植物叶表毛状体对空气PM净沉降的影响

Effects of Leaf-Surface Trichomes on the Net-Deposition of Airborne Particulate Matters

叶片是植物沉降空气颗粒物(PM)的主要器官,而叶表PM的雨水洗脱被认为是叶片对空气PM的净沉降。多毛的叶面具有较强的捕获空气PM的能力,但可能并不利于叶表PM的雨水洗脱。研究通过采集美国华盛顿特区宪法大道西北段步道两侧的6种园林植物叶片,利用扫描电镜技术(SEM)观测叶表微观形态,并通过ImageJ和Adobe Photoshop软件统计降雨前后的PM数量,比较雨水对不同表面结构的叶表PM洗脱率。结果表明:1)叶面毛状体长而繁杂的皱叶荚蒾叶面PM洗脱率(19.26%)显著低于叶面无毛的紫薇、美国冬青和荷花玉兰3种光叶植物(>60%);2)毛状体短、疏、贴伏于叶面的美国榆树叶面PM洗脱率(25.57%)也显著低于这3种光叶植物;3)毛状体短、疏、直立的迎春叶面PM洗脱率(78.00%)与这3种光叶植物无显著差异;4)除皱叶荚蒾外,其他5种植物叶表粒径10~100μm的大颗粒比小颗粒更容易从叶表洗脱。基于研究结果,建议在城市绿化中增加光叶、常绿的园林植物比例;在条件允许的前提下,于旱季定期对树体适量喷水,以提升园林植物对空气PM的年净沉降量。

Leaves are the main organs of plants to settle airborne particulate matter(PM),and the rain water elution of PM on leaf surface is considered as the net deposition of PM by leaves.The hairy leaves are always considered to play a positive effect in capturing PM,but it may not be conducive to the wash-off of leaf retained PM by rainfall.Therefore,this study collects the leaves of 6 landscape plants on the footpath of the Northwest Constitution Avenue in Washington,D.C.,and observes the microscopic morphology of the leaves using scanning electron microscopy(SEM).The amount of PM before and after rainfall is counted using ImageJ and Adobe Photoshop software to compare the elution rates of PM on leaves with different surface structures.The results show that:1)The elution rate of leaf retained PM of Viburnum rhytidophyllum(19.26%)with long and complicated trichomes on the adaxial leaf surface is significantly lower than those of smooth-leaved species of Lagerstroemia indica,Ilex opaca and Magnolia grandiflora(>60%);2)The elution rate of leaf retained PM of Ulmus americana(25.57%)with short,sparse but appressed trichomes on the adaxial leaf surface is significantly lower than those of the above three smooth-leaved species;3)The elution rate of leaf retained PM of Jasminum nudiflorum(78.00%)with short,sparse but erected trichomes on the adaxial leaf surface is not significantly different from those of the above three smooth-leaved species;and 4)Apart from V.rhytidophyllum,the large particles with diameter of 10-100μm on the adaxial leaf surface of the other five species are easier washed off than the small particles.Based on the above conclusions,we suggest that the proportion of smooth leaf and evergreen landscape plants could be increased for urban greening,and if the condition permits,water should be regularly sprayed on trees in dry season,which will be conducive to enhancing the annual net-deposition amount of airborne PM with landscape plants.