925 resultados para Plant functional types (PFTs)
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Effective knowledge transfer between infrastructure projects plays a significant role in organisational success and discovery of new technologies, helping to achieve and maintain competitive advantage and, in effect, sustainable infrastructure development. Knowledge is recognised as an important organisational asset that adds value while being shared. To date, research on knowledge transfer has focused on traditional (functional) types of organisations. However, existing knowledge transfer approaches fail to address the issue of unique characteristics of project-based organisations, and the fact that functional and project-based organisations significantly differ in terms of structure, processes, and characteristics. Therefore, there is a need for a different, separate approach for managing knowledge in the project environment. The aim of this chapter is to highlight this need. An extensive literature review is provided on the areas of project management, knowledge management, and organisational structure; this is further supported by empirical evidence from interviews with project management practitioners. Conducting a ‘cross-field’ literature review provides a better understanding of the knowledge transfer mechanisms and its application to projects, and of the importance of knowledge transfer across projects. This research is crucial to gaining a better understanding of knowledge transfer in the project environment. It stresses that there are dissimilarities between project-based organisations and functional organisations in terms of organisational structure, duration of processes, viewpoint of time, response to change, and mobility of people, and that there is a need for a unique strategic approach in order to achieve effective transfer of knowledge. Furthermore, findings presented in this chapter reveal key elements that play an important role in across project knowledge transfer. These elements include: social communication, lessons learned databases, and project management offices.
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Regrowing forests on cleared land is a key strategy to achieve both biodiversity conservation and climate change mitigation globally. Maximizing these co-benefits, however, remains theoretically and technically challenging because of the complex relationship between carbon sequestration and biodiversity in forests, the strong influence of climate variability and landscape position on forest development, the large number of restoration strategies possible, and long time-frames needed to declare success. Through the synthesis of three decades of knowledge on forest dynamics and plant functional traits combined with decision science, we demonstrate that we cannot always maximize carbon sequestration by simply increasing the functional trait diversity of trees planted. The relationships between plant functional diversity, carbon sequestration rates above-ground and in the soil are dependent on climate and landscape positions. We show how to manage ‘identities’ and ‘complementarities’ between plant functional traits in order to achieve systematically maximal co-benefits in various climate and landscape contexts. We provide examples of optimal planting and thinning rules that satisfy this ecological strategy and guide the restoration of forests that are rich in both carbon and plant functional diversity. Our framework provides the first mechanistic approach for generating decision-making rules that can be used to manage forests for multiple objectives, and supports joined carbon credit and biodiversity conservation initiatives, such as Reducing Emissions from Deforestation and forest Degradation REDD+. The decision framework can also be linked to species distribution models and socio-economic models in order to find restoration solutions that maximize simultaneously biodiversity, carbon stocks and other ecosystem services across landscapes. Our study provides the foundation for developing and testing cost-effective and adaptable forest management rules to achieve biodiversity, carbon sequestration and other socio-economic co-benefits under global change.
