土壤淹水抑制柳树根系Cu转运的作用机制研究

Fast-growing Salix has great potential in phytoremediation of heavy metal polluted soil because of its traits. Most current researches focused on the absorption, accumulation and detoxification of heavy metals by willow under hydroponic solution or upland culture. However, most conclusions obtained from these above mentioned experimental conditions not adequately represent the interaction mechanism between wetland plants willow and heavy metals in wetland soils. To the best of our knowledge,the question as to whether and how soil flooding affects the absorption, accumulation,and translocation of heavy metals in willow has not been adequately addressed. Our previous results suggested that soil flooding significantly suppressed root-shoot translocation of copper by willow. Therefore, this proposal focuses on the mechanisms of accumulation and translocation of copper in willow, through the investigation of the bioavailability of soil copper, and the physiological responses, and copper chemical form and distribution in willow, which grow in flooded soil. X-ray absorption and X-ray fluorescence spectrum will be applied to obtain the direct evidence of micro-distribution,chemical form and coordinated structure of copper in different tissues of willow. The role of Fe/Mn oxide,S element and Fe/Mn plaques in copper accumulation in root will be analyzed. The translocation of copper through xylem and phloem pathways in willow grown in flooded soil will be evidenced. These results will clarify the mechanisms at molecular level on suppressed root-shoot translocation of copper in willow by soil flooding. The results will shed light on the mechanism between woody plants and heavy metals in wetland soils. It will also provide guideline to the application of willow in restoration and phytoremediaton of contaminated wetland.

速生树种柳树在土壤重金属污染修复中潜力巨大。对柳树吸收、积累重金属的能力和耐性研究也取得了一定进展。但是，现有结论多在溶液培养或旱地条件得到，不能充分反映耐水淹树种柳树与湿地土壤中重金属的作用规律。在前期研究基础上，本项目从淹水对土壤Cu的生物有效性的影响、对柳树的生长生理进而对重金属吸收的影响两个方面，系统地研究淹水时柳树对土壤中Cu的积累特征和转运机制。通过定量分析淹水土壤中Cu的形态及移动性，利用组织化学法，结合高效液相色谱、基于同步辐射装置的X射线吸收和荧光光谱技术，揭示柳树中Cu的形态和微区定位，阐明土壤淹水时柳树对Cu的吸收和积累特征。通过光合作用和蒸腾速率、运输通道中有机酸和植物络合素及Cu的测定，从转运驱动力和转运形态方面揭示柳树体内Cu的转运途径，并系统阐明土壤淹水抑制柳树根部Cu转运的作用机制。该研究对于了解树木与湿地土壤中重金属相互作用的某些规律及机制具有重要意义。

以杞柳一支笔(Salix integra Yizhibi)幼苗为研究对象，采用土壤培养模拟淹水试验，设置淹水(F，高于土壤表面10 cm)和不淹水(NF，正常土壤水分)处理及4个Cu浓度梯度(control、50、150和450 mg·kg-1)，培养60 d、90d后，分析了土壤性质、Cu形态和微生物群落的变化；观测了柳树的生长和生理生化响应；采用同步辐射荧光分析技术(µ-XRF)考察了柳树组织内的Cu和其它营养元素的微区分布，揭示了淹水抑制柳树根系Cu转运的影响机制。.1. 淹水增加了土壤有机质含量，降低土壤有效Cu的含量，降低了土壤中蔗糖酶、脲酶和纤维素酶活力，提高过氧化物酶和多酚氧化酶活力，淹水降低了土壤微生物多样性且改变了群落结构, 高Cu处理下真菌群落的丰富度相较细菌群落减少的更多。.2. 淹水处理使下，杞柳茎基部出现了不定根和皮孔，植株能够维持正常的光合作用，抗氧化酶系统和渗透调节物质等积极防御和共同作用来缓解淹水和Cu胁迫对植物的伤害，从而使杞柳具有较强的忍耐Cu污染和淹水的能力。.3. 淹水和Cu污染影响柳树体内的营养元素的积累和分布。土壤Cu浓度升高，显著增加了柳树根系的Ca、K和S浓度，但显著降低P、Na和Zn的浓度。土壤淹水显著增加了柳树根系对Fe、Mn和S的积累，铁锰氧化物和硫化物在根表面的沉淀，干扰Cu和一些营养元素在根部的吸收和固定，一定程度上减轻土壤Cu对柳树的毒性。.4. 柳树组织内的Cu优先积累在根部，主要分布在根尖的根冠和分生区；µ-XRF谱图说明淹水改变了Cu在根系的分布模式，抑制其从根表向维管柱的传输，土壤淹水严重抑制了Cu在茎部木质部导管的转运，这归因于Cu转运的驱动力—叶片蒸腾速率的降低。. 该研究结果有助于加深人们对柳树这一速生耐淹水树种在湿地土壤中对Cu的积累和转运规律及相关机制的认识，丰富人们对树木抗逆生理、土壤环境化学等方面的规律性认识，为速生柳树应用于湿地恢复及植物修复提供理论依据。