Patterns and implications of plant-soil δC and δN values in African savanna ecosystems     

Lixin Wang  Paolo D'Odorico  Stephen A. Macko 《Quaternary Research》2010,73(1):77-3082

Southern African savannas are mixed plant communities where C₃ trees co-exist with C₄ grasses. Here foliar δ¹⁵N and δ¹³C were used as indicators of nitrogen uptake and of water use efficiency to investigate the effect of the rainfall regime on the use of nitrogen and water by herbaceous and woody plants in both dry and wet seasons. Foliar δ¹⁵N increased as aridity rose for both C₃ and C₄ plants for both seasons, although the magnitude of the increase was different for C₃ and C₄ plants and for two seasons. Soil δ¹⁵N also significantly increased with aridity. Foliar δ¹³C increased with aridity for C₃ plants in the wet season but not in the dry season, whereas in C₄ plants the relationship was more complex and non-linear. The consistently higher foliar δ¹⁵N for C₃ plants suggests that C₄ plants may be a superior competitor for nitrogen. The different foliar δ¹³C relationships with rainfall may indicate that the C₃ plants have an advantage when competing for water resources. The differences in water and nitrogen use likely collectively contribute to the tree-grass coexistence in savannas. Such differences facilitate interpretations of palaeo-vegetation composition variations and help predictions of vegetation composition changes under future climatic scenarios.  相似文献   

水电开发对河流水沙年内分配的影响分析   总被引：3，自引：1，他引：2       下载免费PDF全文

黄英  刘新有 《水科学进展》2010,21(3):385-391

以中国西南重要的国际河流澜沧江为研究对象,借鉴"基尼系数"的构建思路,建立了水沙年内分配均匀度计算模型,并通过下游水沙与上游天然水沙和区域降水的关系,建立了河流水沙年内分配均匀度回归还原模型。还原结果与实测对比表明:漫湾、大朝山电站建设以来,澜沧江径流年内分配均匀度年均升高1.14%,变幅在-7.32%~10.81%之间,输沙年内分配均匀度年均降低0.23%,变幅在-18.98%~26.76%之间;漫湾、大朝山电站同时运行期间,澜沧江径流年内分配均匀度年均升高3.90%,输沙年内分配均匀度年均降低0.42%;大朝山水电站建设后,澜沧江径流年内分配均匀度升高而输沙年内分配变化不明显,说明大朝山水电建设后河流水沙关系发生了变化,但变化较小。该成果不仅能为相关研究提供方法借鉴,也为水电开发对澜沧江水沙年内分配影响程度的科学评估提供了新的依据。  相似文献   

河南水灾变化及典型水灾年大气环流异常特征分析   总被引：4，自引：1，他引：3  

匡晓燕  朱业玉  席世平  潘攀 《气象与环境科学》2010,33(2):20-24

利用河南1950-2007年的逐年水灾统计数据,对水灾年的时间特征进行分析,并对典型水灾年大气环流的异常特征进行分析,结果表明:在1950-2007年的58 a中,河南年年都出现水灾,全省水灾受灾面积66.7万hm2的有28年;66.7万hm2的有30年,约2年一遇;受灾面积133.3万hm2的有17年,约4年一遇;333.3万hm2的有4年,约15年一遇。在河南的典型水灾年,中高纬度的长波和南支系统都有很强的稳定性;亚洲中高纬阻塞形势非常明显,在西西伯利亚上空出现了强烈的偏北风分量,因而冷空气暴发南下非常频繁;副热带高压脊线在24°N左右,584 dgpm线呈西南东北走向,将来自孟加拉湾和南海的充沛水汽带到内陆。河南省正处于来自北方的冷空气和南支系统带来的暖湿气流交汇的区域,这是造成河南省出现严重水灾的主要原因。  相似文献   

