Internal segmentation of rhizomes of Phragmites australis: protection of the internal aeration system against being flooded

Segmentation of the aeration system and its anatomy was studied in rhizomes of common reed ( Phragmites australis ). Segmentation is achieved by nodal diaphragms which allow the passage of pressurised gas-flow but which also form effective barriers against flooding of the internal space in case of local injury. The pressures required to force water through the diaphragms were measured and compared with the anatomical structure of the diaphragm. The fine hydrophilic stellate parenchyma of the diaphragms was shown to act as a matrix supporting menisci of air–water interfaces and therefore preventing water movement until the 'limit' pressure (measured values ranged from 18 to >40 kPa) was overcome. Although the surfaces of the large stellate parenchyma and sclerenchyma strands covering the diaphragm are hydrophobic these components do little to prevent the ingress of water.     

Distribution of O2 within infected cells of soybean root nodules: a new simulation

Summary A simulation model is presented for the distribution and consumption of O₂ in infected cells of soybean root nodule central tissue. It differs from earlier models in closer adherence to observed structure and embodies new morphometric data about the distribution of > 12,000 mitochondria per cell and about the geometry of the gas-filled intercellular spaces near which the mitochondria are located. The model cell is a rhombic dodecahedron and O₂ enters only through interfaces (totalling 26% of the cell surface) with 24 gas-filled intercellular spaces. These spaces are located at the edges of each rhombic face of the cell, forming an interconnected network over the cell suface. Next, O₂ is distributed through the cytoplasm by a leghaemoglobin-facilitated diffusive process, initially between the mitochondria and amyloplasts in the outer layers of the cell and then between > 6,000 symbiosomes (each containing 6 bacteroids) towards the central nucleus. The symbiosomes and mitochondria consume O₂, but impede its diffusion; all O₂ entering symbiosomes is considered to be consumed there. For the calculations, the cell is considered to consist of 24 structural units, each beneath one of the intercellular spaces, and each is divided into 126 layers, 0.2 m thick, in and through which O₂ is consumed and diffused. Rates of consumption of O₂ and of N₂ fixation in each diffusion layer were calculated from previously-established kinetics of respiration by mitochondria and bacteroids isolated from soybean nodules and from established relationships between bacteroid respiration and N₂ fixation. The effects of varying the O₂-supply concentration and the concentration and type of energy-yielding substrates were included in the simulations. When the model cell was supplied with 0.5 mM malate, mitochondria accounted for a minimum of 50% of the respiration of the model cell and this percentage increased with increased concentration of the O₂ supply. Gradients of concentrations of free O₂ dissolved in the cytoplasm were steepest near the cell surface and in this location respiration by mitochondria appeared to exert a marked protective effect for nitrogen fixation in layers deeper within the cell. Estimates of N₂ fixation per nodule, calculated from the model cell, were similar to those calculated from field measurements.Abbreviations Lb leghaemoglobin - LbO₂ oxyleghaemoglobin - [O₂] concentration of free, dissolved O₂ - e.m. electron micrograph Dedicated to the memory of Professor John G. Torrey     

粤港澳大湾区小型公园绿地生态系统文化服务的供需匹配特征

小型公园绿地是城市生态系统文化服务的重要载体,自新冠疫情爆发以来,这类型公园绿地更是成为提供重要文化服务的场所。以粤港澳大湾区为研究区域,从潜在供给和潜在需求两个方面量化小型公园绿地文化服务,利用空间自相关与耦合协调度模型,探讨粤港澳大湾区文化服务供需的空间分布及匹配特征。结果如下：(1)生态系统文化服务供给具有明显的梯度分布,大致呈现中间低、四周高的特点;文化服务需求在城市中心区域呈连片分布。(2)文化服务供给在城市之间连片、以高-高聚集区域为主,需求则以低-低聚集为主、连片集中于城市中心,供需双变量则以高供给-低需求的聚集态为主、集中于研究区四周。(3)52.2%的区域属于文化服务需求不足,5.2%的区域供给不足。从小型公园绿地文化服务来看,粤港澳大湾区存在一定比例的生态系统文化服务供需错配现象,为提升人类在抵御重大突发事件过程中的生活质量,可分区管理自然生态系统。     

