生物土壤结皮对一年生植物影响研究进展     

陈孟晨  张景光  刘立超  冯丽  滕嘉玲 《中国沙漠》2017,37(3):483-490

生物土壤结皮在荒漠地区广泛分布,它的形成和演替深刻地改变了土壤表层的结构特征和理化性质,进而影响了荒漠地区一年生植物的种子传播、萌发、幼苗存活及生长过程。本文回顾了国内外有关生物土壤结皮对一年生植物影响的研究,综述了生物土壤结皮对一年生植物的土壤种子库、种子萌发、幼苗存活及生长过程的影响,分析了各研究结论中存在争议的原因,总结了生物土壤结皮对一年生植物种子传播、萌发、幼苗存活及生长影响的内在机理,指出了生物土壤结皮对荒漠地区植被组成的筛选作用,并对进一步的研究进行了展望。  相似文献   

Visualization and damage assessment for flooded area     

Su Guozhong  Yan Li  Liu Nan  Liu Renyi 《地球空间信息科学学报》2013,16(3):180-186

A practical method for visualizing flood area and evaluating damage is presented, which consists of two technical approaches: self-programming and adapting commercial GIS platforms. The low-cost and easy-to-use GIS-Based model developed by self-programming can meet current requirements of most local authorities, especially in developing countries. In this model, two cases, non-source flood and source flood, are distinguished and the Seed-spread algorithm suitable for source-flood is discussed; The flood damage is assessed by overlaying the flood area range with thematic maps and other related social and economic data. and all thematic maps are converted to raster format before overlay analysis. Two measures are taken to improve the operation efficiency of speed seed-spreed algorithm. The accuracy of the model mainly depends on the resolution and precision of the DEM data, and the accuracy of registering all raster layers and the quality of attribute data.  相似文献   

Human and Environmental Factors Affect Patterns of Crop Diversity in an Ethiopian Highland Agroecosystem     

Leah H. Samberg  Carol Shennan  Erika S. Zavaleta 《The Professional geographer》2013,65(3):395-408

The Ethiopian highlands are a center of diversity for numerous globally important crops. Heterogeneous landscapes, traditional agricultural practices, and inaccessibility have created and maintained diverse subsistence agroecosystems. We surveyed sixty-three farms in twelve communities of the Gamo highlands and found high levels of on-farm diversity of crop species and varieties. The extent and nature of this diversity are related to both ecological factors, namely elevation, and anthropogenic factors such as land-use history, accessibility to markets and extension, and strength and scale of farmer exchange networks. These human landscape features have the potential to both enhance and mediate effects of elevation and other environmental factors on crop diversity. The interaction of environmental and anthropogenic forces on the diversity of crops grown by farmers affects the strategies farmers employ to adapt their farming to changing conditions.  相似文献   

Living where others dare not: Microhabitat distribution in Chorizanthe rigida,a serotinous desert annual     

《Journal of Arid Environments》2013

We studied the small scale distribution pattern of Chorizanthe rigida, a serotinous desert annual, in a shrub-mound-to-desert-pavement gradient. Two sites were established in the Mojave Desert and two sites where established in the Sonoran Desert. We placed transects along a soil surface gradient from shrub mounds to desert pavements, and measured land surface properties, soil characteristics, and C. rigida's small scale distribution. A Principal Components Analysis was done on the resulting site × soil variables matrix. C. rigida established preferentially in desert pavements outside shrub canopies. Pavements showed finer soil textures and higher electrical conductivities, while shrub mounds had sandy textures, low surface rockiness, higher nitrogen, and higher cover of annuals. We discuss a probable relationship between seed retention and the establishment on desert pavements: timing seed release allows this species to avoid wind- or animal-induced seed dispersal into shrub mounds and establish outside the nurse mounds, where most annual plants concentrate. The seeds encased in the serotinous involucres, released after rains, are dispersed by run-off into the desert pavements and transition zones where, once developed, the dead seed-retaining structures of adult C. rigida plants persist for years releasing seeds to subsequent rain events.  相似文献   

