太湖草、藻湖区沉积物WSOM组成和分子结构分析

草型湖泊（区）和藻型湖泊（区）是浅水湖泊的两种典型状态，两种湖泊中有机质（OM）的来源和转化存在明显差异.有机质在沉积物上的埋藏是湖泊碳汇功能的重要体现.沉积物中的有机质可能发生后续的转化，影响湖泊碳汇功能；其转化过程与其固有的性质密切相关.目前为止，有关草型和藻型湖泊沉积物中有机质的组成，特别是分子结构差异的信息较少.为此，采集太湖草型湖区（东太湖）和藻型湖区（梅梁湾）沉积物，提取和纯化沉积物中的水溶性有机质（分别记为M-WSOM和A-WSOM），并采用紫外-可见吸收光谱、三维荧光光谱、傅立叶红外光谱和傅里叶变换-离子回旋共振-质谱（FT-ICR MS）对WSOM性质组成和分子结构进行详尽的表征与分析.结果表明：①M-WSOM的相对分子质量比A-WSOM的（E₂ ：E₃指标）稍大；FT-ICR MS的数据显示，M-WSOM和A-WSOM的相对分子质量分别为388.9和379.9.②M-WSOM的芳香性略高于A-WSOM的（SUVA₂₅₄和HIX指标）；同样地，FT-ICR MS的结果显示，M-WSOM中稠环芳烃（6.3%，强度加权平均占比，下同）、芳香类物质（7.7%）的含量高于A-WSOM （分别为1.1%和4.4%）；③荧光组分结果表明A-WSOM中类蛋白质组分的含量大于M-WSOM；FT-ICR MS的结果与之对应，A-WSOM的多肽含量（35.5%）高于M-WSOM的（15.6%）；④质谱数据显示了高分辨的分子信息：M-WSOM和A-WSOM中，沉积物中含杂原子的分子分别占82.9%和91.7%；其中含氮元素的分子占比高达53.5%和78.5%；含磷元素分子占30.4%和41.4%，M-WSOM磷元素主要分布在脂肪烃和高度不饱和低氧物质中，而A-WSOM则主要分布在多肽中.揭示了浅水湖泊两种典型状态沉积物OM的组成和分子结构；有助于研究湖泊沉积物的温室气体排放，及碳、氮、磷元素的生物地球化学过程.

Spectroscopic and Molecular Characterization of Water Soluble Organic Matter from Sediments in the Macrophyte-dominated and Algae-dominated Zones of Taihu Lake

Macrophyte- and algae-dominated lakes (zones) are the two typical states of shallow lakes, where the source and composition of organic matter are distinct. The burial of organic matter (OM) in the sediment supports the role of lakes as carbon sinks. However, organic matter in the sediments could be further processed, influencing the carbon cycle. The post-burial metabolism of the sedimentary OM relates closely to its composition. However, information on the differences in composition remains limited, especially the molecular composition of organic matter from sediments in the macrophyte-dominated and algae-dominated lakes. In this study, sediments were collected from the macrophyte-dominated and algae-dominated zones of Taihu Lake (East Taihu Lake and Meiliang Bay, respectively), and the active pool of sedimentary OM (water soluble organic matter, WSOM) was extracted and purified. The composition of the WSOM was characterized in detail via absorption spectroscopy, fluorescent spectroscopy, infrared spectroscopy, and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). The optical index of E₂:E₃ showed that the molecular size of WSOM in the macrophyte-dominated zone (M-WSOM) was slightly larger than that in the algae-dominated zone (A-WSOM). Consistently, the intensity-weighted molecular weights were identified as 388.9 and 379.9, respectively, via FT-ICR MS analysis. M-WSOM was more humified than A-WSOM, as evidenced by the SUVA₂₅₄ and HIX values. The FT-ICR MS results showed that the relative abundance of the condensed aromatic substance and the aromatics were 6.3% (intensity-weighted) and 7.7% for M-WSOM and 1.1% and 4.4% for A-WSOM, respectively. The excitation-emission matrix fluorescence-parallel factor analysis (EEM-PARAFAC) suggested that the protein-like component was more in A-WSOM than that in M-WSOM, and the FT-ICR MS results showed that the intensity-weighted relative abundances of peptides were 35.6% and 15.6% for A-WSOM and M-WSOM, respectively. The FT-ICR MS results further showed that the heteroatom-containing molecules were abundant in the sedimentary WSOM, i.e., 82.9% and 91.7% for M-WSOM and A-WSOM, respectively. The nitrogen-containing molecules dominated, contributing to 53.5% and 78.5% of M-WSOM and A-WSOM, respectively. There were 30.4% and 41.4% phosphorus-containing molecules in M-WSOM and A-WSOM, respectively. The phosphorus-containing molecules in M-WSOM were mainly aliphatics and highly unsaturated structures with low oxygen, whereas those in A-WSOM were mainly peptides. This study elucidated the detailed molecular composition of WSOM in the macrophyte-dominated and algae-dominated zones of Taihu Lake, which aids understanding of the carbon, nitrogen, and phosphorus biogeochemical cycles in lakes.