土壤-植物系统水分运移过程的阻容电模拟

把土壤-植物系统水分运移作为一维水流运动由阻容电路进行模拟,在于将D arcy-R ichards方程从对单点的描述扩展到对一段流路的描述。由此出发,考虑到水流的非稳态性,某一流路的水阻定义为其水势差与平均流量之比,水容为其贮水量对平均水势的导数。与D arcy-R ichards方程相对应,水阻、时间常数分别为导水度、水分扩散度的倒数,相应地单位化的水阻率、比时间常数分别为导水率、水分扩散率的倒数。把SP系统沿水流通道分为若干部分,每一局部的水阻与其水容相并联,各局部间相串联。在此基础上,文章给出了土壤-植物系统水流模拟通式、总水容与分水容间的关系式、总水阻与分水阻间的关系式及特定条件下叶水势随时间变化的关系式。     

A model of diffusion and mass flow of water in cylindrical membrane systems with application to plant roots

Summary Measurements of the radial diffusion of tritiated water, combined with axial and radial flow in an artificial cylindrical membrane, are examined with the aid of a mathematical model. The results are used to assess how far measurement of diffusion of labeled water in plant roots may throw light on pathways of movement of water and on barriers to flow.     

类固醇雌激素在土壤-植物体系中的迁移转化及其毒理效应

类固醇雌激素(steroidal estrogens, SEs)作为典型的内分泌干扰物,在环境介质中被广泛检出,其进入生物体后可模拟细胞内源性激素作用对生物体生长、发育、生殖等产生不利影响,因此越来越引起关注。目前关于SEs的研究报道多集中于粪便、土壤、水体等介质中的检出及环境行为,以及SEs在水生生物体内的迁移和转化,其累积效应及其机制研究较为系统和全面。相较而言,SEs在土壤-植物体系中的迁移累积报道较少,但是对于掌握农田系统中SEs迁移转化的需求更为迫切。结合现有的国内外相关研究,总结了SEs在土壤-植物体系中的吸收累积和迁移转化行为特征,概述了植物吸收代谢SEs的影响因素以及SEs对植物生长发育的毒理效应。目前针对SEs的植物体吸收大多数仍基于室内模拟实验,对于其在土壤-植物多相态体系中迁移转化机理尚不清楚。因此,对今后的研究方向提出以下几点建议:(1)除室内模拟实验外,对实际土壤-植物系统中的研究更具价值,特别是SEs土壤-土壤水-植物多相态体系中的迁移转化等过程;(2)应结合SEs的来源,探究畜禽粪便、城市污泥及污水等不同源SEs对植物吸收、累积污染物的影响及污染风险;(3)加强对农作物体内SEs残留的监测和风险评估,制定SEs农作物检出及人体摄入的相关标准。     

A mathematical model for water and nutrient uptake by plant root systems

This article deals with modelling the simultaneous uptake of water and highly buffered nutrient, such as phosphate, by root branching structures from partially saturated soil. We use the simultaneous water and nutrient uptake model to investigate the effect that water movement has on nutrient uptake. With the aid of this model we are also able to show that the previous models by Barber and Tinker and Nye systematically underestimated the phosphate uptake, due to the oversimplified approach in dealing with root branching structure. In this article we show how this discrepancy can be remedied and the root branching structure included in the models of plant nutrient uptake. We will also discuss the differences in the results for continuous and spot fertilization combined with variable rainfall.     

