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Abstract: The genesis of a 40-cm-thick buried Holocene humic soil horizon in a 6-m-high sequence near Towada volcano, Japan, was examined by dating stable, plant-derived humin particles by AMS-based radiocarbon (14C), and by analyzing stable carbon isotope ratios (δ13C), phytolith composition, and soil chemical properties. The AMS dating yielded calibrated ages ranging from 7570–7679 to 6180−6313calyr BP. We obtained a strong correlation (r=0.99, ***p<0.001) between sample depth and the mean age. The (now buried) humic soil was formed by the incremental accumulation of tephric loess and aeolian dust at a constant rate of ~30mm per century for at least 1200years. Whilst the soil surface was slowly rising, graminaceous vegetation was supplied at a constant rate so that developmental upbuilding pedogenesis ensued. The soil was buried and isolated by the fall of the Towada-Chuseri tephra about 6200calyr BP. Thus the tephra-soil sequence near Towada volcano represents both developmental and retardant upbuilding pedogenesis. [Copyright &y& Elsevier]

Abstract: To quantitatively clarify the organic carbon accumulation processes on the forest floor during an early stage of humification (3 years), solid-state 13C cross polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) signals were monitored for phased–humified beech and oak litters and soil surface horizons in the northern Kanto District, Japan. The mass loss rate of the carbon components during the humification for both litters was in the following order: O-alkyl > aromatic > aliphatic > carbonyl carbons. This result indicates that the labile O-alkyl carbons, probably dominated by holocellulose were selectively degraded compared to the other components. 44% of O-alkyl carbon mass for beech and 38% for oak lost throughout 3 years of incubation. Inversely, the mass of aliphatic carbons, which is mainly composed of saturated hydrocarbons, decreased quite slowly from 20 to 10% with humification, probably because a large proportion of the aliphatic carbons are secondary products of microorganisms. The aromatic carbon mass, which would be derived from lignin/tannin and their metabolites, also decreased gradually from 17 to 6% over 3 years. While, the carbonyl carbon mass was quite stable at around 2% throughout the incubation period, probably because the hydrolysis reactions of organic carbon would contribute to the formation of the carbonyl carbons. According to an exponential model, the total carbon stocks on the forest floor converged at 4.2 Mg C ha−1 for the first few years at the studying site. The carbon compositions converged to intermediate levels between those of the F and A 1 horizons. The simulation in the present study is able to represent the carbon accumulation process on the forest floor including a part of the mineral. [Copyright &y& Elsevier]