Cell wall disruption: An effective strategy to improve the nutritive quality of microalgae in African catfish (Clarias gariepinus)

The rigid cell walls of microalgae may hinder their utilization in fish feeds. The current experiment assessed the correlation between the accessibility of microalgae nutrients and their in vivo digestibility in African catfish. Nannochloropsis gaditana biomass was subjected to physical or mechanical treatments to weaken its cell wall; untreated—no disruption treatment (UNT), pasteurization (PAS), freezing (FRO), freeze‐drying (FRD), cold pasteurization (L40) and bead milling (BEM). Six experimental diets formulated from differently treated and untreated microalgae (at 30% diet inclusion level) were tested on growth performance and apparent nutrient digestibility (ADCs) in juvenile African catfish. A basal diet (REF) containing no microalgae was used as reference diet. Results showed that biomass gain and feed conversion ratio of fish fed L40 and BEM diets increased by 13% and 11%, respectively, relative to the UNT diet. Additionally, FRD, FRO, L40 and BEM cell wall disruption treatments improved protein digestibility by 0.5%, 5.9%, 8.4% and 16.3%, respectively, compared to the UNT treatment. There was a positive correlation between accessibility of microalgal nutrients and their digestibility in African catfish. Nutrient digestibility of microalgae was dependent on extent of cell disruption. Also, the impact of cell disruption on nutrient digestibility of microalgae differs between African catfish and Nile tilapia.     

甘肃黄河三峡景区旅游资源空间结构研究

旅游空间结构是旅游系统功能组织方式在空间上的投影或表象,其空间结构是否合理直接影响到旅游目的地旅游业的发展态势。黄河三峡景区凭借其丰富、独特的资源优势,已成为黄河流域最著名的景区之一。受河谷地带的基础性影响,其资源类型、空间结构、游览线路等表现出典型的空间特征,深刻影响着景区旅游空间格局。借助Arc GIS空间网络分析模块和Excel平台,对黄河三峡景区旅游资源空间结构进行定量分析,发现旅游资源空间分布呈集聚态势,基尼系数高达0.755,分布均匀度仅为0.245;采用最邻近指数和Voronoi多边形的变异系数分析空间分布类型;用地理集中指数和基尼系数分析空间分布均衡性,运用β指数、γ指数和α指数刻画空间连接度。结果表明:景区内旅游资源的空间分布均匀度低,呈多中心集聚分布。这既有利于景区内各景点之间的整合和旅游规模效应的产生,又可以减弱区间屏蔽作用等外部不经济性。景区内各景点之间的交通网络密度低,空间联系较弱,通达性较低。各景点之间的直接连接较少,旅游路线多为单线往返,缺少串联各个景点的环形线路。     

基于生产生活可达性的农村居民点整治分区及模式

农村居民点整治应满足农户生产生活的需求,提高农村居民点的生产生活可达性。该文从生产生活可达性切入,以农村居民点生产生活可达性作为整治分区和采取何种整治模式的依据,从生产可达性和生活可达性两方面出发构建生产生活可达性评价指标体系,采用空间可达性测度方法和指标综合评判法计算得到农村居民点(斑块)生产生活可达性,将其分为I、II、III、IV 4个等级,分别对应发展区、优化区、引导区和拆迁区。根据整治分区并结合实际情况,划分了城镇化发展模式、城乡统筹发展模式、综合优化模式、辐射引导模式、增减挂钩模式和生态搬迁模式等6种整治模式,并对整治思路和具体做法做了探讨。该研究尝试将生产生活可达性评价结果应用于农村居民点整治,对有序整治农村居民点和改善提高农村人居环境有指导意义。     

Recreational preferences depending on thinning practice in young even-aged stands of pedunculate oak (Quercus robur L.): comparing the opinions of forest and landscape experts and the general population of Denmark

