Purpose

In this study, 1-year decomposition experiments were conducted to measure the litter carbon decomposition dynamics in saltmarsh and to determine the changes in the chemical structure of litter carbon during the litter decomposition process.

Methods

Litterbags containing a mixture of Spartina alterniflora litter and burned sediment were buried at four S. alterniflora saltmarshes and one S. alterniflora–Suaeda salsa co-existing saltmarsh. The contents of total organic carbon (TOC) and recalcitrant carbon (RC) were determined by a Sercon Integra CN isotope ratio mass spectrometer, while the content of labile carbon (LC) was estimated by calculation. ¹³C nuclear magnetic resonance (NMR) spectroscopy was conducted to characterise the chemical structures of the organic carbon compounds in the S. alterniflora litter during decomposition. Solid-state ¹³C–CPMAS-NMR spectra were obtained using an AVANCE III 400 MHz (Bruker) spectrometer.

Results

The results indicated that more RC than LC remained in the litterbag during decomposition. The organic carbon content of the S. alterniflora litter was largely composed of alcoxyl-C compounds (78.9%), the decomposition products of which dominated the litter organic carbon fractions, including the TOC, RC, and LC. In contrast, alkyl-C, aromatic-C, and carboxyl-C products contributed mostly to RC. Differences in the negative correlations between the litter carbon fractions and alkyl-C, aromatic-C, and carboxyl-C were found among the developing saltmarshes. Humus generated by the S. alterniflora litter was mainly composed of macromolecular organic compounds containing functional groups such as methyl, methylene, methine, methoxyl, aromatic rings, phenolic hydroxyl, and carboxyl.

Conclusions

During decomposition, the organic carbon in the S. alterniflora litter was found to be dominated by O-alkyl-C, followed by aromatic-C, alkyl-C, and carboxyl-C. O-alkyl-C plays a major role in the LC proportion of organic carbon, while aromatic-C, alkyl-C, and carboxyl-C contribute more to the RC proportion. Alkyl-C was found to be more easily decomposed than aromatic-C in the S. alterniflora litter. During litter decomposition, the molecular structure complexity, humification degree, and decomposition degree of organic carbon exhibited seasonal variations. In the 3-year saltmarsh, more decomposition of the organic carbon in the S. alterniflora litter was observed as compared to other sites.

中文翻译：

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盐沼沉积物分解过程中互花米草枯落物中有机碳化学成分的变化

目的

在这项研究中，进行了为期 1 年的分解实验，以测量盐沼中凋落物碳的分解动力学，并确定凋落物分解过程中凋落物碳化学结构的变化。

方法

将装有互花米草凋落物和燃烧的沉积物混合物的垃圾袋埋在四个互花米草盐沼和一个互生沙门氏菌– Suaeda salsa共存的盐沼中。总有机碳 (TOC) 和顽固碳 (RC) 的含量由 Sercon Integra CN 同位素比质谱仪测定，而不稳定碳 (LC) 的含量通过计算估算。^{进行 13} C 核磁共振 (NMR) 光谱分析以表征互花米草枯枝落物中有机碳化合物在分解过程中的化学结构。固态¹³使用 AVANCE III 400 MHz (Bruker) 光谱仪获得 C-CPMAS-NMR 光谱。

结果

结果表明，在分解过程中，垃圾袋中残留的 RC 比 LC 多。S. alterniflora凋落物的有机碳含量主要由烷氧基-C 化合物 (78.9%) 组成，其分解产物占凋落物有机碳部分的主导地位，包括 TOC、RC 和 LC。相比之下，烷基-C、芳香-C 和羧基-C 产物对 RC 贡献最大。在发育中的盐沼中发现了枯枝落叶碳馏分与烷基-C，芳族-C和羧基-C之间的负相关性差异。互花米草凋落物产生的腐殖质主要由含有甲基、亚甲基、次甲基、甲氧基、芳香环、酚羟基、羧基等官能团的大分子有机化合物组成。

结论

在分解过程中，发现互花米草中的有机碳以 O-烷基-C 为主，其次是芳香-C、烷基-C 和羧基-C。O-烷基-C在有机碳的LC比例中起主要作用，而芳族-C、烷基-C和羧基-C对RC比例的贡献更大。发现烷基-C 比互花菊垃圾中的芳香-C 更容易分解。凋落物分解过程中，有机碳的分子结构复杂度，腐殖化度和分解度均表现出季节性变化。在 3 年的盐沼中，与其他地点相比，观察到互花米草凋落物中的有机碳分解更多。