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121.
毛乌素沙地丘间低地主要植物叶片性状及其相互关系 总被引:1,自引:0,他引:1
以毛乌素沙地丘间低地30种主要植物为研究对象,比较不同功能群植物叶片性状的变异特征,分析植物叶片各性状之间的关系。结果表明:30种植物的比叶面积的变异系数最大,比叶面积与叶片干物质含量呈现极显著的负相关关系,叶片干物质含量与叶片碳含量呈显著的正相关关系,叶氮含量与叶片碳氮比呈极显著负相关关系,叶面积与其他所有的叶片性状都无相关性。比叶面积、叶片干物质含量、叶面积、叶氮含量和叶碳含量在不同功能群之间存在显著差异,叶片碳氮比在不同功能群之间没有显著差异。研究结果有助于了解毛乌素沙地丘间低地环境变化对植物种群的作用,增进对丘间低地植被演变特征的认识。 相似文献
122.
库布齐沙漠几种沙生灌木叶解剖结构耐旱特征研究 总被引:4,自引:2,他引:2
采用石蜡切片法,对库布齐沙漠的主要造林灌木四翅滨藜、小叶锦鸡儿、杨柴、柽柳、互叶醉鱼草和蒙古莸等叶的解剖结构进行了显微观察。选择叶片厚度、角质层厚度、栅栏组织厚度、栅栏组织细胞长、栅栏组织细胞宽、栅栏细胞密度、CTR等多指标。结果表明,柽柳叶片厚度高于其他5种,互叶醉鱼草叶片厚度最小。互叶醉鱼草角质层厚度最厚,角质层与叶片厚度的比值大小顺序为:互叶醉鱼草>四翅滨藜>柽柳>小叶锦鸡儿>蒙古莸>杨柴。CTR大小顺序为:蒙古莸>杨柴>小叶锦鸡儿>互叶醉鱼草>四翅滨藜>柽柳。利用隶属函数综合评价,结果表明:6种树种耐旱能力大小依次为杨柴>四翅宾藜>柽柳>蒙古莸>小叶锦鸡儿>互叶醉鱼草。 相似文献
123.
Earth is always changing.Knowledge about where changes happened is the first step for us to understand how these changes affect our lives.In this paper,we use a long-term leaf area index data(LAI) to identify where changes happened and where has experienced the strongest change around the globe during 1981-2006.Results show that,over the past 26 years,LAI has generally increased at a rate of 0.0013 per year around the globe.The strongest increasing trend is around 0.0032 per year in the middle and northern high latitudes(north of 30°N).LAI has prominently increased in Europe,Siberia,Indian Peninsula,America and south Canada,South region of Sahara,southwest corner of Australia and Kgalagadi Basin;while noticeably decreased in Southeast Asia,southeastern China,central Africa,central and southern South America and arctic areas in North America. 相似文献
124.
采用PEG和Epon-812二次包埋方法, 利用光学显微镜和扫描电子显微镜对乌鲁木齐河源区海拔4 000 m、 3 400 m、 2 500 m三种不同高度的火绒草(Leontopodium leontopodiodes(Willd.) Beauv.)叶片剖面及表面结构进行了观察. 结果表明: 火绒草叶片既具有中生植物又兼有旱生和湿生植物的部分结构特征; 其叶片厚度、表皮细胞外壁角质层表面、外角质层蜡质分泌物的有无、表皮细胞形状、气孔器分布特征、保卫细胞极区"T"型角质加厚程度、气孔开口(长/宽)、气孔密度、维管束形态、 CTR值、叶肉细胞叶绿体含量等性状特征,在不同海拔的火绒草间呈现出明显差异; 而表皮的气孔水平位置类型、毛状附属器等性状则差异较小. 数值分析火绒草叶结构各类性状以及不同性状状态的组合, 显示出个体形态的多样性及其对高山环境和海拔高度的适宜性特征. 相似文献
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127.
A computational method has been developed to predict the hydrodynamic performance of the propeller–rudder systems (PRS) and azimuthing podded drive (AZIPOD) systems. The method employs a vortex-based lifting theory for the propeller and the potential surface panel method for the steering system. Three propeller models along with three steering systems (rudder and strut, flap and pod (SFP)) are implemented in the present calculations for the cases of uniform and non-uniform conditions. Computed velocity components show good agreement with the experimental measurements behind a propeller with or without the rudder. Calculated thrust, torque and lift also agree well with the experimental results. Computations are also performed for an AZIPOD system in order to obtain the pressure distributions on the SFP, and the hydrodynamic performance (thrust, torque and lift coefficients). The present method is useful for examining the performance of the PRS and AZIPOD systems in the hope of estimating the propulsion and the maneuverability characteristics of the marine vehicles more accurately. 相似文献
128.
对广东目前推广的 4个香蕉良种以及粉蕉和大蕉进行切片显微观察 ,并结合低温处理的电导率测定 ,结果表明 ,香蕉叶片组织细胞结构紧密度 (CTR值 )与品种的耐寒性密切相关 ,且具有相对的稳定性 ,可作为香蕉耐寒性的鉴定指标。供试品种耐寒力强弱依次为粉蕉、大蕉、威廉斯 (8818)、“巴西”、“93- 1”、广东二号 (6 3- 1)。 相似文献
129.
Comparison of tree transpiration under wet and dry canopy conditions in a Costa Rican premontane tropical forest 下载免费PDF全文
Luiza Maria Teophilo Aparecido Gretchen R. Miller Anthony T. Cahill Georgianne W. Moore 《水文研究》2016,30(26):5000-5011
Spatial and temporal variation in wet canopy conditions following precipitation events can influence processes such as transpiration and photosynthesis, which can be further enhanced as upper canopy leaves dry more rapidly than the understory following each event. As part of a larger study aimed at improving land surface modelling of evapotranspiration processes in wet tropical forests, we compared transpiration among trees with exposed and shaded crowns under both wet and dry canopy conditions in central Costa Rica, which has an average 4200 mm annual rainfall. Transpiration was estimated for 5 months using 43 sap flux sensors in eight dominant, ten midstory and eight suppressed trees in a mature forest stand surrounding a 40‐m tower equipped with micrometeorological sensors. Dominant trees were 13% of the plot's trees and contributed around 76% to total transpiration at this site, whereas midstory and suppressed trees contributed 18 and 5%, respectively. After accounting for vapour pressure deficit and solar radiation, leaf wetness was a significant driver of sap flux, reducing it by as much as 28%. Under dry conditions, sap flux rates (Js) of dominant trees were similar to midstory trees and were almost double that of suppressed trees. On wet days, all trees had similarly low Js. As expected, semi‐dry conditions (dry upper canopy) led to higher Js in dominant trees than midstory, which had wetter leaves, but semi‐dry conditions only reduced total stand transpiration slightly and did not change the relative proportion of transpiration from dominant and midstory. Therefore, models that better capture forest stand wet–dry canopy dynamics and individual tree water use strategies are needed to improve accuracy of predictions of water recycling over tropical forests. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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