Salviniales from the Late Cretaceous of the Golfo San Jorge Basin

The freshwater ferns (Salviniales) are well represented in the Maastrichtian deposits of Cerro de los Fragmentos in the headwaters of the Río Chico, Golfo San Jorge Basin. The fossil material of Salviniaceae includes complete megaspore apparatuses with attached microspore massulae and dispersed megaspores, float systems and microspore massulae of Azolla. The new species Azolla colhuehuapensis displays distinctive morphological characters including relative small megaspore apparatuses with easily detached floats and usually attached eglochidiate massulae. The Marsileaceae are represented by the megaspore Molaspora lobata, microspores of Crybelosporites and vegetative remains of Marsileaceaephyllum sp. The assemblage also includes zygospores of the green filamentous algae Zygnemataceae, spores of Marchantiophyta and Monilophyta (Schizaeales), megaspores of Isoetalean affinity and Palm-type angiosperm pollen grains. All these organic microfossils and the associated palynomorphs indicate the presence of a freshwater environment where abundant water ferns were developing and reproducing.     

Mesquite (Prosopis juliflora (Sw.) DC.), huisache (Acacia farnesiana (L.) Willd.) and catclaw (Mimosa biuncifera Benth.) and their effect on dynamics of carbon and nitrogen in soils of the semi-arid highlands of Durango Mexico

In the northern semiarid and arid part of Mexico, mesquite (Prosopis juliflora (SW.) DC.), huisache (Acacia farnesiana (L.) Willd.) and catclaw (Mimosa biuncifera Benth.), N₂-fixing trees or shrubs, dominate the landscape. It is unknown, however, how much the leaves of those shrubs contribute to dynamics of carbon (C) and nitrogen (N) in soil. We investigated this by adding leaves of each species to soil sampled under the canopy of mesquite, huisache, and catclaw and outside their canopy while monitoring production of carbon dioxide (CO₂), and dynamics of inorganic N (ammonium (NH₄⁺) and nitrate (NO₃⁻)) in an aerobic incubation. The (hemi)cellulose and N content of the catclaw leaves was lower and the lignin and polyphenol content was larger than in the mesquite and huisache leaves. If we considered no priming effect, then 41% of the C added with catclaw leaves, 47% with huisache leaves and 49% with mesquite leaves mineralized within 42 days. The addition of the leaves had little or no effect on N mineralized, and only 6% of organic N of the mesquite leaves was mineralized. It was found that catclaw, huisache and mesquite have a positive effect on the arid and semi-arid ecosystems as they increased soil organic matter and soil N content.     

基于二十面体剖分格网的球面实体表达与Voronoi图生成

在分析当前球面空间数据结构的基础上，讨论了利用Snyder等积投影在二十面体上建立球面空间基础剖分方式的思路，然后在初始投影面上采用六边形格网进行层次细分，获得多分辨率的全球铺盖。提出了基于六边形格网的三叶节点管理与瓦片编码的基本思路，确立了球面不同实体的六边形格网表达模式。在此基础上，提出了基于球面六边形铺盖的Voronoi图生成算法，实验验证了算法的正确性与效率。     

Deterioration of eelgrass,Zostera marina L., meadows by water pollution in Seto Inland Sea,Japan

Survival of transplanted Zostera marina L. (eelgrass) and environmental conditions (water quality, bottom sediments, sedimentation on leaves and flow regime) were studied concurrently in the center, edge, and at the outside of a eelgrass meadow located in a eutrophic coastal zone in northern Hiroshima Bay, Seto Inland Sea, Japan. Eelgrass transplants at the outside of the meadow declined significantly, whereas those at the center were consistently well established. Silt content in the bottom sediments at the outside was higher than that at the center. The sediment was oxic from the surface to 2 cm deep at the center, whereas those at the edge and the outside were reductive almost from the surface. The sediment characteristics typical in eutrophic water seemed to be a factor responsible for the deterioration of eelgrass meadows. Although suspended solid concentrations in the water columns were almost the same, the amount of sediments deposited on leaves of eelgrass at the outside was higher than that at the center of the meadow. The amount of the deposition at the outside seems to be enough to inhibit photosynthesis; i.e. photosynthetic photon flux density (PPFD) available for eelgrass was only 36% of that without any deposition. The deposition in the center, however, was small enough to allow 84% of the original PPFD. Flow rates, determined at 30 cm above the bottom, a half height of average eelgrass, suggested that the rate at the outside was not enough to remove deposited sediments from the surface of eelgrass leaves. Thus, the large amount of sediment deposition caused by water pollution and/or eutrophication seemed to be another factor to inhibit the survival of eelgrass at the outside edge of the meadow.     