The aim of this study was to investigate to which extent forestry professionals, other “green” professionals (mainly landscape architects) and natural resource students in Denmark agree with the general population regarding their recreational preferences for contrasting stem densities in young, even-aged stands of pedunculate oak (Quercus robur L.). The study was based on five pairs of colour photographs from each of the five recently thinned experimental plots in a 13-year-old stand. The plots represented five different residual stem densities: 7000 (unthinned), 5300 (traditional thinning), 1000, 300 and 100 stems ha^?1. All cut trees were left on the ground. The analysis was carried out as a survey of forest and landscape experts (n=158) and the general public (n=243) based on questionnaires. Interviewees ranked the photographs according to the criterion: “Which forest environment do you prefer as a visitor?” Principal component factor analysis showed that the general public tended to perceptually group photos according to similar overall pattern of openness, presence of row structure and stand accessibility (including presence/absence of slash). As long as a stand appeared accessible, stand density had little influence on their preferences for a wide range of stand densities (5300?300 stems ha^?1). In contrast, foresters, other “green” professionals and students seemed to perceptually group photos according to treatment type, and the presence of slash had little influence on their preferences. This suggests an influence of professional background, making experts visually analyse and evaluate stands according to contemporary management standards and paradigms within their own profession.     

基于路阻函数的旅游交通可达性研究——以新疆3A级及以上级别景区为例

基于路阻函数,对栅格成本加权距离法进行了一定的改进,在此基础上,以新疆123个3A级及以上级别景区为例,对其旅游交通可达性进行了测算,并以地州和县级行政单元为单位,研究改进前后两种算法结果的差异。结果显示:改进后,由于加入了运费、交通费和实际车速等因子,使得栅格成本加权距离成本更加贴近地区的自然和社会经济发展状况,弥补了改进前单一考虑设计时速因子所带来的缺陷;改进后可达性的空间分布形态从改进前的西北—东南向的对角线式分布形态,转变为西北—东南向的三级阶梯状分布形态。     

基于GIS的太原市景观格局与可达性分析

城市公园绿地是城市绿地系统中重要的组成部分,是衡量一个城市人居环境和城市环境的重要标准.本研究以太原市中心城区(环城高速内)为研究对象,运用遥感技术以及GIS相关技术,对太原市城市公园绿地可达性及景观格局进行分析.结果表明:①太原市城市公园绿地面积偏少且各行政区之间分布不均匀,其中杏花岭区城市公园绿地面积最小仅为0.99 km~2,占研究区的2.37%;②太原市城市公园绿地可达性整体较差,仅有不到50%的城市居民能在30 min内通过步行方式到达最近公园;③太原市城市公园绿地整体分布较为均匀,破碎化程度较低,但其景观形状较为规则,不利于城市生物多样性的维护,且斑块丰富度密度较低.本研究成果可以为太原市合理优化绿地空间结构布局提供理论依据.     

郑州市休闲农业空间分布特征分析

休闲农业作为拓展城市旅游的朝阳产业,满足了城市居民日益增长的游憩需求,同时也为城市发展提供了未来储备。笔者以郑州市为例,综合空间地域、分布类型、交通可达性等多种因素,对郑州市休闲农业的空间特征进行分析评价,并针对休闲农业存在的问题,从规划合理性、类型多样性、空间可达性和提高参与性等方面提出了一些建议,旨在推动郑州市休闲农业的合理化均衡化发展,同时也为城市规划、旅游规划、政府合理优化景点布局等提供参考。     

厦门岛城市绿地可达性研究

文章应用RS技术结合GIS工具,以厦门岛Landsat TM卫星影像作为研究数据来源,并结合厦门岛用地现状图、远景绿线规划图等数据资料制作厦门岛数字地图,以绿地可达性为评价指标,衡量厦门岛的当前绿地系统及远景绿地规划为居民提供生态服务的有效性;通过现状绿地与远景规划绿线之间的整体绿地可达性对比,对远景绿线规划进行评价;对绿地可达性不佳区域,以多种来源的数据作为分析依据,对绿地建设工作提出改进意见,为绿地建设工作提供了一种有效的决策支持平台。       

The porosphere as an ecological medium emphasized in Professor Ghilarov's work on soil animal adaptations

Summary The author recalls that the late Professor Mercury S. Ghilarov, from the Institute of Animal Morphology and Ecology in Moscow, was a great pioneer in soil zoology and a far-sighted scientist in the evolution of terrestrial faunas. Professor Ghilarov agreed that during their evolution insects passed through the soil as a transitional medium from aquatic to terrestrial habitats. His theory, which is based on morphological and physiological observations, fits the thermodynamics of soil water the author describes when considering all porous bodies (porosphere), such as soil and other media, permitting a slow and gradual transition from an aquatic towards a xeric aerial system. In conclusion, a general concept of water accessibility for soil animals is formulated.Dedicated to the late Prof. Dr. M.S. Ghilarov