A dynamical model for plant cell wall architecture formation

We discuss a dynamical mathematical model to explain cell wall architecture in plant cells. The highly regular textures observed in cell walls reflect the spatial organisation of the cellulose microfibrils (CMFs), the most important structural component of cell walls. Based on a geometrical theory proposed earlier [A. M. C. Emons, Plant, Cell and Environment 17, 3–14 (1994)], the present model describes the space-time evolution of the density of the so-called rosettes, the CMF synthesizing complexes. The motion of these rosettes in the plasma membrane is assumed to be governed by an optimal packing constraint on the CMFs plus adherent matrix material, that couples the direction of motion, and hence the orientation of the CMF being deposited, to the local density of rosettes. The rosettes are created inside the cell in the endoplasmatic reticulum and reach the cell-membrane via vesicles derived from Golgi-bodies. After being inserted into the plasma membrane they are assumed to be operative for a fixed, finite lifetime. The plasma membrane domains within which rosettes are activated are themselves also supposed to be mobile. We propose a feedback mechanism that precludes the density of rosettes to rise beyond a maximum dictated by the geometry of the cell. The above ingredients lead to a quasi-linear first order PDE for the rosette-density. Using the method of characteristics this equation can be cast into a set of first order ODEs, one of which is retarded. We discuss the analytic solutions of the model that give rise to helicoidal, crossed polylamellate, helical, axial and random textures, since all cell walls are composed of (or combinations of) these textures. Received: 10 July 1999 / Revised version: 7 June 2000 / Published online: 16 February 2001     

土壤-植物系统复合污染研究进展

土壤-植物系统复合污染研究是污染生态学的科学前沿,对于农业环境的生态安全具有重要意义．本文对复合污染概念的由来及其内涵的发展、土壤-植物系统可能发生的复合污染类型及其研究进展、土壤-植物系统复合污染所导致的生态效应及其定量表征进行了较为系统的概述,提出了土壤-植物系统中重金属-有机污染物和有机污染物-病原微生物也是复合污染的重要类型．指出了多种污染物交互行为、次生产物及其老化、分子毒理机制等方面的研究是今后土壤-植物系统复合污染的研究重点．同时对复合污染的研究方法以及结果的应用进行了展望,为土壤污染的预警防治与修复提供依据。     

A soil-plant model applied to phytoremediation of metals

This study reports a phytoremediation pot experiment using an open-source program. Unsaturated water flow was described by the Richards' equation and solute transport by the advection-dispersion equation. Sink terms in the governing flow and transport equations accounted for root water and solute uptake, respectively. Experimental data were related to application of Vetiver grass to soil contaminated by metal ions. Sensitivity analysis revealed that due to the specific experimental set-up (bottom flux not allowed), hydraulic model parameters did not influence root water (and contaminant) uptake. In contrast, the results were highly correlated with plant solar radiation interception efficiency (leaf area index). The amounts of metals accumulated in the plant tissue were compared to numerical values of cumulative uptake. Pb²⁺ and Zn²⁺ uptake was satisfactorily described using a passive model. However, for Ni²⁺ and Cd²⁺, a specific calibration of the active uptake model was necessary. Calibrated MM parameters for Ni²⁺, Cd²⁺, and Pb²⁺ were compared to values in the literature, generally suggesting lower rates and saturation advance. A parameter (saturation ratio) was introduced to assess the efficiency of contaminant uptake. Numerical analysis, applying actual field conditions, showed the limitation of the active model for being independent of the transpiration rate.     

A new model for cellulose architecture in some plant cell walls

Summary A new model of rotating fibre components (helicoidal model) is proposed to explain the architecture of some plant cell walls. On the basis of tilting observations under the electron microscope, we establish the validity of this model for the cell wall ofChara vulgaris oospores. We suggest that this model explains the architecture seen in a number of published micrographs from a variety of different plant cell walls. Helicoidal architecture is shown to be distinct from the previously established crossed polylamellate architecture. The diagnostic features of helicoidal architecture are given. Morphogenesis of plant cell walls is discussed, with particular reference to self assembly in cholesteric liquid crystals.     