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小G蛋白作为信号转导中重要的分子开关, 进化相当保守,与许多不同的调控因子和效应器分子相互作用,产生细胞功能的多样性。近年来,人们不断发现植物中小G蛋白家族的新成员,也不断揭示小G蛋白的新功能,许多植物特有的信号途径和功能需要小G蛋白这个重要的分子开关来完成,使它越来越成为人们研究的热点问题。但是,有关植物中Ran GTPase及其编码基因的研究工作报道很少,对与之相互作用的调控蛋白研究进展也刚刚开始。 TaRAN1 (AF488730) 是小麦来源的Ran同源蛋白编码基因,全长1055 bp, 编码221个氨基酸,它在植物发育过程中的功能还没有任何报道。本论文在验证了它是小G蛋白Ran家族的成员后,从分子水平上还发现它在植物细胞周期调控、对生长素以及胁迫应答信号转导过程中都起着重要作用,这也说明了它可能作为信号转导过程中重要的转换因子,参与了很多细胞的基本生理过程。 利用原核表达系统及亲和色谱的方法纯化了TaRAN1融合蛋白,并用放射性标记的GTP和竞争实验证实了它具有特异的GTP结合活性。TaRAN1的转录产物在小麦幼茎和花芽等分生组织活动旺盛的器官表达较多,而在老叶中表达较少。利用洋葱表皮瞬时表达系统分析表现,TaRAN1蛋白主要定位于细胞核,但其没有典型的核定位信号。 细胞周期一直是生物学领域中的热门问题,人们虽然在动物细胞中取得了很大进展,但在植物细胞中的研究远落后于动物。裂殖酵母(Schizosaccharomyces pombe)是研究细胞形态和细胞周期的良好系统,利用此系统发现超表达TaRAN1的酵母细胞表现出许多新的细胞学表型,例如G2细胞周期延滞、染色体对紫外线敏感、细胞超长或多隔细胞的出现等;反义表达TaRAN1的酵母细胞呈近圆型、具有高度凝集的核并且生长速度缓慢、核质混合和无核细胞的数目明显增加。流式细胞仪检测实验也证实其细胞周期的异常。这些结果推测TaRAN1蛋白可能参与细胞周期的有丝分裂过程和发育的调控机制,并且在维持染色体结构稳定和完整性方面起着重要的作用。通过免疫荧光实验观察表明,超表达转基因酵母的微管多呈异常的狭小扇形结构,反义表达TaRAN1的酵母微管不能形成丝状结构,推测TaRAN1还可能参与微管(包括纺锤体)的结构形成过程。最后,我们用超表达TaRAN1的转基因拟南芥和水稻也证实了它的功能,其生长点表现出分生组织增多的原基、根生长点的有丝分裂指数有所改变、出现异常的细胞分裂时相等有关细胞周期异常的现象,更进一步说明了TaRAN1确实参与着细胞周期的调控过程,推测其与细胞周期从G2期进入M期的过程有关。 TaRAN1基因受IAA的诱导表达,且随着浓度的增加表达量增强。超表达的TaRAN1植株(包括拟南芥和水稻)的根表现出对外源生长素异常敏感,侧根显著变少,地上部分表现出生长素过量的表现型,顶端优势减弱,分蘖增多,生长周期延长等。HPLC测定转基因植物的IAA含量,明显高于对照。所以,TaRAN1可能还参与了复杂的生长素信号转导过程。TaRAN1基因还受各种胁迫处理的诱导表达,并且超表达植株对胁迫的忍受能力有明显提高,这说明TaRAN1还参与了胁迫信号应答的相应机制。Ran蛋白这些新功能目前还未见到其它报道。
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中国东北样带(NorthEast China Transect, NECT)是位于中纬度温带以降水量作为主要驱动因素的陆地样带。本文的工作以此作为研究平台,利用生态信息系统(Ecological Information System, EIS)以及Microsoft Excel 7.0软件包建立了样带的地理数据库和植物多样性数据库,包括气候数据库、植被数据库、遥感数据库和内蒙内C_4植物数据库以及样带内生态系统特征数据库。在此基础上,主要研究了以下四个方面的内容: 1. 利用Holdridge的生命地带方法对NECT内的生物群区进行了划分。 主要是确定了生物群区间过渡带的位置与宽度,并预测了在全球变化三种模式下NECT内生物群区,尤其是过渡带的变化图景。湿度升高2 ℃后,过渡带的面积都呈扩大化的趋势。森林区对于降水量的变化反应很敏感。荒漠灌丛(即荒漠草原类型)由于其水热条件处于样带内较极端类型,因而对于全球气候变化反应也比较敏感。 2. 研究了NECT内的α、β多样性以及包括生活型、水分生态型、区系地理成分等在内的植物群落特征多样性的梯度变化规律。 研究了样带内的多样性梯度,提出了在样带内存在的α多样性测度问题以及β多样性沿样带的变化规律:样带内由东到西,β多样性逐渐升高,群落内物种被替代的速率变慢;两种植被类型边界上的两个样地之间的相似程度由东到西呈上升趋势;同一类型群落之间的物种周转率比不同类型群落间的物种周转率相对要低。同时将各个环境因子与α、β多样性作了回归分析,找出样带内决定α、β多样性的主要环境因子指标。 样带内沿43.5°N一线附近植物群落的生活型共有17类,水分生态型8类,区系地理成分包括17类,以此为基础分析了群落特征沿样带的变化规律。并探讨了生活型分布的历史地理原因。 3. 对样带气候-NDVI间的关系以及植被-NDVI的关系进行了探讨。 利用来自气象卫星的遥感数据一归一化植被指数(NDVI),和数值化后的样带1:100万植被图进行叠加,找到NECT内每种植被类型对应的NDVI值。样带内共有植被类型147种,反映在NDVI变化上的植被类型有106类。其中,自然植被101种。 影响年均NDVI分布的因子主要有经度、辐射日照百分率及7月温度,与经度呈正相关,与辐射日照时数及7月温度呈负相关。回归方程如下: NDVI = -220.426 + 3.273Lon - 80.338Ratio - 1.962T_7 (R~2 = 0.9714, F = 521.52, p < 0.001) 4. 研究了NECT内的光合功能型。 主要包括内蒙古地区的C_4植物及其生态地理特性。揭标C_4植物的分类群特性、生活型、水分生态型与区系地理成分等生态学特性。C_4植物分布的科属极其集中。C_4光合型为维管植物某些分类群(科、属、种)的特性,为它们固有的遗传特性。推断C_4起源于草本的某些科属。C_4植物为喜热、耐旱的类群。世界种、泛热带种、泛地中海种C_4植物较集中。 样带内的C_3、C_4功能型及其与环境因子的相关性。样带内C_4和C_3光合型植物组成比例由东到西表现出两高两低的趋势。分布主要与年均温和降水量呈显著相关。 提出了一种新的C_3、C_4鉴别方法。即根据野外测定的光合数据建立了C_3、C_4的判别模型: f_1(x) = -1.5493 + 0.1427Pn + 0.1035Tr + 0.3768ΔT + 0.1000Gs f_2(x) = -15.6142 + 1.0542Pn - 0.2503Tr - 0.2957ΔT + 0.6491Gs 最后,综合7个GCMs模型(GFDL,GISS,LLNL,MPI,OSU,UKMOH,UKMOL)的输出结果,利用此结果和本文建立的回归模型,模拟了样带内生物多样性的窨分布格局,并预测了末来全球变化下归一化植被指数NDVI的空间分布格局的变化。
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通过野外测定和控制实验结果发现: 在成林内林窗能促进发芽率、幼苗存活率和光合作用等。高光下,会发生多次生长。幼苗干物质积累与光照明显正相关。生长速度与存活无相关,但对第二年存活有影响。基径可作为光反应的无损伤测定指标。直射光和散射光对幼苗生长影响不同。 适当厚度的枯落物覆盖促进种子发芽和补充更新,埋藏太深则对辽东栎幼苗的生长、生理和存活等有抑制。灌木和树木的冠层对辽东栎在灌丛中的建立。 模拟实验表明完全去叶可导致16.7%的幼苗死亡,完全去除子叶可导致50%幼苗死亡,都严重影响幼苗的生理过程和干物质积累。土壤养分和干旱对辽东栎幼苗生长和光合也有很大影响。 运用通径分析精确测定,结果发现辽东栎冠层不同位置的叶片气体交换的限制因子有很大的差别。上层叶主要是气孔导度影响,叶温是通过饱和蒸汽压(VPD)有间接负作用。冠层下方光照的不足的限制,叶温有促进光合作用。不同部位叶片光合作用对气孔导度的依赖程度不同。 在辽东栎林演替过程中,生理生态变化趋势明显。根据所测的20多个生理指标,可将主要物种划分成不同的功能群。早期种具有较高的光合速率,气孔导度, 蒸腾速率和抗旱性, 而辽东栎和棘皮桦单独为一类。
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近二十年来,碳同位素技术己被广泛应用于植物生态学,特别是植物“碳一水”关系的研究中。植物的碳同位素组成(δ13C值)是叶片组织合成过程中光合活动的整合,它反映了植物长期的水分利用效率。内蒙古锡林河流域位于我国温带典型草原的核心区域,水分是制约本区植物生产力和群落稳定性的限制因素。因此关于本区植物水分利用效率和水分利用状况的研究,对探讨植物对生境干旱化的适应与响应机制具有十分重要的理论和实践意义。本研究沿土壤水分梯度在锡林河流域选取了沼泽化草甸、盐化草甸、草甸草原、典型草原、退化草地和疏林沙地等8个代表性植物群落,研究主要植物种、功能群和群落的碳同位素组成及叶片含水量、脯氨酸含量等与植物抗旱性相关的生理指标的变化,从植物种、功能群和群落三个层次研究了不同水分条件下植物水分利用效率的变化及其对不同水分生境的响应与适应机制。 1)在所调查的8个植物群落中,C3植物占绝对优势;C3植物的δ13C值和水分利用效率越大,其在整个流域中的分布频度越高,生物量也越大;与生长在湿润生境中的植物相比,生长在较干旱生境中的植物能积累更高水平的脯氨酸。以上结果表明,锡林河流域的植物可能通过两种机制适应当地的干旱生境:一是通过调节气孔导度提高植物的水分利用效率;止是通过积累高水平的脯氨酸增强植株的渗透调节能力并维持相对稳定的水分含量。 2)依照生活型将锡林河流域主要植物种划分成6个植物功能群:乔木、灌木、半灌木、多年生禾草、多年生杂类草和一年生植物。