiration of a Quercus ilex L. stand by the Bowen Ratio-Energy Budget method

Actual evapotranspiration from a closed-canopy Quercus ilex L. stand has been estimated by applying the Bowen Ratio-Energy Budget method. Daily water loss was 3.5 mm day^–1, with a peak rate near 0.6 mm hour^–1. The phenomenon of thermal inversion, quite common in mediterranean climates, seemed to play a significant role in reducing evapotranspiration, by promoting dew formation and delaying the establishment of fluxes of latent and sensible heat away from the canopy. Dew, which may form over many hours in the night, appears to be a major sink of available energy in the early morning and may represent a useful water source for stressed foliage. The alternating processes of condensation and evaporation may have a beneficial effect on the closed stand micro-environment.     

Variation in the genetic structure and reproductive biology of holm oak populations

Five polymorphic enzymatic loci were studied in 30 populations of Quercus ilex distributed from Crete to North Africa. A high within-population genetic diversity was found for each locus studied. Most of the alleles were common to all the populations, indicating that the holm oak corresponds to a single genetic entity. Observation of breeding system characteristics showed that the holm oak is monoecious, wind-pollinated, and likely to possess genetic autoincompatibility. Furthermore, studies of flowering phenology in a single population showed that the period of flowering varied notably among trees. An average of 29% of the trees showed inter-annual variation in flowering time. The male, female or vegetative investment also varied widely among trees from one year to another. This results in a diversification of pollen source received by a given tree each year, and also from one year to another.