,1,3,*Vessel length as a key hydraulic structure in woody plants: A review
CHENG Xiang-Fen1, MA Jin1, ZHAO Han1, JIANG Zai-Min2, CAI Jing,1,3,*通讯作者:
编委: 赵平
责任编辑: 李敏
收稿日期:2017-11-11修回日期:2018-03-27网络出版日期:2018-06-20
| 基金资助: |
Received:2017-11-11Revised:2018-03-27Online:2018-06-20
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程向芬, 马晋, 赵涵, 姜在民, 蔡靖. 木本植物水力学结构之导管长度研究进展. 植物生态学报[J], 2018, 42(6): 609-618 doi:10.17521/cjpe.2017.0293
CHENG Xiang-Fen.
导管作为木本植物木质部中运输水分与无机盐的重要管道结构, 普遍存在于大多数被子植物中。它们是由许多长管状的细胞以顶端对顶端的方式连接而成的管状结构。组成导管的每一个细胞称为导管分子, 单个导管由成百上千个死亡的导管分子组成, 导管分子在发育初期是活的细胞, 在成熟过程中, 细胞侧壁木质化并产生次生加厚, 同时, 细胞内的液泡膜破裂, 释放出水解酶, 使上下相连的两个导管分子之间的端壁溶解消失形成穿孔板, 以便于水分在导管分子间的长距离运输, 原生质体解体而成为死细胞, 整个导管成为一个长管状结构, 长度可达0.001-10 m (Cai & Tyree, 2014), 是导管直径的100-1β000倍(Pan et al., 2015)。根据侧壁纹孔的排列方式, 人们将导管分为环纹、螺纹、梯纹、网纹和孔纹等不同类型。导管分子的进化过程与维管植物的进化是相联系的, 穿孔板与纹孔类型在进化过程中都发生了各自的变化, 导管直径变大、长度缩短、连接度增高被普遍认为是导管的进化趋势(李红芳等, 2005)。
木质部导管特征是决定植物水力结构和功能的关键因素, 其直径、长度、内径跨度、壁厚度、连接度等特征都对植物的水力结构与功能有着重要的影响。植物的水分运输, 不是由一条导管从底部通到顶端的, 而是分段经过许多条导管曲折连贯向上运行的。水流既可以通过导管细胞腔及穿孔上升, 又可以通过侧壁上的纹孔横向运输。导管中的水分在运输过程中, 受张力影响处于亚稳定状态, 在地上部分与地下部分的压力差下, 水分以水柱的形式由木质部根的导管向上运输到茎的导管(李荣等, 2015), 最终到达叶片等器官。干旱、冻融交替等损伤, 会使得空气、灰尘等经由纹孔膜进入充水管道, 即形成空穴化, 并进一步形成栓塞, 即整个导管为气体占据, 使植物水力学功能受到影响(Tyree & Dixon, 1986; Sperry & Tyree, 1988)。栓塞会造成植物水力功能障碍, 影响水分运输甚至是植物的正常生长。木质部的进化使得水分运输的效率更高, 但更容易受空穴化的影响, 植物需要既安全又有效的运输形式, 安全性与有效性之间的差异可以用来反映物种在生态位及进化上的差异(Gleason et al., 2016)。即使未发生栓塞, 导管的输导功能也并非是永久保持的, 新的导管形成后, 老的导管会因周围薄壁细胞的侵入形成侵填体而相继失去输导水分的能力。
目前研究多集中在导管内径的测量与功能上, 较少关注导管长度, 对导管长度本身及其在植物水力结构及功能中的作用缺乏系统的了解(Jacobsen et al., 2012)。究其原因是导管特殊的几何结构特点, 无法在显微镜下直接观察测量其长度(Cai & Tyree, 2014), 需借助其他手段及方法等进行测量及计算。而导管长度测量的复杂性, 也是导管长度研究目前被严重忽略的重要原因(Ewers & Fisher, 1989a; Comstock & Sperry, 2000)。本文将从导管长度测量与计算, 导管长度在水力功能中的作用, 导管长度研究中的问题以及未来研究方向等方面展开论述。
1 导管长度测量方法
1.1 拍照法
测量导管长度最直接的方法为显微拍照法——在光学显微镜下将一根导管从头至尾拍下, 但由于导管特殊的几何形状, 使得导管长度的测量需拍摄成百上千张照片进行拼凑, 工作量大且精度较低, 因此不推荐使用该方法(Ewers & Fisher, 1989a; Comstock & Sperry, 2000; Tyree & Zimmermann, 2002)。1.2 注射法
导管长度测量的间接方式是将有色物质注入人为切开的导管使其形象化, 该物质选择的原则是: 被注入导管后, 能够在贯穿导管的基础上不发生堵塞, 也无法穿过纹孔膜扩散到相邻导管(Cai & Tyree, 2014)。灌注前一般用冲洗法(0.1 mol·L-1 KCl, 0.12 MPa, 30 min)将导管中的残余气泡除去, 因为在灌注过程中, 灌注物质会在导管中推着气泡向前, 直至将气泡压缩至压强与液压相等, 灌注物质无法继续向前, 导致灌注不充分。灌注完成后室温下静置干燥, 然后在距离灌注端不同位置处取样切片, 在显微镜下拍照, 观察被灌注导管的数量(截面导管数量或单位面积导管数量), 能够观察到导管填充数量的变化。早期多采用油基漆作为灌注物质, 以一定的压力沿导管运输方向注入枝条, 在导管中, 油会取代水到达导管末端, 水油表面张力较大, 在灌注压力较小的前提下油不会透过纹孔膜进入邻近的导管, 但该过程通常需要数天。灌注完成后, 在近灌注端, 有些导管完全灌注, 有些则是完全不含灌注物, 使计数不充分, 在干燥过程中, 多数导管中的油基漆收缩, 体积变小, 无法充满整个导管, 使得计数难度增加(Zimmermann & Jeje, 1981)。之后, 很多人用100倍稀释后的水基乳胶漆代替了油基漆, 但该方法仍存在较多缺陷。乳胶漆本身颜色较浅, 且其中的非晶体颗粒容易集结、吸附在颜料离子周围, 形成大的团状聚合体, 无法通过穿孔, 还未到达导管末端便发生堵塞, 这一点在小直径导管上尤为明显, 即使在0.1 MPa下灌注一周颜料仍无法充满整个管腔, 在观察导管数量时造成误差, 所测平均导管长度偏小(Sperry et al., 2005)。也有用热蜡作为灌注物质的, 与水基乳胶漆类似, 也存在灌注不充分的问题(Zimmermann & Jeje, 1981)。如今多使用即时配置的硅胶溶液(10 g RTV141A + 1 g RTV141B) 与荧光剂(0.5 mL, 1%荧光增白剂/氯仿(m/m))混合(André, 1998; Sperry et al., 2005; Hacke et al., 2007)。荧光剂不溶于水故不会通过纹孔扩散到相邻导管, 引起测量误差。灌注完成后需室温静置干燥3天左右, 时间大大缩短(Cai & Tyree, 2014)(图1)。和其他方法相比, 混合硅胶解决了先前灌注物质存在的粒子结块、堵塞导管、灌注不充分、流动性弱、干燥时间过长等问题。
图1
新窗口打开|下载原图ZIP|生成PPT图1硅胶注射法测定Populus tremuloides导管长度。A、B、C依次为距离灌注端0.5、1.0和5.0 cm的荧光图片, 亮色部分为紫外灯照射下的被硅胶灌注的导管(蔡靖摄)。
Fig. 1The vessels of Populus tremuloides with injection of silicone rubber mixed with fluorescer. A, B, C are the observations at 0.5, 1.0 and 5.0 cm from the injection surface, respectively. The brightness indicates the rubber-filled vessels under UV light (Photographed by CAI Jing).
1.3 空气注入法
空气注入法是一种相对快速的导管长度动态测量方法。是在一定的压力下向枝条注入空气, 并根据收集气泡的速率与测试样本长度的关系来推算不同长度导管的概率分布。在第一个气泡出现后, 测量此时单位体积空气在单位时间内通过的距离(空气流速), 此时导管长度为该样本的最大导管长度Lmax。然后将枝条逐渐剪短, 重复操作。该方法的前提为假设开口导管的数量与气体导度成正比, 并根据枝条长度与空气流速间的关系来推算导管长度分布。当被切开的新鲜茎段在低压(<100 kPa)下注入气体时, 气体只能通过被切开的导管, 因为导管壁上的湿润纹孔膜可以阻止气流的通过, 使气流不能到达相邻导管(Skene & Balodis, 1968)。气体灌注压力恒定时, 压力梯度与流量均随茎段长度的减小而增加。茎段对空气的传导率(C)(单位时间内, 通过单位横截面积的空气的体积)与开口导管长度无关, 而是与茎段中导管的数量和导管直径大小成比例(Pan et al., 2015)。当枝条长度减小到一定程度时, 由于没有新的导管被切开, 气体导度将不再增大。因此, 气体导度与导管数量有关。根据Hagen-Poiseuille方程的预测, 空气流速与开口导管直径的4次方有关, 且大直径导管对水分运输与空气流通的贡献更大(Tyree & Zimmermann, 2002)。因此空气注入法所得应是水力功能加权后的导管长度分布, 受大直径导管影响较大。且测量最大导管长度时也多用空气注入法(Jacobsen et al., 2012)。在用空气注入法进行导管长度测量时, 随着枝条剪短, 不同枝条长度(x)时分别测得一个相应的C, 并且在茎段中导管随机分布的假设前提下, 可推算出茎段的C的减少量和茎段长度的变化量dx成比例, 因为随着茎段的增长, 导管数量也在增加, 可推导出公式(1):
式中, C0为茎段长度x趋于0时的空气传导率; k为耗散系数(消亡系数)。对于一个有限长度的茎段, 长为x, 对于公式(1)积分可得:
公式(2)适用于不同长度茎段的C分析。
对lnC和x进行线性回归分析, 可以得到C0和k。设一个换算因子为D, 若单位传导率的导管数量已知, 则在进气端的导管数量为DC0。类似的, 可以用引入相同的换算因子D来得出Lmax:
用染料注入法测量导管长度时, 距离注射端不同距离x处的单位横截面积导管数量为N(横截面所有被硅胶注射导管的数量/横截面的面积), 以x为横坐标, lnN为纵坐标进行线性拟合, 斜率为λv, 且满足:
式中, N0是近注射端处的单位横截面积导管数量(x为0.1或0.2 cm), λv为拟合系数(同公式1中的k)。
无论是染料注入法利用测得的被灌注导管的数量或是空气注入法用不同长度茎段下的气体传导率, 皆通过双差法来描绘导管长度分布(Tyree, 1993), 双差法的表达式(Zimmermann & Jeje, 1981)如下:
Px为长度为x的导管所占的比率, 将公式(2)二次积分, 代入公式(5)中, 可得出连续型概率密度函数:
Cohen等(2003)经过计算已经证明公式(6)是一个Gamma概率分布函数, 它的形状因子等于2, 对公式(6)求导数可得:
以上的计算方法目前被广泛使用, 但其结果仍与实际值存在偏差, Cai和Tyree (2014)在计算Populus tremuloides导管长度分布概率时, 对公式(2)中的lnC和x进行了二阶多项式的回归, 将拟合精度提高了3倍左右, 且拟合结果也更符合杨树短导管数量更多的情况。
1.4 高分辨率断层扫描技术
还有一种测量方法是应用高分辨率的X射线计算机断层扫描技术(HRCT), 并配合分析软件来构建包括导管直径、导管长度、导管连接等在内的木质部整体网络结构。HRCT与医用CT技术原理类似, 可高强度、高分辨率地在植物组织的任何部分连续进行切片拍摄, 且不会对内部组织造成损伤(Brodersen et al., 2010), 将拍摄的图片用自定义开发的分析软件(Avizo)进行处理, 先建立初始的网络结构, 然后根据物种的解剖特性进行修改完善。建立的三维图像能够观察一定区域的全部导管及周围组织的完整结构, 并自动测量导管长度及直径等指标。由于该技术测量长枝条所用时间较长, 且该显微摄影技术需要先进的X射线发射源的显微断层摄影设备支持, 对硬件要求较高, 因此目前较少得到应用。但该技术能够无损观测植物组织内部, 其建立的三维木质部导管网络是手动测量无法比拟的, 因此在植物解剖及生理学上具有良好的应用前景(Brodersen et al., 2011)。1.5 不同测量方法的比较
拍照法是最直接的导管长度测量方法, 能够较为直观地观察到导管的微观形态, 但由于测量一根导管所需的照片数目较大, 测量时需对照片进行拼凑, 导致工作量大且精度低, 因此并不推荐使用。染料注入法将导管形象化, 测量结果较为准确, 能够直观地观察导管长度的分布状况, 明显看到导管长度与导管直径的关系, 但其测量周期长, 且最早的染料注射法溶剂多为油基漆等凝固较快的液体, 注入导管内的染料粒子易发生凝聚现象, 堵塞导管, 容易出现灌注不充分的情况。后期开始使用加了荧光剂的硅胶进行注射, 相较之前的注射剂具有凝固较慢, 粒子不易成团等优点, 在低压下, 更能趋近于导管终点, 所得结果更加准确, 也是目前被广泛使用的测量方法。染料注入法也具有自身的缺陷, 由于需要在低压下将染料注入枝条内, 灌注完成后需静置干燥, 耗时较长, 无论改进前的油基漆法还是改进后的硅胶注射法, 普遍存在难以到达导管底部的现象, 使测量结果存在一定误差。
空气注入法相对于染料注入法, 操作比较简单, 测量周期更短, 但普遍认为该方法所得导管长度并非传统意义上的导管长度, 而是与植物水力学特性相关的水力学长度(Venturas et al., 2016; Pan et al., 2015), 当测量的导管长度与水力特征有关时, 空气注入法可能更适合。空气注入法不存在染料注入法的灌注不充分问题, 在生长季后期, 导管中产生胼胝体但尚未完全堵塞时, 染料注入法测量精度会大大降低, 而空气注入法则不受影响(Pan et al., 2015)。Pan等(2015)用两种方法分别对环孔材(栓皮栎Quercus variabilis和葡萄Vitis vinifera)、散孔材(元宝枫Acer truncatum)以及半环孔材(84K杨树Populus alba × Populus glandulosa)的当年生枝条进行测量, 结果发现空气注入法所得4个种的平均导管长度普遍大于硅胶注射法所得的平均导管长度, 且二者存在显著性差异, 作者认为该结果可能是由于硅胶注射法是通过硅胶形象化的导管长度来计算, 而空气注入法则是基于测得的空气导度来推算的。但在Jacobsen等(2012)的研究中, 不同测量方法所得的8个树种的平均导管长度是一致的, 彼此之间并没有显著差异。综上所述, 两种测量方法所得结果的差异性及其原理还需要更多的研究来验证。
高分辨率断层扫描技术借鉴了医学上的计算机断层扫描技术, 分辨率更高, 对植物材料进行连续扫描, 具有精度高、直观化、视野范围广、活体测量、可建立立体化导管网络等优点, 但由于所需仪器及配套设施较为昂贵, 使用及维护不便, 目前难以被广泛应用于植物解剖结构的观测尤其是田间试验上(Brodribb et al., 2017)。
2 导管长度的分布
2.1 导管长度在植物内的分布