太白山国家保护植物优先保护顺序的定量分析   总被引：10，自引：1，他引：10  

傅志军  张萍 《山地学报》2001,19(2):161-164

在野外调查的基础上，运月濒危系数、遗传多样性损失系数和物种价值系数对太白山自然保护区23种国家保护植物的优先保护顺序进行定量分析，结果表明属一级保护的有太白红杉、独叶草、星叶草、杜仲、桃儿七、连香树、大果青杄、青檀、紫斑牡丹9种，属二级保护的有水青树、金钱械、山白树、水曲柳、秦岭冷杉、领春木、羽叶丁香7种，属三级保护的有野大豆、膜荚黄芪、华榛、延龄草、庙台械、天麻6种，属四级保护的仅狭叶瓶尔小草1种。提出了加强珍稀植物保护的措施。  相似文献   

山西关帝山药用植物资源研究     

李卓玉  张峰  李学风 《山地学报》1994,(3)

关帝山位于山西省吕梁山脉中段，计有药用植物４３２种。依疗效可将它们分为１１类：１．解表驱风类９０种；２．清热类３０５种１３．泻下类７种；４．祛湿类９６种；５．理血类８８种；６．止咳化痰平喘类３０种；７．安神平肝熄风类１４种；８．健胃舒气、降压类２６种；９．滋补肝肾、强筋壮骨类２５种；１０．止泻、治痢、收敛类１７种；１１．杀虫、驱虫类５种。最后根据关帝山药用植物资源的现状，提出了开发利用保护的对策。  相似文献   

泸沽湖自然保护区园林树木资源功能分类研究     

赵耘  胡文英 《云南地理环境研究》2004,16(3):32-37

泸沽湖以其独特的摩梭风情和秀丽的山水风光被列为国家级风景名胜区、省级旅游区和省级自然保护区。通过对泸沽湖自然保护区风景园林植物种类资源的调查研究。发现共有141种。分属于39科，80属，并依据风景园林植物的特性、观赏目的、生态习性、栽培方式等。将保护区的园林植物划归为林木类、花木类、果木类、观叶类、遮荫类、蔓木类六大功能类型，为当地因地制宜实施生态保护和园林景点建设提供了科学依据和参考。最后。就野生园林资源的开发、保护、引种、发展和综合利用提出了几点建议。  相似文献   

华北克拉通若干脉状金矿的黄铁矿标型特征与流体成矿过程   总被引：15，自引：6，他引：15  

李晶  陈衍景  刘迎新 《矿物岩石》2004,24(3):93-102

通过对华北克拉通若干典型脉状(造山型)金矿流体成矿过程的研究分析发现：其可分为3个阶段，对比不同阶段黄铁矿的矿物学、微量元素和热电性等方面的特征，显示中阶段细粒黄铁矿(烟灰状黄铁矿)微量元素成分复杂，含量较高，金含量也明显较高，相应的金矿石品位较高；中阶段黄铁矿多呈灰绿-黄绿色，晶形常为五角十二面体，自形程度低(他形-半自形)，粒度细小，晶体表面平滑度差，凹入角发育，表面自由能高，吸附金的能力强，载金能力增强；中阶段黄铁矿热电性较强。结合理论和实验研究成果，认为杂质元素加入导致黄铁矿晶格畸变，电荷不平衡，热电性增强等一系列现象；使黄铁矿的结晶学特征、成分和热电性构成了“三位一体”的标型特征，可作为有效的金矿勘查的直接标志。富金的烟灰状黄铁矿快速沉淀于热液瞬时过饱和或物理化学性质瞬时巨变的条件下，流体沸腾和混合是最重要机制。鉴于黄铁矿标型特征的演化和形成机制与陆陆碰撞体制流体成矿作用的3阶段模式(即CMF模式)完全吻合，借助CMF模式进一步分析烟灰状黄铁矿在脉状造山型金矿床中的发育时间和空间，为CMF模式补充了矿物学方面的支持，同时，赋矿断裂带的脆韧性转变带、挤压向伸展转变期最有利于流体沸腾和混合，是高品位脉状金矿床形成的最佳空间和时间。  相似文献   

The Upper Valanginian (Early Cretaceous) positive carbon-isotope event recorded in terrestrial plants     

