水文胁迫下的植被演替对湿地碳素迁移转化的影响机制

Changes of hydrological regime caused by water conservancy project which can prevent flood and increase benefits will change original ecological hydrologic rhythm of the wetland system and trigger changes of the distribution of wetland vegetation population. This “mediation effect” caused by plant population succession because of forces of hydrologic conditions will affect the carbon migration and transformation process in the wetland. This project plans to select typical vegetation communities (herbal mudflat, emergent aquatic plant marsh and brushwood) as samples to determine influence of hydrological factors on distribution of wetland vegetation population through analyzing and monitoring hydrologic conditions (inundation duration,depth and frequency), materialized environmental conditions (dissolved oxygen, oxidation reduction potential and nutrients), carbon metabolism functional microorganisms (denitrifying anaerobic methane oxidation bacterium, anaerobic methanogens and aerobic heterotrophic bacterium), carbon fluxes of soil and other factors. This project also aims at building the response relationship between the plant population types and materialized factors of wetland and that between microbial communities and carbon conversion process; determining the relationship mode for “hydrological factors-vegetation species-materialized factors-microbial communities-carbon conversion” and revealing the influencing mechanism of vegetation population succession forced by hydrologic conditions on carbon migration and transformation process of the wetland. This project can provide theoretical and scientific basis for evaluating the influence of water conservancy project on evolutionary process of wetland ecological system and formulating hydraulic dispatch way which can meet environmental protection demands.

水利工程引起的水文情势变化将改变流域内湿地的生态水文节律，引起湿地植被种群分布的变化。不同植被种群内部碳循环速率不同，这种由水文条件胁迫的植物种群演替而引起的“介导作用”，将影响湿地内碳素的迁移转化。本课题拟选取洞庭湖典型湿地植被群落（草本滩涂、挺水植物荡、灌木丛）样地，通过监测水文条件（淹水时间、淹没深度和淹没频率）、物化环境条件（溶解氧、氧化还原电位、营养盐）、碳素代谢功能微生物（反硝化甲烷厌氧氧化菌、厌氧产甲烷菌、好氧异养菌）、土壤碳通量等因子，分析水文因子对植被种群分布的影响；建立植物种群类型与湿地物化因子、微生物群落和碳转化过程的响应关系；确定“水文因子-植被种群-物化因子-微生物种群-碳迁移转化”的关系模式；揭示水文条件胁迫下植被种群演替对湿地碳迁移转化过程的影响机制。本课题可为评估水利工程对湿地生态系统演化过程的影响、制定满足生态环境保护需求的水利调度方式提供理论和科学依据。

本文以湿地水文节律和植被群落分布为切入点，研究洞庭湖区关键水文条件对湿地植被种群分布的影响，植物种群类型对湿地土壤微生物群落及碳氮迁移转化过程的影响，植物及藻类衰亡分解过程对温室气体排放的影响，典型植被群落碳氮积累和排放的时空变化等。主要内容及结论如下：.洞庭湖长期的水文节律造成了湿地生态系统中植被的分布及演替。受水文情势变化的影响，各植被带沿地势高程方向依次分布为：芦苇带>薹草带>虉草带>荇菜带>泥滩带。各植被带植物的碳、氮密度与水位上升速率呈显著正相关（P < 0.05）。芦苇带吸收固定的碳、氮密度均为各植被带中最高，其密度分别为467.994 g·m-2和17.674 g·m-2。水文情势导致的干-湿交替环境对湿地的初级生产力、有机物累积和输出、营养物质循环均有着显著影响。五种不同类型研究区域在不同水位时期的C/N比均大于20，表明沉积物中注入的有机物以外源为主。水文情势胁迫下的植被演替对温室气体的排放通量有显著影响。不同水位时期下各研究区域之间的N2O、CO2、CH4排放通量均存在显著性差异。当沉积物C/N比> 25时，N2O排放通量趋向于稳定值0.230μg·m-2·min-1（即：N2O排放通量的阈值）。此外，洞庭湖水文条件的改变对微生物群落结构及丰度有着显著影响：不同植被带之间碳氮转化功能微生物的基因丰度也存在差异，各研究区表层沉积物的OTU单元数及Shannon多样性指数在不同水位时期也各不相同。.水文情势对湿地不同植被群落的影响使湿地内部碳氮迁移转化过程产生改变表明，今后通江湖泊的湿地管理中，水利工程调控措施应更多的关注湖泊湿地生态系统的调控，特别是湿地植被群落的维护，规避极端的水文过程对植被群落结构和多样性产生破坏。