湿地挺水植物根际金属离子的分布及界面扩散通量

挺水植物作为湿地生态系统的重要组成部分,其根系的生长发育过程影响其环境功能的发挥及其根土和水土界面环境生物地球化学过程。界面的氧化还原异质环境是金属离子发生扩散、沉淀和溶解以及吸附和解析等许多瞬时过程的重要场所,这些过程对金属离子在固相和水相的分配起着重要的作用。获取金属离子赋存特征和定量评估大型挺水植物生长对其界面行为的影响,是了解金属离子在界面环境生物地球化学过程的关键环节。利用高分辨率沉积物原位间隙水采样技术（Pore Water Equilibrators,Peeper）获得芦苇、香蒲和茭草3种挺水植物根际与非根际溶液中Al3＋、Fe3＋、Mn2＋和Ca2＋的剖面分布特征,并利用Fick第一定律定量估算它们在沉积物-水界面的扩散通量。结果表明：湿地沉积物孔隙水中Al3＋、Fe3＋、Mn2＋和Ca2＋的含量较上覆水存在着明显的富集现象。其中Fe3＋、Mn2＋分布受大型挺水植物影响最为显著,且随沉积物深度增加,富集效应有进一步加剧趋势。从剖面垂向分布来看,Al3＋含量的峰值靠近沉积物的表层,而Fe3＋、Ca2＋和Mn2＋含量峰值出现位置相对较深存在于沉积物中下层。与无植被的对照区域相比,4种金属离子含量在植物根区附近显著升高（P〈0.05）,其中Al3＋、Fe3＋和Ca2＋受芦苇生长过程影响最为明显,其在根际孔隙水中峰值含量达18.3、513和5408μmol·L-1,较对照分别增加了6.0、2.5及25.8倍,芦苇根际效应显著高于香蒲和茭草。多重比较分析结果显示,Mn2＋在根区的分布受茭草影响最大,在根区孔隙水中浓度为21~97μmol·L-1较对照区的1.1~52.5μmol·L-1,平均浓度增加65%。受植物根区环境的影响,Fe3＋和Ca2＋在植物根区释放速率明显加快,其中茭草根区释放速率分别为（35.38±3.05）和（240.18±20.71）μmol·m-2·d-1较对照区增加10倍;另外湿地植物存在直接导

Metal ions distribution and diffusive fluxes across the sediment-water interface in emergent macrophytes rhizosphere

Emergent macrophytes are considered as a key component of wetland ecosystem, whose growth strongly influenced neighbouring environmental functions and biogeochemical cycles across the interface of root-sediments. Redox heterogeneous environment at the interface benefits ions diffusion, precipitation-dissolution, adsorption and desorption equilibrium, which determines ions distribution between the solid and the liquid phase. It is crucial for comprehending environmental biogeochemical cycle to acquire ions distribution characteristic and molecule diffusive fluxes calculated from the concentration gradients between overlying water and surface pore water. In the preset study, Multiple porewater profiles were obtained from the rhizosphere of Phragmites communis, Typha orientalis Presl and Zizania caduciflora by a high-resolution in-situ porewater equilibrators （peepers）, and quantified Al3＋, Fe3＋, Mn2＋and Ca2＋diffusion fluxes from sediments into the overlying waters using Fick First Law. The results indicated that there is a trend to enrich apparently the ions in surface sediments and the accumulation intensifies with increasing depth, which Fe3＋and Mn2＋distribution were markedly influenced by emergent macrophytes. Porewater Al3＋, Fe3＋, Mn2＋and Ca2＋levels were significantly higher in the emergent macrophytes rhizosphere than those in the control, which had a corresponding 6.0, 2.5 and 25.8 folds difference of Al3＋, Fe3＋and Ca2＋levels between Phragmites communis rhizosphere and the control in little or no vegetation. Multiple comparison analysis of 4 ions characters shows that Mn2＋concentrations reached 21~97μmol L-1 with about a 65%increase in Zizania caduciflora rhizosphere, while it is only 1.1-52.5μmol L-1 relative to the control. Higher diffusive fluxes of Fe3＋and Ca2＋ were found in emergent macrophytes rhizosphere, moreover, reach （35.38±3.05） and （240.18±20.71） μmol·m-2·d-1 in Zizania caduciflora with 10 times of the control. However, the observed Mn2＋diffusi