Wind as an Ecological Agent at Treelines in North America,the Alps,and the European Subarctic   总被引：2，自引：1，他引：1  

《自然地理学》2013,34(3):203-233

The altitudinal treeline ecotone is a windy environment where wind velocities and directions are controlled by local mountain topography and also by the distribution pattern and structures of tree stands. Wind may override the role of heat deficiency in determining treeline position, spatial pattern, ecological conditions, and tree growth. Regular strong permanent winds restrict tree height and usually cause asymmetric and suppressed growth forms that are common in the treeline ecotone. Apart from direct physiological and mechanical effects on trees and ground vegetation, wind also disperses seeds, relocates snow, and locally erodes soils in the treeline ecotone. Wind effects must be considered an important factor that may delay or even preclude establishment of seedling trees on wind-swept terrain. Discussions of a potential climatically driven upward shift of the treeline at the landscape and smaller scales should give greater attention to the varying wind effects because warming cannot compensate for these other factors. The relative importance of microsite facilitation providing shelter from the wind will increase in parallel with the upslope migration of the tree limit into a much windier environment.  相似文献   

内蒙古河套灌区3种沉水植物种子休眠及萌发特性     

王譞  李青丰  胡杨  贾红梅  李玲玲 《湖泊科学》2013,25(1):115-118

沉水植物在湖泊生态系统中具有重要作用,它不仅是湖泊生态系统食物链中重要的生产者,同时还对湖泊的营养物沉积和循环有着重要的意义,并由此影响着湖泊的富营养化进程.本文以黄河内蒙古段河套灌区湖泊中常见的3种沉水植物篦齿眼子菜(Potamogeton pectinatus)、穿叶眼子菜(Potamogeton perfoliatus)和狐尾藻(Myriophyllum verticillatum)为研究对象,对其种子休眠及萌发特性进行了初步研究.结果表明:狐尾藻种子休眠率较高但休眠易破除,通过切破种皮、低温层积、硝酸钾和赤霉素处理均可显著提高萌发率;篦齿眼子菜种子休眠性较强,低温层积及赤霉素浸泡处理能够显著提高其萌发率;穿叶眼子菜有较深的休眠特性,破除硬实、硝酸钾、赤霉素及低温层积处理均不能有效解除其休眠.  相似文献   

种子预处理对唐古特白刺出苗和幼苗生长的影响     

屠彩芸  郭凤霞  李新荣  陈垣  何明珠 《中国沙漠》2011,30(4):981-986

 采用不同方法对唐古特白刺种子预处理,以不处理为对照,再行60 ℃浸种24 h后育苗,通过测定出苗动态和生长指标,探寻促进白刺种子出苗和幼苗生长的技术途径。结果表明,唐古特白刺种子出苗率变化动态均呈“S”型曲线,符合Logistic曲线方程,出苗质量随种子处理不同而异,出苗期为38～55 d,极限出苗率为30.2%～57.8%。沙搓和沙碾均可显著提高白刺种子出苗质量,为培育壮苗奠定良好基础,出苗率较对照分别提高15.6%和13.4%,出苗势分别提高60.1%和6.9%,出苗指数分别提高35.2%和13.2%,活力指数分别提高41.5%和23.3%。尤其沙搓种子出苗集中,较对照缩短5 d。而掐尖、20%醋酸和5%碱水浸泡均抑制发芽。将种子与沙子混合后手搓和棍碾压均可破坏白刺种子坚硬致密的内果皮结构,破除休眠,促进出苗和幼苗生长,但需注意的是沙碾操作不当会造成种子内部结构被破坏。  相似文献   

Study on characteristics and regeneration rules of Salix gordejevii in Hunshandak Sandland, China     

