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31.
Susy Svatek Ziegler 《Global Ecology and Biogeography》2000,9(5):373-389
1 This study compares the structural characteristics of 12 old‐growth and six postfire second‐growth hemlock–northern hardwood stands in north central Adirondack Park, New York, in order to test the null hypothesis that there are no differences in species composition, size structure, age structure and attributes such as dead wood and canopy gaps between old‐growth stands and this type of second‐growth forest. 2 The second‐growth forests of this study regenerated following widespread logging‐related fires in either 1903 or 1908; the old growth and second growth have similar environmental settings. 3 Estimates of stand ages, derived from an increment core of the oldest tree in each stand, range from 88 to 390 years. 4 Structural attributes are related to stand age (i.e. stage of development). In comparison with the second‐growth forests of this study, older stands are characterized as (a) a larger average diameter of canopy trees; (b) a greater basal area of trees; (c) a lower density of canopy trees and of all trees ≥ 10 cm d.b.h.; (d) a higher density of eastern hemlock (Tsuga canadensis (L.) Carrière) trees; (e) a higher density of large trees (≥ 50 cm d.b.h.); (f) larger canopy gaps; and (g) a greater volume of coarse woody debris (both logs ≥ 20 cm d.b.h. and snags ≥ 10 cm d.b.h.). 5 Despite differences between old growth and second growth, especially in species composition, it appears from observations of the 18 stands that second‐growth forests are developing some structural characteristics of old growth. 6 Structural attributes of the old‐growth forests are similar to characteristics of the same forest type in geographically distant areas in eastern USA. 相似文献
32.
引物间同源性和裂口对PCR扩增的影响 总被引:4,自引:0,他引:4
采用PC/Gene软件对能扩增出特异睡不能扩增的PCR引物进行同源性比较,同源间“裂口(gaps)”差数的统计,得出源率小于或等于35%,“裂口”差数大于或等于3,是获得理想PCR扩增效果的关键参数之一的结论,为引物设计提供了一条直观的依据。 相似文献
33.
Nenad Bukvic Carla CesaranoCaterina Ceccarini Marianna BrunoMaria Rosaria Lipsi Maria Grazia GallicchioMaria Assunta Carboni Lucia ValenteGiulia Cotoia Raffaele Antonetti 《Gene》2013
Herein, we describe a case of an infertile man detected in postnatal diagnosis with FISH characterization and array-CGH used for genome-wide screening which allowed the identification of a complex rearrangement involving sex chromosomes, apparently without severe phenotypic consequences. The deletion detected in our patient has been compared with previously reported cases leading us to propose a hypothetical diagnostic algorithm that would be useful in similar clinical situations, with imperative multi disciplinary approach integrated with genetic counseling. Our patient, uniquely of reproductive age, is one of six reported cases of duplication of Xp22.3 (~ 8.4 Mb) segment and contemporary deletion of Yq (~ 42.9 Mb) with final karyotype as follows:
- 46,X,der(Y),t(X;Y)(Ypter → Yq11.221::Xp22.33 → Xpter).ish der(Y) (Yptel+,Ycen+,RP11-529I21+,RP11-506M9-Yqtel −,Xptel +). arrXp22.33p22.31(702–8,395,963, 8,408,289x1), Yq11.221q12 (14,569,317x1, 14,587,321–57,440,839x0) 相似文献
34.
Paolo Gondoni Matteo Ghidelli Fabio Di Fonzo Andrea Li Bassi Carlo S. Casari 《Journal of visualized experiments : JoVE》2013,(72)
Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (>80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4. 相似文献
35.
Structure and regeneration of a mid-montane (2200 m a.s.l.)mixed forest codominated by evergreen (Lithocarpuscleistocarpus), deciduous (Acer flabellatum)andconiferous (Tsuga chinensis, Abies fabri, andTaxus chinensis) trees were analyzed in a 40m× 60 m plot on Mt. Emei, Sichuan, China. Plant communitystructure and composition varied depending on topographic micro-habitat withinthe plot. Four topographic communities (topo-communities) were distinguishedwith dominant species corresponding to topography: (1)Abies – valley bank, (2) Acer– lower steep slope, (3) Lithocarpus – uppergentle slope, and (4) Tsuga – ridge. The coexistencemechanisms of the evergreen, deciduous, and coniferous trees were determined byidentifying the regeneration process characteristic of each dominant species,asrepresented by their seedling dispersion patterns and seedling establishmentalong the topographic gradients. The saplings and seedlings of the dominantswere distributed differently according to the topography:Lithocarpus under the canopy of parent trees and in gapsofthe upper gentle slope and ridge, Acer mainly in bothwell-lit and shady sites on the lower steep slope and on fallen logs,Abies on the valley bank but only in well-lit sites,Tsuga on the ridge, Taxus mostly onrock and well-lit sites on the slopes. Distribution of surviving saplings andseedlings was also related to the species of nearby canopy trees. We suggestthat Lithocarpus, Tsuga and Acer tendto be self-replacing in their own topographic habitats, andAbies survives as a fugitive by occupying occasionalsuitable gaps. The variation in soil conditions, particularly nutrients, withtopography affected seedling establishment and the growth of trees. Thesuccessional change of quantitative species composition, as predicted by theMarkovian model, shows the mixed forest to be in a sustained climax stage. 相似文献
36.