在较湿润生境,多年生杂类草更加丰富并构成了群落地上生物量的绝大部分;而在较干旱生境下,多年生禾草在群落中起更重要的作用;随着土壤含水量下降,灌木和半灌木逐渐增多,且在退化草地和沙地中其相对生物量迅速增加;多年生禾草别3c值显著高于其它功能群;随着土壤水分可利用性降低,多年生禾草和杂类草的别3c值表现出增加的趋势,而灌木/半灌木则表现出相反的趋势。以上结果进一步证明了,在典型草原区以生活型为基础划分的植物功能群可以用来进行较大尺度植物一水分关系的研究。 3)依照植物的水分生态类群,将锡林河流域主要植物种划分为六个植物功能群:旱生植物、中旱生植物、旱中生植物、中生植物、湿中生植物和湿生植物。在较湿润生境中(沼泽化草甸和盐化草甸),湿中生和湿生植物成为优势种并构成地上生物量的主体;在干旱生境中(草甸草原、典型草原和退化草地),旱生和中早生植物占绝对优势并构成群落生物量的90%以上;随着不同水分生态类群所适应的生境从干旱到湿润逐渐转变,植物的δ13C值和水分利用效率显著降低;旱生植物叶片脯氨酸含耸最高,湿中生和湿生植物脯氨酸含量最低,不同水分生态类群脯氨酸含量与其δ13C值和地上生物星.显著正相关关系。 4)不同群落类型的平均δ13C值有显著不同,表现为:典型草原>退化草地>沙地>退化恢复草地>草甸草原之盐化草甸>沼泽化草甸。C4植物的出现、不同物种δ13C值的差异和同一物种在不同生境下δ13C值的变化是影响群落平均δ13C值的主要因素,而这些因素与土壤水分状况和干扰历史(特别是放牧)密切相关。 此外,本文还研究了氮素添加对羊草和大针茅光合和水分利用效率的影响。土壤含氮量的增加可以显著提高羊草叶片光合能力和叭JE,而对大针茅的影响不大。作为锡林河流域两种优势植物,羊草和大针茅通过不同的生理机制来维持较高的WUE适应干旱生境:羊草为高光合、高蒸腾,而大针茅为低光合、低蒸腾。羊草较高的WUE是以降低氮利用效率 (NuE)为代价的;而大针茅在维持较高WUE的同时仍能维持较高的NUE,这一特征使大针茅可以广泛分布于更加干旱和贫瘩的地区。 以上研究结果,为深入开展典型草原生态系统植物与水分关系的研究提供了有价值的信息,进一步证实了稳定性碳同位素技术可以有效地指示不同群落类型中主要植物种长期水分利用效率。同时,通过对其它相关生理指标的测定,可以更好地探讨植物对水分限制的适应策略。我们的研究结果从植物种、功能群和群落三个层次进一步揭示了植物对干旱生境的适应机制,并初步阐明了人类干扰特别是过度放牧对草原群落建群种和优势种的生态替代或/和灌丛入侵的影响。这些研究对生物多样性保护、全球变化和区域可持续发展等热点问题的研究都具有重要的意义。在今后的研究中,结合其它稳定性同位素(如2H,18O和15N)技术,将有助于我们进一步深入研究蒙古高原植物对气候变化和过度放牧的适应与响应机制。
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元素化学计量学指从化学计量学的角度出发,通过分析比较生命物质不同结构层次(分子、细胞、器官、机体、种群、群落等)或生态系统中元素的相对比值,来研究各层次相互之间以及生态学过程中元素之间的关系。生态化学计量学研究可以把生态实体的各个层次存元素水平上统一起来,足近年来新兴的一个生态学研究领域,广泛应用于生态学研究中。C,N,P是生物地球化学循环中的重要元素,在生态系统中占有重要地位,许多环境问题都与它们有关,由此这三种元素的化学计量学受到生态学家们的普遍关注。C:N:P化学计量学在水生生态系统中研究较为深入,目前已发展到染色体水平,而在陆地生态系统中的研究较为匮乏近年来由于人类活动的强烈影响,这三种元素的循环在速度和规模上都发生了前所未有的改变,导致一系列环境问题的出现,因此C:N:P化学计量学在陆地生态系统中的研究就显得尤为重要。作为地球生命存在基础的绿色植物,在地球上已有数亿年的演化历史,研究陆地植物的元素化学计量学不仅有助于深入了解植物存在于地球上的内在机制,而且可以为许多环境问题的解决提供理论依据。本文首先建立中国不同地区植物氮磷含量数据库,通过数据分析找出一般规律,并进一步揭示植物不同进化阶段N:P化学计量比的变化规律。在此基础上,通过在内蒙古羊草草原设立不同施肥样地来模拟自然界不同氮磷环境,从试验水平上研究不同施肥处理及施肥梯度下生态系统中氮、磷、有机质的变化规律,并从化学计量学角度研究其内在机制。 利州新建成的中国维管植物数据库(包含1603种植物)研究了不同进化水平以及不同功能群(生活型)间植物N:P比的变化规律,并沿胡焕庸线(胡线)把中团分为为东西两部分,从总体水平上对比了东、西部间叫植物氮磷含量以及N:P的异同。结果表明:l)从演化水平来看,尽管氮磷含量表现出极大的差异,除豆科植物外,植物N:P基本保持稳定水平;2)木本植物与草本植物的N:P比差异.显著,木本植物之间(常绿乔木,常绿灌木,落叶乔木,落叶灌木)N:P不具有显著差异;3)中国东西部植物养分含量和N:P比表现出极显著差异,东部的养分含量低于西部,而N:P显著高于西部。 在内蒙古羊草草原两块永久实验样地(样地A:1980年围封样地和样地B:1999年田封样地)进行了为期两年的N素和P素添加试验。氮素添加梯度为0,5,15,30,50,80 g NHN03.m.2.yr-1。P素添加梯度为0,2,4,8,16,and 32 g P2Osm-2 yr-1(仪分析了羊草器官的结果)。分别从植物器官、物种、功能群水平研究了N素添加对N:P化学计量学的影响,此外还研究了土壤和凋落物C:N:P化学计量学对N素添加的响应。结合生物量的变化趋势,探讨了元素化学计量学对养分状况的指示作用。 1.羊草器官对施肥的响应结果表明,添加N素可以显著提高羊草器官中的含N量,p素可以显著提高器官中的含P量:除2001年样地A中的根茎外,根茎中的含P量基本不受N素添加的影响;茎中的含P量同样表现出不受N素添加影响的趋势(2000年B区茎除外):N素添加可以显著增大羊草叶片中的含P量(B区2000年叶片除外)。P素添加对羊草器官的含N量没有影响;羊草器官中的氮磷含量施肥处理下表现出显著的正相关关系(N素添加下B区叶片除外)。N素添加对羊草器官的N:P比没有显著影响(A区茎2000年和B区叶片2000年除外):P素添加显著降低了羊草器官中的N:P比。 2.四种优势植物(羊草、羽茅、针茅和苔草)地上生物量和N:P化学计量学对氮肥的响应研究发现,四个物种的氮磷含量均具有极显著相关关系;氮肥可以显著提高样地A中的羽茅生物量,降低苔草的生物量,而使样地B中的羊草生物量增大;两块样地中,四个物种的氮磷含量及N:P比均随N素水平的增高而增大(样地A中的羽茅N:P比除外)。 3.基于生活型划分的功能群(多年生根茎禾草,多年生丛生禾草,豆科植物,多年生杂类草,一二年生植物,灌木和半灌木)对N素添加的响应研究表明:施N可以提高样地A中的多年生丛生禾草的生物量,而使样地B中的多年生根苇禾草增加;多年生杂类草的相对多度在两个样地中均随施氨水平的增加而显著 降低:在样地B中,施氮可以显著提高不同功能群的氮磷含量;在样地A中,功能群N、P含量对施肥的响应并没有一致的变化规律,添加N素可以显著提高不同功能群的含N量(豆科植物除外),多年生根茎禾草和多年生杂类草的P含量有显著增大的趋势(P < 0.005),而其它功能群(豆科植物、灌木和小半灌木、多年生杂类草和~二年生杂类草)的P含量基本恒定(P>0.05);在样地A中,多年生丛生禾草,多年生杂类草,一二年生植物,灌木和半灌木的N:P比随施氨水平的增加而显著增大,多年生根茎禾草和豆科植物的N:P比基本不变;在样地B中,多年生丛生禾草的N:P比随施氨水平的增加而显著增大,多年生根茎禾草、多年生杂类草和…二年生杂类草不受施氨水平的影响。 4.添加N素对根实验结果表明:两块样地中,上层根(0-10 cm)的生物量仅在施N后第一年显著增加,而下层根(10-20 cm)的地下生物量在两年的施N处理下均不受施肥梯度的影响i在样地A中,施肥后第一年对根的N、P含量影响不显著,施肥后第二年可以显著增大上层根的N、P含量;在样地B中,添加N素后第一年可以显著增大根的含P量; 在两个样地中,两年的N肥处理对根的N:P比没有显著影响:在施氨处理中,根的N、P含量及N:P比在施肥第一年的响应要高于第二年。 5.所有处理中,上层土壤(O-lO cm)养分含量(有机碳,全氮,全磷)均高于下层土壤(10-20 cm);在样地A中,氮素添加对r十壤有机碳没有显著性作用,在施肥第一年可以显著增加上层土壤的N、P含量,而在施肥后第二年对土壤N、P含量没有显著影响;在样地B中,添加N素对两年的土壤养分均没有显著影响:养分添加两个样地土壤中的元素比值(C:N比,C:P比,N:P比)没有显著影响;土壤养分对施N一年后的响应要高于第二年。 6.养分添加对凋落物化学特征及化学计量学特征的影响研究结果表明:凋落物现存量不受施肥的影响;2001年凋落物现存量与2000年和2001年的地上生物量相关关系不显著;添加N素可以显著提高凋落物的N含量,而对有机碳含量和P含量没有显著影响;凋落物C:N比随施肥梯度的增大而显著降低,N:P比显著增高,而C:P比没有明显变化。 以上研究结果表明,不同植物功能群的N:P比存在差异,人类活动强烈影响自然植被中的植物N:P比;但植物的N:P比不受植物进化的影响(豆科植物除外);由于植物已有数亿年的演化历史,同时N与P在植物的结构和功能上具有密切的联系,在生物地球化学循环中办存在耦合作用。因此植物N:P比值恒定可能是一普适性规律。 N素添加试验表明,在植物根、地上器官、物种和功能群水平上N与P均呈显著正相关关系,反映了植物体内的氮磷含量具有协同作用。共存种对N肥的响应不同,表明物种受不同元素的制约。因此除非把生态系统中所有物种对施肥的响应刻画清楚,笼统的认定生态系统缺乏某种元素是不适当的。 施肥试验表明,两种围封时间样地的主要限制性元素不同。极度退化(样地B)植物生长主要缺N,而在保护较好样地(样地A),P也逐步成为一种限制因素。反映了随着保护时间的增加,植物生长逐渐由N限制型向N、P共同限制型过渡。添加的养分要么被植物吸收,挥发到大气中,或以凋落物的形式返还到土壤表层。但是对养分的预算有待于进一步研究。土壤中的养分含量对N素添加有…个滞后效应,而植物响应较为迅速。功能群N:P比在施肥实验中不能保持恒定,可能是由于实验时间较短的缘故;化学计量学的研究表明羊草草原分解凋落物的微生物受P素的制约,可能是由于植物体内具有高的P素再转运机制。这一结论有待于进一步的验证。氮肥降低了凋落物的C:N比,因此凋落物的分解速率可能将要发生改变。这需要进一步开展C循环的研究。
