Abstract There is considerable variability in the ability of seagrass ecosystems to sequester organic carbon (Corg) in their sediments, which act as natural carbon sinks contributing to climate change mitigation. In this work, we studied the chemistry of two Posidonia seagrass species aiming to elucidate whether differences in chemical composition might explain differences in their Corg sequestration capacity. Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and Thermally assisted Hydrolysis and Methylation (THM) GC-MS data showed a remarkable difference in phenolic compound patterns between P. oceanica and P. australis bulk plants and individual organs (leaves, sheaths, roots and rhizomes). The lignin of P. australis generates a series of p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) products that are typical of herbaceous plants, whereas P. oceanica is particularly rich in p-hydroxybenzoic acid (pBA) derivatives. The structural characteristics of the lignins were further investigated by two-dimensional Nuclear Magnetic Resonance (2D-NMR) spectroscopy and Derivatization Followed by Reductive Cleavage (DFRC), focusing on sheath tissues. The analyses confirmed important differences in the lignin content (19.8% in P. australis and 29.5% in P. oceanica) and composition between the two species; intriguingly, the cell-walls of P. oceanica sheaths were highly enriched in pBA, a component that was completely absent in P. australis. 2D-NMR and DFRC data further revealed that pBA was esterified to the lignin, acylating the γ-OH of the lignin side-chain. Interestingly, P. oceanica lignin presented an extremely high degree of p-hydroxybenzoylation in both guaiacyl (73%) and syringyl (61%) lignin units; the highest p-hydroxybenzoylation degree reported in plant lignins to date. It is tempting to conclude that the higher Corg storage capacity of P. oceanica ecosystems might be related to the higher abundance of pBA-rich lignin and its recalcitrant nature.

中文翻译：

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Posidonia 物种中完全不同的木质素成分可能与有机碳封存能力的差异有关

摘要 海草生态系统在其沉积物中封存有机碳 (Corg) 的能力存在相当大的差异，这些有机碳充当有助于减缓气候变化的天然碳汇。在这项工作中，我们研究了两种 Posidonia 海草物种的化学成分，旨在阐明化学成分的差异是否可以解释其 Corg 封存能力的差异。热解-气相色谱-质谱 (Py-GC-MS) 和热辅助水解和甲基化 (THM) GC-MS 数据显示，P. Oceanica 和 P. australis 散装植物和个体器官（叶、鞘、根和根茎）。P. australis 的木质素会生成一系列典型的草本植物对羟基苯基 (H)、愈创木酚 (G) 和丁香基 (S) 产物，而 P. Oceanica 尤其富含对羟基苯甲酸 (pBA) 衍生物。通过二维核磁共振 (2D-NMR) 光谱和衍生化后还原裂解 (DFRC) 进一步研究木质素的结构特征，重点是鞘组织。分析证实了两个物种之间的木质素含量（P. australis 为 19.8%，P. oceanica 为 29.5%）和组成的重要差异；有趣的是，P. Oceanica 鞘的细胞壁高度富含 pBA，而 PBA 中完全没有这种成分。2D-NMR 和 DFRC 数据进一步显示 pBA 被酯化到木质素上，酰化了木质素侧链的 γ-OH。有趣的是，P。Oceanica 木质素在愈创木酰基 (73%) 和丁香酰基 (61%) 木质素单元中均呈现出极高程度的对羟基苯甲酰化；迄今为止在植物木质素中报道的最高对羟基苯甲酰化程度。很容易得出这样的结论，即 P. Oceanica 生态系统较高的 Corg 存储能力可能与富含 pBA 的木质素的丰度较高及其顽固性有关。