阔叶红松混交林林隙内丘坑复合体特征及分布格局

对小兴安岭凉水国家级自然保护区红松阔叶混交林不同大小林隙及郁闭林分内丘坑复合体特征及分布格局进行了对比和分析.结果表明： 大、中、小林隙及郁闭林分中丘坑复合体的丘宽、丘高、丘厚均大于与之对应的坑宽、坑长、坑深.大林隙内丘坑复合体的丘宽、丘高、丘厚、坑宽、坑长、坑深均最大,分别为2.85、0.37、2.00、2.99、2.10、0.39 m;郁闭林分均最小,分别为2.35、0.19、1.60、2.66、1.65、0.21 m.丘的平均体积（1.66 m³）均大于坑的（1.44 m³）.同一大小林隙内绝大多数丘坑复合体之间的特征值差异显著,而郁闭林分内绝大多数丘坑复合体之间的特征值差异不显著.不同大小林隙及郁闭林分丘坑复合体之间的特征值大多差异显著.2012年样地内丘坑复合体大多数特征值显著小于2011年.89.5%和60.5%的丘坑复合体类型为铰链式,形状为半椭圆状,丘坑复合体的分布格局为相对集中.     

Stochastic simulations of nanoparticle internalization through transferrin receptor dependent clathrin-mediated endocytosis

Background

Receptor dependent clathrin-mediated endocytosis (CME) is one of the most important endocytic pathways for the internalization of bioparticles into cells. During CME, the ligand-receptor interactions, development of clathrin-coated pit (CCP) and membrane evolution all act together to drive the internalization of bioparticles. In this work, we develop a stochastic computational model to investigate the CME based on the Metropolis Monte Carlo simulations.

Ultrastructure of the ciliary pits in the Geocentrophora group (Platyhelminthes,Lecithoepitheliata)

The ultrastructure of the paired lateral ciliary pits in several endemic species of Geocentrophora from Lake Baikal and in one cosmopolitan species, G. baltica, has been compared and the possible functional significance is discussed. The pit is composed of two distinctive parts; the bottom of the pit is an extensive sensitive area, filled with uni-and biciliary sensory receptors with reduced rootlets and numerous neurotubules. The walls of the pit are formed by several large dark cells, characterized by a dark cytoplasm with numerous mitochondria, a large nucleus, intracellular canaliculi, basal infoldings of the cell membrane, glycogen granules and a varying number of cilia. A protruding, densely ciliated ridge occurs along the anterior wall of the pit. The cilia have a strengthened rootlet system and seem to provide a strong water current into the pit. Dark cell processes penetrate the basement membrane of the pit and come into the vicinity of large cells with a cytoplasm similar to that of the dark cells of the pit. These large cells in their turn come close to the terminal parts of the protonephridial canals, containing a weir. Smaller protonephridial capillaries without a weir seem to open directly into the pit lumen. The morphological data obtained suggest that the ciliary pit in not only a sensory structure, but plays a part in osmoregulation and ion exchange as well.     

Post‐Hurricane Regeneration of Pioneer Plant Species in South Florida Subtropical Hardwood Hammocks1

After Hurricane Andrew crossed southern Florida (U.S.A.) on 24 August 1992, native and exotic pioneer species in subtropical hardwood forests (hammocks) regenerated from seed banks. Regeneration occurred in hammocks of metropolitan Dade County and the Long Pine Key region of Everglades National Park. The density of the native pioneer Trema micrantha was significantly higher in hammocks of Long Pine Key than in those of metropolitan Dade County. In contrast, the basal area of the exotic pioneer Carica papaya was greater in Dade County hammocks than Long Pine Key hammocks. Although T. micrantha tended to be restricted to areas of soil disturbance (tip‐up pits) formed by trees uprooted during Hurricane Andrew, especially in Long Pine Key, C. papaya was located throughout hammocks. These results suggest differences in the regeneration niches in which the native T. micrantha required more specific disruptions (i.e., both canopy and soil) than C. papaya (only removal of canopy) for establishment. A broad regeneration niche could in part account for the capability of an exotic species with a dormant seed bank to invade native subtropical forests following natural large‐scale disturbances.     

Structural determinants of increased susceptibility to dehydration‐induced cavitation in post‐fire resprouting chaparral shrubs

It is well established that transpiration and photosynthetic rates generally increase in resprouting shoots after fire in chaparral shrublands. By contrast, little is known about how plant hydraulic function varies during this same recovery period. We hypothesized that vascular traits, both functional and structural, would also shift in order to support this heightened level of gas exchange and growth. We examined stem xylem‐specific hydraulic conductivity (K_s) and resistance to cavitation (P₅₀) for eight chaparral shrub species as well as several potential xylem structural determinants of hydraulic function and compared established unburned plants and co‐occurring post‐fire resprouting plants. Unburned plants were generally more resistant to cavitation than resprouting plants, but the two groups did not differ in K_s. Resprouting plants had altered vessel structure compared with unburned plants, with resprouting plants having both wider diameter vessels and higher inter‐vessel pit density. For biomechanics, unburned plants had both stronger and denser stem xylem tissue than resprouting plants. Shifts in hydraulic structure and function resulted in resprouting plants being more vulnerable to dehydration. The interaction between time since disturbance (i.e. resprouting versus established stands) and drought may complicate attempts to predict mortality risk of resprouting plants.     

