Graduate School of Veterinary Medicine & Animal Sciences, Kitasato Univ., Aomori, Japan.
J Environ Qual. 2012 May-Jun;41(3):823-33. doi: 10.2134/jeq2011.0342.
Chromophoric dissolved organic matter (CDOM) leached from leaf litter is a major source of humus in mineral soil of forest ecosystems. While their functions and refractoriness depend on the physicochemical structure, there is little information on the quality of CDOM, especially for that leached in the very early stages of litter decomposition when a large amount of dissolved organic matter (DOM) is leached. This study aimed to better understand the variations/changes in the composition of CDOM leached from senescent leaf litter from two tree species during the early stage of decomposition. Leaf litter from a conifer tree (Japanese cedar, D. Don) and a deciduous broad-leaved tree (Konara oak, Thunb.) were incubated in columns using simulated rainfall events periodically for a total of 300 d at 20°C. The quality of CDOM was investigated based on the fluorescence properties by using a combination of excitation-emission matrix fluorescence (EEM) and parallel factor analysis (PARAFAC). In addition, the phenolic composition of DOM was investigated at a molecular level by thermally assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC-MS) in the presence of tetramethylammonium hydroxide (TMAH). The EEM was statistically decomposed into eight fluorescence components (two tannin/peptide-like peaks, one protein-like peak, and five humic-like peaks). A significant contribution of tannin/peptide-like peaks was observed at the beginning of incubation, but these peaks decreased quickly and humic-like peaks increased within 1 mo of incubation. The composition of humic-like peaks was different between tree species and changed over the incubation period. Since tannin-derived phenolic compounds were detected in the DOM collected after 254 d of incubation on THM-GC-MS, it was suggested that tannins partially changed its structure, forming various humic-like peaks during the early decomposition.
从凋落物中淋溶出的发色溶解性有机质（CDOM）是森林生态系统矿质土壤腐殖质的主要来源。虽然它们的功能和抗分解性取决于其物理化学结构，但关于 CDOM 的质量，特别是在大量溶解性有机质（DOM）淋溶出的凋落叶分解的早期阶段，信息很少。本研究旨在更好地了解两种树种衰老叶凋落叶在分解早期阶段淋溶出的 CDOM 组成的变化。使用模拟降雨事件，每隔一段时间在 20°C 下用柱状物培养针叶树（日本雪松，D. Don）和落叶阔叶树（椎木，Thunb.）的凋落叶，共 300 天。通过使用激发-发射矩阵荧光（EEM）和并行因子分析（PARAFAC）相结合的方法，根据荧光特性研究 CDOM 的质量。此外，通过在四甲基氢氧化铵（TMAH）存在下进行热辅助水解和甲基化-气相色谱-质谱法（THM-GC-MS），在分子水平上研究 DOM 的酚类组成。EEM 被统计分解为八个荧光成分（两个单宁/肽样峰、一个蛋白样峰和五个腐殖质样峰）。在培养开始时观察到单宁/肽样峰的显著贡献，但这些峰迅速减少，腐殖质样峰在培养 1 个月内增加。腐殖质样峰的组成在树种之间不同，并在培养期间发生变化。由于在 THM-GC-MS 上收集的在培养 254 天后的 DOM 中检测到单宁衍生的酚类化合物，因此表明单宁部分改变了其结构，在早期分解过程中形成了各种腐殖质样峰。