Dimensions and distribution of intercellular spaces in cryo-planed soybean nodules

The ability of legume nodules to regulate their permeability to gas diffusion has been attributed to physiological control over the size and distribution of gas-filed intercellular spaces within the nodule cortex. To examine the size and distribution of intercellular spaces and to determine whether they were filled with gas (high diffusion permeability) or liquid (low diffusion permeability), whole nodules were frozen in liquid nitrogen slush (-210°C), and then either cryo-fractured or cryo-planed before being examined by cold-stage scanning electron microscopy (SEM). The cryo-planed tissue was found to have many advantages over cryo-fractured nodules in providing images which were easier to interpret and quantify. Intercellular spaces throughout the nodule were examined in both tangential and medial planed faces. Since no differences were observed between views in either the size or shape of the open intercellular spaces, it was concluded that the intercellular spaces of nodules were not radially oriented as assumed in many mathematical models of gas diffusion. The inner cortex region in the nodules had the smallest intercellular spaces compared to other zones, and less than 10% of the intercellular spaces were occluded with any type of material in the central zone regions. Vacuum infiltration of nodules with salt solutions and subsequent cryo-planing for SEM examination showed that open and water-filled intercellular spaces could be differentiated. The potential is discussed for using this method to study the mechanism of diffusion barrier regulation in legume nodules.     

基于DTTD-MCR-PLUS模型的三生空间格局优化——以长沙市为例

优化三生空间格局有助于实现区域国土空间可持续高质量发展。研究提出利用动态交通时间数据优化最小阻力成本模型指标体系，对生态累计最小阻力与生活最小累计阻力差值进行聚类分析，利用突变点对各情景下的三生空间数量进行优化，从生活扩张、生态优先及基于资源与环境承载力视角下的粮食安全3个方面，提出了一种基于DTTD-MCR-PLUS的三生空间格局优化方法。研究发现：1) 基于动态数据优化的长沙市生态功能优化分区结果显示生态空间保护核心区面积为4111.41 km2，生态空间保护边缘区面积为2285.29 km2，生产空间开发重点区面积为2144.79 km2，生产空间开发边缘区面积为1928.59 km2，生活空间扩张集中区面积为1235.55 km2； 2) 耦合DTTD-MCR-PLUS模型模拟的多情景结果表明：生活优先情景下，生活空间面积增幅高达43.57%，主要分布在望城区南部，长沙县西部和雨花区东部；生态优先情景下，生态空间转出速度最低，与生活优先情景相比下降了3.11%；粮食安全情景下，生产空间侵占生态空间速度加快，增幅高达58.79%；3) 协调基本农田、生态保护红线、以及自然保护区下的2030 年长沙市三生空间格局优化布局方案结果表明：生产空间、生活空间和生态空间比例分别为37.63%、7.67%和54.70%。     

Vegetation cover change in growing urban agglomerations in Chile

Cities in Latin America expose high rates of urbanization and poorly controlled processes of creation of new urban peripheries. In this study we evaluated the changes in vegetation cover as a proxy of the success of urban planning in the creation or conservation of elements able to provide ecosystem services to citizens and therefore strengthening urban sustainability. Three urban agglomerations in Chile located in different climates were analysed. Four indicators were processed to understand the changes and correlations between vegetation and urban dynamics: normalized difference vegetation index (NDVI), vegetation cover, normalized difference built-up index (NDBI) and built-up area. The indicators were calculated for a period over 20 years covering two parts of the city as an urban development: the urban core and the new peripheries. An overall loss of vegetation was observed in all cities has a consequence of urban expansion despite their geographical location. Moreover, the greatest losses were in new peripheries. Santiago broke this pattern of change. First its urban core showed a small increase in indicators for vegetation cover despite the increase in indicators for urban dynamics. Secondly, despite their peripheries experiencing a decrease in vegetation cover, a more detailed analysis found differences on the northern and eastern peripheries where increases of vegetation cover were observed, and other new peripheries where vegetation loss was massive. Urban planning needs to play a role not only to facilitate the creation of green spaces or other public spaces able to host vegetation, but also to form an urban structure supported by regulations that facilitate the planting and maintenance of vegetation in private spaces.     

