Abstract: Fujian Province is the largest producer of cultivated seaweed Gracilaria lemaneiformis in China, and carbon sequestration during the degradation phase of this seaweed is of great significance for marine carbon sinks. However, a unified accounting standard for this sequestration is still lacking. Here, we determined the average shedding rate of G. lemaneiformis during the cultivation stage in Dongshan Bay (Fujian Province) to be 7.45% using an in‑situ detritus collector. A 420‑day mesocosm decomposition experiment combined with FT‑ICR MS and metagenomic sequencing was conducted to systematically investigate carbon transformation, molecular evolution, and microbial driving mechanisms in the degradation phase of G. lemaneiformis. Detritus decomposition proceeded through initial leaching and subsequent intensive microbial utilization, accompanied by cell structural disintegration and degradation of intracellular materials. Carbon flow analysis showed that approximately 72% of the detrital carbon was mineralized and released as CO₂. The remaining 28% was retained and consisted of both refractory organic carbon and inorganic carbon. The refractory organic carbon accounted for a net sequestration rate of 17.25%, with sedimentary carbon being the dominant fraction (9.40%), followed by dissolved (RDOC, 2.71%) and particulate (RPOC, 5.14%) forms. Molecular fingerprinting revealed that the unsaturation, aromaticity, and CRAM proportion of refractory carbon molecules gradually increased, whereas the H/C ratio steadily decreased over time. Lignin‑like compounds characterized detritus‑derived refractory molecules, whereas microbe‑transformed ones were enriched in unsaturated hydrocarbons, aromatic compounds and tannins. Metagenomic analysis further uncovered a functional division of microbial communities: epiphytic microbiota were the primary producers of substantial intermediate products, while free‑living microbiota participated in secondary metabolism and carbon redistribution. However, the late‑stage modification and accumulation of recalcitrant macromolecules were mainly driven by abiotic processes, with microbial contributions being largely indirect. This study established a comprehensive carbon budget system for cultivated seaweed and clarified the functional boundaries of microbial communities, thereby providing critical data and a theoretical basis for assessing seaweed carbon sequestration.
摘要：福建省是中国境内最大的条斑紫菜生产地。这种海藻在分解过程中所实现的碳封存对海洋碳汇具有非常重要的意义。不过，目前尚缺乏针对这一过程的统一核算标准。本研究利用现场采集的碎屑样本，测得福建省东山湾地区条斑紫菜在养殖阶段的平均脱落率为 7.45%。此外，研究人员还进行了为期 420 天的中试分解实验，并结合傅里叶变换离子回旋共振质谱和宏基因组测序技术，系统研究了条斑紫菜在分解过程中的碳转化机制、分子演变过程以及微生物的作用机制。在分解过程中，碎屑首先被溶解，随后被微生物大量利用，同时海藻的细胞结构也会发生破坏，细胞内的物质也会被分解。流动分析结果显示，大约 72%的碎屑碳发生了矿化作用，以 CO2 的形式释放出来。剩下的 28%则被保留下来，其中既包括难降解的有机碳，也包括无机碳。在难降解的有机碳中，有 17.25%的碳被有效封存下来。其中，沉积态碳占主导地位，占比为 9.40%；其次是溶解态碳，占比 2.71%；颗粒态碳则占比 5.14%。分子特征分析表明，难降解碳分子的饱和度、芳香性以及 CRAM 比例逐渐增加，而 H/C 比率则随时间推移而下降。来自碎屑的难降解碳分子具有类似木质素的特性，而经过微生物转化后的碳分子则富含不饱和烃、芳香化合物和单宁类物质。 宏基因组分析进一步揭示了微生物群落的职能分工：附生微生物是各种中间产物的主要生产者，而自由生活的微生物则参与次级代谢过程以及碳的重新分配。不过，那些难以分解的大分子的后期转化和积累过程，主要是由非生物因素驱动的，微生物的贡献则主要是间接的。 这项研究建立了针对人工养殖海藻的全面碳预算体系，并明确了微生物群落的功能边界。从而为评估海藻的碳封存作用提供了重要的数据与理论依据。











Keywords: seaweed; detritus; refractory organic carbon; carbon sequestration accounting; microbial degradation
关键词：海藻；碎屑物质；难降解有机碳；碳封存核算；微生物降解
 

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