XiuPing Cui  GuoHou Liu 《寒旱区科学》2012,4(5):0417-0421

Salix gordejevii, a species of dune-fixing pioneer shrub in the Hunshandak Sandland in China, plays a vital role in maintenance and improvement of the local ecological environment. Salix gordejevii has an r-type reproductive countermeasure, which means it produces large quantities of seeds that have a high germination rate but relatively low seedling viability. Our research on the seed regeneration and sprouting regeneration characteristics of Salix gordejevii shows that its sprouting regeneration process is more productive and efficient than its seed regeneration process. At the same time, growth of Salix gordejevii would decline when the drifting sand dune was fixed. To assess its sprouting regeneration process, we analyzed the number, length, and diameter of new shoots under different cutting treatments, and found significant differences based on various cutting heights and different cutting times (April vs. October). We conclude that cutting measures which take advantage of this species’ robust sprout tillering can increase the biomass of this shrub and also can improve its canopy density and its forage properties for livestock grazing, with the added benefits of improved sand-fixing and prevention of wind erosion.  相似文献   

Fluvial seed dispersal of riparian trees: transport and depositional processes          下载免费PDF全文

Adrienne Cunnings  Edward Johnson  Yvonne Martin 《地球表面变化过程与地形》2016,41(5):615-625

Fluvial seed dispersal considers both the transport and deposition of seeds where channel geomorphic structures, hydrology and seed dispersal traits contribute to transport times and depositional locations. This study examines the influence of stream flow patterns on fluvial seed dispersal of buoyant white alder (Alnus rhombifolia) seeds by applying a one‐dimensional transport model. Conceptually, the model separates the stream into two components: (i) the main channel where the seeds are transported downstream; and (ii) the transient storage zone where seeds are temporarily detained or deposited on the river bank. Transport processes are characterized by an advection–dispersion equation which is coupled to a transient storage model using an exponential decay term. The model parameters: longitudinal dispersion (D_L), exchange coefficient (α), main channel area (A) and storage zone (A_s) are estimated based on field experiments conducted in a confined, bedrock‐gravel bed river with pool‐riffle morphology located in coastal northern California. The riparian zone is inhabited by Alnus rhombifolia that disperse buoyant seeds in mid‐spring coinciding with the end of the wet, Mediterranean season. Artificial seeds, with similar traits of buoyancy and density to alder seeds, were used to quantify transport times and depositional locations. Preferential deposition resulted in stream reaches with larger A_s, high A_s/A ratios, and faster exchange coefficients corresponding to divergent stream flow (back‐eddies, re‐circulating flow, flow expansions) caused by geomorphic structures such as the ends of bar/riffle features and bends in the stream. The results demonstrate the importance of transient storage for seed transport and depositional processes. Morphological features that increase a channel's complexity create complex flow structures that detain seeds and provide a greater opportunity for deposition to occur. The model provides a simplification of river hydraulics to represent dispersal dynamics and lends itself to further understanding of hydrochory processes and associated population structure. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

塔里木河下游漫溢区土壤种子库及幼苗库特征     

傅荩仪  徐海量  安红燕  赵新风  白元 《中国沙漠》2013,33(6):1705-1710

结合土壤种子库萌发实验和幼苗库野外调查,研究塔里木河下游漫溢区土壤种子库和幼苗库特征及两者之间的差异,同时对不同微地形条件下两者多个生态指标进行分析比较。结果显示:（1）土壤种子库和幼苗库共发现有11科21属22种植物。土壤种子库有效种子密度为681±166个\5m-2,而幼苗库的密度为74±30株·m-2。土壤种子库和幼苗库均以多年生草本植物为主。（2）土壤种子库的Margalef指数值显著大于幼苗库,Simpson指数和Shannon-Wiener指数的值则略大于幼苗库。土壤种子库和幼苗库之间的物种相似度为0.553。（3）在不同微地形条件下,土壤种子库和幼苗库的密度和多样性指数变化趋势有所不同,但总体上均表现为土壤种子库大于幼苗库。  相似文献