混合样品代表地衣元素积累的平均水平——来自元素含量不同的两种地衣的证据

地衣是大气元素沉降的良好监测生物,其元素积累能力具有物种间和个体间差异。地衣原位监测法常使用混合样品代表每个样点的地衣元素积累水平,但混合样品的代表性及其在不同地衣之间的差异尚需进一步研究。以电感耦合等离子体质谱法（inductively coupled plasma mass spectrometry,ICP-MS）测定了内蒙古多伦县的丽石黄衣Xanthoria elegans和皮果衣Dermatocarpon miniatum 52种元素的含量并比较了样点内变异和物种间差异。结果显示,丽石黄衣与相似生境中的地衣元素含量大致相似,证实了研究区域以沙尘沉降为主的大气沉降特点。两种地衣的元素排序基本一致,表明其元素来源相同。7种营养元素（Ca、K、Mo、P、Rb、S和Se）的含量在物种间差异不显著,与地衣的生理调节有关。Hg含量的物种间差异不显著,可能与Hg的挥发性有关。皮果衣中44种元素（Al、As、B、Ba、Be、Bi、Cd、Ce、Co、Cr、Cs、Cu、Dy、Er、Eu、Fe、Gd、Ge、Ho、La、Li、Lu、Mg、Mn、Na、Nb、Nd、Ni、Pb、Pr、Sb、Sc、Sm、Sr、Tb、Th、Ti、Tl、Tm、U、V、Y、Yb和Zn）的含量是丽石黄衣的1.32-2.05倍,表明皮果衣具有较高的、元素特异性的元素积累能力。样点内除Ca含量变异较大（CV>31%）之外,其他51种元素的含量样点内变异在皮果衣和丽石黄衣中均<27.5%,表明混合样品在两种地衣中均可较好地代表地衣元素积累的平均水平。

Composite sample being representative of mean accumulation level of lichen elements:evidence from two lichens differing in element concentrations

Lichen is a reliable biomonitor for atmospheric element deposition, and its element accumulation ability has differences between species and between individuals. In the lichen biomonitoring studies using in situ specimens, the composite sample is often used to represent the average accumulation level of lichen elements at each sample point, but the representativeness of the composite sample and its difference between different lichens need to be further studied. The inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the concentrations of 52 kinds of elements in Xanthoria elegans and Dermatocarpon miniatum in Duolun County, Inner Mongolia, China. The intra-site variability and inter-species differences of these elements were compared. The results show that element concentrations in Xanthoria elegans are roughly similar to those in the congeneric species from similar habitats, confirming the characteristics of atmospheric deposition dominated by sand dust deposition in the study area. The element ranks in Dermatocarpon miniatum and Xanthoria elegans are roughly the same, indicating the same source of elements in both lichens. The concentrations of 7 nutrient elements (Ca, K, Mo, P, Rb, S and Se) are not significantly different between Dermatocarpon miniatum and Xanthoria elegans, indicating bioregulation of these elements in lichen thallus. The difference in Hg concentration between species is of no significance, possibly due to the volatility of Hg. Dermatocarpon miniatum has 1.32-2.05 times higher concentrations of the 44 elements (Al, As, B, Ba, Be, Bi, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Gd, Ge, Ho, La, Li, Lu, Mg, Mn, Na, Nb, Nd, Ni, Pb, Pr, Sb, Sc, Sm, Sr, Tb, Th, Ti, Tl, Tm, U, V, Y, Yb and Zn) than Xanthoria elegans, showing that Dermatocarpon miniatum has a higher element-specific accumulation ability. Except for Ca (CV>31%), the intra-site variability of the concentration of the other 51 elements is <27.5% in both Dermatocarpon miniatum and Xanthoria elegans, indicating that the composite sample can represent the average level of element accumulation in both lichens.