Salt marsh vegetation is an important contributor of dissolved organic matter (DOM) to coastal waters. The dynamics of DOM leaching from different marsh plants, however, have not been well studied or compared.
In this study, we conducted laboratory experiments to investigate the processes of DOM leaching from three common marsh plants (Phragmites australis, Suaeda salsa and Aeluropus littoralis) collected from the Yellow River Delta (YRD) salt marsh in October 2016. The YRD is one of the largest and most well-protected coastal ecosystems on the east coast of China.
We found that the plant leaves released DOM at much higher concentrations than the plant roots or stems, as measured by the dissolved organic carbon (DOC) and dissolved nitrogen (DN). On average, 15% of the biomass C and 30% of the biomass N were released from the plant leaves as DOC and DN during the 27-day incubation period. The DOM released from the plants was very labile, and 92.4%–98.1% of the DOC and 88.0%–94.6% of the DN released from the plants were consumed by bacteria during the 27-day incubation period. The fluorescence characteristics of the plant-released DOM indicated that chromophoric dissolved organic matter was a major fraction of the DOM and that protein-like components were the primary organic fractions released from the plants. Bacterial degradation altered both the fluorescence properties and the chemical composition of the DOM. The results of the laboratory experiments were well supported by the field investigation, which indicated that a large amount of DOM was outwelled from the YRD salt marshes in late autumn. Our study suggests that the DOM released from the biomass of salt marsh plants provides an important source of both DOC and DN for marsh and coastal waters. The highly labile DOC and DN provide essential food sources to support microbial communities in the YRD salt marsh and adjacent coastal waters.
盐沼植被是沿海水体中溶解有机物(Dissolved Organic Matter, DOM)的重要贡献者。然而，不同盐沼植物释放DOM的动力学特征尚缺乏系统研究和比较。黄河三角洲湿地是中国东海岸面积最大，保护最完善的沿海生态系统之一。本论文研究了2016年10月从黄河三角洲(Yellow River Delta, YRD)盐沼中采集的三种常见沼泽植物(芦苇(Phragmites australis)，碱蓬(Suaeda salsa)和獐茅(Aeluropus littoralis)的DOM释放过程。通过测定溶解有机碳(Dissolved Organic Carbon, DOC)和溶解氮(Dissolved Nitrogen, DN)发现，植物叶片释放的DOM浓度远高于其根和茎。在27天的培养期内，平均有15%的生物碳和30%的生物氮以DOC和DN的形式通过植物叶片释放。从植物中释放的DOM非常不稳定，在27天的培养期内，细菌共消耗了92.4%–98.1%的DOC和88.0%–94.6%的DN。植物释放DOM的荧光特性表明，发色溶解的有机物(Chromophoric Dissolved Organic Matter, CDOM)是DOM的主要组分，而类蛋白组分是植物释放CDOM的主要组分。细菌的降解作用改变了DOM的荧光性质和化学组成。上述的室内研究结果得到了实地调查的充分支撑，表明在深秋时期黄河口湿地有大量DOM溢出。本研究结果表明，盐沼植物释放的DOM是沼泽和沿海水域DOC和DN的重要来源，而且易降解DOC和DN为黄河口湿地和邻近沿海水域中的微生物群落提供了重要的食物来源。