The morphogenesis of lobed plant cells in the mesophyll and epidermis: organization and distinct roles of cortical microtubules and actin filaments

The morphogenesis of lobed plant cells has been considered to be controlled by microtubule (MT) and/or actin filament (AF) organization. In this article, a comprehensive mechanism is proposed, in which distinct roles are played by these cytoskeletal components. First, cortical MT bundles and, in the case of pavement cells, radial MT arrays combined with MT bundles determine the deposition of local cell wall thickenings, the cellulose microfibrils of which copy the orientation of underlying MTs. Cell growth is thus locally prevented and, consequently, lobes and constrictions are formed. Arch-like tangential expansion is locally imposed at the external periclinal wall of pavement cells by the radial arrangement of cellulose microfibrils at every wall thickening. Whenever further elongation of the original cell lobes occurs, AF patches assemble at the tips of growing lobes. Intercellular space formation is promoted or prevented by the opposite or alternate, respectively, arrangement of cortical MT arrays between neighboring cells. The genes that are possibly involved in the molecular regulation of the above morphogenetic procedure by MT and AF array organization are reviewed.     

China in Laos: Enclave spaces and the transformation of borders in the Mekong Region

Where China Meets Southeast Asia: Social and Cultural Change in the Border Regions edited by Grant Evans et al., is among the few works that take borderlands between China and mainland Southeast Asia seriously. A major contribution of this collection of border studies is its attempt to understand how border experiences and the process of bordering have changed since the early 1990s. Various Chinese–local interactions are explored in this book, with an emphasis on complex local responses to border transformations and diverse forms of mobility and network building. This article further examines the role of China and the Lao state, and the new wave of Chinese movement at the border. In establishing an economic integration that spills across the region, the penetration of Chinese power has been effective. The consequent retreat of the Lao state at the border has not only put an end to the old frontier but turned various borderlands into an estranged space of neoliberal enclave.     

Effects of vegetation status in urban green spaces on particle removal in a street canyon atmosphere

Green spaces contribute to the removal of significant amounts of air pollutants. This quantitative study, using seasonally monitoring data of Total Suspended Particles (TSP) from green spaces along one street of Pudong, Shanghai, China, demonstrates that vegetation can remove large amounts of TSP. Furthermore, correlation analysis was performed between the vegetation status, measured by canopy density and shelterbelt porosity, and the TSP removal percentage. The results show that (1) vegetation in green spaces greatly contributes to reduce TSP pollution. The width of green spaces along the road should not be smaller than 5 m, with the best width being 10 m, and more evergreen trees should be chosen in order to get a noticeable TSP purification effect; (2) The TSP removal percentage is correlated to the canopy density and inversely correlated to the shelterbelt porosity. The optimum intervals of the canopy density and shelterbelt porosity are 0.70–0.85 and 0.25–0.33, respectively. The proposed optimum intervals can help to estimate the vegetation structure of green spaces and provide technical support for the programming and construction of urban green spaces.     

生态系统修复国内外研究进展与展望

气候变化和人类活动的增加不仅导致生态系统退化、生物多样性丧失、生物圈资源供给能力降低, 而且极大地制约了社会经济的可持续发展。尽管在全世界范围内已实施了大量的保护工作, 但全球生态系统退化仍在继续, 逐渐成为备受关注的全球性问题。文章首先厘清生态系统修复的发展历程、相关概念与理论。其次, 归纳生态系统修复的全球议题, 涉及生态系统服务及其价值评估、生物多样性保护、应对气候变化与碳储存、自然保护地、监测体系与适应性管理、公平性与多主体参与等方面。然后, 总结我国森林、草原、河流与湿地、海洋与海岸带的生态系统退化问题与修复进展, 梳理生态保护红线、自然保护地生态系统修复和国土空间生态保护修复3种措施的进展与不足。最后, 对山水林田湖草沙一体化保护与系统治理、生态系统修复的多元融资政策与渠道、荒野生态保护修复的探索与实践、城镇生态系统修复的研究与应用以及生态系统修复对生物多样性的保护与维持等五个方面进行展望, 以期为我国进一步开展生态系统保护修复的相关研究与实践提供指导。