尽管某些藤本植物的导管长度可达数十米, 但植物的大部分导管仍为短导管(Ewers et al., 1990), Ilex verticillata最大导管长度为130 cm, 但有99.5%的导管处在0-10 cm间, Vaccinium corymbosum最大导管长度为130-140 cm, 有85%的导管处于0- 10 cm间, 6.5%的导管处于10-20 cm间(Zimmermann & Jeje, 1981), 大部分的导管无法延伸至整个样本。Venturas等(2016)对Populus trichocarpa、夏栎(Quercus robur)和葡萄进行导管长度分布概率的比较, 发现其大部分导管长度均在平均导管长度(分别为(1.8 ± 0.1)、(10.9 ± 1.9)、(11.7 ± 1.5) cm)之下。因此, 随样本长度增大, 被切开导管数量急剧下降, 即使被证实拥有较长的导管的植物也是如此。且Jacobsen等(2012)整合分析发现, 最大导管长度约为平均导管长度的5.6倍。有研究表明导管长度随枝条的直径、长度或年龄增大而增大(Zimmermann & Jeje, 1981; Zimmermann & Potter, 1982; Ewers & Fisher, 1989b; Ewers et al., 1990)。对榆树的研究发现, 导管长度随枝条年龄增大而增长, 纯种Ulmus minor枝条在第5年时达到稳定值, 而杂交种U. minor × U. pumila在第6年时达到稳定, 91%的最长导管来自最长的枝条, 83%的最长导管来自最粗的枝条(Martín et al., 2013)。对Artemisia tridentata的根和茎的导管长度做比较, 发现根的导管长度要明显大于茎(Kolb & Sperry, 1999)。
2.2 导管长度在生活型间的分布
不同生活型的木本植物的平均导管长度具有显著性差异(Baas et al., 2004; Zhu & Cao, 2009; Martínez-Cabrera et al., 2011; Gleason et al., 2012; McCulloh et al., 2015; Apgaua et al., 2017), 藤本植物较灌木及乔木拥有更长的导管, 灌木与乔木的平均导管长度没有显著差异(Zimmermann & Jeje, 1981; Sperry & Saliendra, 1994)。不区分生活型时, 平均导管长度在不同木材孔隙结构类型上并无差异, 但就乔木而言, 环孔材导管比散孔材更长(Jacobsen et al., 2012), 该结论与前人研究结果一致(Frost, 1930; Cochard et al., 2005, 2010; Choat et al., 2010)。3 导管长度与导管直径的关系
导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(Zimmermann & Potter, 1982; Ellmore & Ewers, 1986; Ewers & Fisher, 1989b; Kolb & Sperry, 1999; Hacke & Jansen, 2009)。不同的研究对于导管直径与导管长度的关系有不同的结论。从种间水平看有些****认为二者相关: Hacke等(2006)通过对28个树种进行比对, 得出平均导管直径和平均导管长度具有线性相关性(线性回归曲线的斜率为1.48, R2 = 0.63)。对枫属(Acer)不同种的研究中也发现, 越窄的导管越短, 导管直径与长度成正相关关系(Lens et al., 2011)。对不同穿孔板类型及导管数量的植物分别研究发现, 不同类群中, 导管直径均与导管长度成不同程度的正比关系(Sperry et al., 2007), Jacobsen等(2012)对88个种进行整合分析发现, 种间导管长度与导管直径仅有弱的相关性(F1,87 = 14.09, p < 0.001, R2 = 0.14), 也有些****认为二者没有关系, 如Wheeler等(2005)对16个来自不同科属的植物进行了研究, 并没有发现导管直径与长度之间的相关性; Sperry等(2005)对种子植物研究发现导管长度与导管直径没有明显的相关性, 而是与导管直径的平方成正比。对藤本植物的研究也发现, 种间不存在导管直径与长度的关系, 而在种内研究水平看, 窄导管普遍较短, 而宽导管则有长有短(Ewers & Fisher, 1989b; Ewers et al., 1990); Cai等(2010)对杨树种内无性系研究发现, 导管长度随导管直径增大而增大, 大直径导管趋向于导管长度更长。目前普遍认可的是种内最大导管直径与最大导管长度成正比(Ewers et al., 1990)。无论种内还是种间, 导管直径在沿导管方向变异较大, 并不是均一的, 使得导管直径与导管长度的关系更加多变(Akachuku, 1987; Ewers & Fisher, 1989b; Brodersen et al., 2011)。4 导管长度与木质部水力学特性的关系
4.1 导管长度与导水率的关系
与木质部导水率相关的导管特征研究多集中在导管直径上。根据Hagen-Poiseuille方程, 导管的导水率与其水力直径Dv成正比:其中: n是所测导管数量, d是单个导管腔直径(Ewers & Fisher 1989a; Schreiber et al., 2011)。目前已有大量研究证明导管直径与导水率相关, 且普遍认为导管直径与导管长度成正比, 因此导管直径与长度关系的研究从侧面解释了导管长度与导水率的关系。当导管较长且弯曲时, 会使导管之间的连接度增大, 使导管网络更加高效协调, 有利于水分的横向运输(Loepfe et al., 2007; Espino & Schenk, 2009)。水分在维管植物木质部导管或筛管(以下简称维管)中运输时的阻力是由腔阻力与末端壁阻力近似串联而成, 腔阻力是维管内径的函数, 而末端壁的阻力(穿过穿孔的流阻)则是维管长度的函数。在维管内径相同时, 导管长度越短, 导管内的端壁数量越少, 水的流阻越小, 则导水率越大。维管的腔阻力与末端壁阻力约为1:1, 但导管越长, 末端阻力越小。 可能是因为导管越长, 拥有纹孔的末端壁重叠区域就越大(Sperry et al., 2005)。因此, 导水率与导管长度的关系与导管直径、端壁数量及末端壁的重叠区域大小有关。当导管直径随导管长度增大时, 导水率也随之增大。就导管而言, 长度越长, 端壁数量越多, 而末端壁重叠区域也越大, 因此导水率的变化受到二者综合作用。
Comstock和Sperry (2000)指出导管长度增长时, 单个导管中导管分子数量增多,就会减少水分在运输时穿过导管端壁所受到的阻力, 因此是有利于提高水分运输有效性的进化方向, 但事实上植物体内的导管并非无限增长的, 这是由于植物受到了安全性的限制。水分在植物体内的运输是受压力梯度驱动的, 导管两端存在压力差, 导管末端通常具有更负的负压, 更易受空穴化的威胁。空穴在导管内会迅速扩展至整个导管, 使其丧失水力功能, 相比之下短导管的空穴化则对整个茎段的水力功能影响较小。因此, 导管长度的进化状态是导管水分运输安全性与有效性的中和效果。
4.2 导管长度与栓塞脆弱曲线的关系
4.2.1 栓塞脆弱曲线的定义木质部水势与木质部栓塞的关系可以用“脆弱曲线” (vulnerability curve, VC)来表示(Tyree & Sperry, 1989), 该曲线是根据木质部导水率损失的百分数(PLC)与相对应水势绘制而成的曲线, 作为描述植物水力学特征及水分运输安全性的一个重要指标, 目前已被广泛引用(Maherali et al., 2004)。栓塞脆弱曲线的建立通常有: 自然干燥法、空气注入法、压力套法(Cochard et al., 1992)、Cavitron离心机法(Cochard, 2002; Cochard et al., 2005)和Sperry离心机技术(Sperry et al., 2010)。以上方法均是将样本置于不断脱水的环境中诱导并加深栓塞, 并测量不同时期对应的木质部水势与水力功能损失状况, 以此来判断植物的抗栓塞能力。
4.2.2 栓塞脆弱曲线测量存在的争议
离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(Pockman et al., 1995)。压力套法是将枝条两端切平后, 插入压力室中, 两端在外, 室中部分树皮划开一部分(Sperry & Saliendra, 1994)或完全剥离(Ennajeh et al., 2011), 便于加压时的空气进入以诱导栓塞, 同时测量通过枝条的导水率, 以此来构建脆弱曲线(Cochard et al., 1992; Salleo et al., 1992)。目前对离心机法与压力套法建立的脆弱曲线的合理性存在着较大的争议(Christman et al., 2012; Jacobsen & Pratt, 2012; Sperry et al., 2012; Hacke et al., 2015)。
研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(Cochard et al., 2010)尚不确定。一种观点认为上述两种方法在建立长导管植物的栓塞脆弱曲线时, 当导管长度大于样本枝条长度时, 所得结果大大高估了样本的脆弱性。Cochard等(2013)在对Choat等(2012)建立的1 200个树种VC曲线数据库分析后, 对该问题进行了详细的论述, 当所用样本长度大于最大导管长度时, 由于此时枝条中开口导管比例小, 用压力套法和离心机法所得结果接近于真实的P50 (导水率损失50%时的木质部水势: 一般用来表示枝条的抗栓塞能力), 而当样本长度接近或小于最大导管长度时, 所得结果(P50)与实际值相比要更低, 目前已发表的脆弱曲线中可能有20%存在该问题。在用压力套法建立脆弱曲线时, 样本的最大导管长度对压力套法所得结果具有关键性影响。无论是长导管植物还是短导管植物, 均是在样本长度大于最大导管长度时, 所得脆弱曲线与自然干燥法建立的脆弱曲线一致, 枝条短于最大导管长度时, 结果与自然干燥法与植物在大田中的表现相比, 显示出了极高的脆弱性(Ennajeh et al., 2011; Choat et al., 2010)。在对葡萄的研究中, 用不同方法建立栓塞脆弱曲线, 其P50显示出巨大差异(自然干燥法: -2.97 MPa, 冲洗离心机法: -0.7 MPa), 作者认为有可能是由于离心过程中水分会更容易从开口导管流出, 才造成脆弱性过大的假象(Choat et al., 2010)。也有人认为, 离心机法在使用前要对样本进行冲洗, 若样本短于最大导管长度, 此时样本中被切开导管比例较大, 由于开口的导管更容易使冲洗液中的气泡及其他粒子进入导管, 使枝条的栓塞脆弱性被高估, 因而造成了“r”形曲线的假象, 而短导管植物在测定时样本中被切开导管比例小, 且短导管纹孔数量少, 膜的直径更小, 气泡与碎屑无法进入(Choat et al., 2008; Jansen et al., 2009; Limousin et al., 2010; Ennajeh et al., 2011), 因此曲线多呈“s”形。而压力套法则是枝条中的树汁被空气过饱和, 且无法被导管滤除, 在枝条末端压力被释放后, 空气在水中的溶解度降低, 并形成气泡, 最终诱发了空穴化(Wheeler et al., 2013)。
另一种观点则认为长导管植物不会对离心机建立的栓塞脆弱曲线造成影响。Sperry等(2012)对Quercus gambelii、复叶槭(Acer negundo)及Sorbus scopulina (平均导管长度分别为17.4、3.1、4.7 cm左右)不同长度的枝条(14、27 cm), 用离心机法和自然干燥法建立脆弱曲线, 结果显示曲线形状及栓塞脆弱性没有显著差异, 黎明前的Quercus gambelii枝条用离心机法所测得的VC曲线与自然干燥法所得一致, 皆证明了导管长度对离心机法建立脆弱曲线没有影响。对火烧后的Rhamnus ilicifolia次生演替灌木丛研究表明, 火烧前后, 导管长度没有显著差异, 但脆弱曲线却从火烧前的“s”形变成了火烧后的“r”形, 这也说明脆弱曲线的形状与导管长度无关(Jacobsen et al., 2016), 这为“r”形曲线真实存在提供了证据。Barotto等(2016)对桉属3个种(赤桉(Eucalyptus camaldulensis)、E. viminalis、蓝桉(E. globulus))的研究发现, 拥有最长导管的种栓塞脆弱性反而最低(P12和P50更低), 且脆弱曲线为“s”形。
目前针对长导管植物建立脆弱曲线存在的一系列问题以及“r”形曲线的正确与否, 还需要未来更多的研究数据, 以及更精准的测量方法来进一步求证。
5 问题和建议
针对以上与导管长度相关的问题, 特提出以下几条建议:1)目前为止, 导管长度的测量方法已有了较大的改进, 染料注入法的灌注物质也经过了数代的变化, 目前以硅胶注入法最为常用, 硅胶由于本身并没有颜色, 需要加入荧光剂在紫外线下拍照, 而荧光剂存在随时间淬灭的现象, 会造成一定的测量误差(Pan et al., 2015), 因此, 有必要寻找本身显色、黏滞系数较低, 不易堵塞导管的替代物。导管长度的测量还多采用计算的方式, 而计算方法的精度还可以继续提高(Cai & Tyree, 2014), 在未来的研究中可以通过更多的实验数据来获得更接近真实导管长度的计算方法。无论是早期的拍照法, 还是目前广泛使用的空气注入法和硅胶注入法, 都是将植物离体测量, 人为将导管剪开, 这有可能对结果造成影响, 近些年兴起的将X射线计算机断层扫描技术应用于植物解剖学则解决了该问题, 未来可以向动态监测导管在木质部中的变化过程, 包括导管数量的增多, 小直径导管的增大增长, 以及导管直径与导管长度的关系随导管生长所发生的变化等方向发展, 在植物活体上, 动态、连续地观察植物导管的生长过程。
2)导管长度的研究多集中在茎的木质部中, 根及叶脉中的研究较少(Jacobsen et al., 2012), 但植物作为土壤-植物-大气连续体中的重要组成环节, 水分从根部吸收直至通过蒸腾作用回归大气, 需经过根、茎、叶3个部分的木质部, 因此, 研究植物水力学特性需从植物整体出发, 了解各个器官的导管分布状况及各部分的配合作用, 才能更好地掌握植物的水分运输及利用状况。尽管已有对不同生活型树种的导管长度的整合分析, 且普遍认为藤本植物拥有更长的导管, 但导管长度分布在种内乃至种间的变异程度、与植物系统发育学的关系乃至导管形态是否存在于其他水力学特性协同进化的现象还未可知, 且目前对导管长度的研究多集中在小范围内的植物种类, 缺乏对某一类群植物的系统化研究。针对上述问题, 未来研究可以利用日益完善的数据库资源来建立不同地域、气候区的导管结构分布图。
3)有关导管直径与导管长度的关系还缺乏具体定论, 已有研究表明导管直径在整个导管长度方向上是不均一的(Akachuku, 1987; Ewers & Fisher, 1989b; Brodersen et al., 2011), 但此现象是具有物种特殊性, 还是在木本植物中普遍存在?其生理学意义还需要进一步探究, 结果或许会对目前大家对二者关系的普遍认识产生较大的冲击。目前我们所了解的导管长度与导管其他特性之间的关系, 多集中在导管直径上, 日后导管长度与连接度、密度等的关系还需要深入研究, 建立完整的木质部结构模型, 立体化地了解植物导管功能。
4)离心机法与压力套法测得的“r”形曲线的真实性还存在较大的争议, 论点主要集中在人为切开的导管造成空气或水的进入上, 若可以在长枝甚至活体上, 非侵入性的测量植物的栓塞脆弱性, 则会大大提高测量精度及可信度。近些年以照相机与显微镜为设备支持的光学测量技术, 为栓塞脆弱性的测量打开了新的思路(Brodribb et al., 2016; Brodribb et al., 2017; Zhang & Brodribb, 2017)。光学测量技术具有操作方便、节约成本、无需离体等明显的优点, 在未来的试验中可能会取代现有的测量方法, 并对原有的方法或操作造成的错误脆弱曲线进行更正, 可能会改变目前对植物尤其是长导管植物栓塞脆弱性的认识。
导管的特性对了解植物水力学结构及功能具有重要的作用, 其中导管长度对评价植物水分运输的安全性和有效性具有指导性意义。而对植物水力学特性的了解则会在抗旱品种改良、优良品种选育上具有重要的作用, 更是为干旱及半干旱地区的植被恢复及建设提供先决条件。
