克隆植物对异质性生境的适应对策研究

植物的生境在时间和空间上都是异质性的，即使在很小的尺度上这种异质性也是存在的。克隆生长使得克隆植物在理论上更适应利用异质性环境，本文以几种克隆植物为对象，采用实验生态学方法，着重从生理生态特性、信号物质传导方面探讨克隆植物对异质性环境的适应对策。 以匍匐茎克隆植物野草莓(Fragaria vesca)为对象，研究了不同海拔梯度种群(1800m和3900m)对光照和养分资源斑块性分布生境的响应。研究结果显示：与资源的空间同质性处理(I) 和(II) 相比, 资源的空间异质性处理(III) 和(IV) 两个种群野草莓的近端、远端和整个克隆片段的生物量和分株数均获得显著增加。经历低光高养近端分株与经历高光低养的远段分株相连时，相比与低光高养的同质生境，来自两个海拔的种群分配更多的生物量到根；经历高光低养近端分株与经历低光高养远端分株相连时，相比于高光低养的同质生境，来自两个海拔的种群分配更少的生物量到根，类似的生物量分配格局在远端分株也被观察到。相比于高光低养同质性生境，当与低光高养远端分株相连时经历高光低养近端分株有更大的叶面积；相比于高光低养同质性生境，当与低光高养近端分株相连时经历高光低养远端分株有更大叶面积。实验结果表明, 资源交互斑块性生境中野草莓发生了克隆内分工。通过克隆内分工, 克隆植物能有效的利用异质性分布的资源, 缓解资源交互斑块性分布对克隆植物生长的不利影响。 以匍匐茎克隆植物蛇莓(Duchesnea indica)为对象, 研究其在高光照低水分斑块和低光照高水分斑块组成的资源交互斑块性生境中的克隆内分工。结果显示，当生长于高光照低水分(HL)条件下近端分株(basal ramets)与生长于低光照高水分(LH)条件下的远端分株(apical ramets)之间的匍匐茎连接时，近端分株根冠比显著下降，而远端分株根冠比显著增加，近端分株叶面积和远端分株总根长显著增加；当与低光照高水分条件下的远端分株相连时，近端分株叶片光合速率和叶绿素含量也相应增加。此外，克隆分株间资源交互传输显著提高蛇莓的生长表现（生物量和分株数）。因此，在光、水资源交互斑块性环境中克隆植物蛇莓分株在生物量分配、资源获取器官形态和生理特性方面发生了环境诱导的功能特化。这种对局部丰富资源的趋富特化在一定的程度上增强了克隆分株对资源的吸收利用能力，克隆内资源共享有助于缓解资源交互性斑块生境对克隆植物生长的不利影响，有效地提高克隆植物在其生境中存活与定居能力。 一个盆栽实验被采用以便调查克隆整合对经受局部沙埋的根状茎克隆植物沙生苔草(Carex praeclara)的影响，结果显示随着沙埋深度的增加，切断分株间的根状茎连接将显著降低经受沙埋处理分株的存活。当克隆植物经历局部沙埋时，切断分株间根状茎连接对其克隆生长（生物量、分株数和叶片数量）有显著负影响。耗-益(cost-benefit)分析显示，当与经历沙埋处理的远端分株相连时，近端分株的生长表现没有遭受任何负面影响。与经历沙埋处理远端分株相连时，近端分株的光合能力随沙埋深度的增加而增加。分株间的源-汇反馈调节机制所导致的补偿性反应减缓了局部沙埋对克隆植物生长的负效应。因此，克隆整合有助于提高经历局部沙埋克隆植物的存活，克隆植物在沙化地区植被恢复与重建方面具有重要意义。 克隆植物分株间的匍匐茎或根状茎连接不仅可以传输水分、矿质养分、光合产物，而且还可以传输信号物质。以根状茎克隆植物黑褐苔草(Carex alrofusca)为对象，采用盆栽实验研究外源茉莉酸诱导克隆片段相连分株间信号物质传导。结果显示，相比中龄和老龄分株，幼年分株对1mM茉莉酸诱导有显著反应。茉莉酸引起幼年分株叶片浓缩单宁含量显著增加，同时其叶片可溶性碳水化合物和氮含量降低。茉莉酸诱导后，幼年分株被昆虫咬食叶面积比率显著下降。因此匍匐茎或根状茎传也是克隆植物分株间信号物质传导重要通道，克隆植物通过分株间的风险扩散策略增强了对幼嫩植物组织器官的保护，这对克隆植物的存活或生长具有重要意义。