广西野生蔗及其近缘植物营养器官内部结构的初步研究

广西野生蔗及其近缘植物营养器官内部结构基本相同。但割手密叶片下表皮具有明显的气孔窝斑茅等则无。斑茅茎节间的维管束分布较均匀,河八王茎中央没有维管束分布,割手密与蔗茅茎中维管束的分布。居于二者之间。     

浓香型白酒发酵过程中窖内古菌群落分布特征

泥窖池多菌种固态发酵是浓香型白酒的典型特点,其中古菌是重要的酿造功能菌,但目前对发酵过程古菌的群落分布及多样性尚缺乏研究。采用高通量测序技术,分析了浓香型白酒发酵过程酒醅与窖泥中古菌的生物量、群落组成与演替规律,并通过共现性网络分析了古菌与细菌的潜在互作关系。结果表明,窖泥中古菌平均生物量约是酒醅的200倍,两者之间古菌群落的结构差异不显著(r=0.017,P=0.074),但演替规律存在显著相关性(r=0.30,P=0.03)。甲烷杆菌属Methanobacterium是酒醅与窖泥中丰度占比最高的古菌,其他优势群类依次为甲烷八叠球菌属Methanosarcina、甲烷粒菌属Methanocorpusculum、甲烷囊菌属Methanoculleus和甲烷短杆菌属Methanobrevibacter。共现性网络分析显示甲烷杆菌属在酒醅与窖泥中与多数细菌为正相关,特别是与窖泥中主要细菌氢孢菌属Hydrogenispora和产己酸菌属Caproiciproducens。研究结果揭示了浓香型白酒窖池中古菌群落的时空分布特点及潜在功能。     

The comparative morphology of pit organs in elasmobranchs

The pit organs of elasmobranchs (sharks, skates and rays) are free neuromasts of the mechanosensory lateral line system. Pit organs, however, appear to have some structural differences from the free neuromasts of bony fishes and amphibians. In this study, the morphology of pit organs was investigated by scanning electron microscopy in six shark and three ray species. In each species, pit organs contained typical lateral line hair cells with apical stereovilli of different lengths arranged in an “organ‐pipe” configuration. Supporting cells also bore numerous apical microvilli taller than those observed in other vertebrate lateral line organs. Pit organs were either covered by overlapping denticles, located in open grooves bordered by denticles, or in grooves without associated denticles. The possible functional implications of these morphological features, including modification of water flow and sensory filtering properties, are discussed. J. Morphol. 2009. © 2009 Wiley‐Liss, Inc.     

Effects of larval antlions Euroleon nostras (Neuroptera, Myrmeleontidae) and their pits on the escape-time of ants

Abstract. Pit-building antlions are predators with a unique predation strategy, namely using pitfall traps constructed in loose sand to catch prey. Here, prey escape-time in the field is measured by introducing ants into one of four different treatment arenas. The first treatment lacks pits and antlions, the second includes 10 antlions that did not build pits, the third comprises eight artificially constructed pits, and the fourth is a treatment of eight antlions in pits and two without pits. Their pits are of a similar size to those used in the third treatment. When antlions are present without constructing pits, they impede the dispersal of prey. The mean escape-time for one half of the released ants is twice as long with antlions present as without them. When pits are present, the time taken for one half of the released ants to escape the predator is more than 10 times as long as when pits are absent. Escape-time from artificial pits is three times that from nonpit building antlions. Pits hinder the escape of ants and therefore increase the amount of time that the prey is available for capture. In the area where the pits are occupied by antlions, escape-time is four times longer than in a treatment with similar sized artificial pits. Thus, it appears that not only a pit, but also the presence of antlions influences the capture success.     

干旱砾漠区露天采煤对草地植物群落特征及其稳定性影响

露天煤炭开采对区域地形地貌、水文循环和土壤植被等生态环境因子产生了较大干扰,但干旱砾漠区露天开采对周边植物群落及其稳定性的影响范围和程度仍有待深入研究,这个问题的探明才能为矿区植被恢复的精准施策提供科学依据。该文通过定量比较距露天开采区不同距离植物群落组成、多样性、生产力和稳定性变化特征,分析干旱砾漠区露天采煤对植物群落的影响范围和程度,并结合土壤性状和微气象因子的测量,探究影响干旱矿区植物群落特征的主导因子。结果表明:(1)干旱砾漠区露天开采排土场原始植被消失殆尽,开采区外围0~500 m范围内原优势物种重要值降低,伴生物种重要值增加,500 m后随着距开采区距离的增加优势植物重要值逐渐增加,至开采区800 m外植物群落组成趋于稳定;(2)开采区外围0~500 m范围内植物群落地上生物量、多样性和群落稳定性较5000 m处分别平均下降了53%、70%和37%,开采区500 m以外上述群落指标整体上变化不明显,而植被覆盖度在开采区外围不同距离并未表现出显著变化趋势;(3)土壤水分、有机质、有效氮磷钾、可溶性盐与植物群落地上生物量、多样性和稳定性呈正相关关系,而土壤pH、光照强度和地表温度与上述植物群落指标呈负相关关系。因此干旱砾漠区露天开采排土场及开采区外围0~500 m范围是矿区生态修复过程中重点考虑区域,同时研究表明干旱砾漠区植被主要分布在砾漠戈壁浅沟和季节性河道等生境相对良好的凹陷微地形条件下,综合可得出干旱砾漠区植被修复过程中可通过微地形塑造、土壤改良和乡土物种繁殖促进,以实现干旱矿区生态系统的稳定和可持续发展。