湿地植物铅的富集特征及根际铅移动性的影响因素研究

【目的】 揭示湿地植物铅的富集特征及根际铅移动性影响因素的作用机理，为人工湿地修复重金属污染水体提供理论指导和依据。 【方法】 通过根箱法研究了五种挺水湿地植物 (大叶皇冠草、黑籽荸荠、圆币草、草龙、小婆婆纳) 根际 pH、氧化还原电位 (Eh)、Fe2+ 和 Fe3+ 浓度、铅 (Pb) 的化学形态及移动性的变化。 【结果】 与非根际相比，五种植物根际pH下降，Fe2+ 和 Fe3+ 浓度显著下降，Eh显著升高，Pb的移动性显著降低 (P<0.05)。与非根际相比，根际pH下降幅度为 0.1～0.4个单位，根际Fe2+和 Fe3+浓度下降幅度为0.6～2.7 mmol/kg。土壤中铅的存在形态主要以残渣态为主 (36.39%～47.54%)，其次是铁锰氧化物结合态 (30.16%～41.64%)、有机质结合态 (8.85%～15.08%) 和碳酸盐结合态 (6.89%～12.46%)。五种湿地植物根际Pb的移动性降低的主要原因是根际碳酸盐结合态Pb含量显著下降，其中大叶皇冠草受根际pH、Eh、Fe3+和Fe2+的影响导致其根际Pb移动性降低效应最为显著。 【结论】 五种供试植物Pb主要分布在根部；根表富集的铁膜数量显著高于锰膜数量；供试植物根际Fe3+含量与Pb的移动性因子呈极显著正相关，湿地植物根系铁氧化能力对降低其根际重金属的移动性有重要作用。本研究为人工湿地修复重金属污染水体提供了有力的理论依据。

Characterization of Pb accumulation and factors influencing Pb mobility in rhizosphere soils of wetland plants

【Objectives】 Characterization of Pb accumulation and factors influencing Pb mobility in rhizosphere soils of wetland plants could provide theoretical guidance on the remediation of heavy metal polluted water in constructed wetland. 【Methods】 A rhizobox experiment was conducted to compare iron (Fe) oxidation and variation of pH, redox potential (Eh) and fractions of lead (Pb) in rhizosphere and non-rhizosphere soils of five emergent-rooted wetland plants, Echinodorus macrophyllus, Eleocharis geniculata, Hydrocotyle vulgaris, Jussiaea linifolia and Veronica serpyllifolia. 【Results】 The results showed that all the wetland plants decreased pH and concentrations of Fe(II) and Fe(Ⅲ) but increased the Eh in the rhizosphere soils. The pH in rhizosphere soils was significantly lower (P<0.05) than that in non-rhizosphere soils, with differences in a range of 0.1–0.4 pH units. Concentrations of extractable Fe(II) and Fe(Ⅲ) in the rhizosphere soils were significantly lower than those in the bulk soils, with differences in a range of 0.6–2.7 mmol/kg. In rhizosphere and non-rhizosphere soils, Pb was mainly in RES (36.39%–47.54%) and OX (30.16%–41.64%), followed by OM (8.85%–15.08%) and WSA (6.89%–12.46%), and EX was again below the detection limit. Lead was transformed from unstable fractions (WSA) to more stable fractions (OX) in the rhizosphere soils, so decreased their potential metal mobility factors (MFs). Among the five plants,E. macrophyllus with higher iron oxidation ability on root surface and in rhizosphere possessed the greatest ability to reduce the MFs of Pb in the rhizosphere soils. 【Conclusions】 Pb in the five plants is mainly distributed in roots. The amounts of Fe plaque on root surfaces were significantly higher than the amounts of Mn plaque on root surfaces. Wetland plants, with higher iron oxidation ability in rhizospheres and root surfaces, may thus be effective in decreasing potential long-term heavy metal bioavailability. Our results will provide strong theoretical basis for the restoration of heavy metal polluted water by constructing wetland.