黄河口潮汐湿地土壤碳矿化途径及其对水盐环境变化的响应

Tidal wetlands are located at the intersection of land and sea. Carbon mineralization in tidal wetlands is regulated by water and salt because of tidal effects. However, it is unclear about how and what mechanisms carbon mineralization pathways (CMPs), such as sulfate reduction, Fe(III) reduction, denitrification and methanogenesis, response to changes of water-salt environment in tidal wetlands. In order to illustrate the subject, three types of tidal marshes including fresh marsh, brackish marsh and salt marsh are to be selected in the Yellow River estuary, and the method of an in situ observation and a dislocated incubation combined with intact soil cores sampling as well as pipes buried in the field are to be used. Our aims are 1) to study the spatial and temporal characteristics of CMPs and their contributions to total carbon mineralization of the tidal marshes through in situ observation, 2) to analyze relationships between CMPs and the environmental factors, such as water, salinity, ionic strength and nutrient level of soil and pore water, as well as microbial community structure, 3) to study effects of the water-salt environment change on CMPs as well as ionic strength, electron acceptor magnitude, matrix quality and microbial community structure through the dislocated experiment, and 4) to illuminate microbial mechanisms of CMPs’ response to water-salt environment in tidal marshes, based on the relation of CMPs-microbial community-water and salt factors. The expected results of the project can be helpful to understand the carbon turnover in tidal wetlands and provide valuable data to evaluate the influence of seawater intrusion on carbon storage in northern tidal wetlands.

潮汐湿地是陆、海交汇处的一个典型两相地带，受潮汐作用的影响，土壤碳矿化过程明显受制于水盐环境条件，但碳矿化途径对水盐变化的响应与机制尚不明晰。本申请项目拟选择黄河口潮汐湿地(淡水湿地、微咸水湿地、咸水湿地)作为研究对象，通过野外原位试验，采用土芯采集法，研究潮汐湿地碳矿化途径（硫酸盐还原、铁还原、反硝化、甲烷生成）及其贡献的时空特征，结合环境与微生物因子分析，阐明碳矿化途径的关键影响因子；通过野外移位试验，采用埋管培养法，研究水盐环境变化对碳矿化途径的影响，阐明碳矿化途径及其贡献对水盐环境变化的响应规律；探明水盐环境变化对离子强度、电子受体数量、基质性质、微生物特征的调控作用，基于水盐环境因子-微生物群落结构-碳矿化途径间的驱动关系，揭示碳矿化途径响应水盐变化的微生物机制。预期研究结果将有助于揭示潮汐湿地碳转化过程机理，并为评估海水入侵对北方潮汐湿地碳储存的影响提供科学依据。

河口潮汐湿地是陆、海交汇处的一个典型两相地带，受潮汐作用的影响，土壤碳矿化途径明显受制于水盐环境条件。为探明河口潮汐湿地土壤碳矿化途径及其对水盐环境变化的响应与相关机制，本资助项目执行期间，基于野外观测、移位培养与室内模拟等试验方法，重点开展了黄河口潮汐湿地碳矿化途径及其贡献、碳矿化途径对潮汐水文变化的响应、盐胁迫对碳矿化途径的影响等研究内容，研究发现：（1）潮汐湿地不同潮位带土壤碳矿化为23~60 μg C·g-1·d-1，铁/硫还原途径的贡献为34%~87%，其中以铁还原为主导；碳矿化与铁/硫还原的具有明显的时空分异特征，与土壤水分、盐度、碳源基质和黏粒正相关，与氧化还原电位负相关；细菌、铁还原菌和硫酸盐还原菌群落多样性及其结构组成因潮位而异，且与碳矿化、铁/硫还原途径密切相关。（2）暴露于潮汐环境中后，淡水湿地土壤盐度升高、基质质量下降、微生物群落多样性和结构组成改变，碳矿化速率降低了49%~69%，而铁/硫还原的贡献则升高了59%~122%；微生物介导的铁/硫还原途径对潮汐环境变化的响应主要受控于水分条件、氧化还原电位、基质碳源和盐胁迫。（3）盐胁迫对淡水湿地土壤碳矿化、铁/硫酸盐还原途径及其贡献均具有明显的抑制作用；盐度升高可降低淡水湿地土壤微生物多样性，增大微生物类群的盐度梯度分异性，改变微生物群落结构组成；盐胁迫下淡水湿地营养供给水平而非碳源基质可能是微生物介导的铁/硫还原途径的限制性因素。本项目研究明确了河口潮汐湿地碳矿化途径及其贡献，阐明了碳矿化途径对潮汐环境变化和盐胁迫的响应，揭示了水盐环境、基质性质和微生物的控制机制。项目执行期间，发表学术论文17篇，其中SCI收录8篇；培养研究生4人、本科生2人；参加国内学术会议交流13人次。相关研究成果为揭示河口湿地碳转化对环境变化的响应机制提供了科学依据，为评估全球变化背景下河口湿地碳损益提供了科学参考。