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植物源挥发性有机碳化合物(Volitale organic compounds, VOC)是大气VOC的主要来源,与对流层大气质量、大气化学密切相关。鉴于温带草地的分布范围很广,草地植物VOC释放潜力某种程度上影响植物源VOC的总释放量。另外,植物源VOC也是光合作用固定碳素的损失方式之一,可能在特定区域或生态系统中具有重要意义。基于上述想法,本文设计了四个方面的实验作为研究内容:1) 温带草地物种水平VOC释放潜力、及其与植物功能群的关系?2) 沙地植物物种水平VOC释放潜力、及其与植物功能群的关系?3) 沙地植物-草地植物VOC释放潜力存在显著性差异吗?4) 温带典型草地和退化草地的VOC释放速率如何?在生态系统水平,植物源VOC对温带草地碳循环的贡献多大? 在所测定的175种温带草地植物中,不同植物间异戊二烯和单萜释放潜力差异很大;除少数物种外,大多数植物的异戊二烯和单萜释放潜力都较低,尤其是典型草地的优势物种。在此基础上,作者探讨了分类学赋值方法对温带草地植被的可行性,并初步建立了锡林河流域温带草地植物的VOC释放目录(共277种植物)。另外,温带草地植物的异戊二烯和单萜释放潜力与植物功能群(植物生活型和水分功能群)具有一定的联系,尤其是植物生活型。总的来说,温带草原的优势生活型(物种),即多年生根茎禾草(或多年生丛生禾草),具有较低的异戊二烯和单萜释放潜力。各水分功能群间差异不显著,但中旱生植物、旱中生植物 (温带草原的优势功能群),具有较低的异戊二烯、单萜释放潜力。因此,温带草原退化过程中,那些具有较高VOC释放潜力的植物,重要性将会增加。 沙地植物种类组成非常丰富,不同物种间的异戊二烯和单萜释放潜力变异也很大。另外,沙地植物的异戊二烯和单萜释放潜力与其功能群间关系较密切,不同植物生活型间差异显著;其中也以多年生根茎禾草、多年生从生禾草的释放潜力最低,而乔木的释放潜力相对最高;该结论基本与草地的研究结论一致。然而,沙地植物的异戊二烯和单萜释放潜力与其水分功能群的关系比较模糊,中生植物具有更高的释放潜力,湿生植物的释放潜力较小。 通过对比沙地植物和草地植物的释放潜力,发现沙地植物的异戊二烯和单萜释放潜力比草地植物高,且这种差异整体上显著。另外,这种显著性差异,在不同植物生活型、水分功能群间也同样存在。沙地植物比对应的草地植物具有更高的异戊二烯和单萜释放潜力,最可能的原因:沙地正午的温度明显比草地温度高,前者实测温度可超过 45 ℃,这种经常性、周期性高温,促使沙地植物采用与草地植物不同的适应策略,即沙地植物通过释放更多的异戊二烯或单萜来减少其可能遭的热胁迫或热伤害,这种长期适应策略,使沙地植物具有更高的萜类化合物释放潜力。 本文还调查了温带典型草地生态系统和退化草地生态系统的异戊二烯和单萜释放速率,结果表明典型草地的标准异戊二烯和单萜释放速率分别为0.50 μgC g-1 h-1和0.69 μgC g-1 h-1;退化草地的标准异戊二烯和单萜释放潜力分别为0.32 μgC g-1 h-1和1.59 μgC g-1 h-1。总的来说,温带草地的异戊二烯和单萜释放速率都比较低,尤其是典型草地。整个生长季,典型草地释放的异戊二烯和单萜分别为31.6 mgC•m-2 和 70.4 mgC•m-2;退化草地的异戊二烯和单萜释放量分别为20.8 mgC•m-2 和 168.8 mgC•m-2。退化草地萜类化合物总释放速率远高于典型草地,尤其是单萜释放能力。过度放牧引起的草地退化,通过改变植被种类组成,对温带草地的异戊二烯和单萜释放速率产生显著影响;总体而言,温带草地退化将会使草地释放更多萜类化合物。 在温带草地生态系统中,Clost as VOC相对其NPP而言很小,在环境PAR和温度高时,它的贡献率相对较大;Clost as VOC约占典型草地生态系统NEP的5.32 %,退化草地生态系统NEP的0.23 %。植物源VOC释放所损失的碳素相对草地生态系统NPP而言几乎可以忽略不计;但是,相对其NEP,Clost as VOC还是具有一定的相关性。虽然,草地生态系统Clost as VOC对NPP或NEP的贡献率较小,但考虑到全球尺度植物源VOC的巨大释放速率,它在碳循环中的贡献率仍然不容忽视;在某些特殊的生态系统中,仍可能扮演重要角色。
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水分是半干旱草原生态系统植物多样性和初级生产力的限制因素。近年来由于人为干扰和气候干旱,特别是过度放牧,导致半干旱地区草原严重退化,草地生产利用和生态服务功能日益衰减,自然灾害频繁发生。草原退化演替主要表现为不同植物种的消长和替代过程。在内蒙古草原,过度放牧导致多年生根茎禾草和丛生禾草被豆科灌木或具根茎和不定根的杂类草替代,丰富的多年生杂类草被一、二年生植物替代。目前,对于上述功能群之间的替代机制,以及草原退化的机理尚不十分清楚。本研究在中国科学院内蒙古草原生态系统定位研究站选取了79年围封的大针茅(Stipa grandis)样地、其外围的自由放牧样地及中德合作项目“ Matter Fluxes in grassland of Inner Mongolia as influenced by stocking rate (MAGIM) ”的传统平地放牧处理小区为研究对象,从植物-水分关系的角度,利用氢和碳稳定性同位素技术,研究主要植物种和功能群水分来源和水分利用效率对放牧的响应,进而揭示放牧干扰下草原退化的机理。本研究取得了如下主要研究结果和结论: 1. 在干旱年份,雨水仅湿润了大针茅草原0-20cm的表层土壤。土壤中保存的冬季降水贡献了植物可利用水分的30%,而在正常年份只有10%。干旱季节羊草(Leymus chinensis)和大针茅能够利用土壤60cm以下保存的多年降水,而糙隐子草(Cleistogenes squarrosa)和冰草(Agropyron cristatum)只能利用生长季的雨水。长期过度放牧使冰草和糙隐子草的相对生物量和相对多度均显著增加,而羊草的相对生物量和相对多度显著降低。这种由放牧引起的群落结构与组成的改变,降低了植被对冬季降水的利用,加剧了干旱对生态系统的影响。 2. 依据羊草草原群落植物的生活型和光合类型划分为:C4禾草、C4杂类草、C4灌木、C3禾草、C3杂类草、C3鳞茎类植物和C3灌木七个功能群,各功能群间的水分利用效率差异显著。不同功能群植物在对土壤水分的利用上存在着明显的生态位分离。C4禾草和C3鳞茎类植物主要利用表层水分,而C4灌木则利用深层土壤水分,C3其它功能群介于二者之间。在无放牧和低载畜率下,各功能群植物均主要吸收浅层土壤水分,功能群间竞争相对强烈。在较高载畜率下,C3禾草转为利用深层土壤水分,功能群间出现水分生态位的分离,部分地缓解了植物对土壤表层水分的竞争。沿着载畜率梯度,群落对浅层土壤水分的利用呈现出先增加,尔后下降的趋势。 3. 在放牧干扰下,羊草草原群落中主要植物种稳定性碳同位素值的变化范围为-13.100/00~-27.590/00。不同功能群植物间的水分利用效率有着显著的差异:C4禾草> C4杂类草> C4灌木> C3禾草、C3杂类草> C3鳞茎类植物> C3灌木。C3鳞茎类植物和C4杂类草的水分利用效率随载畜率增加而降低。C3和C4禾草的水分利用效率随载畜率的增加表现为先增加,尔后下降的趋势。群落水平的水分利用效率主要由占生物量90%的禾草的水分利用效率决定。随着载畜率增加,群落水分利用效率有逐渐降低的趋势。
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由于人为因素导致的全球范围内的第六次物种大灭绝已经成为不争的事实,但人类还不清楚这种现象对生态系统功能的影响。在回答生物多样性与生态系统功能关系的问题上,补偿作用是一个争论的热点。为了阐明生物多样性对生态系统功能的影响,于2005年夏开始,在内蒙古温带典型草原开展了一个研究生物多样性与生态系统功能的物种去除试验。本研究是该项目的一部分。 元素循环是生态系统的重要功能之一,而氮素是限制草地生态系统生产力的主要因素,氮矿化是氮循环的关键步骤,因此,本研究重点讨论植物功能群对土壤氮矿化作用的影响,提出3点假设:1. 不同植物功能群对土壤氮矿化速率影响不同;2. 植物功能群去除前后氮矿化速率不同;3.植物功能群之间存在补偿效应。为了证明这些假设,于2006年9月、2007年6月和2007年8月份分别进行了室内培养(温度25℃,湿度60%田间最大持水量)用于测量氮矿化速率,同时于2007年6月和2007年8月份进行野外培养用于测量野外条件下的氮矿化速率,并在去除处理2年后得到以下主要结果: 1. 植物功能群去除数与土壤氮矿化速率呈单峰曲线关系(P<0.05),去除少量植物功能群氮矿化速率上升,去除更多的植物功能群后氮矿化速率下降; 2. 植物功能群去除数与土壤硝态氮含量呈线性正相关关系(P<0.0001),植物功能群的丧失加剧了土壤NO3--N的流失; 3. 多年生非禾草(PF)比其他植物功能群显著降低了氮矿化速率(P<0.05); 4. 短期内(去除处理1年内)在凋落物回填的情况下,去除0个植物功能群与去除全部植物功能群的氮矿化速率无显著差异(P>0.05); 5. 内蒙古温带典型草原在近3年内(2005、2006、2007)土壤碳库、氮库变化较小。