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DOI:10.1163/22941932-90001529URL [本文引用: 1]
A reliable and simple microcasting method is applied to the study of the vascular structure in bamboo nodes; it provides new insights into their complexity, revealing the exact arrangement of branched vessels and clustered tracheary elements. Axial differentiation gradients in the metaxylem cell files, probable relics of the intercalary meristem, can also be found using this method. This anatomical finding can be linked to arecent hypothesis on the continuum in the tracheary element differentiation.
DOI:10.1111/1365-2435.12787URL [本文引用: 1]
1. Understanding the anatomical basis of plant water transport in forest ecosystems is crucial for contextualizing community-level adaptations to drought, especially in life-form-rich tropical forests. To provide this context, we explored wood functional anatomy traits related to plant hydraulic architecture across different plant functional groups in a lowland tropical rain forest.2. We measured wood traits in 90 species from six functional groups (mature-phase, understorey and pioneer trees; understorey and pioneer shrubs; vines) and related these traits to intrinsic water-use efficiency (WUE56) as a measure of physiological performance. We also examined vessel size distribution patterns across groups to determine trade-offs in theoretical hydraulic safety vs. efficiency.3. Some plant functional groups exhibited significant differences in vessel parameters and WUE56. Vessel diameters in vines and pioneer trees were two- to threefold greater on average than in understorey trees and shrubs. Contrastingly, vessels in understorey trees and shrubs fell within the smaller size classes, suggesting greater safety mechanisms. In addition to these trends, large vessel dimensions were important predictors of WUEi among the functional groups.4. We conclude that wood functional anatomy profiles varied across plant functional groups in a tropical rain forest. These groups can therefore serve as a framework for further investigations on structure–function relationships and a sound basis for modelling species responses to drought.
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DOI:10.1111/nph.2011.191.issue-4URL [本文引用: 3]
[本文引用: 1]
DOI:10.1073/pnas.1522569113URLPMID:27071104 [本文引用: 1]
Abstract The intricate patterns of veins that adorn the leaves of land plants are among the most important networks in biology. Water flows in these leaf irrigation networks under tension and is vulnerable to embolism-forming cavitations, which cut off water supply, ultimately causing leaf death. Understanding the ways in which plants structure their vein supply network to protect against embolism-induced failure has enormous ecological and evolutionary implications, but until now there has been no way of observing dynamic failure in natural leaf networks. Here we use a new optical method that allows the initiation and spread of embolism bubbles in the leaf network to be visualized. Examining embolism-induced failure of architecturally diverse leaf networks, we found that conservative rules described the progression of hydraulic failure within veins. The most fundamental rule was that within an individual venation network, susceptibility to embolism always increased proportionally with the size of veins, and initial nucleation always occurred in the largest vein. Beyond this general framework, considerable diversity in the pattern of network failure was found between species, related to differences in vein network topology. The highest-risk network was found in a fern species, where single events caused massive disruption to leaf water supply, whereas safer networks in angiosperm leaves contained veins with composite properties, allowing a staged failure of water supply. These results reveal how the size structure of leaf venation is a critical determinant of the spread of embolism damage to leaves during drought.
DOI:10.1104/pp.17.00552URLPMID:28684434 [本文引用: 2]
Abstract The vulnerability of plant water transport tissues to a loss of function by cavitation during water stress is a key indicator of the survival capabilities of plant species during drought. Quantifying this important metric has been greatly advanced by noninvasive techniques that allow embolisms to be viewed directly in the vascular system. Here, we present a new method for evaluating the spatial and temporal propagation of embolizing bubbles in the stem xylem during imposed water stress. We demonstrate how the optical method, used previously in leaves, can be adapted to measure the xylem vulnerability of stems. Validation of the technique is carried out by measuring the xylem vulnerability of 13 conifers and two short-vesseled angiosperms and comparing the results with measurements made using the cavitron centrifuge method. Very close agreement between the two methods confirms the reliability of the new optical technique and opens the way to simple, efficient, and reliable assessment of stem vulnerability using standard flatbed scanners, cameras, or microscopes. 2017 American Society of Plant Biologists. All Rights Reserved.
DOI:10.1007/s00468-014-0999-9URL [本文引用: 6]
DOI:10.1111/j.1365-3040.2010.02142.xURLPMID:20199614 [本文引用: 1]
The objective of this method paper was to examine a computational algorithm that may reveal how vessel length might depend on vessel diameter within any given stem or species. The computational method requires the assumption that vessels remain approximately constant in diameter over their entire length. When this method is applied to three species or hybrids in the genus Populus, vessel length is sometimes a linear function of vessel diameter and sometimes an exponential function of vessel diameter within a stem, based on R2 values. Our results give within-species variation of vessel length versus diameter, and we compare this to between-species variation of mean diameter versus mean length.
DOI:10.1111/nph.2008.177.issue-3URL [本文引用: 1]
[本文引用: 3]
DOI:10.1038/nature11688URL [本文引用: 1]
DOI:10.1111/j.1469-8137.2011.03984.xURL [本文引用: 1]
DOI:10.1046/j.1365-3040.2002.00863.xURL [本文引用: 1]
A technique for measuring hydraulic conductances of excised xylem segments exposed to high negative pressures is described. A centrifugal force is used to generate negative pressures ( P ) in the sample and to create a positive hydrostatic pressure difference (Δ P ) between its two ends. Δ P forces water through the sample at a flow rate ( F ) determined optically during centrifugation. The sample hydraulic conductance k is derived from F and Δ P . The sample vulnerability curve is given by the dependence of k on P . Results for Cedrus atlantica Manetti and Laurus nobilis L. shoots are given. The technique is appropriate for the analysis of xylem refilling under negative pressure.