Electro-Osmotic Flow and Mixing in Heterogeneous Microchannels

Analytical and numerical studies of secondary electro-osmotic flow EOF and its mixing in microchannels with heterogeneous zeta potentials are carried out in the present work. The secondary EOFs are analyzed by solving the Stokes equation with heterogeneous slip velocity boundary conditions. The analytical results obtained are compared with the direct numerical simulation of the Navier-Stokes equations. The secondary EOFs could transport scalar in larger areas and increase the scalar gradients, which significantly improve the mixing rate of scalars. It is shown that the heterogeneous zeta potentials could generate complex flow patterns and be used to enhance scalar mixing.

State Vector: A New Approach to Prediction of the Failure of Brittle Heterogeneous Media and Large Earthquakes

The concept of state vector stems from statistical physics, where it is usually used to describe activity patterns of a physical field in its manner of coarsegrain. In this paper, we propose an approach by which the state vector was applied to describe quantitatively the damage evolution of the brittle heterogeneous systems, and some interesting results are presented, i.e., prior to the macro-fracture of rock specimens and occurrence of a strong earthquake, evolutions of the four relevant scalars time series derived from the state vectors changed anomalously. As retrospective studies, some prominent large earthquakes occurred in the Chinese Mainland (e.g., the M 7.4 Haicheng earthquake on February 4, 1975, and the M 7.8 Tangshan earthquake on July 28, 1976, etc) were investigated. Results show considerable promise that the time-dependent state vectors could serve as a kind of precursor to predict earthquakes.

Catastrophic Rupture Induced Damage Coalescence in Heterogeneous Brittle Media

In heterogeneous brittle media, the evolution of damage is strongly influenced by the multiscale coupling effect. To better understand this effect, we perform a detailed investigation of the damage evolution, with particular attention focused on the catastrophe transition. We use an adaptive multiscale finite-element model (MFEM) to simulate the damage evolution and the catastrophic failure of heterogeneous brittle media. Both plane stress and plane strain cases are investigated for a heterogeneous medium whose initial shear strength follows the Weibull distribution. Damage is induced through the application of the Coulomb failure criterion to each element, and the element mesh is refined where the failure criterion is met. We found that as damage accumulates, there is a stronger and stronger nonlinear increase in stress and the stress redistribution distance. The coupling of the dynamic stress redistribution and the heterogeneity at different scales result in an inverse cascade of damage cluster size, which represents rapid coalescence of damage at the catastrophe transition.

The Heterogeneous Growth of P(3MeTh)--An Ellipsometric Study

Successive thicker P(3MeTh) layers are analysed by ex situ conventional and imaging ellipsometry. Thin films display a smooth surface, are compact and homogeneous while for a growth charge above 20 mC cm(-2) the polymer structure modifies to a still uniform but less dense layer. A two-layer model is used and a mathematical procedure is developed to obtain, simultaneously, from the experimental ellipsometric parameters, Delta and Psi, the thickness and the complex refractive index of P(3MeTh) films grown up to 80 mC cm(-2). Thicker polymer layers are disordered and present a high degree of surface roughness. 

Long-Range Stress Redistribution Resulting From Damage in Heterogeneous Media

It has been shown in CA simulations and data analysis of earthquakes that declustered or characteristic large earthquakes may occur with long-range stress redistribution. In order to understand long-range stress redistribution, we propose a linear-elastic but heterogeneous-brittle model. The stress redistribution in the heterogeneous-brittle medium implies a longer-range interaction than that in an elastic medium. Therefore, it is surmised that the longer-range stress redistribution resulting from damage in heterogeneous media may be a plausible mechanism governing main shocks.

Adaptive Mesh Refinement FEM for Damage Evolution of Heterogeneous Brittle Media

Damage evolution of heterogeneous brittle media involves a wide range of length scales. The coupling between these length scales underlies the mechanism of damage evolution and rupture. However, few of previous numerical algorithms consider the effects of the trans-scale coupling effectively. In this paper, an adaptive mesh refinement FEM algorithm is developed to simulate this trans-scale coupling. The adaptive serendipity element is implemented in this algorithm, and several special discontinuous base functions are created to avoid the incompatible displacement between the elements. Both the benchmark and a typical numerical example under quasi-static loading are given to justify the effectiveness of this model. The numerical results reproduce a series of characteristics of damage and rupture in heterogeneous brittle media.

