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.
MethodsLitterbags 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.
ResultsThe 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.
ConclusionsDuring 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.
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