DOI:10.1093/jxb/ert193URLPMID:23888067 [本文引用: 1]
Abstract Xylem cavitation resistance has profound implications for plant physiology and ecology. This process is characterized by a 'vulnerability curve' (VC) showing the variation of the percentage of cavitation as a function of xylem pressure potential. The shape of this VC varies from 'sigmoidal' to 'exponential'. This review provides a panorama of the techniques that have been used to generate such a curve. The techniques differ by (i) the way cavitation is induced (e.g. bench dehydration, centrifugation, or air injection), and (ii) the way cavitation is measured (e.g. percentage loss of conductivity (PLC) or acoustic emission), and a nomenclature is proposed based on these two methods. A survey of the literature of more than 1200 VCs was used to draw statistics on the usage of these methods and on their reliability and validity. Four methods accounted for more than 96% of all curves produced so far: bench dehydration-PLC, centrifugation-PLC, pressure sleeve-PLC, and Cavitron. How the shape of VCs varies across techniques and species xylem anatomy was also analysed. Strikingly, it was found that the vast majority of curves obtained with the reference bench dehydration-PLC method are 'sigmoidal'. 'Exponential' curves were more typical of the three other methods and were remarkably frequent for species having large xylem conduits (ring-porous), leading to a substantial overestimation of the vulnerability of cavitation for this functional group. We suspect that 'exponential' curves may reflect an open-vessel artefact and call for more precautions with the usage of the pressure sleeve and centrifugation techniques.
DOI:10.1104/pp.100.1.205URL [本文引用: 2]
DOI:10.1111/j.1399-3054.2005.00526.xURL [本文引用: 2]
A new technique for generating xylem cavitation and vulnerability curves was evaluated. The centrifugal force was used to lower the negative pressure in a xylem segment and to induce a positive pressure difference between sample's ends. This enabled the determination of sample hydraulic conductance during centrifugation and, hence, its variation with decreasing xylem pressures. The centrifuge technique was compared with standard methods on a large number of species including conifers, diffuse-porous and ring-porous woody angiosperms. A very good agreement was found for coniferous and diffuse-porous species. However, the technique was not appropriate for ring-porous species, probably because many vessels were cut open in the centrifuged xylem segments. The main advantage of this technique is its rapidity, the vulnerability curve of a xylem segment being constructed typically in less than half an hour. This will greatly facilitate the study of xylem cavitation in ecological or genetic researches.
[本文引用: 2]
DOI:10.1093/jxb/erg202URLPMID:12815034 [本文引用: 1]
Studies showing that rootstock dwarfing potential is related to plant hydraulic conductance led to the hypothesis that xylem properties are also related. Vessel length distribution and other properties of apple wood from a series of varieties were measured using the 'air method' in order to test this hypothesis. Apparatus was built to measure and monitor conductivity to air of fresh wood segments of different lengths. Theory for determining vessel length distribution was improved to give a single parameter uni-modal vessel length probability density function.
DOI:10.1046/j.1469-8137.2000.00763.xURL [本文引用: 3]
DOI:10.1002/j.1537-2197.1986.tb09709.xURL [本文引用: 1]
Hydraulic conductivity through the outermost growth ring of Ulmus americana was quantified to determine the significance of this single growth increment to fluid flow in xylem of a ringporous tree. Gravity flow rates through trunks deprived of the outermost growth ring dropped to 8% of the rate achieved in control trunks whose cross section was intact. However, colored dye, fed through stem segments, appeared in up to 4-yr old wood, corroborating earlier reports that fluid flows through more than just the outermost growth ring of ring-porous trees. Finally, the pathway of flow through older rings was shown to consist of narrow latewood elements while the wider and more hydraulically significant earlywood vessels came into play only in the outermost growth ring of U. americana. These data indicate that the outermost growth ring of Ulmus is responsible for over 90% of xylem transport in this ring-porous tree, because wide earlywood vessels function only for one growth season.
DOI:10.1111/ppl.2011.142.issue-3URL [本文引用: 3]
DOI:10.1111/nph.2009.183.issue-1URL [本文引用: 1]
DOI:10.1002/j.1537-2197.1989.tb11360.xURL [本文引用: 3]
Results were compared between the latex paint and compressed air methods for determining total vessel lengths, and between the sectioning and maceration methods for determining vessel diameters. The minimum, mean, median, and maximum vessel diameters were less with the sectioning method than with the maceration technique. Vessel diameter distributions were always nonnormal and had roughly similar patterns with the two techniques, but were statistically different from one another. In all six species where the paint and air methods for determining vessel length were compared, both methods showed a similar skewed vessel length distribution, with many short vessels and few long ones. Although there was no consistent pattern to the difference in results with these two methods, the vessel length frequency distributions were statistically different from one another. With the paint method, many vessels, especially many of the narrowest ones, were not paint-filled at the paint infusion port. The air method utilized the paint method, in part, and, in addition, is based upon the incorrect assumption that all vessels in the stem are the same diameter. Both techniques tended to exclude vessel lengths of the narrowest vessels. However, the narrow vessels, although numerous, contributed an insignificant amount to the total theoretical hydraulic conductance in stems.
DOI:10.1002/j.1537-2197.1989.tb15126.xURL [本文引用: 5]
Within-species and within-stem variation in vessel diameter and total vessel length were examined using the latex paint method on six species of tropical and subtropical lianas (woody vines). Narrow vessels were almost always rather short, but wide vessels ranged from short to long. Within Pithecoctenium crucigerum, larger diameter stems tended to have longer as well as wider vessels, with a maximum vessel length and width of 6.25 m and 366 渭m, respectively. Within stems of Saritaea magnifica, P. crucigerum, Hippocratea volubilis, and Vitis rotundifolia, narrow vessels had lower mean, median, and maximum vessel lengths than wide vessels. Vessels with intermediate diameters tended to have intermediate lengths. In Stigmaphyllon ellipticum and Bauhinia fassoglensis the outer system of secondary xylem tended to have longer as well as wider vessels than the inner system. Those narrow vessels (<50 渭m) that did occur in the outer system were short (<0.20 m), and were similar in length and diameter to those of the inner system.
DOI:10.1007/BF00328172URLPMID:28312972 [本文引用: 4]
Vessel dimensions (total diameter and length) were determined in tropical and subtropical plants of different growth forms with an emphasis upon lianas (woody vines). The paint infusion and compressed air methods were used on 38 species from 26 genera and 16 families in the most extensive survey of vessel length made to date. Within most stems there was a skewed frequency distribution of vessel lengths and diameter, with many short and narrow vessels and few long and wide ones. The longest vessel found (7.73 m) was in a stem of the liana (woody vine) Pithecoctenium crucigerum. Mean vessel length for 33 species of lianas was 0.38 m, average maximum length was 1.45 m. There was a statistically significant inter-species correlation between maximum vessel length and maximum vessel diameter. Among liana stems and among tree+shrub stems there were statistically significant correlations between stem xylem diameter and vessel dimensions. Lianas with different adaptations for climbing (tendril climbers, twiners, scramblers) were similar in their vessel dimensions except that scramblers tended to have shorter (but not narrower) vessels. Within one genus, Bauhinia, tendril climbing species had greater maximum vessel lengths and diameters than tree and shrub species. The few long and wide vessels of lianas are thought to hydraulically compensate for their narrow stem diameters. The many narrow and short vessels, which are present in the same liana stems, may provide a high resistance auxiliary transport system.
DOI:10.1086/334026URL [本文引用: 1]
1. Tracheids are characterized by great average length, small cross-sectional diameter, angularity of outline, evenly thickened walls, thin walls, and the absence of a distinct end wall. 2. Vessel segments which retain these primitive characteristics nearly always have scalariform perforations; the scalariform perforation is therefore primitive. 3. There is a high correlation between the diffuse arrangement of vessels and the scalariform condition of the end wall. 4. Vessel segments with scalariform perforations are characterized by scalariform lateral pitting; therefore scalariform lateral pitting is primitive, and this leads to the natural inference that the tracheid type from which the vessel was derived was also scalariform. 5. A high correlation was found between the scalariform condition of the lateral walls of vessel segments and the presence of bordered pits in the fibrous elements. 6. There was some evidence to indicate that a sequence from the protoxylem to the secondary xylem would reflect the origin of the vessel. 7. Many primitive woods show, in this positional sequence, all transitions from scalariform tracheids to scalariform vessel segments. 8. The evidence would indicate that vessel segments with scalariform pitting on both the end and side walls are more primitive than vessel segments with scalariform pitting on the end walls and opposite to alternate pitting on the side walls. 9. The wood of the vessel-less angiosperms Trochodendron, Tetracentron, and Drimys is unquestionably very primitive. The primitive tracheids of these genera resemble, to a considerable degree, the scalariform tracheids characteristic of the primary wood of primitive angiosperms.
DOI:10.1111/j.1365-2435.2012.01962.xURL [本文引用: 1]
1. Plants must balance water expenditure from their crown with water supplied through root and stem tissues. Although many different combinations of hydraulic traits could accomplish water balance, we ask whether variation across species in stem hydraulic traits has been concentrated along few, or many, dimensions of trait variation.2. We measured stem hydraulic traits for 120 woody dicot species across a range of different biomes in eastern Australia. Mean annual temperatures ranged from 10 to 27 00°C and aridity (precipitation/potential evapotranspiration) from 000·33 to 100·02 across study sites.3. Xylem-specific conductivity, species090005 height and ratio of leaf area to xylem area were positively correlated, manifesting as a single axis of trait variation, with other traits mostly orthogonal to this axis. Thus, as height and ratio of leaf area to xylem area increased across species and habitats (increasing resistance per leaf area), xylem-specific conductivity partially compensated for this resistance. Xylem-specific conductivity was well predicted by increasing height (r2 = 000·45) and ratio of leaf area to xylem area (r2 = 000·36). This three-trait axis was positively correlated with increasing precipitation (r2 = 000·28) and temperature (r2 = 000·15), but most of the explained variance lay within sites (39%) rather than across sites (10%). Thus, the spread of species090005 traits along this functional axis reflected structural and hydraulic differences among co-occurring species, at least as much as it reflected differences associated with contrasting climates.4. High xylem-specific conductivity in stems was accomplished by high vessel diameter to number ratio (r2 = 000·32) and/or by high vessel lumen fraction (r2 = 000·13). Low midday water potential (higher xylem tension) was associated with low ratio of vessel diameter to number (r2 = 000·25), whereas low specific gravity (r2 = 000·18) and stiffness (r2 = 000·12) were associated with high vessel lumen fraction.5. Light capture (i.e. increasing height and leafiness) may be facilitated by high xylem-specific conductivity, but marked increases in xylem-specific conductivity may also be associated with reduced hydraulic and mechanical safety. Although the trade-offs associated with increasing xylem-specific conductivity remain unclear, our data suggest that xylem-specific conductivity is important for maintaining water balance across a large range of species and biomes.
DOI:10.1111/nph.13646URL [本文引用: 1]
DOI:10.1111/j.1469-8137.2009.02783.xURL [本文引用: 1]
DOI:10.1086/520724URL [本文引用: 1]
Two structure‐function hypotheses were tested for vesselless angiosperm wood. First, vesselless angiosperm wood should have much higher flow resistance than conifer wood because angiosperm tracheids lack low‐resistance torus‐margo pits. Second, vesselless wood ought to be exceptionally safe from cavitation if the small cumulative area of pits between tracheids confers safety (the pit area hypothesis). Data were obtained from branch wood of 19 vesselless angiosperms:Amborella trichopoda,Trochodendron aralioides,Tetracentron sinense, and 16 Winteraceae fromTasmannia,Zygogynum,Bubbia,Pseudowintera, andDrimys. Contrary to the first hypothesis, vesselless and conifer species with narrow tracheids (below ca. 18 μm) had similar area‐specific resistivities. The reason was that vesselless angiosperms had an intertracheid pit resistance (mean\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $16\pm 2$ \end{document}MPa s m611) that was nearly as low as that of conifers (\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $6\pm 1$ \end{document}MPa s m611) and much lower than that of eudicot intervessel pits (\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $336\pm 81$ \end{document}MPa s m611). Low pit resistance was associated with greater pit membrane porosity inferred from scanning electron microscopy observations and silicone penetration and may represent incipient pit membrane loss. Pit resistance was often greater in wider angiosperm tracheids and obscured any drop in wood resistivity with tracheid width. In support of the second hypothesis, vesselless woods averaged a cavitation pressure of\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $-3.4\pm 0.3$ \end{document}MPa, which is low for their wet habitats. In agreement with the pit area hypothesis, resistance to cavitation increased with decreasing total pit area between conduits. However, vesselless angiosperms were more vulnerable for a given pit area than eudicots, consistent with their more permeable pit membranes. Small total pit area between conduits may allow angiosperm tracheids to have more porous membranes for conducting efficiency without creating a cavitation problem.