Stable carbon isotope composition of terrestrial leaves: inter‐ and intraspecies variability,cellulose and whole‐leaf tissue difference,and potential for climate reconstruction

Stable carbon isotope analysis of terrestrial plant leaves preserved in Quaternary lake sediments has the potential to provide high‐resolution reconstructions of past climatic conditions. Preferably, δ¹³C measurements should be made on a single leaf component, e.g. cellulose, but this approach is often precluded by limited leaf availability. Previous work suggests that reliable palaeoclimatic information also may be derived from δ¹³C measurements on whole‐leaf tissue, given a similar degree of leaf decomposition between samples. Leaf δ¹³C data for 12 Scandinavian species of dwarf‐shrubs, shrubs and trees, and a comparison of δ¹³C data on recent and late Holocene Salix herbacea leaves, revealed that the δ¹³C signal registered by holocellulose is largely reflected by measurements on whole‐leaf tissue. Holocellulose was found to be consistently enriched in ¹³C, although this δ¹³C offset was smaller for subfossil leaves. This supports the use of δ¹³C measurements on whole‐leaf tissue for climate reconstruction, at least for leaves preserved in soft, late Holocene sediments with minimal diagenetic effects. Leaf carbon and nitrogen data on fresh leaves of the same 12 Scandinavian species, and corresponding data on late Holocene Salix herbacea leaves, suggest that the leaf C:N ratio is a suitable indicator of the degree of leaf decomposition. Copyright © 2003 John Wiley & Sons, Ltd.     

南极中山站电离图所显示的高纬现象

在南极中山站使用ＴＤ－４Ａ测高仪，从１９９０年３月至今已取得了１０万余帧的电离图记录。由于中山站处在极尖区附近这样一个特殊位置，所以这些电离图能显示出大多数高纬现象，诸如极光卵现象、ＦＬＩＺ（Ｆ层不均匀区）现象、倾斜Ｅｓ和空白现象、Ｆ区磁纬中午现象、Ｅ和Ｄ区的粒子沉降效应，以及粒子Ｅ层（夜间Ｅ层）现象等。本文对这些现象进行了描述和初步分析。     

A generalized layered radiative transfer model in the vegetation canopy

In this paper, a generalized layered model for radiation transfer in canopy with high vertical resolution is developed. Differing from the two-stream approximate radiation transfer model commonly used in the land surface models, the generalized model takes into account the effect of complicated canopy morphology and inhomogeneous optical properties of leaves on radiation transfer within the canopy. In the model, the total leaf area index （LAI） of the canopy is divided into many layers. At a given layer, the influences of diffuse radiation angle distributions and leaf angle distributions on radiation transfer within the canopy are considered. The derivation of equations serving the model are described in detail, and these can deal with various diffuse radiation transfers in quite broad categories of canopy with quite inhomogeneons vertical structures and uneven leaves with substantially different optical properties of adaxial and abaxial faces of the leaves. The model is used to simulate the radiation transfer for canopies with horizontal leaves to validate the generalized model. Results from the model are compared with those from the two-stream scheme, and differences between these two models are discussed.     

叶片水分含量光谱响应变化研究

植被光谱反射或发射特性是化学和形态学特征决定的,这种特性与植被发育、健康状态、含水量、叶绿素含量密切相关,植物的水分胁迫状况能够在光谱反射率数据中有所体现。本文通过实验研究野外活体植物叶片和采集下的叶片随着水分流失波谱曲线变化的规律,并发现随不同的叶片水分损失率,红边、与红边相关的参数及波形呈现不同的变化。     

基于空间特征的蚀变信息提取研究

为了实现在植被覆盖区提取蚀变信息,本文依据地物波谱理论,结合研究区地质控矿构造特征,分析特征数据空间载荷因子特征和工作区内已知矿床、矿点及矿化点附近异常色调的不同空间特征的灰度值,以及异常色调的空间特征分布概率,建立适合北方落叶时相多光谱数据的多元统计蚀变信息提取模型。该模型成功地应用于吉林省东部小西南岔地表植被严重区蚀变信息提取研究,取得较好的效果。     

GPS scintillation studies in the arctic region during the first winter-phase 2008 Indian Arctic Expedition

We present the results of scintillation studies based on the data obtained during the first winter-phase Indian Arctic Expedition in March 2008 at the Indian Himadri Station, Ny-Ålesund (78.9°N, 11.9°E), in the vicinity of the daytime cusp and under the nightside polar cap. A global-positioning-system ionospheric scintillation and TEC monitor (GISTM) receiver (model GSV4004A) was used to record scintillations and the total electron content (TEC). The polar ionosphere is more sensitive to phase than to amplitude scintillations. Occurrence of amplitude scintillation is confined to well-defined regions, while phase scintillation shows a strong characterization both in magnetic latitude and magnetic local time. Occurrence of amplitude and phase scintillation increases during disturbed compared with quiet days. During disturbed days, the phase-scintillation region is displaced towards lower latitudes, following the auroral oval. The observed noon peak in scintillation occurrence may indicate that the irregularities that generate scintillation are caused by precipitation in the daytime cusp/cleft region. A significant enhancement of the TEC and the rate of change of the TEC index (ROTI) signified transits of polar-cap patches across different satellite trajectories during geomagnetic storms. We found that patches are most likely to occur when IMF Bz is southward and/or K_p > 4. Loss of signal lock was more for the L2 signal than for L1, and shows a maximum in the morning sector. Positional errors tend to increase during disturbed conditions.