Mao Jason Feijian, Liu Changbing, Li Guoliang, Wang Yuli, Yuan Qiyi, Gin Karina Yew-Hoong, Zhang Huifang, Chen Xu, Li Wenxuan
State Key Laboratory of Tibetan Plateau Earth System, Resources and Environment, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100101, China.
Tibetan Ecology and Environment Monitoring Center, Lhasa, 850000, China.
Water Res. 2025 Jul 19;286:124261. doi: 10.1016/j.watres.2025.124261.
Dissolved organic matter (DOM) plays a central role in ecosystem health and carbon cycling. However, uncertainties remain regarding DOM molecular assembly mechanisms under varying organic carbon concentrations triggered by natural and anthropogenic factors. This study integrates geochemical analyses with molecular characterization of surface water and pore water DOM from seven rivers spanning diverse biomes and non-purgeable organic carbon (NPOC) gradients. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that the low NPOC groups were characterized by the increase of polycyclic condensed aromatics and sugar-like substances. Intermediate NPOC conditions favored the accumulation of DOM molecules with higher thermodynamic efficiency and activity compared to low- and high-NPOC groups. Alpha diversity analysis showed that decreasing NPOC concentrations led to narrower molecular coverage, reduced dispersion, and lower divergence. Stochastic processes primarily governed the DOM assembly process in high-NPOC environments, indicating constrained production and transformation pathways of DOM molecules. Conversely, deterministic processes dominated the assembly process for low-NPOC conditions, suggesting selective preservation or transformation of specific groups of DOM molecules. These findings highlight organic carbon concentration as a key driver of DOM molecular architecture and assembly processes, with implications for carbon sequestration and nutrient cycling in river ecosystems.
溶解有机物（DOM）在生态系统健康和碳循环中起着核心作用。然而，对于自然和人为因素引发的不同有机碳浓度下DOM分子组装机制仍存在不确定性。本研究将地球化学分析与来自跨越不同生物群落和不可吹扫有机碳（NPOC）梯度的七条河流的地表水和孔隙水DOM的分子特征相结合。傅里叶变换离子回旋共振质谱（FT-ICR MS）显示，低NPOC组的特征是多环缩合芳烃和类糖物质增加。与低NPOC组和高NPOC组相比，中等NPOC条件有利于具有更高热力学效率和活性的DOM分子的积累。α多样性分析表明，NPOC浓度降低导致分子覆盖范围变窄、分散性降低和离散度降低。随机过程在高NPOC环境中主要控制DOM组装过程，表明DOM分子的生产和转化途径受到限制。相反，确定性过程在低NPOC条件下主导组装过程，表明特定组的DOM分子被选择性保存或转化。这些发现突出了有机碳浓度作为DOM分子结构和组装过程的关键驱动因素，对河流生态系统中的碳固存和养分循环具有重要意义。