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九寨沟湖泊湿地在维持九寨沟的生态平衡中起着重要的作用,在旅游产业的发展下,湿地生态系统及生物多样性面临着较大的威胁。尽管九寨沟湿地具有重要的生态价值,但目前对其研究尚比较薄弱。湿地植物群落和植物地理研究可以为湿地资源的可持续利用和监测保护提供科学依据。作者从2004年8月到2007年11月对九寨沟湿地的植物物种组成、地理分布、优势植物群落的结构、生长动态、湿地土壤种子库进行了调查研究。主要结果如下: 1. 九寨沟湿地物种组成、地理分布特点及湿地植物群落特点 九寨沟湿地共有苔藓植物8科13属16种,维管植物为48科107属199种。九寨沟湿地植物的地理成份较为丰富,维管植物在科级水平上有7种地理分布型(变型),在属级水平上有13种地理分布型(变型), 在种级水平上共有29种地理分布型(变型)。九寨沟湿地植物以温带成份和我国特有成份为主,同时兼有热带、亚热带成份和环极—高山成份。九寨沟湿地植物的分布表现出明显的垂直地带性和水平地带性。湿地植物群落可划分21个群落类型,不同植物群落类型的物种多样性及物种组成存在较大的差异。九寨沟湿地植物的物种多样性和群落多样性以及较高的生产力特征,是维持其湿地生态景观多样性和稳定性的基础。 2. 土壤、水环境、海拔等对湿地植物的分布及生物多样性的影响 九寨沟湿地土壤、水等环境因子存在较大的差异。帕米尔苔草和宽叶香蒲等群落的凋落物较多,土壤有机碳、土壤总磷较高,可能是九寨沟湿地的重要土壤碳库。 九寨沟湿地植物沿水环境梯度的分布规律表现为:沉水植物(轮藻—篦齿眼子菜,水苦荬,杉叶藻)——挺水植物(水木贼,芦苇,宽叶香蒲)——湿生草本(苔草、节节草、披散木贼)——湿生灌木(柳灌丛,小檗灌丛)等。海拔也影响湿地植物的物种组成。 水深对物种多样性有影响,水深与物种丰富度负相关。随着水深的增加,水木贼、芦苇、杉叶藻、宽叶香蒲等群落的物种多样性下降;在长期淹水和季节性淹水的地方,水木贼群落物种多样性存在显著差异。土壤总氮与水木贼群落物种丰富度正相关。 3. 土壤营养元素、水环境对植物生长的影响 水深影响湿地植物生物量的分配。芦苇无性系分株在47 cm水深的环境中单株平均生物量最大;在干滩地中(地面水深0 cm),叶生物量百分比最大,而茎生物量百分比最小,茎的生物量百分比和生长速率随水深的增加而增加;在较干的滩地生境中,开花率、花序的生物量百分比明显大于水较深的生境。 水深与水木贼地上生物量负相关,但水木贼地上生物量在长期淹水和季节性淹水的地方没有显著的差异。在水浅的地方,杉叶藻、水木贼、芦苇等植物群落中,其他伴生物种的生物量占样方总生物量的百分比较大。 土壤有机碳、土壤总氮、土壤总磷等对湿地植物生物量的影响比较大:宽叶香蒲地上生物量与土壤总磷正相关;水木贼地上生物量与土壤总氮正相关;杉叶藻地上生物量与土壤有机碳正相关。 水深、土壤营养成分对湿地植物高度、密度等有影响。水木贼的平均高度在季节性淹水的地方比长期淹水的地方低,平均密度在长期淹水的地方比季节性淹水的地方低;除了5月份,其他观察月份水木贼的密度都与水深负相关,同时与土壤有机碳正相关。另外,芦苇密度与土壤有机碳含量正相关,宽叶香蒲密度与水深负相关,帕米尔苔草高度与土壤有机碳负相关。 4. 优势植物群落的动态变化 在优势植物群落中,优势种的高度、密度、盖度、生物量等在群落中占绝对优势。除五花海,水木贼群落的物种组成、高度、生物量在两年间没有显著的变化。芦苇群落的物种丰富度在近两年有所增加。 湿地植物生长表现为明显的季节动态,生长的峰值大多在7月-8月。优势植物群落的物候与水文周期有关。湿地植物群落的物种组成和密度,可以作为对湿地监测和保护的生物指示。 5. 九寨沟湿地土壤种子库特征及其在湿地生物多样性恢复中的作用 水深和现存植被物种丰富度可以解释湿地土壤种子库的变化。水深可以解释表层物种丰富度45%的变化。现存植被物种丰富度可以分别解释10 cm土层、2-5 cm土层及5-10 cm土层土壤种子库45%、48%和25%的变化。 湿地土壤种子库的密度为0-15945粒m-2, 种子库中共发现23个物种。现存植被优势物种和种子库优势物种不同。各层土壤种子库密度和物种丰富度并不存在显著的差异,但第二层土壤种子库密度最大。海拔、现存植被优势种盖度、土壤总磷、土壤总氮、土壤有机碳对湿地土壤种子库的密度和垂直结构没有影响。土壤种子库物种丰富度小于地上植被物种丰富度。湿地土壤种子库与地上植被的相关性不大。在浅水区域,湿地土壤种子库在湿地植被恢复中有一定作用。但在深水区域,保护现存植被更重要。 The lakeshore wetlands are valuable ecological units of the Jiuzhaigou lakes. Pressure for travel industry development pose a continuing and severe threat to the biodiversity-support function of the wetland system. Despite the ecological importance of wetlands in Jiuzhaigou, they are so far poorly studied. Both general plant communties and biogeographical studies are needed in order to attain basis for sustainable use the wetland resources and adequate protection of these areas. The present study was undertaken to examine aquatic plants distribution and the species compositon, structure and growth dynamics of their communities with variations of environmental factors along altitudes, water depth and soil properities gradients in Jiuzhaigou. Analysis of field survey data collected during August 2004 and November 2007 in lakeshore wetlands in Jiuzhaigou National Nature Reserve, Sichuan, China. The results were as following: (i) Species composition and biogeography in wetland vegetation 8 families, 13 genus, 16 species of moss and 48 families, 107 genus and 199 species of vascular plants in Jiuzhaigou wetlands were found. The floristic compositions were abundunt. Ten geographical distribution types at family level, 13 geographical distributions types at generic level and 29 geographical distribution types at specific level in vascular plants were found. Most species in Jiuzhaigou wetlands are temperate elements and Chinese endemic elements, with a few of tropical and subtropical and some circumarctic elements. And the plant distributions show clear vertical and horizontal patterns. There were 21 major wetland plant community types. Species composition and species richness in different plant communities are different. The species diversity and plant community diversity and their high biomass are the basis for the diversity and stability of wetland landscapes in Jiuzhaigou. (ii) Water depth, soil nutrients and altitudes influence on the species diversity and plant distribution. Total phosphorous and organic cabon in soil were higher in C. pamiernensis and T. latifolia communities, where are important cabon reservoirs in Jiuzhaigou wetlands. Along gradients of water depth, among populations of the dominant plant species present: submerged macrophytes (Chara vulgaris, Potagemonton pectinatus, Veronica anagalis-aquatica,Hippuris