辽河口湿地土壤溶解性有机碳对盐分的响应规律及其机制

Soluble loss of dissolved organic carbon(DOC) as the main carbon discharge playes an important role in the carbon source-sink change in estuary wetlands. Salinity is a key factor influencing DOC dynamics and components in wetland soil. However, how changes and mechanisms of DOC production-consumption processes responding to salinity in estuary wetlands are not clear. In order to study the effects of salinity on the DOC dynamics in soil and discuss involved mechanisms, a salinity zone is to be selected in Liaohe estuatry wetland, and the methods of an in situ observation and incubations combined UV254 and fluorescence spectroscopy analysis in laboratory are to be used. Our aims are 1) to study the changes of DOC in soil along the salinity zone and analysis the relationships of DOC concentration and salinity factors such as the total salinity, EC1:5, SAR and pH values, 2) to study the dynamics of DOC production, biodegradability and absorption in different salinity incubations, and also to differentiate the effects of salinity on DOC biogeochemical process, 3) to make it clear that how DOC production-consumption process interactively responses to salinity change based on a DOC turnover model, and 4) to study the changes of microbial activity such as microbial biomass carbon, soil base respiration and soil enzyme activity in the salinity zone, and DOC components such as UV254 values and fluorescence characteristics in incubations, to discuss the mechanisms of DOC dynamics responding to salinity change. The expected results of the research could contribute to understand the carbon turnover in estuary wetland and provide the data to evaluate the influence of seawater intrusion on DOC soluble loss in north estuary wetlands.

溶解性有机碳(DOC)的溶失是河口湿地重要的碳损失途径，对于河口湿地碳源/汇转换具有不可忽视的作用。盐分，作为一个关键的生态因子，对土壤中DOC动态及其组成变化具有显著影响，但河口湿地DOC产生-消耗过程对盐分的响应规律及其机制尚不明确。本申请项目拟通过野外样带观测，研究辽河口湿地不同盐分带土壤DOC浓度的变化特征，阐明土壤DOC浓度对盐分的响应规律；通过室内模拟培养，研究不同盐分梯度下土壤有机碳矿化及DOC生成、降解与吸附动态，明确盐分对土壤DOC关键生物地球化学过程的影响；建立土壤DOC周转模型，揭示DOC产生-消耗过程与盐分之间的响应关系；利用微生物活性分析、UV254和荧光光谱分析方法，研究盐分与土壤微生物和酶活性、盐分与DOC组成和结构特征的关系，探讨DOC动态对盐分的响应机制。本研究将有助于揭示河口湿地碳过程机理，并为评估海水入侵对北方河口湿地DOC溶失的影响提供科学依据。

本资助项目执行期间，基于野外观测与室内模拟培养等试验方法，重点开展了河口典型湿地DOC的时空分布特征及其与环境因子的关系，DOC生成、吸附-解吸、降解及碳矿化过程对盐分的响应规律，DOC释放及土壤呼吸响应盐分的生物化学机制等研究内容。研究发现：（1）4—10月的观测期内，三类典型湿地（芦苇、翅碱蓬、裸滩）土壤剖面DOC浓度均值分别为1.478mg/gsoil、1.063mg/gsoil和0.971 mg/gsoil，芦苇湿地＞翅碱蓬湿地＞裸滩。土壤溶液电导率（EC）是DOC分布的主要控制因素；（2）盐分升高减缓了DOC生成、降解及碳矿化过程，促进了土壤对DOC的吸附作用；基于DOC周转模型，当土壤溶液盐度提高到10 mS/cm时，可使土壤碳矿化降低9%—14%，DOC生成速率降低10%—45%。（3）不同盐度水平下，河口湿地土壤DOC释放及土壤呼吸强度对盐分的响应规律不同。盐度较低时（＜10mS/cm），盐度对DOC释放及土壤呼吸的影响不显著；盐度较高时（＞10mS/cm），DOC释放及土壤呼吸变缓，而增大了DOC中芳香族结构（SUVA）的比例；低盐分条件下微生物活性对DOC数量的影响更显著，而高盐分条件下微生物活性与SUVA的关系更密切；（4）盐分升高在一定程度上提高了细菌物种多样性，增大了嗜盐、硝化及铁、硫还原细菌等物种的相对丰度，但却降低了微生物量碳含量。本研究结果表明，河口湿地土壤DOC过程响应盐分变化的机制在于：盐分升高使DOC中芳香族结构比例的上升，降低了DOC的生物可利用性，同时微生物群落结构组成及数量的变化使其降解速率下降，而土壤胶体吸附作用的增强最终导致DOC生成量的减少。本项目研究系统揭示了河口湿地DOC响应盐分变化的内在过程及其生物化学机制，其研究成果将有助于拓展我们对河口湿地碳循环过程及其控制机制（如基质结构性质、阳离子交换性能、微生物介导作用）的认知。