Radiocarbon and stable carbon isotope compositions of chemically fractionated soil organic matter in a temperate-zone forest

• Published in: Journal of environmental radioactivity Vol. 79; no. 2; pp. 137 - 156
• Main Authors: Koarashi, Jun, Iida, Takao, Asano, Tomohiro
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 2005; Elsevier
• Subjects: 13C; 14C; Accelerator mass spectrometry (AMS); Agronomy. Soil science and plant productions; Biological and medical sciences; Carbon Isotopes - analysis; Carbon Radioisotopes - analysis; Chemical fractionation; Chemical, physicochemical, biochemical and biological properties; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Isotope geochemistry; Isotope geochemistry. Geochronology; Organic Chemicals - chemistry; Organic matter; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil - analysis; Soil organic matter; Soil Pollutants, Radioactive - analysis; Soil science; Solubility; Temperature; Time Factors; Trees - metabolism; Asia; Honshu; Japan; 14C; Soil organic matter; 13C; Accelerator mass spectrometry (AMS); Chemical fractionation; Isotopic analysis; Deciduous forest; Fractionation; Organic matter; Atmospheric fallout; Forest soil; Biogeochemical cycle; Radioisotope; Temperate zone; Carbon balance; Carbon cycle; Carbon nitrogen ratio; Carbon 14; Material balance; Coniferous forest
• ISSN: 0265-931X; 1879-1700
• DOI: 10.1016/j.jenvrad.2004.06.002

To better understand the role of soil organic matter in terrestrial carbon cycle, carbon isotope compositions in soil samples from a temperate-zone forest were measured for bulk, acid-insoluble and base-insoluble organic matter fractions separated by a chemical fractionation method. The measurements also made it possible to estimate indirectly radiocarbon ( 14C) abundances of acid- and base-soluble organic matter fractions, through a mass balance of carbon among the fractions. The depth profiles of 14C abundances showed that (1) bomb-derived 14C has penetrated the first 16 cm mineral soil at least; (2) Δ 14C values of acid-soluble organic matter fraction are considerably higher than those of other fractions; and (3) a significant amount of the bomb-derived 14C has been preserved as the base-soluble organic matter around litter–mineral soil boundary. In contrast, no or little bomb-derived 14C was observed for the base-insoluble fraction in all sampling depths, indicating that this recalcitrant fraction, accounting for approximately 15% of total carbon in this temperate-zone forest soil, plays a role as a long-term sink in the carbon cycle. These results suggest that bulk soil organic matter cannot provide a representative indicator as a source or a sink of carbon in soil, particularly on annual to decadal timescales.