The study was carried out in ten natural canopy gaps in the SantaGenebra County Reserve (22°4945S, 47°0633W)in the county of Campinas, São Paulo State, Brazil. The size and canopyopenness of the gaps were studied using hemispherical photographs. Thevegetation survey included all shrubs and trees with height 0.50m in the gaps interiors and all the individuals with PBH(perimeterat breast height) 15 cm in a 3 m surroundingborder of the gaps. The similarity among the gaps and among their surroundingareas was assessed by the Jaccard similarity index and by cluster analyzes. Thegap size varied from 20.09 to 468 m2, with apredominance of small gaps. The families with the greatest species richness inthe gaps were Rutaceae, Rubiaceae and Euphorbiaceae. The species with thegreatest number of individuals in the gaps were Coffeaarabica L., Hybanthus atropurpureus (St. Hil.)Taub. and Actinostemon klotschii (Muell. Arg.) Pax, allwidely distributed in the understorey. Shade-tolerant species (late secondaryspecies) predominated in function of the predominance of small gaps. The highnumber of species found in the gaps reflects the importance of thesedisturbances in the maintenance of species diversity in the studied forest. 相似文献
37.
Following the discovery of photosynthetic bacteria in the nineteenth century, technical developments of the 1950s led to their
use in membrane biogenesis studies. These investigations had their origins in the isolation of subcellular particles designated
as ‘chromatophores’ by Roger Stanier and colleagues, which were shown to be photosynthetically competent by Albert Frenkel,
and to originate from the intracytoplasmic membrane (ICM) continuum observed in electron micrographs. These ultrastrucutral
studies by the G. Drews group, Germaine Cohen-Bazire and others also suggested that the ICM originates by invagination of
the cytoplasmic membrane, as later established in the biochemical and biophysical work of the R. Niederman and Drews groups.
Through a combination of genetic approaches, first introduced in the early 1980s by Barry Marrs, and the atomic resolution
structures determined for light-harvesting antennae and reaction centers, a detailed understanding is emerging of mechanisms
regulating their levels in the membrane and the roles played by specific protein domains and additional factors in their assembly
and supramolecular organization. Prospects for additional progress during the twenty-first century include further elucidation
of molecular aspects of the assembly process and the application of newer spectroscopic probes to photosynthetic unit formation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
38.
Role of bicarbonate at the acceptor side of Photosystem II 总被引:1,自引:0,他引:1
van Rensen JJ 《Photosynthesis research》2002,73(1-3):185-192
Besides being the substrate for the carboxylation reaction of photosynthesis, CO2 (bicarbonate) is required for the activity of Photosystem II (water plastoquinone oxido-reductase). It plays a role on the
electron donor side as well as the electron acceptor side. In this contribution, attention will mostly be focused on the history
of research into the effects of bicarbonate on electron flow reactions on the acceptor side. Donor side reactions are discussed
in this issue by Alan Stemler.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
39.
Ormerod J 《Photosynthesis research》2003,76(1-3):135-143
Dogmas are unscientific. What is perhaps the greatest biological dogma of all time, the `unity of biochemistry' is, in the
main, still having its day. According to present knowledge, the exceptions to this dogma are mere details when seen in relation
to the biosystem as a whole. Nevertheless the exceptions are scientifically interesting and the understanding of them has
led to a better comprehension of photosynthesis and ecology. Until the discovery of 14C, photosynthetic CO2 fixation was like a slightly opened black box. With 14C in hand scientists mapped out the path of carbon in green plant photosynthesis in the course of a few years. The impressive
reductive pentose phosphate cycle was almost immediately assumed to be universal in autotrophs, including anoxygenic phototrophs,
in spite of the odd observation to the contrary. A new dogma was born and held the field for about two decades. Events began
to turn when green sulfur bacteria were found to contain ferredoxin-coupled ketoacid-oxidoreductases. This led to the formulation
of a novel CO2-fixing pathway, the reductive citric acid cycle, but its general acceptance required much work by many investigators. However,
the ice had now been broken and after some years a third mechanism of CO2 fixation was discovered, this time in Chloroflexus, and then a fourth in the same genus. One consequence of these discoveries is that it has become apparent that oxygen is an
important factor that determines the kind of CO2-fixing mechanism an organism uses. With the prospect of the characterization of hordes of novel bacteria forecast by molecular
ecologists we can expect further distinctive CO2 fixation mechanisms to turn up.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
40.
Ary T. Oliveira-Filho Nilton Curi Enivanis A. Vilela Douglas A. Carvalho 《Biotropica》1998,30(3):362-375
The interrelationships between the distribution of woody species and environmental variables were investigated in an area of deciduous dry forest in Santa Vitöria, central Brazil. This is the first study of a vanishing type of dry forest which grows on base-rich soils originating from the basalt bedrocks of southern Goiás and western Minas Gerais. A survey of topography, soil properties, canopy gaps and woody plants (≥5 cm diameter at the base of the stem) was conducted in 50–15 × 15 m quadrats. The soils were classified into the following soil series: Hapludolls → Haplustolls → Haplustolls → Ustropepts → Rhodustalfs. This series corresponded to a gradient of increasing elevation and effective soil depth and decreasing slope gradient, soil organic matter and total exchangeable bases. A canonical correspondence analysis and a detrended correspondence analysis indicated that plant species’abundance distribution was significantly correlated with both the relative area of canopy gaps in the quadrats and the soil-topography gradient. Presumably, the critical factors involved in these two gradients are, respectively, light and ground water regimes. The influence of canopy gaps (i.e., light) was surprising and has not been documented previously for tropical deciduous dry forests. 相似文献