Catastrophic Rupture Induced Damage Coalescence in Heterogeneous Brittle Media

In heterogeneous brittle media, the evolution of damage is strongly influenced by the multiscale coupling effect. To better understand this effect, we perform a detailed investigation of the damage evolution, with particular attention focused on the catastrophe transition. We use an adaptive multiscale finite-element model (MFEM) to simulate the damage evolution and the catastrophic failure of heterogeneous brittle media. Both plane stress and plane strain cases are investigated for a heterogeneous medium whose initial shear strength follows the Weibull distribution. Damage is induced through the application of the Coulomb failure criterion to each element, and the element mesh is refined where the failure criterion is met. We found that as damage accumulates, there is a stronger and stronger nonlinear increase in stress and the stress redistribution distance. The coupling of the dynamic stress redistribution and the heterogeneity at different scales result in an inverse cascade of damage cluster size, which represents rapid coalescence of damage at the catastrophe transition.

Habitat degradation and conservation status assessment of gallinaceous birds in the Trans-Himalayas, China

The greatest concentration of Chinese Galliformes occurs in the Trans-Himalayas. We selected 4 northwestern Yunnan counties (Lijiang, Shangri-la, Deqin, and Weixi) in the Trans-Himalayas to assess the conservation status of 9 gallinaceous forest birds. We

Habitat use by wintering Ruddy Shelduck at Lashihai Lake, Lijiang, China

Habitat use by wintering Ruddy Shelduck (Tadorna ferruginea) in Lijiang Lashihai Lake of southwest China was studied from 1 November 1999 to 29 April 2000. We divided habitats into five types-deep water, shallow water, mudflat, grassland and farmland. Shallow water and grassland, with rich food and easily accessible water, were preferred by wintering Ruddy Shelducks, Farmland was preferred in mid-winter but avoided in early winter and late winter. Even in mid-winter, the feeding Ruddy Shelduck on farmland were not equally distributed in fields and preferred wet fields (just irrigated) and avoided dry fields. In dry fields, the distances to water sources had great impact on the feeding distribution. Mudflats were only selected in later winter, coinciding with the growth of water-weeds. Deep-water areas were always avoided. Prohibition of human disturbance and retaining shallow water areas and grassland are important measures to mitigate conflict between Ruddy Sheldruck and local people.

Molecular phylogeography and population structure of a mid-elevation montane frog Leptobrachium ailaonicum in a fragmented habitat of southwest China

Leptobrachium ailaonicum is a vulnerable anuran restricted to a patchy distribution associated with small mountain streams surrounded by forested slopes at mid-elevations (approximately 2000-2600 m) in the subtropical Mount Wuliang and Mount Ailao ranges in southwest China (Yunnan Province) and northern Vietnam. Given high habitat specificity and lack of suitable habitat in lower elevations between these ranges, we hypothesized limited gene flow between populations throughout its range. We used two mitochondrial genes to construct a phylogeographic pattern within this species in order to test our hypothesis. We also examined whether this phylogeographic pattern is a response to past geological events and/or climatic oscillations. A total of 1989 base pairs were obtained from 81 individuals of nine populations yielding 51 unique haplotypes. Both Bayesian and maximum parsimony phylogenetic analyses revealed four deeply divergent and reciprocally monophyletic mtDNA lineages that approximately correspond to four geographical regions separated by deep river valleys. These results suggest a long history of allopatric separation by vicariance. The distinct geographic distributions of four major clades and the estimated divergence time suggest spatial and temporal separations that coincide with climatic and paleogeographic changes following the orogeny and uplift of Mount Ailao during the late Miocene to mid Pliocene in southwest China. At the southern distribution, the presence of two sympatric yet differentiated clades in two areas are interpreted as a result of secondary contact between previously allopatric populations during cooler Pleistocene glacial cycles. Analysis of molecular variance indicates that most of the observed genetic variation occurs among the four regions implying long-term interruption of maternal gene flow, suggesting that L ailaonicum may represent more than one distinct species and should at least be separated into four management units corresponding to these four geographic lineages for conservation. (C) 2009 Elsevier Inc. All rights reserved.