DOI:10.1093/treephys/26.6.689URLPMID:16510385 [本文引用: 1]
Abstract We tested the hypothesis that greater cavitation resistance correlates with less total inter-vessel pit area per vessel (the pit area hypothesis) and evaluated a trade-off between cavitation safety and transport efficiency. Fourteen species of diverse growth form (vine, ring- and diffuse-porous tree, shrub) and family affinity were added to published data predominately from the Rosaceae (29 species total). Two types of vulnerability-to-cavitation curves were found. Ring-porous trees and vines showed an abrupt drop in hydraulic conductivity with increasing negative pressure, whereas hydraulic conductivity in diffuse-porous species generally decreased gradually. The ring-porous type curve was not an artifact of the centrifuge method because it was obtained also with the air-injection technique. A safety versus efficiency trade-off was evident when curves were compared across species: for a given pressure, there was a limited range of optimal vulnerability curves. The pit area hypothesis was supported by a strong relationship (r2 = 0.77) between increasing cavitation resistance and diminishing pit membrane area per vessel (A(P)). Small A(P) was associated with small vessel surface area and hence narrow vessel diameter (D) and short vessel length (L)--consistent with an increase in vessel flow resistance with cavitation resistance. This trade-off was amplified at the tissue level by an increase in xylem/vessel area ratio with cavitation resistance. Ring-porous species were more efficient than diffuse-porous species on a vessel basis but not on a xylem basis owing to higher xylem/vessel area ratios in ring-porous anatomy. Across four orders of magnitude, lumen and end-wall resistivities maintained a relatively tight proportionality with a near-optimal mean of 56% of the total vessel resistivity residing in the end-wall. This was consistent with an underlying scaling of L to D(3/2) across species. Pit flow resistance did not increase with cavitation safety, suggesting that cavitation pressure was not related to mean pit membrane porosity.
DOI:10.1111/nph.13017URL [本文引用: 1]
[本文引用: 7]
DOI:10.3732/ajb.1200140URL [本文引用: 1]
[本文引用: 1]
DOI:10.3732/ajb.0800248URL [本文引用: 1]
[本文引用: 2]
DOI:10.1111/nph.2011.190.issue-3URL [本文引用: 1]
DOI:10.3321/j.issn:1000-4025.2005.02.035URL [本文引用: 1]
介绍了导管及其穿孔板的研究进 展,包括导管的特征 穿孔板的类型、多穿孔板与侧壁穿孔板、纹孔膜残留 ,导管的起源与穿孔板的演化,蕨类植物、裸子植物与被子植物导管的比较,并就导管进化与穿孔板演化,导管的二型性现象、侧壁穿孔板、多穿孔板与穿孔中纹孔 膜,生态对导管进化的影响等方面以及对今后的研究作了展望.
DOI:10.3321/j.issn:1000-4025.2005.02.035URL [本文引用: 1]
介绍了导管及其穿孔板的研究进 展,包括导管的特征 穿孔板的类型、多穿孔板与侧壁穿孔板、纹孔膜残留 ,导管的起源与穿孔板的演化,蕨类植物、裸子植物与被子植物导管的比较,并就导管进化与穿孔板演化,导管的二型性现象、侧壁穿孔板、多穿孔板与穿孔中纹孔 膜,生态对导管进化的影响等方面以及对今后的研究作了展望.
DOI:10.17521/cjpe.2015.0080URL [本文引用: 1]
从树木木质部栓塞脆弱性的定义 ,脆弱曲线的建立方法 ,木质部栓塞脆弱性与植物木质部结构、部位、抗旱性、分布及栓塞发生经历之间的关系 ,脆弱曲线模型的比较方面对植物木质部栓塞脆弱性研究的概况进行了回顾 ,以促进木质部栓塞脆弱性及树木抗旱机理方面的研究工作。
DOI:10.17521/cjpe.2015.0080URL [本文引用: 1]
从树木木质部栓塞脆弱性的定义 ,脆弱曲线的建立方法 ,木质部栓塞脆弱性与植物木质部结构、部位、抗旱性、分布及栓塞发生经历之间的关系 ,脆弱曲线模型的比较方面对植物木质部栓塞脆弱性研究的概况进行了回顾 ,以促进木质部栓塞脆弱性及树木抗旱机理方面的研究工作。
[本文引用: 1]
DOI:10.1016/j.jtbi.2007.03.036URLPMID:17509617 [本文引用: 1]
The xylem is one of the two long distance transport tissues in plants, providing a low resistance pathway for water movement from roots to leaves. Its properties determine how much water can be transported and transpired and, at the same time, the plant's vulnerability to transport dysfunctions (the formation and propagation of emboli) associated to important stress factors, such as droughts and frost. Both maximum transport efficiency and safety against embolism have classically been attributed to the properties of individual conduits or of the pit membrane connecting them. But this approach overlooks the fact that the conduits of the xylem constitute a network. The topology of this network is likely to affect its overall transport properties, as well as the propagation of embolism through the xylem, since, according to the air-seeding hypothesis, drought-induced embolism propagates as a contact process (i.e., between neighbouring conduits). Here we present a model of the xylem that takes into account its system-level properties, including the connectivity of the xylem network. With the tools of graph theory and assuming steady state and Darcy's flow we calculated the hydraulic conductivity of idealized wood segments at different water potentials. A Monte Carlo approach was adopted, varying the anatomical and topological properties of the segments within biologically reasonable ranges, based on data available from the literature. Our results showed that maximum hydraulic conductivity and vulnerability to embolism increase with the connectivity of the xylem network. This can be explained by the fact that connectivity determines the fraction of all the potential paths or conduits actually available for water transport and spread of embolism. It is concluded that the xylem can no longer be interpreted as the mere sum of its conduits, because the spatial arrangement of those conduits in the xylem network influences the main functional properties of this tissue. This brings new arguments into the long-standing discussion on the efficiency vs. safety trade-off in the plants xylem.
DOI:10.1890/02-0538URL [本文引用: 1]
The ability of plants to supply water to their leaves is intimately associated with survival. Water supply to leaves depends on maintaining an intact water column in the xylem from the roots to shoots. Because this hydraulic pathway is under tension, it is vulnerable to breakage through the induction of air emboli (cavitation). Although the physiological benefit of resistance to water-stress-induced xylem cavitation for desiccation tolerance is clear, there is considerable interspecific variation within and across climates. To understand the adaptive significance of this variation and the potential trade-off with water transport, we compiled a database of 167 species from 50 seed plant families and examined relationships among resistance to xylem cavitation, water transport capacity (as determined by the specific conductivity of xylem [Ks]), and climate. Relationships were evaluated using standard cross-species correlations (r). Because inferences about the adaptive significance of these correlations can be biased by the potential similarity of closely related species, we also analyzed our data using phylogenetically independent contrast correlations (PIC) calculated over a range of alternate seed plant phylogenies. Resistance to cavitation, expressed as the xylem tension at which 50% of hydraulic conductivity was lost ( 50), ranged from -0.18 to -9.9 MPa for angiosperms and from -1.5 to -14.1 MPa for conifers. Conifers were most resistant to cavitation, with mean 5080% more negative than angiosperms. In contrast, Kswas 270% higher in angiosperms than conifers. Across all species, cavitation resistance increased with decreasing mean annual precipitation. However, significant phylogenetically independent contrast correlations between 50and annual precipitation were found within the evergreen angiosperms and conifers but not in the deciduous angiosperms. Thus, the adaptive significance of increased resistance to cavitation as a mechanism of drought tolerance may be of primary importance in evergreen angiosperms and conifers. In contrast, analysis of independent contrasts indicated that Ksincreased with decreasing rainfall in deciduous angiosperms, whereas there was no association between Ksand water availability for evergreen angiosperms and conifers. These results suggest that the evolution of increased Ksmay be a critical adaptation to water limitation in deciduous angiosperms. Although there was a significant cross-species correlation between 50and Ks, this relationship was not supported by the independent contrast correlation, suggesting that the evolutionary basis for a trade-off between cavitation resistance and water transport capacity is weak.
[本文引用: 1]
DOI:10.3732/ajb.1000335URLPMID:21613189 [本文引用: 1]
Abstract PREMISE OF THE STUDY: Trees and shrubs tend to occupy different niches within and across ecosystems; therefore, traits related to their resource use and life history are expected to differ. Here we analyzed how growth form is related to variation in integration among vessel traits, wood density, and height. We also considered the ecological and evolutionary consequences of such differences. METHOD: In a sample of 200 woody plant species (65 shrubs and 135 trees) from Argentina, Mexico, and the United States, standardized major axis (SMA) regression, correlation analyses, and ANOVA were used to determine whether relationships among traits differed between growth forms. The influence of phylogenetic relationships was examined with a phylogenetic ANOVA and phylogenetically independent contrasts (PICs). A principal component analysis was conducted to determine whether trees and shrubs occupy different portions of multivariate trait space. KEY RESULTS: Wood density did not differ between shrubs and trees, but there were significant differences in vessel diameter, vessel density, theoretical conductivity, and as expected, height. In addition, relationships between vessel traits and wood density differed between growth forms. Trees showed coordination among vessel traits, wood density, and height, but in shrubs, wood density and vessel traits were independent. These results hold when phylogenetic relationships were considered. In the multivariate analyses, these differences translated as significantly different positions in multivariate trait space occupied by shrubs and trees. CONCLUSIONS: Differences in trait integration between growth forms suggest that evolution of growth form in some lineages might be associated with the degree of trait interrelation.
DOI:10.1093/treephys/tpv035URL [本文引用: 1]
DOI:10.1111/pce.12566URLPMID:26084355 [本文引用: 6]
Abstract Vessel lengths are important to plant hydraulic studies, but are not often reported because of the time required to obtain measurements. This paper compares the fast dynamic method (air injection method) with the slower but traditional static method (rubber injection method). Our hypothesis was that the dynamic method should yield a larger mean vessel length than the static method. Vessel length was measured by both methods in current year stems of A cer , P opulus , V itis and Q uercus representing short- to long-vessel species. The hypothesis was verified. The reason for the consistently larger values of vessel length is because the dynamic method measures air flow rates in cut open vessels. The Hagen oiseuille law predicts that the air flow rate should depend on the product of number of cut open vessels times the fourth power of vessel diameter. An argument is advanced that the dynamic method is more appropriate because it measures the length of the vessels that contribute most to hydraulic flow. If all vessels had the same vessel length distribution regardless of diameter, then both methods should yield the same average length. This supports the hypothesis that large-diameter vessels might be longer than short-diameter vessels in most species.
DOI:10.1038/378715a0URL [本文引用: 1]
[本文引用: 1]
DOI:10.1111/j.1469-8137.2010.03594.xURLPMID:21223285 [本文引用: 1]
Intensive forestry systems and breeding programs often include either native aspen or hybrid poplar clones, and performance and trait evaluations are mostly made within these two groups. Here, we assessed how traits with potential adaptive value varied within and across these two plant groups. Variation in nine hydraulic and wood anatomical traits as well as growth were measured in selected aspen and hybrid poplar genotypes grown at a boreal planting site in Alberta, Canada. Variability in these traits was statistically evaluated based on a blocked experimental design. We found that genotypes of trembling aspen were more resistant to cavitation, exhibited more negative water potentials, and were more water-use-efficient than hybrid poplars. Under the boreal field test conditions, which included major regional droughts, height growth was negatively correlated with branch vessel diameter (D v ) in both aspen and hybrid poplars and differences in D v were highly conserved in aspen trees from different provenances. Differences between the hybrid poplars and aspen provenances suggest that these two groups employ different water-use strategies. The data also suggest that vessel diameter may be a key trait in evaluating growth performance in a boreal environment.
