基于水分调控的强化蜈蚣草对砷污染土壤修复的机理研究

Recently, Pteris vittata has been used widely in remediating arsenic (As) contaminated soil. Most of the current research used activators or regulated agronomic measures to improve the enrichment ability of P. vittata, but studies based on soil moisture regulation to strengthen the ability of P. vittata As absorption are few. Through 2 years of field experiments, we found that regulation of soil moisture significantly improved the As enrichment ability of P. vittata, but the mechanism is not clear so far. Therefore, in order to improve the As enrichment ability of P. vittata from large-scale engineering perspective, we will put forward a series of methods to strengthen As enrichment ability of P. vittata by regulation of soil water moisture. We hypothesis that As enrichment ability of P. vittata could be obviously improved through changing the soil redox by the regulation of soil moisture and improving As bioavailability by desorption of phosphorus (P) fertilizer. In this study, we will explore the mechanism of soil As activation by the regulation of soil water related to desorption kinetics of soil As and the adsorption kinetics of P in soil. In addition, As transport process and activation of As in vivo metabolism mechanism of P. vittata under water and P treatments will be revealed by the use of SRXRF synchrotron radiation technology. The results of this project will play an important theoretical role and guild the application in practical engineering for P. vittata.

利用蜈蚣草技术修复砷污染土壤具有广泛的发展前景。目前大多研究是通过施用活化剂和调控农艺措施来提高蜈蚣草对砷富集能力，但基于土壤水分控制强化蜈蚣草吸收砷的研究还较少。本课题组通过田间2年定位试验发现，调控土壤水分可以显著提高蜈蚣草对砷的富集能力，但其中的机理并不明晰。因此，本研究以提升蜈蚣草砷富集能力为目标，从大规模工程应用的角度提出一套强化蜈蚣草砷富集能力的土壤水分调控思路，通过调控土壤水分，改变土壤氧化还原环境，同时辅以磷肥促进土壤胶体表面砷的解吸，提高土壤砷的生物有效性，从而增强蜈蚣草的砷富集能力。本研究拟从土壤砷的解吸动力学特征及磷在土壤中的吸附动力学特征的角度揭示土壤水分调控下土壤砷的活化机制。同时利用SRXRF同步辐射技术研究蜈蚣草在水分调控条件下对As的迁移-转运过程，揭示活化砷在蜈蚣草体内的代谢机制。项目研究成果对蜈蚣草在实际修复工程中的应用具有重要的理论意义和指导意义。

从污染物毒性和污染面积来看，砷是中国土壤污染最严重的污染物之一。与室内蜈蚣草的富集能力相比，在野外实际修复过程中，蜈蚣草对土壤砷的富集能力仍有提升的空间。.通过野外大田试验，明确短期内（蜈蚣草生长2个月）肥料有效磷是主控因素，其对蜈蚣草砷富集能力的贡献达到0.716。蜈蚣草生长周期在3个月以上，磷肥pH是影响蜈蚣草砷富集能力的首要因素，其贡献达到0.812。蜈蚣草生长周期达到4个月时，磷肥pH依然是主控因素；土壤水分对蜈蚣草砷富集能力的贡献超过肥料有效磷。提出大田试验条件下蜈蚣草对土壤砷富集的关键参数及主要影响因素。（1）受气候因素影响，蜈蚣草对土壤砷的富集特征与室内盆栽结果有明显差异。蜈蚣草地上部生物量在第180天达到4.82 t/hm2后趋于平稳，地上部As浓度增长至第90天出现峰值116.20 ± 17.64 mg/kg，随后开始下降直至第180天后持平；蜈蚣草生长120天后As富集量为318.11 g/hm2，达到模型预测最高值的96.7%。（2）进一步明确了大田试验条件下土壤湿度是影响蜈蚣草砷富集的关键因子，其对蜈蚣草富集能力的影响大于降雨、光照强度等因素，适当提高土壤湿度是提升蜈蚣草As富集能力的优先选择。（3）从蜈蚣草地上部As富集总量看，蜈蚣草As外排对其萃取效率的影响不大。生长后期（120天-270天）As富集量在318.12-331.27 g/hm2之间，平均值327.13 g/hm2，与预测最高值（329.05 ± 1.87 g/hm2）无明显差异，降雨淋溶导致蜈蚣草砷流失总量占比较小，不超过2.2%。.本研究获取的蜈蚣草吸收土壤砷方面的关键参数可为工程修复提供重要支撑。在降雨量充足时，磷肥pH、肥料有效磷含量是提高蜈蚣草砷富集能力的主要因素；降雨量不足时，土壤含水率对蜈蚣草砷富集能力的影响大于肥料有效磷含量，通过灌溉等措施重点调控土壤湿度，提高土壤含水率，保障植物生长所需的水分，进而提升蜈蚣草砷富集能力。这些试验参数对中国中南地区开展砷污染土壤修复具有重要指导意义。