vulgaris), emergent macrophytes (Equisetum fluviatile, Phragamites australis, Typha latifolia), helophytes (Carex pamirensis )and shrubs (Salix sp., Berberis sp. ). Altitudes influence on the assemblage of plant communities. Water depth negatively correlated with species richness. Specie richness showed differences between permanently flooded sites and seasonally flooded sites in E. fluvatile communities. And total nitrogen in soil was negatively correlated with species richness in E. fluviatile communities. Altitudes show no significant influence on species richness, but in fact, through our analyses, they do have influence on the assemblage of wetland plants. (iii) Water depth, soil nutrients influence on the plant growth Water depth influences the biomass allocation in Phragmities australis. The average aboveground biomass of a single ramet (4.2 g) was the largest in the habitat with water level 47 cm above the soil surface. At the habitat with water level under soil surface 15 cm (-15 cm), the leaf biomass percentage (of the total ramet biomass) was the largest (46.1%), and the height and percentage of ramose ramets ( with branches on stem )(of the total ramets in a plot) were found obviously different. The deeper in water, the larger the biomass percentage and growth rate of stems were. The flowering rate and biomass of panicles were greater in shallow water than those in deep water. Water depth negatively correlated with aboveground biomass of E. fluviatile. However, above-ground biomass of E. fluviatile showed no significant difference between permanently flooded sites and seasonally flooded sites. But in shallow water, more biomasses of accompanying species were found in dominant plant communities such as H. vulgaris communities, E. fluviatile communities and P. australis communities. Water depth, soil nutrients influence on shoot density and shoot length of wetland plants. The shoot density of E. fluviatile was correlated to water depth in all growth months. Annual average density was significantly lower at permanently flooded sites than at seasonally flooded sites. But the annual average shoot length was significantly lower at seasonally flooded sites than at permanently flooded sites. (iv) Growth dynamics of dominant communities in Jiuzhaigou wetland The shoot length and shoot density, coverage and biomass of domiant species were dominated in plant communities. The species composition increased in P. australis communities in recent two years. The species richness in E. fluviatile communities showed no difference between 2005 and 2007. The above-ground biomass and shoot density in Five-flower Lake from July 2005 to July 2007 were significantly different, while in other sites, the differences were not significant. Shoot height, shoot density and above-ground biomass showed significant seasonal changes in all sites. Growth dynamics correlated with the cycle of water levels in lakes. Most plants growth parameters peaked at July or August. The biomass of T. latifolia peaked in August. But the shoot length of T. latifolia in deeper water peaked in July. The shoot length of E. fluviatile increased significantly from May to August except in seasonally flooded sites in Arrow-bamboo Lake. The species composition of communities and shoot density can be used as bioindicators in Jiuzhaigou wetland. (v) Soil seed bank in Jiuzhaigou wetland and its role in vegetation restoration Seed density in all soil layer samples was negatively correlated to water depth. Water depth can explain 45% variance of species richness in surface layer in sediment. Species richness in extant vegetation can explain 45%, 48%, 25% variance of species richness in total 10 cm and in 2-5 cm and 5-10 cm layer sediment respectively. Mean seed densities in wetlands ranged from 0 to 15945 m–2. A total of 23 species germinated in seed bank. The dominant species in seed bank and extant vegetation showed great difference. The total number of species and seedlings that germinated in different layers was not significantly different. But the second layer had the greatest seed density. In shallow water, seed bank can contribute to vegetation restoration, while in deeper water, protection of extant vegetation may be a better strategy.
