广州市常见行道树种叶片表面形态与滞尘能力

Abstract

以广州市常见的18种行道树为对象,通过扫描电镜观察比较了行道树的叶表面形态结构、应用接触角测定仪测定了绿化树种叶片的接触角对滞尘能力的影响。结果表明:不同树种的滞尘量差异显著,18种植物叶片雨后第26天的最大滞尘量在0.066-1.831g/m²,物种间相差达27倍以上。叶表面具有网状结构,气孔密度较大(20<气孔密度<60个)且气孔开口较大(如芒果)容易滞留粉尘;叶表面平滑具有蜡质层,气孔排列整齐,无明显起伏(如红花羊蹄甲、桃花心木、大叶紫薇、鹅掌藤),滞尘能力较弱。植物叶片接触角与滞尘量呈负相关(<em>r</em>=-0.614),接触角<90°的表现为亲水性。易润湿的植物叶片雨后第26天最大滞尘量在1.0-1.831g/m²,叶片表面的形态结构凹凸不平,具有钩状或脊状褶皱、突起等且20<气孔密度<60范围内,测得的接触角较小(芒果、重阳木、高山榕),使得粉尘与植物叶片接触面积较大,粉尘不易从叶面脱落,滞尘能力较强。而接触角较大的盆架树、麻楝、大叶紫薇、鹅掌藤和红花羊蹄甲的滞尘量均<1.0g/m²,其特殊的表面结构和疏水的蜡质使颗粒物不易吸附在植物叶片上,因此滞尘能力较弱。由此可见,植物叶表面蜡质含量和气孔密度及其叶片接触角的大小是影响植物叶片滞尘能力的主要因素,在进行城市绿化时,适当考虑选择叶表面形态有利于滞尘的绿化树种,将可提高城市植被的环境效应。;In this study, we selected eighteen species of common street trees along main roads in Guangzhou Municipality to observe and compare their leaf surface morphology using Scanning Electron Microscopy (SEM), and to evaluate how the contact angle of water droplet on leaf surfaces measured by goniometer influence the dust-retaining capability. It was found that the maximum leaf dust-retaining capabilities per unit area of the eighteen species of trees 26 days after rainfall were 0.066-1.831g/m², indicating significant differences (up to 27 times) among different trees. The plants with network structure on leaf surface, having high stomatal density and large opening of stomata, such as <em>Mangifera Indica</em>, have strong dust-retaining capability; while those whose leaf surfaces are smooth and covered by epicuticular wax with stomata arranged regularly without obvious undulation, such as <em>Bauhinia blakeana</em>,<em> Swietenia mahogani</em>,<em> Lagerstroemia indica Linn</em>. and<em> Scheffera arboricola</em>, have poor dust-retaining capability. There was a significant negative relationship between leaf contact angle and dust-retaining capability (<em>r</em>=-0.614). Leaves with contact angle smaller than 90° demonstrate hydrophilicity. Their maximum dust-retaining capabilities 26 days after rainfall ranged from 1.0 to 1.831 g/m². For leaves with rugged morphological structure, hook or ridge-shaped rumple, prominence and stomata density ranging from 20 to 60, the measured contact angles are smaller, making the contact area between leaf and dust larger. Therefore, it is not easy for dust on such trees as <em>Mangifera Indica</em>, <em>Bischofia Polycarpa</em> and <em>Ficus altissima Bl.</em>, to detach from leaf surface and these species have a strong dust-retaining capability. On the contrary, the special surface structure and hydrophobic wax of tree leaves with larger contact angle, such as <em>Alstonia scholaris</em>,<em> Chukrasia tabularis</em>,<em> Lagerstroemia indica Linn.</em>,<em> Scheffera arboricola </em>and <em>Bauhinia blakeana</em>, make it difficult for dust particles to attach to leaves, resulting in small dust-retaining capabilities of less than 1.0g/m². This study has shown that the wax content of surface foliage, stomata density and contact angle of leaves are the three main factors controlling the dust-retaining capability. It is therefore advisable to consider choosing tree species whose leaf surface morphology enhances dust-retaining capability for urban greening and thus to improve the environmental effectiveness of urban vegetation.