Details

Autor(en) / Beteiligte

• Wijesinghe, Jithya Nawodi
• Koarashi, Jun
• Atarashi-Andoh, Mariko
• Saito-Kokubu, Yoko
• Yamaguchi, Noriko
• Sase, Takashi
• Hosono, Mamoru
• Inoue, Yudzuru
• Mori, Yuki
• Hiradate, Syuntaro

Titel

Formation and mobility of soil organic carbon in a buried humic horizon of a volcanic ash soil

Ist Teil von

• Geoderma, 2020-09, Vol.374, p.114417, Article 114417

Ort / Verlag

Elsevier B.V

Erscheinungsjahr

2020

Quelle

Elsevier ScienceDirect Journals

Beschreibungen/Notizen

• •Hydrophilic fulvic acid fractions had received much biological transformations.•Humic acid fractions had formed at early stage of soil formation with less biological transformation.•Fire event could be a possible formation mechanism of HA fractions.•Mobility of soil organic carbon fractions was limited to <4 mm per century.•The thick humic horizon reflects the successive up-building accumulation of soil particles containing soil organic carbon. A buried humic horizon (14C age between 5.4 and 6.8 kyr BP) of a volcanic ash soil in Aomori, Japan, which was collected from the depth between 147 and 187 cm at 5 cm-interval (total eight sub-horizon samples), was investigated to clarify the degree of biological transformation and mobility of soil organic carbon (SOC) fractions. The SOC fractions were prepared from each sub-horizon sample by extraction and precipitation procedures with controlling pH of the extracted solution, resulting in humin, humic acid (HA), and four fulvic acid (FA) fractions (two hydrophilic FA fractions: FA1 and FA2, and two hydrophobic FA fractions: FA3 and FAIHSS). The prepared SOC fractions were characterized by 14C age and stable isotopic ratios of 13C (δ13C) and 15N (δ15N). The hydrophilic FA fractions showed the highest δ13C and δ15N values, indicating that these SOC fractions had been most enriched with 13C and 15N by biological metabolic processes. On the other hand, the HA fraction showed the lowest δ13C and δ15N values, therefore this fraction would have been less-metabolized, although HA fraction has been regarded as well-processed in general. The 14C age of the HA fraction was almost same as the deposition age of the corresponding sub-horizon, indicating that the C in the HA fraction would have been fixed in situ right after photosynthesis by plants at the early stage of soil formation and chemically stabilized at soil surface, by fire event, etc. The average rates of vertical translocation of the SOC fractions were low (humin and HA fractions: <1 mm per century, FA fractions: 1–4 mm per century), implying that the vertical translocation of SOC would not be the main mechanisms for forming thick humic horizons. The present study showed strong evidence of the in situ formation of SOC on soil surface, and successive up-building accumulation of soil particles containing SOC would contribute to the formation of the thick humic horizons.