[本文引用: 1]
[本文引用: 1]
DOI:10.1111/j.1365-3040.1988.tb01774.xURL [本文引用: 1]
Abstract . Hydraulic conductivity of the xylem is computed as the quotient of mass flow rate and pressure gradient. Measurements on excised plant stems can be difficult to interpret because of time-dependent reductions in flow rate, and because of variable degrees of embolism. Using Acer saccharum Marsh. stems, we found that certain perfusing solutions including dilute fixatives (e.g. 0.05% formaldehyde) and acids with pH below 3 (e.g. 10 mol m 3 oxalic) prevent long-term decline in conductivity. Xylem embolism can be quantified by expressing the initial conductivity as a percentage of the maximum obtained after flow-impeding air emboli have been removed by repeated high-pressure (175 kPa) flushes. Correlation between microbial contamination and declining conductivity suggests that long-term (> 4h) declines are caused by microbial growth within the vessels. Unpredictable trends in short-term (< 4h) measurements may be caused by movements of air emboli in vessels and/or participate matter.
DOI:10.1086/520726URL [本文引用: 1]
We tested two hypotheses for how vessel evolution in angiosperms influenced xylem function. First, the transition to vessels decreased resistance to flow—often considered the driving force for their evolution. Second, the transition to vessels compromised safety from cavitation—a constraint emerging from the “pit area hypothesis” for vulnerability to cavitation. Data were obtained from branch wood of 17 basal taxa with vessels and two eudicots possessing “primitive” perforation plates. Results were compared with previous data from vesselless angiosperms and eudicots with simple perforation plates. Contrary to the first hypothesis, basal taxa did not have significantly lower sapwood‐specific resistivity than vesselless angiosperms, despite vessels being wider than tracheids. Eudicot resistivity was ca. 4.5 times lower. On a vessel‐area basis, resistivity of “primitive” vessels (\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $435\pm 104$ \end{document}MPa s m612) was lower than angiosperm tracheids (\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $906\pm 89$ \end{document}MPa s m612) but still greater than eudicot vessels (\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $91\pm 9$ \end{document}MPa s m612). High resistivity of primitive vessels could be attributed to their being shorter per diameter than eudicots and to high perforation plate resistivity (\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $57\% \pm 15\% $ \end{document}of total) in the species with scalariform plates. In support of the second hypothesis, primitive vessels had a cavitation pressure 1.4 MPa more vulnerable than angiosperm tracheids. This “vulnerability bottleneck” may have been even more extreme without a shift in vessels to less porous interconduit pit membranes. Vessel evolution was not driven by lower flow resistance, and it may have been limited to wet habitats by cavitation risk. A subtle, context‐dependent advantage to primitive vessels is consistent with the distribution of the vesselless condition in the angiosperm tree. The results imply that truly efficient and safe vessels evolved much later than vessels per se, perhaps in concordance with larger radiations among core angiosperms.
DOI:10.1111/j.1365-3040.2005.01287.xURL [本文引用: 4]
The hydraulic resistivity ( R , pressure gradient/flow rate) through end walls of xylem conduits was estimated in seven species of diverse anatomy and affinity including a vessel-bearing fern, a tracheid-bearing gymnosperm, and angiosperms with versus without vessels. Conduit lengths were measured with a silicone injection method which was easier and more accurate than the usual paint injection. The R declined linearly with the removal of end walls as stems were shortened from 10 to 0.3 cm. This relationship gave the minimum R with no end walls present, or the lumen resistivity ( R L ). This was indistinguishable from the Hagen–Poiseuille value. The maximum R with all end walls present gave R C , the resistivity of end wall and lumen in series. Average end-wall resistivity ( R W ) was the difference R C 61 R L and the 'wall fraction' was R W / R C . Wall fraction was approximately constant, averaging 0.54 ± 0.07. This suggests that end wall and lumen resistivities are nearly co-limiting in vascular plants. Average conduit length was proportional to the diameter squared across species ( r 2 = 0.94). Together with a constant wall fraction, this was consistent with the end wall resistance ( r w , pressure difference/flow rate) being inversely proportional to conduit length. Lower r w in longer conduits is consistent with their having more end wall pits than shorter conduits.
[本文引用: 2]
DOI:10.1104/pp.88.3.581URL [本文引用: 1]
[本文引用: 1]
DOI:10.1111/j.1399-3054.1986.tb05941.xURL [本文引用: 1]
A comparison was made of the relative vulnerability of xylem conduits to cavitation and embolism in three species [ Thuja occidentalis L., Tsuga canadensis (L.) Carr. and Acer saccharum Marsh.]. Waterlogged samples of wood were air dehydrated while measuring relative water loss, loss of hydraulic conductance, cumulative acoustic emissions (= cavitations) and xylem water potential. Most cavitation events and loss of hydraulic conductance occurred while water potential declined from – 1 to –6 MPa. There were differences in vulnerability between species. Other people have hypothesized that large xylem conduits (e.g. vessels) should be more vulnerable to cavitations than small conduits (e.g. tracheids). Our findings are contrary to this hypothesis. Under water stress, the vessel bearing wood retained water better than tracheid bearing wood. However, within a species large conduits were more prone to cavitation than small conduits.
DOI:10.1146/annurev.pp.40.060189.000315URL [本文引用: 1]
The Ge contents of plants and animals were investigated by a wet ashing procedure by hydride generation and inductively coupled plasma atomic emission spectrometry with flow injection. The analytical results obtained indicated that Ge contents widely vary in plant and animal kingdoms in the range of 8-203 ppb.
[本文引用: 2]
DOI:10.1093/treephys/tpw055URL [本文引用: 2]
[本文引用: 1]
[本文引用: 1]
DOI:10.1098/rspb.2016.2642URLPMID:28469026 [本文引用: 1]
Water stress is known to cause xylem cavitation in the leaves, roots and stems of plants, but little is known about the vulnerability of flowers to xylem damage during drought. This is an important gap in our understanding of how and when plants become damaged by water stress. Here we address fundamental questions about if and when flowers suffer cavitation damage, using a new technique of cavitation imaging to resolve the timing of cavitation in water-stressed flower petals compared with neighbouring leaves. Leaves and flowers from a sample of two herbaceous and two woody eudicots were exposed to a severe water stress while the spatial and temporal propagation of embolism through veins was recorded. Although in most cases water potentials inducing 50% embolism of herbaceous flower veins were more negative than neighbouring leaves, there was no significant difference between the average vulnerability of leaves and petals of herbaceous species. In both woody species, petals were more vulnerable to cavitation than leaves, in one case by more than 3 MPa. Early cavitation and subsequent damage of flowers in the two woody species would thus be expected to precede leaf damage during drought. Similar cavitation thresholds of flowers and leaves in the herb sample suggest that cavitation during water shortage in these species will occur simultaneously among aerial tissues. Species-specific differences in the cavitation thresholds of petals provide a new axis of variation that may explain contrasting flowering ecology among plant species.
DOI:10.1007/s11258-009-9592-5URL [本文引用: 1]
[本文引用: 6]
DOI:10.1163/22941932-90000759URL [本文引用: 2]
CiteSeerX - Scientific documents that cite the following paper: Vessel-length distribution in branches, stem, and roots of Acer rubrum
A study of lumen diameter variation along the longitudinal axis of wood vessels in
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1987
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
... 3)有关导管直径与导管长度的关系还缺乏具体定论, 已有研究表明导管直径在整个导管长度方向上是不均一的(
A study of the vascular organization of bamboos (Poaceae-Bambuseae) using a microcasting method
1
1998
... 早期多采用油基漆作为灌注物质, 以一定的压力沿导管运输方向注入枝条, 在导管中, 油会取代水到达导管末端, 水油表面张力较大, 在灌注压力较小的前提下油不会透过纹孔膜进入邻近的导管, 但该过程通常需要数天.灌注完成后, 在近灌注端, 有些导管完全灌注, 有些则是完全不含灌注物, 使计数不充分, 在干燥过程中, 多数导管中的油基漆收缩, 体积变小, 无法充满整个导管, 使得计数难度增加(
Plant functional groups within a tropical forest exhibit different wood functional anatomy
1
2017
... 不同生活型的木本植物的平均导管长度具有显著性差异(
Evolution of xylem physiology. In: Hemsley AR, Poole I eds. The Evolution of Plant Physiology
1
2004
... 不同生活型的木本植物的平均导管长度具有显著性差异(
First insights into the functional role of vasicentric tracheids and parenchyma in
1
2016
... 另一种观点则认为长导管植物不会对离心机建立的栓塞脆弱曲线造成影响.Sperry等(2012)对Quercus gambelii、复叶槭(Acer negundo)及Sorbus scopulina (平均导管长度分别为17.4、3.1、4.7 cm左右)不同长度的枝条(14、27 cm), 用离心机法和自然干燥法建立脆弱曲线, 结果显示曲线形状及栓塞脆弱性没有显著差异, 黎明前的Quercus gambelii枝条用离心机法所测得的VC曲线与自然干燥法所得一致, 皆证明了导管长度对离心机法建立脆弱曲线没有影响.对火烧后的Rhamnus ilicifolia次生演替灌木丛研究表明, 火烧前后, 导管长度没有显著差异, 但脆弱曲线却从火烧前的“s”形变成了火烧后的“r”形, 这也说明脆弱曲线的形状与导管长度无关(
Automated analysis of three-dimensional xylem networks using high-resolution computed tomography
3
2011
... 还有一种测量方法是应用高分辨率的X射线计算机断层扫描技术(HRCT), 并配合分析软件来构建包括导管直径、导管长度、导管连接等在内的木质部整体网络结构.HRCT与医用CT技术原理类似, 可高强度、高分辨率地在植物组织的任何部分连续进行切片拍摄, 且不会对内部组织造成损伤(
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
... 3)有关导管直径与导管长度的关系还缺乏具体定论, 已有研究表明导管直径在整个导管长度方向上是不均一的(
The dynamics of embolism repair in xylem:
1
2010
... 还有一种测量方法是应用高分辨率的X射线计算机断层扫描技术(HRCT), 并配合分析软件来构建包括导管直径、导管长度、导管连接等在内的木质部整体网络结构.HRCT与医用CT技术原理类似, 可高强度、高分辨率地在植物组织的任何部分连续进行切片拍摄, 且不会对内部组织造成损伤(
Revealing catastrophic failure of leaf networks under stress
1
2016
... 4)离心机法与压力套法测得的“r”形曲线的真实性还存在较大的争议, 论点主要集中在人为切开的导管造成空气或水的进入上, 若可以在长枝甚至活体上, 非侵入性的测量植物的栓塞脆弱性, 则会大大提高测量精度及可信度.近些年以照相机与显微镜为设备支持的光学测量技术, 为栓塞脆弱性的测量打开了新的思路(
Optical measurement of stem xylem vulnerabilty
2
2017
... 高分辨率断层扫描技术借鉴了医学上的计算机断层扫描技术, 分辨率更高, 对植物材料进行连续扫描, 具有精度高、直观化、视野范围广、活体测量、可建立立体化导管网络等优点, 但由于所需仪器及配套设施较为昂贵, 使用及维护不便, 目前难以被广泛应用于植物解剖结构的观测尤其是田间试验上(
... 4)离心机法与压力套法测得的“r”形曲线的真实性还存在较大的争议, 论点主要集中在人为切开的导管造成空气或水的进入上, 若可以在长枝甚至活体上, 非侵入性的测量植物的栓塞脆弱性, 则会大大提高测量精度及可信度.近些年以照相机与显微镜为设备支持的光学测量技术, 为栓塞脆弱性的测量打开了新的思路(
Measuring vessel length in vascular plants: Can we divine the truth? History, theory, methods, and contrasting models
6
2014
... 导管作为木本植物木质部中运输水分与无机盐的重要管道结构, 普遍存在于大多数被子植物中.它们是由许多长管状的细胞以顶端对顶端的方式连接而成的管状结构.组成导管的每一个细胞称为导管分子, 单个导管由成百上千个死亡的导管分子组成, 导管分子在发育初期是活的细胞, 在成熟过程中, 细胞侧壁木质化并产生次生加厚, 同时, 细胞内的液泡膜破裂, 释放出水解酶, 使上下相连的两个导管分子之间的端壁溶解消失形成穿孔板, 以便于水分在导管分子间的长距离运输, 原生质体解体而成为死细胞, 整个导管成为一个长管状结构, 长度可达0.001-10 m (
... 目前研究多集中在导管内径的测量与功能上, 较少关注导管长度, 对导管长度本身及其在植物水力结构及功能中的作用缺乏系统的了解(
... 导管长度测量的间接方式是将有色物质注入人为切开的导管使其形象化, 该物质选择的原则是: 被注入导管后, 能够在贯穿导管的基础上不发生堵塞, 也无法穿过纹孔膜扩散到相邻导管(
... 早期多采用油基漆作为灌注物质, 以一定的压力沿导管运输方向注入枝条, 在导管中, 油会取代水到达导管末端, 水油表面张力较大, 在灌注压力较小的前提下油不会透过纹孔膜进入邻近的导管, 但该过程通常需要数天.灌注完成后, 在近灌注端, 有些导管完全灌注, 有些则是完全不含灌注物, 使计数不充分, 在干燥过程中, 多数导管中的油基漆收缩, 体积变小, 无法充满整个导管, 使得计数难度增加(
... 以上的计算方法目前被广泛使用, 但其结果仍与实际值存在偏差,
... 1)目前为止, 导管长度的测量方法已有了较大的改进, 染料注入法的灌注物质也经过了数代的变化, 目前以硅胶注入法最为常用, 硅胶由于本身并没有颜色, 需要加入荧光剂在紫外线下拍照, 而荧光剂存在随时间淬灭的现象, 会造成一定的测量误差(
A computational algorithm addressing how vessel length might depend on vessel diameter
1
2010
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
Structure and function of bordered pits: New discoveries and impacts on whole- plant hydraulic function
1
2008
... 研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(
Measurement of vulnerability to water stress-induced cavitation in grapevine: A comparison of four techniques applied to a long-vesseled species
3
2010
... 不同生活型的木本植物的平均导管长度具有显著性差异(
... 研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(
... 显示出巨大差异(自然干燥法: -2.97 MPa, 冲洗离心机法: -0.7 MPa), 作者认为有可能是由于离心过程中水分会更容易从开口导管流出, 才造成脆弱性过大的假象(
Global convergence in the vulnerability of forests to drought
1
2012
... 研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(
Rare pits, large vessels and extreme vulnerability to cavitation in a ring-porous tree species
1
2012
... 离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(
A technique for measuring xylem hydraulic conductance under high negative pressures
1
2002
... 木质部水势与木质部栓塞的关系可以用“脆弱曲线” (vulnerability curve, VC)来表示(
Methods for measuring plant vulnerability to cavitation: A critical review
1
2013
... 研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(
Use of positive pressures to establish vulnerability curves: Further support for the air-seeding hypothesis and implications for pressure- volume analysis
2
1992
... 木质部水势与木质部栓塞的关系可以用“脆弱曲线” (vulnerability curve, VC)来表示(
... 离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(
Evaluation of a new centrifuge technique for rapid generation of xylem vulnerability curves
2
2005
... 不同生活型的木本植物的平均导管长度具有显著性差异(
... 木质部水势与木质部栓塞的关系可以用“脆弱曲线” (vulnerability curve, VC)来表示(
Does sample length influence the shape of xylem embolism vulnerability curves? A test with the Cavitron spinning technique
2
2010
... 不同生活型的木本植物的平均导管长度具有显著性差异(
... 研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(
Air method measurements of apple vessel length distributions with improved apparatus and theory
1
2003
...
