The Leave PM Retention and Its Relation to Leaf Micro-Morphological Structure of the Major Tree Species in Tuyunguan Forest Park, Guiyang, China
- LIU Yan-hui, DING Fang-jun, HOU Yi-ju, SHU De-yuan, ZHAO Wen-jun, CUI Ying-chun
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To give a scientific basis for selecting proper tree species in city forests establishment, the difference in particulate matter (PM) retention and its dynamic progress of the leaves of major tree species were investigated in the Tuyunguan Forest Park of Guiyang City, Guizhou Province of China, and the impacts from the micro-morphological and structural characteristics of leaves was analyzed. The 12 tree species, including 5 coniferous and 7 broad-leaved tree species, were selected for study. The leaf samples were collected on the 3rd day after a rainfall event which can clean the leaves in the spring, summer, autumn, and winter of 2017; and on the 1st, 2nd, 3rd, 5th, 6th and 7th day after big rainfall events in the summer. The weight of total PM and its components with different size ranges (PM>10-100, PM>2.5-10, PM>1-2.5, and PM ≤ 1) absorbed on unit area of leaves were measured in the lab with re-suspension method. It shows that the daily PM retention (Md) decreased with rising time and following a power function. Such function was fitted for each tree species. The values of fitted parameters in these fitted functions can reflect the differences in the initial PM retention (M0), i.e. on the first day, and the decreasing rate of Md among the tree species studied. The tree species of Cupressus funebris, Pinus armandii, Cinnamomum camphora had a higher M0 but their Md decreased faster. The M0 for Pinus massoniana was higher but its daily PM retention decreased the slowest. The coniferous tree of Cunninghamia lanceolata and all other broadleaved tree species had both lower M0 and lower decreasing rate of Md. The PM retention ability and its components of different size ranges (TSP、PM10、PM2.5, PM1) were generally higher for coniferous tree species than for broad-leaved tree species (except Betula luminifera), and showed a remarked difference among tree species. The order of total PM retention of all tree species was:Cupressus funebris and > Pinus massoniana > Pinus armandii > Betula luminifera > Cunninghamia lanceolata > Cryptomeria japonica > Liquidambar formosana > Camptotheca acuminata > Camptotheca acuminata > Celtis sinensis > Ligustrum lucidum > Ginkgo biloba. All the tree species showed similar size distribution of the absorbed PM, with a mean ratio of 58.75%, 38.98%, 2.16% and 0.11% for the large, coarse, fine and super fine PM, respectively. The results of path analysis showed that the ratio of leaf circumference to leaf area was the most important factor affecting the daily PM retention. Secondly, the groove width of leaf surface (Wg) has a major impact on the retention capacity of large and coarse particles. The stomatal opening (Os) and stomata opening area (Aso) were the main factors affecting the retention capacity of fine particles. The Wg and the stomatal opening area per unit leaf surface (Sso) were the main factors affecting the retention of super fine particles. It seems that the leaves with smaller area, more complex form (with larger ratio of leaf circumference to leaf area), bigger groove width and larger stomatal opening size, will have a higher PM retention. The differences in the PM retention and its temporal dynamics should be considered when selecting the proper tree species for establishing city forests. The tree species with higher or lower PM retention ability should be rightly selected according to the different protection requirement against the air PM pollution.