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常绿阔叶林以其富饶的生物资源、丰富的生物多样性和巨大的生态与环境效益引起了人们越来越大的重视,它的研究已成为国际植被科学界关注的主题之一。我国分布着世界上面积最大的亚热带常绿阔叶林,在世界植被中具有重要地位,它的分布表现出明显的地带性差异,存在着多样的植物群系及其对应的气候特征。但是在植物功能性状领域,与全球范围其它生物群系相比,常绿阔叶林物种的研究较少,其功能性状间、功能性状与环境间的关系尚不清晰。 本研究以常绿阔叶林木本植物的当年生小枝为对象,试图从小枝水平上的生物量分配格局、叶片大小与数量的权衡关系、小枝茎的构型效应、叶片元素化学计量学,以及小枝大小的成本与效益分析等方面,较为系统地揭示小枝水平上的植物功能性状间及其与气候间的关系。因此,在华西雨屏带内部的不同纬度设置峨眉-青城-雷波-平武的温度梯度进行比较,并对有降水差异的川西南偏湿性(雷波)与偏干性常绿阔叶林(西昌)进行对比研究,同时在不同山体进行不同海拔梯度的比较研究。 本文主要研究结果如下: (1)小枝生物量分配格局叶水平上,叶片重-叶柄重(Y轴vs.X轴,下同)呈斜率小于1的异速生长关系,表明叶柄对叶内部的生物量分配影响显著。小枝水平上,叶和茎的生物量以及它们与小枝总生物量间基本呈等速生长关系,表明大的小枝或大叶物种不一定在叶生物量的分配上占优势。不同生活型间,在小枝或者茎的生物量一定时,常绿物种叶片的生物量比例较落叶物种稍高。与温度和水分较优越(峨眉及其低海拔)的生境相比,在相对低湿(螺髻)与低温(平武)的生境中的植物会减少对叶的投入而增加对支撑部分的投资比例。 (2)小枝叶片大小与数量的权衡无论是不同气候带还是不同生活型以及不同海拔梯度,叶片大小与出叶强度基本都是呈负的等速生长关系,表明了叶片大小-数量在小枝水平上的权衡。在不同气候梯度的对比中,叶片数量(出叶强度)一定时,高温和高水分生境(峨眉)比低温(平武)和低湿(螺髻山)生境中的物种的叶片大小(质量和面积)更大,表明不同生境的比较中,小的叶片可能具有较高的出叶强度和更高的适合度收益。“出叶强度优势”(Leafingintensitypremium)假说可能不适宜解释不同生境物种叶片大小差异。 (3)小枝茎的构型效应虽然茎长和茎径与叶片大小都呈正相关关系,与出叶强度都呈负相关关系,但茎长/茎径比与叶/茎生物量之比呈负相关关系;与叶片的大小呈负相关关系,与出叶强度呈正相关关系。这说明小枝构型能影响小枝叶/茎生物量分配和叶大小-数量的权衡关系。其影响机制可能是小枝内部的顶端优势。另外,茎长/茎径比在低湿和低温等不利生境中的植物中较高,而在降水和温度较适宜环境中较低。 (4)叶片C、N、P化学计量学N含量和P含量,C/N比和比叶重(LMA,leafmassperarea)呈正的等速生长关系,而N和LMA,P和LMA呈负的等速生长关系。在LMA一定时,C/N比随着生境胁迫压力的增加而降低,N、P含量随着生境压力的增加而增加。在P含量一定时,N含量随着生境压力的增加而降低,即N/P比在生境条件较优(峨眉及其低海拔)时较高。常绿和落叶植物叶片的N/P比没有差异,在LMA一定时,常绿植物的N、P含量较高、C/N比较低。总之,植物的C、N、P化学计量学特征受叶片属性如LMA与气候,及其相互作用的影响。 (5)小枝大小的代价与效益分析、TLA与小枝总重总叶面积(TLA,totalleafarea,Y轴,下同)与总叶重(X轴)均呈斜率小于1的异速生长关系,TLA与小枝横切面积呈斜率为1的等速生长关系。表明叶片面积的增加总是小于叶重和小枝总重的增加,随着小枝的增大,它的叶面积支撑效率下降。在热量和降水优越的生境(峨眉及其低海拔)中,相同小枝重或者相同茎横切面积的小枝,其叶面积支撑效率较低湿与低温环境下(螺髻山、平武及高海拔)的高。 总体上,本文初步研究了小枝水平上可能存在的以下三种权衡关系:叶-茎生物量分配权衡;叶片大小-数量的权衡;小枝茎长-茎径的权衡关系,以及气候要素等对这三种权衡关系的影响。在此基础上,我们还讨论了这些权衡关系的可能形成机制,及其与物种生态适应的联系。本研究丰富了生活史对策中关于权衡关系的研究内容,为我国常绿阔叶林功能生态学研究积累了材料。 Evergreen broad-leaved forests are attracting much more attention from vegetation ecologists than ever before because of their abundant nature resource and biological diversity, and also great ecological benefits. China has the largest distribution of subtropical evergreen broad-leaved forests (temperate rainforests) that are typical and representative in the world. The forests span over more than ten degrees in latitude and more than 30 degrees in longitude, providing an ideal place to study plant functional ecology, i.e., the climatic effect on plant functional traits and the relationship between the traits. However, relative to the other biomes, there are few studies addressing functional ecology of the plant species from subtropical evergreen broad-leaved forests. In this study, I focused on the leaf size-twig size spectrum of the woody species of subtropical evergreen broad-leaved forests in southwestern china. I collected data on leaf size and number, twig size in terms of both mass and volume, and stem architecture from five temperate mountains, and then I analyzed the relationships between leaf and stem biomass and between leaf size and number, the effect of stem length/diameter ratio on biomass allocation and on the relationship between leaf size and number, leaf C:N:P stoichiometry, and the twig efficiency of supporting leaf area in relation to twig size. I also addressed the climate effect on the spectrum. The temperature gradient from warm to cool sites was represented by Emei Mountain, Qingchengshan, Leibo, and Pingwu, and the rainfall gradient was assumed to emerge from the comparison between Leibo (High) and Luojishan (Low). In addition, altitudinal effects were analyzed with comparisons between low and high altitudes for each mountains. My main results are as follows. Isometric relationships were found between leaf mass and twig mass and between lamina mass and twig mass, suggesting that the biomass allocation to leaves or laminas was independent of twig mass. Petiole mass disproportionably increase with respect to lamina mass and twig mass, indicating the importance of leaf petioles to the within-twig biomass allocation. In addition, the investigated species tended to have a larger leaf and lamina mass, but a smaller stem mass at a given twig mass at favorable environments including warm and humid sites or at low altitude than unfavorable habitats, which might be due to the large requirements in physical support and transporting safety for the species living at unfavorable conditions. Moreover, the evergreen species invested more in leaves and laminas than the deciduous at given stem or twig biomass within any specified habitats. Negative, isometric scaling relationships between leaf number and size broadly existed in the species regardless of climate, altitude, and life forms, suggesting a leaf size/number trade-off within twigs. Along the climatic gradients, at given leaf number or leafing intensity, the leaves were larger in the favorable environments than the poor habitats. This suggested that the fitness benefit gained by small leaves could be larger than that with high leafing intensity in the stressful sites. I concluded that the “leafing intensity premium” hypothesis was not appropriate to interpreting between-habitat variation in leaf size. Both stem length and diameter were positively correlated to leaf size but negatively correlated to leafing intensity. The ratio of stem length to diameter was negatively correlated to leaf mass fraction, and it was negatively correlated to leaf size but positively correlated to leafing intensity. This suggested that the stem architecture influenced twig biomass allocation and the relationship between leaf size and number. The mechanism underlying the architectural effect might lie in the apical dominance within twig. Moreover, the ratio was greater in unfavorable habitats but smaller in favorable environments. Positive, isometric relationships were found between N and P contents per leaf mass, and between C/N ratio and leaf mass per area (LMA), but N and P contents scaled negatively to LMA. C/N ratio decreased but N and P increased with increasing habitat stress at a given LMA. N content declined with increasing habitat stress at given P content. These indicated that N/P and C/N were higher but LMA was lower in favorable habitats than in the other circumstances. The evergreen and deciduous species were non-heterogeneous in N/P, but the evergreen species have higher N and P contents and lower C/N than the deciduous ones. In general, C:N:P stoichiometry were related to both climatic conditions and other important functional traits like LMA. Total leaf area (TLA) allometricly scaled to leaf mass with a slope shallower than 1, similar to the relationship between TLA and total twig mass (leaf mass plus stem mass), suggesting that TLA failed to keep pace with the increase of leaf mass and twig size. However, TLA scaled isometricly to twig cross-sectional area. Thus, it could be inferred that the twig efficiency of displaying leaf area decreased with increasing twig size. In addition, the efficiency at a given twig size was large in favorable than unfavorable habitats. In general, in this preliminary study, I studied three tradeoff relationships within twigs, i.e., between leaf and stem biomass, between leaf number and size, and between stem length and diameter, as well as the climatic effect on the relationships. I discussed the mechanisms underlying the tradeoff relationships in view of biophysics and eco-physiology of plants. I believe that this study can serve as important materials advancing plant functional ecology of subtropical forest and that it will improve the understanding of life history strategies of plants from this particular biome.
