| Particulate Matter capturing capability (PM-capturing capability) is an important ecosystem services that forest ecosystem provide to human-beings. During the recent years, haze events occurring in wide-range frequently have adverse effect on human health and daily life. Particulate matters pollution is getting large attentions. Thus, research on the regulating rules of forest becomes the hotspot.In this paper, Aeolian Aerosol Recurrence Analyzer (AARA) was used to analyze PM-capturing capability of leaf. Effective precipitation which adequately removed the PM captreured by leaves of different species were determined by a simulated rainfall experiment using the Norton Veejet 80100 rainfall simulator. On this basis, The LAI (Leaf Area Index) of different tree species stands changed with season and stand age of forest in 7 Central Shaanxi Plain cities were investigated by WinSCANOPY to convert the leaf-particles-capturing-capability to stand particles-capturing capability. Then, the conversion of stand to forest particles-capability of forest in Central Shaanxi Plain were estimated using distributed measurement. In order to analyze the effect of the leaf surface microstructure on particulate-capturing capability and the removal difficulty level in the rain event, we took leaf-surface images using Scanning Electron Microscope (SEM), and quantized the related microstructure by analyzing the images. Then the images taken by Atomic Force Microscopy (AFM) showed the three-dimensional microstructure of leaf suface. The main conclusions are as follows:(1)The results analyzed by AARA showed the saturated amounts of TSP captured by all tested species were between 2.80～17.93 μg·cm-2, and the Juniperus chinensis had the largest saturated amounts,1.05～6.40 times of other species. While the saturated amounts of PM10 were between 1.09～12.44 μg·cm-2, the Juniperus chinensiss showed the largest amount.1.10～11.43 times of other species. And, the saturated amounts of PM2.5 between 0.15-4.74 μg·cm-2, the Juniperus chinensis had the largest saturated amounts,1.52～30.75 times of other species. The leaf PM-capturing capability of coniferous species were generally higher than deciduous species.(2) Analysis of the the PM-capturing capability of the leaf samples under the same dustfall treatment were conducted by both AARA and gravimetric method. It turned out that the AARA method showed less workload for experimenter, more accurate distinction of different size particles, shorter experimental period, more simple experiment steps than the gravimetric methods. So AARA analysis is an advanced method with lower risk of bias, more fast and efficient method than the gravimetric method.(3) The results of simulated rainfall experiment showed that, under the rainfall intensity of 0.8 mm·min-1, the particulate captured by leaves of Populus X canadensis, Phyllostachys glauca, and Ginkgo biloba removed adequately under the precipitation of 7.9 mm, while Salix matsudana, Robinia pseudoacacia, Quercus aliena var. acutiserrata Picea asperata and Abies fabri needed 11.3 mm precipitation, and Pinus bungeana, Pinus tabuliformis, Cedrus deodara, Pinus armandii, Pinus sylvestris var. mongolica, Platycladus orientalis and Juniperus chinensis needed 15.9 mm. The coniferous species with high saturated amounts of particulate may lead to the higher precipitation than deciduous species to removed particulate adequately. However, the wash-off amount of particulate of coniferous species probaly higher than that of decidous species. The amount of TSP remainin on the leaves decreased more sharplly than that of PM2.5 and PM10 indecated that the coarse particulate could be washed off easily than fine particulate.(4) The stand PM-capturing capability per unit area of different species were different. The highest amount of capturing capability of TSP, PM10 and PM2.5 were 103.19、71.57、 27.27 kg·ha-1·a-1,1.06～15.61,1.11～14.08,1.15～58.66 times to other species, respectively. The stands of the highest capturing capability of TSP, PM10 and PM2.5 were all appeared in the mature stand of Juniperus chinensis.(5) The leaf-surface micro-morphology structure influence the leaf PM-capturing capability and the removal difficulty level in the rainfall event. This study concluded that the leaf with convex epidermal cells and covered by uniform wax layer caused the lower particle capturing capability. Conversely, the leaf surface with epidermal trichomes, large size and high density stomates and high proportion groove area showed higher PM-capturing capability. The three-dimensional microstructure of leaf surface gotten by AFM images showed massive groove and valley which enhanced the roughness of leaf surface and the contacted area between particulate and leaf surface, resulting in the higher PM-capturing capability. The microstructure also affected the removal difficulty level of particulate on the leaf surface. Particulate captured by the leaf with convex epidermal cells and covered by uniform wax layer could be wash off easier. While, the exsistence of epidermal trichomes, large size and high density stomates and high proportion groove area resulted in more difficult particulate removal in the rainfall event.(6) The results showed that the TSP, PM10, and PM2.5 capturing capability of forest in Central Shaanxi Plain were 5090.30×10-4、3507.14×104、384.27×104 kg·a-1, respectively. The quercus forest which take up the largest area of forest in Central Shaanxi Plain made the largest contribution to the PM-capturing capability. Due to the diversity of forest area、age and composition, the PM-capturing capability of cities in Central Shaanxi Plain varied. The forest PM-capturing capability of Baoji, Xi’an and Weinan are higher than other city in Central Shaanxi Plain. By 2015, the TSP, PM10, and PM2.5 capturing capability of afforestation project (2010～2015) will be 576.9×104、413.57×104、126.78×104 kg·a-1. |
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