title: Radiocarbon and stable carbon isotope compositions of chemically fractionated soil organic matter in a temperate-zone forest.
abstract: 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 ((14)C) abundances of acid- and base-soluble organic matter fractions, through a mass balance of carbon among the fractions. The depth profiles of (14)C abundances showed that (1) bomb-derived (14)C has penetrated the first 16cm mineral soil at least; (2) Delta(14)C values of acid-soluble organic matter fraction are considerably higher than those of other fractions; and (3) a significant amount of the bomb-derived (14)C has been preserved as the base-soluble organic matter around litter-mineral soil boundary. In contrast, no or little bomb-derived (14)C 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.
authors.affiliation: Radiation Protection Division, Japan Nuclear Cycle Development Institute, Tokai-mura, Naka-gun, Ibaraki 319-1194, Japan. koarashi.jun.go.jp
authors.forename: Jun
authors.initials: J
authors.lastname: Koarashi
authors.forename: Takao
authors.initials: T
authors.lastname: Iida
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Asano
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis*; D002250:Carbon Radioisotopes / Q000032:analysis*; D009930:Organic Chemicals / Q000737:chemistry*; D012987:Soil / Q000032:analysis*; D012990:Soil Pollutants, Radioactive / Q000032:analysis; D012995:Solubility; D013696:Temperature; D013997:Time Factors; D014197:Trees / Q000378:metabolism*
chemical_list: D002247:Carbon Isotopes; D002250:Carbon Radioisotopes; D009930:Organic Chemicals; D012987:Soil; D012990:Soil Pollutants, Radioactive