Darren R. Gröcke  Gregory D. Price 《Earth and Planetary Science Letters》2005,240(2):495-509

Our understanding of the ancient ocean-atmosphere system has focused on oceanic proxies. However, the study of terrestrial proxies is equally necessary to constrain our understanding of ancient climates and linkages between the terrestrial and oceanic carbon reservoirs. We have analyzed carbon-isotope ratios from fossil plant material through the Valanginian and Lower Hauterivian from a shallow-marine, ammonite-constrained succession in the Crimean Peninsula of the southern Ukraine in order to determine if the Upper Valanginian positive carbon-isotope excursion is expressed in the atmosphere. δ¹³C_plant values fluctuate around − 23‰ to − 22‰ for the Valanginian-Hauterivian, except during the Upper Valanginian where δ¹³C_plant values record a positive excursion to ∼− 18‰. Based upon ammonite biostratigraphy from Crimea, and in conjunction with a composite Tethyan marine δ¹³C_carb curve, several conclusions can be drawn: (1) the δ¹³C_plant record indicates that the atmospheric carbon reservoir was affected; (2) the defined ammonite correlations between Europe and Crimea are synchronous; and (3) a change in photosynthetic carbon-isotope fractionation, caused by a decrease in atmospheric pCO₂, occurred during the Upper Valanginian positive δ¹³C excursion. Our new data, combined with other paleoenvironmental and paleoclimatic information, indicate that the Upper Valanginian was a cool period (icehouse) and highlights that the Cretaceous period was interrupted by periods of cooling and was not an equable climate as previously thought.  相似文献   

Paleoenvironment of the Folsom archaeological site, New Mexico, USA, approximately 10,500 C yr B.P. as inferred from the stable isotope composition of fossil land snail shells     

Meena Balakrishnan  David J. Meltzer 《Quaternary Research》2005,63(1):31-44

Well-preserved aragonitic land snail shells (Vallonia) from late Pleistocene Eolian sediment in the Folsom archaeological site in New Mexico exhibit an overall decrease of δ¹⁸O_PDB from maximum values of +2.7‰ (more positive than modern) to younger samples with lower average values of about −3.6‰ (within the modern range). The age of the samples (approximately 10,500 ¹⁴C yr B.P.) suggests that the decrease in δ¹⁸O may manifest climatic changes associated with the Younger Dryas. Some combination of increased relative humidity and cooler temperatures with decreased δ¹⁸O of precipitation during the times of snail activity can explain the decrease in shell δ¹⁸O. A well-known Paleoindian bison kill occurred at the Folsom site during this inferred environmental transition.Average δ¹³C values of the aragonite shells of the fossil Vallonia range from −7.3 to −6.0‰ among different archaeological levels and are not as negative as modern values. This suggests that the proportion of C₄ vegetation at the Folsom site approximately 10,500 ¹⁴C yr B.P. was greater than at present; a result which is consistent with other evidence for higher proportions of C₄ plants in the region at that time.  相似文献   

人工湿地中植物的作用   总被引：20，自引：0，他引：20  

张洪刚  洪剑明 《湿地科学》2006,4(2):146-154

近20 a来,人工湿地系统由于具有独特的净化机理和功能而越来越多地被用于处理生活污水、工业废水和农业污水。人工湿地系统之所以受到国际上广泛的关注,这是由于它具有低能耗,低成本,运行费用少和操作简便等优势。湿地植物在人工湿地中起着非常重要的作用,不但可以直接摄取和利用污水中的营养物质、吸收富集污水中的重金属等有毒有害物质;而且还能输送氧气到根区,提供根区微生物生长、繁殖和降解过程中对氧的需求。通过详细阐述植物对水中营养元素的吸收作用,说明了植物在人工湿地处理污水中的重要性,并提出了一些改进人工湿地处理污水能力的设想以及人工湿地系统水生植物有待进一步研究的问题,研究结果可以为进一步优化人工湿地系统的设计提供参考。  相似文献