人工湿地生态系统甲烷过程对生物多样性响应研究

Methane emission during wastewater treatment processes has become a huge source of greenhouse gases due to population increasing and urbanization. The constructed wetlands for wastewater treatment are huge methane emission sources although the fluxes are lower than that from wastewater treatment plants. So it is urgent to study the methane processes in constructed wetland systems in order to reduce methane emission. Plants could have significant influences on the transformation and emission processes of methane through affecting physical and chemical factors, and microbial communities and activities in the substrate of constructed wetlands. However, what are the features of methane processes in the root zones of different plant species under high carbon and nitrogen concentrations in wastewater? Whether plant diversity assemblage can alter methane processes? How does carbon and nitrogen concentration affect methane processes and emissions? The mechanisms associated with these questions are of great importance but are lack of studies. This program use constructed wetlands as the research platforms and combined approaches of mass-balance with stable isotopic method, to study the interspecific differences of root zone methane production, oxidation and transportation processes as well as emission intensities among more than 30 plant species under different carbon and nitrogen concentrations and nitrogen chemical forms, and the mechanisms for the effect of plant diversity on methane processes. The results could broaden the study of relationships between biodiversity and ecosystem functions; meanwhile, the exploration of screening the tool plant species with both high decontamination capability and low methane emissions would contribute to the development of resources botany.

随着人口增长和城市化水平提高，污水处理过程中排放的大通量的甲烷已经成为巨大的温室气体源。人工湿地污水处理系统甲烷排放虽然低于污水处理厂，但通量仍然很大，因此迫切需要研究人工湿地系统中的甲烷过程，以寻找降低甲烷通量的途径。植物通过影响基质中理化因子和微生物群落来影响根区的甲烷的产生、转化和释放过程，但是在污水这种高碳和高氮条件下，不同植物种类根区甲烷过程具有什么特征？植物多样性配置是否会改变系统的甲烷过程？碳氮条件如何影响甲烷过程和释放通量？这些重要的机理问题目前尚无系统的研究。本项目拟以人工湿地系统为研究平台，通过控制条件下的物质平衡结合稳定同位素方法，研究在不同碳氮浓度和氮形态下30余种植物根区甲烷产生、氧化、运输过程和排放强度的种间差异，以及多样性配置对系统甲烷过程的影响机理，拓展生物多样性-生态系统功能关系的研究；同时筛选兼具高去污能力和低甲烷释放植物并探索原理，发展资源植物学。

人工湿地污水处理系统是甲烷（CH4）重要排放源。本项目探索植物多样性（物种丰富度和差异性）对人工湿地CH4排放及相关温室气体排放和氮去除的影响，设计了5套处理实验来分析不同因素的作用，以加深生物多样性-生态系统功能的理解。主要创新点及发现有：物种丰富度在砂基质和无基质水培浮床系统中均提高CH4排放；植物种类差异在砂基质中不影响CH4排放，但在无基质中虉草或羊蹄的存在提高CH4排放。砂基质系统中CH4排放高于无基质系统，原因是砂基质为产甲烷菌提供了附着表面。砂颗粒大小也影响多样性-系统CH4排放关系：粗砂基质系统中物种丰富度和差异性均不影响CH4排放；细砂基质系统中物种丰富度不影响CH4排放，但物种特性显著影响：群落中羊蹄的存在增加系统CH4排放而水芹存在则降低排放。细砂的CH4排放（-8.46 ~ 21.03 mg m-2 d-1）范围大于粗砂（5.06 ~ 6.85 mg m-2 d-1），说明细砂基质人工湿地系统减排CH4的潜力更高。在厌氧条件下，当基质可用碳资源较低时，物种丰富度提高CH4排放，原因是丰富度提高群落生产力进而提高基质的有机质含量为产甲烷菌提供更多碳源；但是基质碳较高时物种丰富度不影响CH4排放，只有物种组合有显著影响。在兼氧条件下，高铵氮系统中的CH4排放高于低铵氮系统，丰富度和差异性均不影响CH4排放，而高铵抑制CH4氧化从而促进排放；高硝氮系统CH4排放低于低硝氮的系统，但丰富度不影响CH4排放，物种组合影响CH4排放，机理是硝氧化CH4从而降低排放。进一步，我们提出了一个“加性多功能指数AMF”来整合生态系统多功能（CH4、N2O、生产力、基质碳固存和氮去除），发现植物丰富度可在提高氮去除的同时显著削减温室效应。总之，我们发现植物丰富度对甲烷有弱的正效应，但物种差异性的作用明显；多功能综合分析表明人工湿地中配置植物多样性能够降低温室效应。同时，我们找出了优化的植物种类及组合：在高氮和细砂基质中选择虉草单种，高氮粗砂基质中选择羊蹄；高氮水培浮床中用羊蹄+水芹+虉草和羊蹄+水芹+吉祥草的物种组合。