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The absorption spectra of phytoplankton in the visible domain hold implicit information on the phytoplankton community structure. Here we use this information to retrieve quantitative information on phytoplankton size structure by developing a novel method to compute the exponent of an assumed power-law for their particle-size spectrum. This quantity, in combination with total chlorophyll-a concentration, can be used to estimate the fractional concentration of chlorophyll in any arbitrarily-defined size class of phytoplankton. We further define and derive expressions for two distinct measures of cell size of mixed. populations, namely, the average spherical diameter of a bio-optically equivalent homogeneous population of cells of equal size, and the average equivalent spherical diameter of a population of cells that follow a power-law particle-size distribution. The method relies on measurements of two quantities of a phytoplankton sample: the concentration of chlorophyll-a, which is an operational index of phytoplankton biomass, and the total absorption coefficient of phytoplankton in the red peak of visible spectrum at 676 nm. A sensitivity analysis confirms that the relative errors in the estimates of the exponent of particle size spectra are reasonably low. The exponents of phytoplankton size spectra, estimated for a large set of in situ data from a variety of oceanic environments (similar to 2400 samples), are within a reasonable range; and the estimated fractions of chlorophyll in pico-, nano- and micro-phytoplankton are generally consistent with those obtained by an independent, indirect method based on diagnostic pigments determined using high-performance liquid chromatography. The estimates of cell size for in situ samples dominated by different phytoplankton types (diatoms, prymnesiophytes, Prochlorococcus, other cyanobacteria and green algae) yield nominal sizes consistent with the taxonomic classification. To estimate the same quantities from satellite-derived ocean-colour data, we combine our method with algorithms for obtaining inherent optical properties from remote sensing. The spatial distribution of the size-spectrum exponent and the chlorophyll fractions of pico-, nano- and micro-phytoplankton estimated from satellite remote sensing are in agreement with the current understanding of the biogeography of phytoplankton functional types in the global oceans. This study contributes to our understanding of the distribution and time evolution of phytoplankton size structure in the global oceans.
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In July 2004, dominant populations of microbial ultraplankton (<5 μm), in the surface of the Celtic Sea (between UK and Eire), were repeatedly mapped using flow cytometry, at 1.5 km resolution over a region of diameter 100 km. The numerically dominant representatives of all basic functional types were enumerated including one group of phototrophic bacteria (Syn), two groups of phytoplankton (PP, NP), three groups of heterotrophic bacterioplankton (HB) and the regionally dominant group of heterotrophic protists (HP). The distributions of all organisms showed strong spatial variability with little relation to variability in physical fields such as salinity and temperature. Furthermore, there was little agreement between distributions of different organisms. The only linear correlation consistently explaining more than 50% of the variance between any pairing of the organism groups enumerated is between two different groups of HB. Specifically, no linear, or non-linear, relationship is found between any pairings of SYB, PP or HB groups with their protist predators HP. Looking for multiple dependencies, factor analysis reveals three groupings: Syn, PP and low nucleic acid content HB (LNA); high nucleic acid content HB (HNA); HP and NP. Even the manner in which the spatial variability of Syn, PP and HB abundance varies as a function of lengthscale (represented by a semivariogram) differs significantly from that for HP. In summary, although all microbial planktonic groups enumerated are present and numerically dominant throughout the region studied, at face value the relationships between them seem weak. Nevertheless, the behaviour of a simple, illustrative ecological model, with strongly interacting phototrophs and heterotrophs, with stochastic forcing, is shown to be consistent with the observed poor correlations and differences in how spatial variability varies with lengthscale. Thus, our study suggests that a comparison of microbial abundances alone may not discern strong underlying trophic interactions. Specific knowledge of these processes, in particular grazing, will be required to explain the causes of the observed microbial spatial variability and its resulting consequences for the functioning of the ecosystem.
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The North Atlantic Oscillation (NAO) is a major mode of variability in the North Atlantic, dominating atmospheric and oceanic conditions. Here, we examine the phytoplankton community-structure response to the NAO using the Continuous Plankton Recorder data set. In the Northeast Atlantic, in the transition region between the gyres, variability in the relative influence of subpolar or subtropical-like conditions is reflected in the physical environment. During positive NAO periods, the region experiences subpolar-like conditions, with strong wind stress and deep mixed layers. In contrast, during negative NAO periods, the region shifts toward more subtropical-like conditions. Diatoms dominate the phytoplankton community in positive NAO periods, whereas in negative NAO periods, dinoflagellates outcompete diatoms. The implications for interannual variability in deep ocean carbon flux are examined using data from the Porcupine Abyssal Plain time-series station. Contrary to expectations, carbon flux to 3000 m is enhanced when diatoms are outcompeted by other phytoplankton functional types. Additionally, highest carbon fluxes were not associated with an increase in biomineral content, which implies that ballasting is not playing a dominant role in controlling the flux of material to the deep ocean in this region. In transition zones between gyre systems, phytoplankton populations can change in response to forcing induced by opposing NAO phases.