外来入侵种紫茎泽兰竞争策略与扩散动态

紫茎泽兰（Eupatorium adenophorum Spreng.）作为重要的外来入侵种之一，已严重破坏了入侵地生态系统的结构与功能，同时使当地农林业生产蒙受巨大的损失。因此，明确紫茎泽兰的竞争策略与扩散潜力，对制定合理的控制措施具有重要意义。 土壤氮素增加常常有助于外来种的入侵，那么降氮能否抵制入侵呢？向土壤中添加碳素，增强微生物对氮素的吸收，从而降低土壤中可被植物吸收的氮素是目前常用的降氮方法。为检验这一假说对入侵种紫茎泽兰的适用性，选取入侵种紫茎泽兰和本地种禾本科雀麦（Bromus japonicus）、菊科鱼眼草（Dichrocephala integrifolia），分别单栽或与紫茎泽兰混栽，向各植物组合中添加碳素（按1650克有机质/平方米计）或氮素（按30克氮素/平方米计），并设立对照进行盆栽实验。在碳素添加条件下，紫茎泽兰地上与地下生物量分别比对照降低了71.9% 和 74.9%，而本地种的生物量却没有受到显著影响。同时，碳素添加导致紫茎泽兰对本地种的竞争强度（RII）明显下降。氮素添加则减弱或逆转了上述碳素的作用。因此，向土壤中添加碳素有助于抵抗氮沉降对外来种入侵的促进作用，特别对抵御那些与氮素有亲和力的入侵种更为有效。在不同氮素条件下，紫茎泽兰对本地种竞争中，资源竞争强度均明显大于化感作用。尽管在紫茎泽兰发育早期化感作用较小，但是，碳素添加使紫茎泽兰可利用氮素减少，激发了化感作用在竞争中占有更大的比例，说明资源竞争与化感是相互结合、共同发挥作用的。 去叶作为模拟采食方法之一，至少可以通过两种方式影响植物竞争。一是去叶对目标种生长产生负面影响，二是邻种去叶有利于目标种生长，进而改变种间竞争关系。基于以上假定，对紫茎泽兰与相邻本地种分别单栽、同种合栽和异种混栽，进行去叶处理。结果恰与假定相悖：在整个生长季内，去叶增加目标株生物量的1.0 – 198.9%。对于入侵种而言，当邻居本地种去叶时，紫茎泽兰能完全弥补竞争产生的负面效应，即它与未去叶的单栽紫茎泽兰生长无显著差异;而紫茎泽兰去叶降低了相邻本地种的生长，加剧了原本由于竞争给对本地种带来的负面影响。因此，去叶效应与邻种的存在与否及邻种的类型均有关。在应用生物控制对目标株采食时，特别是在没有造成严重伤害或致死情况下，可以使本来具有竞争优势的入侵种变得更具强势。竞争与去叶之间存在复杂的相互作用，采食带来的间接效应可能比预想的更为复杂。因此，在生物控制措施实施之前，充分地估计生物控制的间接作用至关重要。 为检验反应—扩散模型（reaction–diffusion model）能否正确模拟紫茎泽兰小尺度扩散速率，本研究调查了四川攀枝花山区5个不同的生境的紫茎泽兰群落。对各样地内紫茎泽兰定位和年龄确定，基于克里金插值法做出其入侵格局的等年线图，通过等年线之间的垂直距离即可得到紫茎泽兰扩散速率的经验值。同时，计算内禀增长率和扩散系数，根据模型计算得到扩散速率的预测值。结果表明：紫茎泽兰扩散速率经验值明显小于模型预测值。因此，尽管反应—扩散模型已在大尺度扩散预测方面得到广泛的应用和验证，但在小尺度上，由于没有借助于复杂的生活史模型和分层模型，单凭反应—扩散模型不足以得到准确的预测。另外，在没有遭受干扰的生境中，可以发现紫茎泽兰扩散早期存在明显的时滞期。倘若这种时滞效应在入侵扩散中是频繁发生的，那么在判定物种是否具有入侵性时，很可能由于物种处于时滞期而被误认为非入侵种。 基于紫茎泽兰入侵至中国60年来所收集到的441已知分布记录和23个环境变量，采用GARP模型对其潜在分布范围做出了预测，并通过Kappa和ROC（receiver–operator characteristic）对预测结果进行检验。结果表明紫茎泽兰目前分布以云贵高原为主体，逐渐向四川盆地东部、山东半岛、东南沿海、台湾沿海以及海南岛等地扩散。冷季降水量、年极端低温和年均最高温对分布影响较大。RDA（Redundancy Analysis）分析结果显示温度和降水是限制紫茎泽兰扩散的重要因素。在过去的20年里，紫茎泽兰已经从温度较高、天气波动较小的亚热带气候逐渐向气候温凉、降水减少的高海拔地区扩散。紫茎泽兰可以适应相对较宽的温度和降水梯度，年均温度在10—22 ˚C，年降水量在800—2000 mm区间均有分布。本研究结果为发展早期预警工作、防止紫茎泽兰在中国进一步入侵提供了科学依据。