A model for water uptake by plant roots

We present a model for water uptake by plant roots from unsaturated soil. The model includes the simultaneous flow of water inside the root network and in the soil. It is constructed by considering first the water uptake by a single root, and then using the parameterized results thereby obtained to build a model for water uptake by the developing root network. We focus our model on annual plants, in particular the model will be applicable to commercial monocultures like maize, wheat, etc. The model is solved numerically, and the results are compared with approximate analytic solutions. The model predicts that as a result of water uptake by plant roots, dry and wet zones will develop in the soil. The wet zone is located near the surface of the soil and the depth of it is determined by a balance between rainfall and the rate of water uptake. The dry zone develops directly beneath the wet zone because the influence of the rainfall at the soil surface does not reach this region, due to the nonlinear nature of the water flow in the partially saturated soil. We develop approximate analytic expressions for the depth of the wet zone and discuss briefly its ecological significance for the plant. Using this model we also address the question of where water uptake sites are concentrated in the root system. The model indicates that the regions near the base of the root system (i.e. close to the ground surface) and near the root tips will take up more water than the middle region of the root system, again due to the highly nonlinear nature of water flow in the soil.     

A one-dimensional unsteady separable and reattachable flow model for collapsible tube-flow analysis

Taking into account both flow separation and reattachment observed in available experimental results on flows in a quasi-two-dimensional channel, we present a one-dimensional unsteady flow model, which is applicable to a flow in a collapsible tube. The flow model has been derived from the two-dimensional Navier-Stokes equations by introducing the concept of a dividing streamline, which divides a separated flow into a jet and a dead-water zone. We also present a criterion for the determination of a separation point. Numerical results show that the locations of the predicted separation points agree well with the experimental data. The predicted static pressure of the separated flow is almost constant downstream of the separation point and increases quickly just before the reattachment point as observed in the experiment. Finally, using the present flow model and the separation criterion, we examine the oscillatory behavior of an unsteady flow in a symmetric channel whose walls move sinusoidally.     

森林生态系统林木根系对优先流的影响

土壤水和溶质运移是土壤学和环境科学研究的难点和热点,优先流是一种常见的土壤溶质运移形式,绕过土壤基质而优先运移至地下水源,造成土壤养分的流失和水质的恶化。林木根系是土壤层的重要部分,其结构形态影响着优先流过程,为量化林木根系结构对土壤优先流的影响,以首都圈森林生态系统鹫峰定位监测站为研究区域,利用野外染色示踪与室内分析相结合的方法,定量分析根长密度和根系生物量在优先流区和基质流区的变化。结果表明:1)随着土层深度的增加,根长密度表现为减小的趋势,对径级d1 mm,1d3 mm和3d5 mm根系而言,根长密度在优先流区大于基质流区发生概率分别为66.7%,88.9%和83.3%;2)根系d1 mm对优先流贡献度最大,均值为94.8%,1d3 mm和3d5 mm根系对优先流贡献度较小,均值分别为4.3%和0.9%;3)研究点根系生物量进行统计,66.7%优先流区根系生物量大于基质流区根系生物量。开展根系对优先流的影响研究,有助于探明土壤水分运移规律,分析地表地下水质恶化根源,为生态环境安全提供理论指导和技术支持。     

How plant architecture affects light absorption and photosynthesis in tomato: towards an ideotype for plant architecture using a functional-structural plant model

Background and Aims

Manipulation of plant structure can strongly affect light distribution in the canopy and photosynthesis. The aim of this paper is to find a plant ideotype for optimization of light absorption and canopy photosynthesis. Using a static functional structural plant model (FSPM), a range of different plant architectural characteristics was tested for two different seasons in order to find the optimal architecture with respect to light absorption and photosynthesis.

Methods

Simulations were performed with an FSPM of a greenhouse-grown tomato crop. Sensitivity analyses were carried out for leaf elevation angle, leaf phyllotaxis, leaflet angle, leaf shape, leaflet arrangement and internode length. From the results of this analysis two possible ideotypes were proposed. Four different vertical light distributions were also tested, while light absorption cumulated over the whole canopy was kept the same.