Theoretical considerations of optimal conduit length for water transport in vascular plants
3
2000
... 目前研究多集中在导管内径的测量与功能上, 较少关注导管长度, 对导管长度本身及其在植物水力结构及功能中的作用缺乏系统的了解(
... 测量导管长度最直接的方法为显微拍照法——在光学显微镜下将一根导管从头至尾拍下, 但由于导管特殊的几何形状, 使得导管长度的测量需拍摄成百上千张照片进行拼凑, 工作量大且精度较低, 因此不推荐使用该方法(
...
Fluid flow in the outermost xylem increment of a ring-porous tree,
1
1986
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
How reliable is the double-ended pressure sleeve technique for assessing xylem vulnerability to cavitation in woody angiosperms?
3
2011
... 离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(
... 研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(
... ;
Hydraulically integrated or modular? Comparing whole-plant-level hydraulic systems between two desert shrub species with different growth forms
1
2009
... 其中: n是所测导管数量, d是单个导管腔直径(
Techniques for measuring vessel lengths and diameters in stems of woody plants
3
1989a
... 目前研究多集中在导管内径的测量与功能上, 较少关注导管长度, 对导管长度本身及其在植物水力结构及功能中的作用缺乏系统的了解(
... 测量导管长度最直接的方法为显微拍照法——在光学显微镜下将一根导管从头至尾拍下, 但由于导管特殊的几何形状, 使得导管长度的测量需拍摄成百上千张照片进行拼凑, 工作量大且精度较低, 因此不推荐使用该方法(
... 其中: n是所测导管数量, d是单个导管腔直径(
Variation in vessel length and diameter in stems of six tropical and subtropical lianas
5
1989b
... 有研究表明导管长度随枝条的直径、长度或年龄增大而增大(
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
... 对种子植物研究发现导管长度与导管直径没有明显的相关性, 而是与导管直径的平方成正比.对藤本植物的研究也发现, 种间不存在导管直径与长度的关系, 而在种内研究水平看, 窄导管普遍较短, 而宽导管则有长有短(
... ;
... 3)有关导管直径与导管长度的关系还缺乏具体定论, 已有研究表明导管直径在整个导管长度方向上是不均一的(
A survey of vessel dimensions in stems of tropical lianas and other growth forms
4
1990
... 尽管某些藤本植物的导管长度可达数十米, 但植物的大部分导管仍为短导管(
... 有研究表明导管长度随枝条的直径、长度或年龄增大而增大(
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
... 对杨树种内无性系研究发现, 导管长度随导管直径增大而增大, 大直径导管趋向于导管长度更长.目前普遍认可的是种内最大导管直径与最大导管长度成正比(
Specialization in secondary xylem of dicotyledons. I. Origin of vessel
1
1930
... 不同生活型的木本植物的平均导管长度具有显著性差异(
Stem xylem conductivity is key to plant water balance across Australian angiosperm species
1
2012
... 不同生活型的木本植物的平均导管长度具有显著性差异(
Weak tradeoff between xylem safety and xylem-specific hydraulic efficiency across the world’s woody plant species
1
2016
... 木质部导管特征是决定植物水力结构和功能的关键因素, 其直径、长度、内径跨度、壁厚度、连接度等特征都对植物的水力结构与功能有着重要的影响.植物的水分运输, 不是由一条导管从底部通到顶端的, 而是分段经过许多条导管曲折连贯向上运行的.水流既可以通过导管细胞腔及穿孔上升, 又可以通过侧壁上的纹孔横向运输.导管中的水分在运输过程中, 受张力影响处于亚稳定状态, 在地上部分与地下部分的压力差下, 水分以水柱的形式由木质部根的导管向上运输到茎的导管(
Embolism resistance of three boreal conifer species varies with pit structure
1
2009
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
Water transport in vesselless angiosperms: Conducting efficiency and cavitation safety
1
2007
... 早期多采用油基漆作为灌注物质, 以一定的压力沿导管运输方向注入枝条, 在导管中, 油会取代水到达导管末端, 水油表面张力较大, 在灌注压力较小的前提下油不会透过纹孔膜进入邻近的导管, 但该过程通常需要数天.灌注完成后, 在近灌注端, 有些导管完全灌注, 有些则是完全不含灌注物, 使计数不充分, 在干燥过程中, 多数导管中的油基漆收缩, 体积变小, 无法充满整个导管, 使得计数难度增加(
Scaling of angiosperm xylem structure with safety and efficiency
1
2006
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
The standard centrifuge method accurately measures vulnerability curves of long- vesselled olive stems
1
2015
... 离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(
No evidence for an open vessel effect in centrifuge-based vulnerability curves of a long- vesselled liana (
7
2012
... 目前研究多集中在导管内径的测量与功能上, 较少关注导管长度, 对导管长度本身及其在植物水力结构及功能中的作用缺乏系统的了解(
... 空气注入法是一种相对快速的导管长度动态测量方法.是在一定的压力下向枝条注入空气, 并根据收集气泡的速率与测试样本长度的关系来推算不同长度导管的概率分布.在第一个气泡出现后, 测量此时单位体积空气在单位时间内通过的距离(空气流速), 此时导管长度为该样本的最大导管长度Lmax.然后将枝条逐渐剪短, 重复操作.该方法的前提为假设开口导管的数量与气体导度成正比, 并根据枝条长度与空气流速间的关系来推算导管长度分布.当被切开的新鲜茎段在低压(<100 kPa)下注入气体时, 气体只能通过被切开的导管, 因为导管壁上的湿润纹孔膜可以阻止气流的通过, 使气流不能到达相邻导管(
... 空气注入法相对于染料注入法, 操作比较简单, 测量周期更短, 但普遍认为该方法所得导管长度并非传统意义上的导管长度, 而是与植物水力学特性相关的水力学长度(
... 尽管某些藤本植物的导管长度可达数十米, 但植物的大部分导管仍为短导管(
... 不同生活型的木本植物的平均导管长度具有显著性差异(
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
... 2)导管长度的研究多集中在茎的木质部中, 根及叶脉中的研究较少(
A global analysis of xylem vessel length in woody plants
1
2012
... 离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(
Structural determinants of increased susceptibility to dehydration-induced cavitation in post-fire resprouting chaparral shrubs
1
2016
... 另一种观点则认为长导管植物不会对离心机建立的栓塞脆弱曲线造成影响.Sperry等(2012)对Quercus gambelii、复叶槭(Acer negundo)及Sorbus scopulina (平均导管长度分别为17.4、3.1、4.7 cm左右)不同长度的枝条(14、27 cm), 用离心机法和自然干燥法建立脆弱曲线, 结果显示曲线形状及栓塞脆弱性没有显著差异, 黎明前的Quercus gambelii枝条用离心机法所测得的VC曲线与自然干燥法所得一致, 皆证明了导管长度对离心机法建立脆弱曲线没有影响.对火烧后的Rhamnus ilicifolia次生演替灌木丛研究表明, 火烧前后, 导管长度没有显著差异, 但脆弱曲线却从火烧前的“s”形变成了火烧后的“r”形, 这也说明脆弱曲线的形状与导管长度无关(
Morphological variation of intervessel pit membranes and implications to xylem function in angiosperms
1
2009
... 研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(
Transport constraints on water use by the Great Basin shrub,
2
1999
... 有研究表明导管长度随枝条的直径、长度或年龄增大而增大(
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
Testing the hypotheses that link wood anatomy to cavitation resistance and hydraulic conductivity in the genus
1
2011
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
维管植物导管及其穿孔板的研究进展
1
2005
... 导管作为木本植物木质部中运输水分与无机盐的重要管道结构, 普遍存在于大多数被子植物中.它们是由许多长管状的细胞以顶端对顶端的方式连接而成的管状结构.组成导管的每一个细胞称为导管分子, 单个导管由成百上千个死亡的导管分子组成, 导管分子在发育初期是活的细胞, 在成熟过程中, 细胞侧壁木质化并产生次生加厚, 同时, 细胞内的液泡膜破裂, 释放出水解酶, 使上下相连的两个导管分子之间的端壁溶解消失形成穿孔板, 以便于水分在导管分子间的长距离运输, 原生质体解体而成为死细胞, 整个导管成为一个长管状结构, 长度可达0.001-10 m (
维管植物导管及其穿孔板的研究进展
1
2005
... 导管作为木本植物木质部中运输水分与无机盐的重要管道结构, 普遍存在于大多数被子植物中.它们是由许多长管状的细胞以顶端对顶端的方式连接而成的管状结构.组成导管的每一个细胞称为导管分子, 单个导管由成百上千个死亡的导管分子组成, 导管分子在发育初期是活的细胞, 在成熟过程中, 细胞侧壁木质化并产生次生加厚, 同时, 细胞内的液泡膜破裂, 释放出水解酶, 使上下相连的两个导管分子之间的端壁溶解消失形成穿孔板, 以便于水分在导管分子间的长距离运输, 原生质体解体而成为死细胞, 整个导管成为一个长管状结构, 长度可达0.001-10 m (
木本植物木质部栓塞脆弱性研究新进展
1
2015
... 木质部导管特征是决定植物水力结构和功能的关键因素, 其直径、长度、内径跨度、壁厚度、连接度等特征都对植物的水力结构与功能有着重要的影响.植物的水分运输, 不是由一条导管从底部通到顶端的, 而是分段经过许多条导管曲折连贯向上运行的.水流既可以通过导管细胞腔及穿孔上升, 又可以通过侧壁上的纹孔横向运输.导管中的水分在运输过程中, 受张力影响处于亚稳定状态, 在地上部分与地下部分的压力差下, 水分以水柱的形式由木质部根的导管向上运输到茎的导管(
木本植物木质部栓塞脆弱性研究新进展
1
2015
... 木质部导管特征是决定植物水力结构和功能的关键因素, 其直径、长度、内径跨度、壁厚度、连接度等特征都对植物的水力结构与功能有着重要的影响.植物的水分运输, 不是由一条导管从底部通到顶端的, 而是分段经过许多条导管曲折连贯向上运行的.水流既可以通过导管细胞腔及穿孔上升, 又可以通过侧壁上的纹孔横向运输.导管中的水分在运输过程中, 受张力影响处于亚稳定状态, 在地上部分与地下部分的压力差下, 水分以水柱的形式由木质部根的导管向上运输到茎的导管(
Change in hydraulic traits of Mediterranean
1
2010
... 研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(
The relevance of xylem network structure for plant hydraulic efficiency and safety
1
2007
... 其中: n是所测导管数量, d是单个导管腔直径(
Adaptive variation in the vulnerability of woody plants to xylem cavitation
1
2004
... 木质部水势与木质部栓塞的关系可以用“脆弱曲线” (vulnerability curve, VC)来表示(
Vessel length and conductivity of
1
2013
... 有研究表明导管长度随枝条的直径、长度或年龄增大而增大(
Integration of vessel traits, wood density, and height in angiosperm shrubs and trees
1
2011
... 不同生活型的木本植物的平均导管长度具有显著性差异(
A comparison of hydraulic architecture in three similarly sized woody species differing in their maximum potential height
1
2015
... 不同生活型的木本植物的平均导管长度具有显著性差异(
A comparison of two methods for measuring vessel length in woody plants
6
2015
... 导管作为木本植物木质部中运输水分与无机盐的重要管道结构, 普遍存在于大多数被子植物中.它们是由许多长管状的细胞以顶端对顶端的方式连接而成的管状结构.组成导管的每一个细胞称为导管分子, 单个导管由成百上千个死亡的导管分子组成, 导管分子在发育初期是活的细胞, 在成熟过程中, 细胞侧壁木质化并产生次生加厚, 同时, 细胞内的液泡膜破裂, 释放出水解酶, 使上下相连的两个导管分子之间的端壁溶解消失形成穿孔板, 以便于水分在导管分子间的长距离运输, 原生质体解体而成为死细胞, 整个导管成为一个长管状结构, 长度可达0.001-10 m (
... 空气注入法是一种相对快速的导管长度动态测量方法.是在一定的压力下向枝条注入空气, 并根据收集气泡的速率与测试样本长度的关系来推算不同长度导管的概率分布.在第一个气泡出现后, 测量此时单位体积空气在单位时间内通过的距离(空气流速), 此时导管长度为该样本的最大导管长度Lmax.然后将枝条逐渐剪短, 重复操作.该方法的前提为假设开口导管的数量与气体导度成正比, 并根据枝条长度与空气流速间的关系来推算导管长度分布.当被切开的新鲜茎段在低压(<100 kPa)下注入气体时, 气体只能通过被切开的导管, 因为导管壁上的湿润纹孔膜可以阻止气流的通过, 使气流不能到达相邻导管(
... 空气注入法相对于染料注入法, 操作比较简单, 测量周期更短, 但普遍认为该方法所得导管长度并非传统意义上的导管长度, 而是与植物水力学特性相关的水力学长度(
... ), 当测量的导管长度与水力特征有关时, 空气注入法可能更适合.空气注入法不存在染料注入法的灌注不充分问题, 在生长季后期, 导管中产生胼胝体但尚未完全堵塞时, 染料注入法测量精度会大大降低, 而空气注入法则不受影响(
... ).
