珠江三角洲不同污染梯度下森林优势种叶片和枝条S含量比较

植物的吸储作用对降低环境中含硫污染物浓度有积极意义。筛选珠江三角洲地区具有不同污染程度的3处森林类型,检测了32个树种叶片和枝条中的总S含量(其中广州市白云区帽峰山次生常绿阔叶林16个树种,广州市南沙区海岸防护人工林11个树种,佛山市顺德区龙凤山人工改造恢复林5个树种)。结果显示:该32个物种的叶片和枝条中硫含量平均值分别为(0.24±0.02)%和(0.14±0.02)%,叶片硫含量显著高于枝条中的(P=0.000)。相同森林类型不同物种间叶片(和枝条)中硫含量呈现显著差异。帽峰山和南沙森林样地中优势种叶片(和枝条)中硫含量近似,分别为(0.22±0.01)%和(0.22±0.02)%(枝条:(0.13±0.01)%和(0.10±0.01)%);而龙凤山的最高,叶片和枝条中分别为(0.39±0.13)%和(0.28±0.09)%;多重检验结果显示,在龙凤山森林类型植物体吸储硫元素的量,显著大于帽峰山和南沙森林类型,这与不同森林类型所处空气环境中S污染物格局较为吻合。在近缘类群中(如豆科、樟科),叶片(和枝条)中硫含量的差异显著,暗示近缘植物类群(在科的水平上)在吸储硫元素方面受系统发育约束作用不明显。在本土树种和引进树种中,叶片(和枝条)中硫含量没有显著差异,可能与所处环境的过滤作用相关。广州和佛山地区各林型的植物体内硫含量存在的差异,基本反映出该两地区空气环境中受含硫污染物的影响程度。今后在该地区的造林过程中,应更多考虑应用S污染物吸储能力较强的树种,并注重本土树种和引进树种的组配,构建适应当地环境条件的森林群落。

Sulfur contents in leaves and branches of dominant species among the three forest types in the Pearl River Delta

Plants play an important role in reducing the concentrations of sulfur-containing pollutants by means of biological absorption. The present study sampled 32 tree species, and measured the sulfur (S) contents in leaves and branches (in dry weight) of dominant species for three main forest types in the Pearl River Delta, specifically coniferous and broadleaved mixed restoration (CBMR) forest in Longfeng Mountain (5 species), Foshan city; seashore shelter evergreen broadleaved (SSEB) forest of Nansha Forest Plot (11 species) and secondary evergreen broadleaved (SEB) forest (16 species) in Maofeng Mountain, Guangzhou city. Firstly, we compared the S contents in leaves and branches of three main forest types. Our results showed that mean value of S content was (0.24±0.02)% in leaves and (0.14±0.02)% in branches for these tree species; and S content in leaves was significantly higher than that of in branches (P=0.000). A significant interspecific difference (P=0.000) of S content in leaves (and branches) was also detected. Among the three forest types, CBMR forest exhibited the highest S content both in leaves (0.39±0.13)% and branches (0.28±0.09)%, followed by SEB forest ((0.22±0.01)% in leaves, and (0.13±0.01)% in branches), and SSEB forest ((0.22±0.02)% in leaves, and (0.10±0.01)% in branches). Result of a Turkey Post Hoc Test showed that the amount of S elements absorbed by tree organs in CBMR forest was significantly higher than that of in SEB forest and SSEB forest, which was generally consistent with the pattern of atmospheric S-containing pollutants in heterogeneous environment in the Pearl River Delta. Secondly, we attempted to compare the S content between closely related species as well as distantly related species. In closely related species (e.g., four species in Fabaceae, and three species in Lauraceae), S contents in leaves (and branches) exhibited a significant difference respectively. The results suggested that environmental filtering effect, rather than phylogenetic constraint effect, played a more important role in the S-absorption process at the Family level. Finally, we compared the S content in leaves and branches between native species and introduced species. For native and introduced tree species, no significant difference was detected in either leaves or branches, suggesting that local habitat may determine the physiological and ecological behaviors of tree species. In conclusion, the results from three analyses collectively showed that the differences of leaves and branches of dominant species in three main forest types in Guangzhou and Foshan reflected a general status of S pollution in the atmosphere. Our results implied important strategies for urban forest management that top priorities should be given to selection of tree species with higher ability of S-absorption and a combination of native and introduced tree species for urban afforestation.