关键词: 大气沉降, 生物监测, 地衣移植法, 中国树花, 重金属

Abstract: Lichen samples are often hung under tree canopies by transplantation to monitor atmospheric element depositions. However, few studies have examined the effects of canopy (presence or absence) and exposure duration on the element composition of lichen transplants. We transplanted lichen Ramalina sinensis from a remote site to a polluted site of Hebei, China, and evaluated the bioaccumulation levels of 55 elements on the basis of the EC (exposed to control ratio). We further examined the effects of the canopy (2 levels: presence or absence) and exposure duration (3 levels: 7, 8, or 9 months exposure) on element concentrations of the transplanted samples. The results showed that background element concentrations of Ramalina sinensis were lower than the reported background/baseline values, indicating a low degree of atmospheric element deposition in the background site. Ramalina sinensis was applicable for the atmospheric deposition bio-monitoring of 53 elements except Co and Hg which had high background concentration variations. After transplantation, the concentrations of most elements were significantly higher than those in the background site. The traffic-related elements, Pb and Sb, demonstrated “extremely heavy accumulation”. The agriculture and plant physiology-related elements (As, K, P, S, and Se), as well as Ag and Ge, demonstrated “no accumulation” or “slight accumulation”. The other 44 elements (Al, B, Ba, Be, Bi, Ca, Cd, Ce, Cr, Cs, Cu, Dy, Er, Eu, Fe, Gd, Ho, La Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, Pr, Rb, Tb, Sc, Si, Sm, Sn, Sr, Th, Ti, Tl, Tm, U, V, Y, Yb, and Zn) demonstrated “moderately accumulated”. These results suggest a great contribution of traffic emissions and high level of atmospheric element deposition in the exposure site. The effects of canopy and exposure duration on the element concentrations of Ramalina sinensis were element-specific. Concentrations of 26 elements under the canopy were higher than that outside the canopy, possibly due to the canopy leaching; whereas Pb showed an opposite pattern, possibly due to the canopy interception. After exposure for seven months, the concentrations of most elements (41 out of 53 elements) remained stable, while that of 11 elements increased and that of Ni decreased. Our results indicated that the presence or absence of canopy should be consistent and the length of exposure should not be too long in bio-monitoring atmospheric element deposition using transplanted lichen techniques.

Key words: atmospheric deposition, bio-monitoring, lichen transplantation, Ramalina sinensis, heavy metal.