... 1)目前为止, 导管长度的测量方法已有了较大的改进, 染料注入法的灌注物质也经过了数代的变化, 目前以硅胶注入法最为常用, 硅胶由于本身并没有颜色, 需要加入荧光剂在紫外线下拍照, 而荧光剂存在随时间淬灭的现象, 会造成一定的测量误差(
Sustained and significant negative water pressure in xylem
1
1995
... 离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(
A method for inducing xylem emboli
1
1992
... 离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(
Genetic variation of hydraulic and wood anatomical traits in hybrid poplar and trembling aspen
1
2011
... 其中: n是所测导管数量, d是单个导管腔直径(
A study of vessel length in
1
1968
... 空气注入法是一种相对快速的导管长度动态测量方法.是在一定的压力下向枝条注入空气, 并根据收集气泡的速率与测试样本长度的关系来推算不同长度导管的概率分布.在第一个气泡出现后, 测量此时单位体积空气在单位时间内通过的距离(空气流速), 此时导管长度为该样本的最大导管长度Lmax.然后将枝条逐渐剪短, 重复操作.该方法的前提为假设开口导管的数量与气体导度成正比, 并根据枝条长度与空气流速间的关系来推算导管长度分布.当被切开的新鲜茎段在低压(<100 kPa)下注入气体时, 气体只能通过被切开的导管, 因为导管壁上的湿润纹孔膜可以阻止气流的通过, 使气流不能到达相邻导管(
Vulnerability curves by centrifugation: Is there an open vessel artefact, and are ‘r’ shaped curves necessarily invalid?
1
2012
... 离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(
A method for measuring hydraulic conductivity and embolism in xylem
1
2010
... 木质部水势与木质部栓塞的关系可以用“脆弱曲线” (vulnerability curve, VC)来表示(
Hydraulic consequences of vessel evolution in angiosperms
1
2007
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
Comparative analysis of end wall resistivity in xylem conduits
4
2005
... 早期多采用油基漆作为灌注物质, 以一定的压力沿导管运输方向注入枝条, 在导管中, 油会取代水到达导管末端, 水油表面张力较大, 在灌注压力较小的前提下油不会透过纹孔膜进入邻近的导管, 但该过程通常需要数天.灌注完成后, 在近灌注端, 有些导管完全灌注, 有些则是完全不含灌注物, 使计数不充分, 在干燥过程中, 多数导管中的油基漆收缩, 体积变小, 无法充满整个导管, 使得计数难度增加(
... ;
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
... 其中: n是所测导管数量, d是单个导管腔直径(
Intra- and inter-plant variation in xylem cavitation in
2
1994
... 不同生活型的木本植物的平均导管长度具有显著性差异(
... 离心机法是将枝条放在转子经过改造的离心机中快速旋转, 通过改变转速不断增大离心力模拟植株生长过程中的木质部负压来诱导枝条产生栓塞, 从而测定枝条导水率损失百分数(PLC)(
Mechanism of water stress-?induced xylem embolism
1
1988
... 木质部导管特征是决定植物水力结构和功能的关键因素, 其直径、长度、内径跨度、壁厚度、连接度等特征都对植物的水力结构与功能有着重要的影响.植物的水分运输, 不是由一条导管从底部通到顶端的, 而是分段经过许多条导管曲折连贯向上运行的.水流既可以通过导管细胞腔及穿孔上升, 又可以通过侧壁上的纹孔横向运输.导管中的水分在运输过程中, 受张力影响处于亚稳定状态, 在地上部分与地下部分的压力差下, 水分以水柱的形式由木质部根的导管向上运输到茎的导管(
Theory of vessel-length determination: The problem of nonrandom vessel ends
1
1993
... 无论是染料注入法利用测得的被灌注导管的数量或是空气注入法用不同长度茎段下的气体传导率, 皆通过双差法来描绘导管长度分布(
Water stress induced cavitation and embolism in some woody plants
1
1986
... 木质部导管特征是决定植物水力结构和功能的关键因素, 其直径、长度、内径跨度、壁厚度、连接度等特征都对植物的水力结构与功能有着重要的影响.植物的水分运输, 不是由一条导管从底部通到顶端的, 而是分段经过许多条导管曲折连贯向上运行的.水流既可以通过导管细胞腔及穿孔上升, 又可以通过侧壁上的纹孔横向运输.导管中的水分在运输过程中, 受张力影响处于亚稳定状态, 在地上部分与地下部分的压力差下, 水分以水柱的形式由木质部根的导管向上运输到茎的导管(
Vulnerability of xylem to cavitation and embolism
1
1989
... 木质部水势与木质部栓塞的关系可以用“脆弱曲线” (vulnerability curve, VC)来表示(
Xylem Structure and the Ascent of Sap. 2nd edn. Springer
2
2002
... 测量导管长度最直接的方法为显微拍照法——在光学显微镜下将一根导管从头至尾拍下, 但由于导管特殊的几何形状, 使得导管长度的测量需拍摄成百上千张照片进行拼凑, 工作量大且精度较低, 因此不推荐使用该方法(
... 空气注入法是一种相对快速的导管长度动态测量方法.是在一定的压力下向枝条注入空气, 并根据收集气泡的速率与测试样本长度的关系来推算不同长度导管的概率分布.在第一个气泡出现后, 测量此时单位体积空气在单位时间内通过的距离(空气流速), 此时导管长度为该样本的最大导管长度Lmax.然后将枝条逐渐剪短, 重复操作.该方法的前提为假设开口导管的数量与气体导度成正比, 并根据枝条长度与空气流速间的关系来推算导管长度分布.当被切开的新鲜茎段在低压(<100 kPa)下注入气体时, 气体只能通过被切开的导管, 因为导管壁上的湿润纹孔膜可以阻止气流的通过, 使气流不能到达相邻导管(
Single vessel air injection estimites of xylem resistance to cavitation are affected by vessel network characteristics and sample length
2
2016
... 空气注入法相对于染料注入法, 操作比较简单, 测量周期更短, 但普遍认为该方法所得导管长度并非传统意义上的导管长度, 而是与植物水力学特性相关的水力学长度(
... 尽管某些藤本植物的导管长度可达数十米, 但植物的大部分导管仍为短导管(
Cutting xylem under tension or supersaturated with gas can generate PLC and the appearance of rapid recovery from embolism
1
2013
... 研究发现: 这两种方法建立栓塞脆弱曲线时, 对具有较长导管的植物, 曲线不呈典型的“s”形, 而多为“r”形, 而“r”形脆弱曲线是否能正确反映出植物真实的栓塞脆弱性(
Inter-?vessel pitting and cavitation in woody Rosaceae and other vesselled plants: A basis for a safety versus efficiency trade-off in xylem transport
1
2005
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
Are flowers vulnerable to xylem cavitation during drought?
1
2017
... 4)离心机法与压力套法测得的“r”形曲线的真实性还存在较大的争议, 论点主要集中在人为切开的导管造成空气或水的进入上, 若可以在长枝甚至活体上, 非侵入性的测量植物的栓塞脆弱性, 则会大大提高测量精度及可信度.近些年以照相机与显微镜为设备支持的光学测量技术, 为栓塞脆弱性的测量打开了新的思路(
Hydraulic properties and photosynthetic rates in co-occurring lianas and trees in a seasonal tropical rainforest in southwestern China
1
2009
... 不同生活型的木本植物的平均导管长度具有显著性差异(
Vessel-length distribution in stems of some American woody plants
6
1981
... 早期多采用油基漆作为灌注物质, 以一定的压力沿导管运输方向注入枝条, 在导管中, 油会取代水到达导管末端, 水油表面张力较大, 在灌注压力较小的前提下油不会透过纹孔膜进入邻近的导管, 但该过程通常需要数天.灌注完成后, 在近灌注端, 有些导管完全灌注, 有些则是完全不含灌注物, 使计数不充分, 在干燥过程中, 多数导管中的油基漆收缩, 体积变小, 无法充满整个导管, 使得计数难度增加(
... ).也有用热蜡作为灌注物质的, 与水基乳胶漆类似, 也存在灌注不充分的问题(
... 无论是染料注入法利用测得的被灌注导管的数量或是空气注入法用不同长度茎段下的气体传导率, 皆通过双差法来描绘导管长度分布(
... 尽管某些藤本植物的导管长度可达数十米, 但植物的大部分导管仍为短导管(
... 有研究表明导管长度随枝条的直径、长度或年龄增大而增大(
... 不同生活型的木本植物的平均导管长度具有显著性差异(
Vessel-length distribution in branches, stem and roots of
2
1982
... 有研究表明导管长度随枝条的直径、长度或年龄增大而增大(
... 导管长度与导管其他结构特征之间有着密切的关系, 现阶段研究的最多的是其与导管直径的关系(
