叶片微观结构变化对其颗粒物滞纳能力的影响

叶片作为植物滞留大气颗粒物最主要的载体,其表面微观结构特征和粗糙度的差异是颗粒物滞纳能力的重要决定因素.叶片微观结构会随着生长(内部因素)以及环境污染强度(外部因素)发生变化,然而现有的粉尘喷洒模拟实验,一般持续时间较短,而微观结构变化响应具有明显的滞后性,其结果无法客观反映由内外因素作用引起的微观结构变化对颗粒物滞纳能力的影响.本研究利用新叶和老叶研究叶片生长,并选择自然状态下不同污染源条件研究污染强度,分析叶片表面微观结构的变化及其对颗粒物滞纳能力的影响.研究得到3种常绿树种(矮紫杉Taxus cuspidata var.、侧柏Platycladus orientalis和油松Pinus tabuliformis)的老叶滞纳TSP、 PM_(10)、 PM_(2.5)和PM_1量均高于新叶,随着叶片的生长其颗粒物滞纳量在增大,且新叶与老叶对不同粒径颗粒物的滞纳量间均存在极显著的差异.生长中叶片粗糙度Rq值的增大是老叶颗粒物滞纳能力增大的主要原因. 5个树种(侧柏、油松、国槐Sophora japonica、毛白杨Populus tomentosa和银杏Ginkgo biloba)TSP和PM_(10)滞纳量为重度污染区高于相对清洁区.而PM_(2.5)和PM_1滞纳量则是油松、银杏和侧柏为重度污染区高于相对清洁区,国槐和毛白杨为相对清洁区高于重度污染区.不同污染强度区域间叶片TSP、PM_(10)和PM_(2.5)滞纳量存在着极显著的差异,PM_1滞纳量也存在着差异.主要归因于与相对清洁区相比,重度污染区叶片的气孔指数降低,蜡质层退化,表面纹理和细胞边界更加不规则,绒毛变长,变硬,叶片微观结构的这些变化使得重度污染区叶片粗糙度Rq值高于相对清洁区,且叶片背面的增加较正面更明显.研究结果将为深入揭示叶片颗粒物滞纳能力的驱动因素,以及提出更科学地提升净化颗粒物功能的城市森林管理措施提供数据支持.

Impacts of Leaf Surface Micromorphology Variation on the Ability to Capture Particulate Matter

As the most important carrier of atmospheric particles captured by plants, the differences in micromorphology characteristics and leaf roughness are important determinants of particle capture capacity. Leaf micromorphology usually changes with growth (internal factor), and with environmental pollution intensity (external factor). The existing dust-spray simulation was always short; however, the leaf micromorphology changes had a clear delayed response, and therefore its results could not reflect the micromorphology changes caused by internal and external factors that influence the particulate capture capacity of leaves. In the present study, new and old leaves were used to study leaf growth, and different pollution source conditions were selected to study pollution intensity under natural conditions, to analyze the changes in leaf surface micromorphology and their impacts on particulate capture capacity. It was found that the amounts of TSP, PM₁₀, PM_2.5, and PM₁ on the old leaves of three evergreen trees (Taxus cuspidata var., Platycladus orientalis, and Pinus tabuliformis) were higher than those of the new leaves, and the amounts of the particles with respect to the old leaves increased with leaf growth. Moreover, there were significant differences between the new and old leaves regarding the captured amount of different-sized particles. The increase in needle roughness (Rq) of the three evergreen trees, caused by growth, was the main factor that led to an increase in particle capture capacity for old leaves. The TSP and PM₁₀ captured amounts of P. orientalis, P. tabuliformis, Sophora japonica, Populus tomentosa, and Ginkgo biloba were higher in the heavily polluted area than in the clean area. The amounts of PM_2.5 and PM₁ captured by P. tabuliformis, G. biloba, and P. orientalis in the heavily polluted area were higher than those in the clean area; however, the amounts of PM_2.5 and PM₁ captured by S. japonica and P. tomentosa in the clean area were higher than those in the heavily polluted area. Pollution intensity very significantly affected the capture capacity of TSP, PM₁₀, and PM_2.5 by leaves, as well as significantly affecting the capture capacity of PM₁. This was mainly caused by the leaf micromorphology changes found in the heavily polluted area, such as stomatal index decrease, waxy layer degradation, more irregular surface texture and boundaries of the epidermal cells, and longer and hardened trichomes. These changes caused the Rq values to be generally higher in the heavily polluted area than in the clean area, and the roughness of the abaxial surface increased more notably than that of the adaxial surface. These results will provide data support for further revealing the driving factors of particulate matter capture capacity of leaves and proposing more scientific urban forest management measures to improve their particulate matter removal function.