不同污染程度下毛白杨叶表面PM2.5颗粒的数量及性质和叶片气孔形态的比较研究

选择了北京市环境PM_(2.5)浓度不同的两个采样点的毛白杨(Populus tomentosa Carr.)作为研究对象,利用环境扫描电镜及X-射线能谱仪对杨树叶片表面滞留的PM_(2.5)颗粒进行了观察、统计和成分分析,并研究了叶片气孔对环境颗粒物污染的适应性变化。结果表明:夏秋两季西直门叶片样品上下表面的PM_(2.5)数量均多于森林公园样品这说明环境PM_(2.5)浓度是影响叶片表面滞留颗粒物数量的主要原因;其中叶片上表面是滞留PM_(2.5)颗粒的主要区域。森林公园样品中PM_(2.5)颗粒性质比较单一,硅铝酸盐颗粒和石英颗粒占很大比例,二者的主要来源均为天然源,如土壤扬尘、矿物颗粒等;而西直门采样点叶片样品滞留的PM_(2.5)颗粒的元素组成更为复杂,其中50%以上的硅铝酸盐颗粒检测出了明显的铜、钾、氯、钠等元素的谱峰其来源主要是工业排放;西直门样品PM_(2.5)的含硫量高于森林公园样品,且夏季明显高于秋季。研究还发现有少数PM_(2.5)颗粒进入了毛白杨叶片的气孔而且不同污染程度下气孔的形态特征存在差异。与森林公园毛白杨叶片的气孔相比,西直门处的毛白杨叶片气孔的长度、宽度、面积和气孔密度均较小,说明较高的PM_(2.5)污染程度对毛白杨叶片的形态发育有一定影响。研究结果可以为揭示植物叶片阻滞、吸收大气颗粒污染物的机制、合理选择和优化城市绿化树种从而改善空气质量提供一定的科学理论依据。

A comparative study of the stomata and PM2.5 particles on the leaf surface of Chinese white poplar (Populus tomentosa Carr.) in different polluted places

Observation and analysis of PM_2.5 particles on a leaf surface can help us explore the correlation between PM_2.5 particles and environmental factors and the response of stomata to particulate pollution in the air. This not only provides an important scientific reference for elucidating the mechanism of PM_2.5 retention and absorption by leaves, but is also helpful for reasonably selecting and optimizing urban greening tree species to reduce particulate matter pollution and improve the atmospheric environment in the city. In Beijing, National Olympic Forest Park and Xizhimen traffic hub are two representative sites for monitoring the environment. In June and September 2013, we measured the atmospheric PM_2.5 level of these monitoring sites using a real-time PM_2.5 monitoring instrument, and found that the average atmospheric PM_2.5 level in Xizhimen traffic hub was about 1.5 times higher than that in the National Olympic Forest Park. In this study, PM_2.5 particles retained on the leaf surface of Chinese white poplar (Populus tomentosa Carr.) from these two sites were identified, counted, and analyzed by using an environmental scanning electron microscope (ESEM) and an X-ray energy dispersive spectrometer (EDS). At the same time, the adaptive response of leaf stomata to the PM_2.5 pollution was studied. These results showed that the numbers of PM_2.5 particles on both the adaxial and abaxial surfaces of leaf samples at the Xizhimen traffic hub were more than those in the National Olympic Forest Park in both summer and autumn, indicating that the number of PM_2.5 particles adsorbed by leaves is largely affected by the atmospheric PM_2.5 concentration. The adaxial surface of leaves is the main area of PM_2.5 retention. The number of PM_2.5 particles on the autumn samples was more than that on the summer samples. The PM_2.5 particles on the leaves from the National Olympic Forest Park were mainly composed of aluminosilicate particles and quartz grains, and these particles are mainly from soil dust and mineral particles. However, the composition of PM_2.5 particles from the Xizhimen traffic hub samples was more complex. The spectral peaks of Cu, Na, K, Cl, and other elements were found in the energy spectra in most aluminosilicate particles. These elements are mainly from industrial emissions. The sulfur content of PM_2.5 from the Xizhimen traffic hub samples was higher than that from the National Olympic Forest Park samples in both summer and autumn. Moreover, the sulfur content was higher in summer than in autumn. Our results indicate that the amount and composition of particulate matter are affected by environmental factors to a great extent. It was also observed that a few PM_2.5 particles are present in the stomata of P. tomentosa leaves. Also, the morphological characteristics of stomata varied at different atmospheric PM_2.5 levels. The length, width, area, and density of stomata of the Xizhimen traffic hub samples were smaller than those of the National Olympic Forest park samples due to more serious PM_2.5 pollution. Additionally, the secondary electron image and the back-scattering image were combined to better locate, observe, and analyze PM_2.5 particles on the leaf surface of P. tomentosa.