砷胁迫高原湖滨湿地典型植物根系分泌物对磷形态转化的影响机制

Plateau Lake has very high contamination risks as its limitation of recharging sources and long period of changing water feature, and the plants in the plateau lakeshore wetland is becoming the focuses of scientists both domestic and overseas as it plays the important role in the process of phosphorus retention by plateau lakeshore wetland, and the effects of root exudates from plants on the speciation transformation of phosphorus is also becoming the hot spot. The influence of arsenic stress on the speciation transformation of sediment phosphorus mediated by root exudates from plant in plateau lakeshore wetland deserves much more attention as the existing research could not explain the effects of arsenic stress on the speciation transformation of phosphorus mediated by root exudates from plants in the plateau lakeshore wetland. Thus, in this proposal we would choose root exudates from typical submerged and emergent aquatic plant in arsenic contaminated plateau lakeshore wetland as the research objects, and carry out the experiment of effects of root exudates on the speciation transformation of sediment phosphorus. We intend to solve the following two scientific problems: (1) To identify the characteristics of root exudates from typical plant in plateau lakeshore wetland and the key root exudates which mediate the speciation transformation of sediment phosphorus; (2) To explore the important processes and relative mechanisms which dominate the effects of arsenic stress on the speciation transformation of sediment phosphorus mediating by root exudates from typical plant in plateau lakeshore wetland. To fulfill our target, we plan to carry out the indoor simulation experiment. First of all, we intend to ascertain the components and also the concentrations of root exudates from typical plants in plateau lakeshore wetland. Secondly, based on the data which elucidate the species of the root exudates from typical plant in plateau lakeshore wetland, we would set up a series of speciation and concentrations of exogenous phosphorus and to precisely identify the key root exudates which dominantly mediated the speciation transformation of sediment phosphorus. Finally, we would carry out the experiment with the same system under the arsenic stress, and to systematically explore the mechanism of arsenic stress on the speciation transformation of sediment arsenic mediated by root exudates from plant in plateau lakeshore wetland through analyzing the components and concentrations of key root exudates under arsenic stress and the changing rules of phosphorus speciation. The research results could provide theoretical basis for accurate assessment of phosphorus reduction benefit by arsenic contaminated lakeshore wetland. It could also provide scientific proof for the remediation of Plateau Lake with both eutrophication and arsenic contamination.

高原湖滨湿地植物根系分泌物及其对磷形态转化的影响成为研究热点，砷胁迫对这一过程的影响值得关注。本项目以砷污染高原湖滨湿地典型沉水和挺水植物的根系分泌物为研究对象，通过开展根系分泌物对沉积物磷形态转化影响的研究，拟解决以下两个科学问题：（1）识别高原湖滨湿地典型植物根系分泌物特征及影响磷形态转化的关键分泌物；（2）揭示砷胁迫下湖滨湿地典型植物关键根系分泌物影响磷形态转化的过程及机制。本项目在探明高原湖滨湿地典型植物根系分泌物组成及浓度的基础上，通过设置外源添加磷形态及浓度梯度的室内模拟实验，准确判别影响磷形态转化的湖滨湿地典型植物的关键根系分泌物；结合砷胁迫条件下关键根系分泌物组成、浓度及磷形态的变化规律，系统揭示砷胁迫对湖滨湿地典型植物根系分泌物影响磷形态转化的机制。研究成果可为准确评价砷污染湖滨湿地对磷的削减效益提供理论基础，同时为利用植物修复富营养化及砷污染的高原湖泊提供科学依据。

为探讨面源污染物磷对湿地植物根系分泌物的影响和不同环境下湿地植物对水质的净化效果以及湖滨湿地中砷影响下的磷形态转化问题，本研究以云南省阳宗海和尖山河近年来水体中总磷浓度作为参考值，以湿地浮水植物大薸、沉水植物黑藻和挺水植物伞莎草为研究对象，基于野外监测和室内模拟试验的方式共设置6个磷浓度，在室内采用Hoagland营养液培养，在不同时间段下用GC-MS检测植物根系分泌物，同时测定植物的茎叶和根系鲜重和干重、根长及植物生长环境中的水质指标总磷（TP）、化学需氧量（COD）、pH、溶解氧、氧化还原电位和电导率，以及阳宗海底泥中总砷（TAs）、总磷（TP）及各形态磷的含量的关系及其影响。揭示湿地植物通过根系分泌物对于外界环境胁迫时做出的防御措施及植物对污染水质的净化，以期为湿地污染水质植物根微修复提供依据。主要研究结果如下：（1）大薸、黑藻和伞莎草三种植物的干重根冠比存在显著差异（P<0.05）。三种植物在添加不同浓度磷的营养液水培环境下对生物量的分配均主要以茎叶部分为主，随着培养时间加长后植物应对环境变化的自我调节能力开始减弱，相对于茎叶，外源磷对湿地植物根系的影响更大。（2）三种植物根系分泌物主要包括烯烃类、烷烃类、醇类、苯类、酯类、酮类、醛类、胺类和酸类化合物，以烷烃类和酸类化合物最多。主要通过分泌有机酸来改变根际微环境，而大量分泌邻苯二甲酸是湿地植物在受到外界营养元素磷改变时主动适应环境的一种重要响应机制。（3）三种植物对TP和COD都有明显的去除作用，最终去除率均为大薸>伞莎草>黑藻（P<0.5），且随着生物量的增加，TP和COD去除率逐渐增长；湿地植物根系酸性分泌物邻苯二甲酸与TP去除率存在较好的相关性。（4）阳宗海湖滨湿地对砷和外源磷具有截留作用，且总砷含量在表层富集，砷含量对无机磷中的磷石灰型、活性磷酸二钙磷和磷酸八钙磷形态的转化存在显著影响（P<0.05）。