Competition between Stipa grandis and Cleistogenes squarrosa

Competitive strategy for resources between Cleistogenes squarrosa (Trin.) Keng which is a dominant species of grasslands degraded by moderate-heavy grazing, and Stipa grandis P. Smirnov, which is a dominant species of ungrazed communities, was studied using a replacement series method in a greenhouse. The knowledge would be helpful in managing grasslands and restoring the degraded C. squarrosa grassland. Although there was neither inter- nor intra-specific competition between the two species when no nutrients were added, intra-specific competition of C. squarrosa was observed and increased with increased nutrient availability and more sulfur (S) was allocated to the aboveground partition of the plant. Relative competitive ability of C. squarrosa was greater than that of S. grandis when nutrients were supplied regardless of S. There was no significant difference between shoot and root competition based on dry matter yields. However, root competition was significantly greater than that of shoot based on S uptake under all treatments. A significant interaction was not observed between shoot and root competition. Therefore, nutrients addition benefits the restoration of degraded grassland of C. squarrosa, which may not exclude S. grandis. Also productivity and forage quality of the community will be increased. (C) 2007 Elsevier Ltd. All rights reserved.

Two-Point Closure Strategy in the Mapping Closure Approximation Approach

A two-point closure strategy in mapping closure approximation (MCA) approach is developed for the evolution of the probability density function (PDF) of a scalar advected by stochastic velocity fields. The MCA approach is based on multipoint statistics. We formulate a MCA modeled system using the one-point PDFs and two-point correlations. The MCA models can describe both the evolution of the PDF shape and the rate at which the PDF evolves.

Competitive protein adsorption studied with atomic force microscopy and imaging ellipsometry

The adsorption and competitive adsorption of collagen and bovine serum albumin (BSA) were directly visualized and quantified using atomic force microscopy (AFM) and imaging ellipsometry. Chemically modified silicon surfaces were used as hydrophilic and hydrophobic substrates. The results showed that collagen and BSA in single component solution adsorbed onto a hydrophobic surface two times more than that onto a hydrophilic surface. The competitive adsorption between collagen and BSA showed that serum albumin preferentially adsorbed onto a hydrophobic surface, while collagen on a hydrophilic surface. In the binary solution of BSA (1 mg/ml BSA) and collagen (0.1 mg/ml), nearly 100% of the protein adsorbed onto the hydrophobic surface was BSA, but on the hydrophilic surface only about 6% was BSA. Surface affinity was the main factor controlling the competitive adsorption.

Competitive adsorption between bovine serum albumin and collagen observed by atomic force microscope

Atomic force microscopy (AFM) was used to study the competitive adsorption between bovine serum albumin (BSA) and type I collagen on hydrophilic and hydrophobic silicon wafers. BSA showed a grain shape and the type I collagen displayed fibril-like molecules with relatively homogeneous height and width, characterized with clear twisting (helical formation). These AFM images illustrated that quite a lot of type I collagen appeared in the adsorption layer on hydrophilic surface in a competitive adsorption state, but the adsorption of BSA was more preponderant than that of type I collagen on hydrophobic silicon wafer surface. The experiments showed that the influence of BSA on type I collagen adsorption on hydrophilic surface was less than that on hydrophobic surface.

Competitive adsorption of collagen and bovine serum albumin - effect of the surface wettability

The competitive adsorption of collagen and bovine serum albumin (BSA) on surfaces with varied wettability was investigated with imaging ellipsometry, and ellipsometry. Silane modified silicon surfaces were used as substrates. The results showed that surface wettability had an important effect on protein competitive adsorption. With the decrease of surface wettability, the adsorption of collagen from the mixture solution of collagen and BSA decreased, while the adsorption of BSA increased. (C) 2003 Elsevier B.V. All rights reserved.

A new strategy of enhancing two-photon absorption in benzothiazole-containing fluorene molecules: Introduction of auxiliary donor-acceptor effects

A series of benzothiazole-containing fluorene molecules have been designed and their one- and two-photon absorption properties have been investigated theoretically by using the ZINDO method. The effects of electron-excessive/deficient heterocyclic bridges as auxiliary donors (auxD)/acceptors (auxA) on TPA cross-sections were studied. The results show that the molecules with D-pi-auxA-A, D-aux D-pi-A, or D-auxD-pi-auxA-A structure types have large TPA cross-section, which can be a valuable strategy in the design of two-photon absorption materials. Also, a linear relationship between the first hyperpolarizability and the TPA cross-section is observed. (c) 2006 Elsevier B.V. All rights reserved.

Dual-wavelength competitive output in Nd:Y3Sc1.5Al3.5O12 ceramic disk laser

In this paper, we demonstrated a dual-wavelength competitive output in Nd:Y3SC1.5Al3.5O12 ceramic disk laser. Different dual-wavelength output behaviors for Nd:YSAG and Nd:YAG ceramic disk laser were investigated and discussed. By applying the energy transfer model, we suggested the reasonable explanation for this new phenomenon as the disordered replacing of Al3+ ions by Sc3+ ions. The main advantage of the dual-wavelength ceramic laser is the possibility to serve as the seed source to generate Terahertz radiation. (C) 2008 Elsevier B.V. All rights reserved.