Key Results

Photosynthesis was augmented by 6 % in winter and reduced by 7 % in summer, when light absorption in the top part of the canopy was increased by 25 %, while not changing light absorption of the canopy as a whole. The measured plant structure was already optimal with respect to leaf elevation angle, leaflet angle and leaflet arrangement for both light absorption and photosynthesis while phyllotaxis had no effect. Increasing the length : width ratio of leaves by 1·5 or increasing internode length from 7 cm to 12 cm led to an increase of 6–10 % for light absorption and photosynthesis.

Conclusions

At high light intensities (summer) deeper penetration of light in the canopy improves crop photosynthesis, but not at low light intensities (winter). In particular, internode length and leaf shape affect the vertical distribution of light in the canopy. A new plant ideotype with more spacious canopy architecture due to long internodes and long and narrow leaves led to an increase in crop photosynthesis of up to 10 %.     

A model for water transport in the stele of plant roots

Summary The mechanism of water movement across roots is, as yet, not well understood. Some workable black box theories have already been proposed. They, however, assumed unrealistic cell membranes with low values of , or were based on a poor anatomical knowledge of roots. The role of root stele in solute and water transport seems to be especially uncertain. An attempted explanation of the nature of root exudation and root pressure by applying the apoplast canal theory (Katou andFurumoto 1986 a, b) to transport in the root stele is given. The canal equations are solved for boundary conditions based on anatomical and physiological knowledge of the root stele. It is found that the symplast cell membrane, cell wall and net solute transport into the wall apoplast are the essential constituents of the canal system. Numerical analysis shows that the canal system enables the coupled transport of solutes and water into a xylem vessel, and the development of root pressure beyond the level predicted by the osmotic potential difference between the ambient medium and the exudate. Observations on root exudation and root pressure previously reported seem to be explained quite well. It is concluded that the movement of water in the root stele although apparently active is essentially osmotic.Abbreviations J _v ^ex volume exudation per root surface - J₀ non-osmotic exudation - L^r overall radial hydraulic conductivity of an excised root - reflection coefficient - C_s difference in the osmotic concentration between the bathing medium and the exudate - R gas constant - T absolute temperature - C_K molar concentration of K⁺ - C_Cl molar concentration of Cl^– - C_j molar concentration of ion species j - P_j membrane permeability of ion j - z_j valence of ion j - F Faraday constant - V_ix intracellular electric potential with reference to the canal     

A computational model for the primate neocortex based on its functional architecture

Experimental evidence has shown that the primate neocortex consists in the main of a set of cortical regions which form a perception hierarchy, an action hierarchy and connections between them. By using a computer science analysis, we develop a computational architecture for the brain in which each cortical region is represented by a computational module with processing and storage abilities. Modules are interconnected according to the connectivity of the corresponding cortical regions. We develop computational principles for designing such a hierarchical and parallel computing system. We demonstrate this approach by proposing a causal functioning model of the brain. We report on results obtained with an implementation of this model. We conclude with a brief discussion of some consequences and predictions of our work.     

A model for radial water transport across plant roots

Summary A model based on the canal theory (Katou andFurumoto 1986 a, b) is proposed for the absorption of solute and water at the root periphery. The present canal model in the periphery and the model which was previously proposed for the exudation in the stele (Katou et al. 1987), are organized into a model for radial transport across excised plant roots, in the light of anatomical and physiological knowledge of maize roots. The canal equations for both canals are numerically solved to give quite a good explanation for the observed exudation of maize roots. It is found that the regulation of solute transport has a primary importance in the regulation of water transport across excised roots. The internal cell pressure of the symplast adjusts the water absorption at the root periphery to the water secretion into the vessels. There seems no need for this explanation of the radial water transport across roots to assume cell membranes with low reflection coefficient or variable water permeability. It would seem that the apoplast wall layers play a crucial role in metabolic control of water transport in roots as well as in hypocotyls.Abbreviations J _s ^ex* the theoretically estimated rate of solute exudation per unit surface area of model maize roots - J that of volume exudation per unit surface area of model maize roots - the reflection coefficient of the cell membrane against solutes