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

None

小嵐 淳   ; 飯田 孝夫*; 浅野 智宏

Koarashi, Jun; Iida, Takao*; Asano, Tomohiro

陸域炭素循環における土壌有機物の役割を明らかにするために、化学的に分画された土壌有機物の安定および放射性炭素同位体組成を加速器質量分析計により定量した。炭素マスバランスに基づいて、化学的に可溶な有機物の炭素同位体組成も評価した。その結果、核実験起因のC-14が少なくとも土壌深さ16cmまで侵入しているが、その大部分は鉱物土壌-リタ-境界層近傍に化学的に可溶な有機物として保持されていることが明らかになった。また、この森林においては、約15%の炭素が化学的に安定な有機物(年代が5001600年)として存在し、この有機物が炭素の長期的なシンクとなっていることが明らかになった。

To better understand the role of soil organic matter in terrestrial carbon cycle, carbon isotope compositions 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 chemically soluble organic matter fractions, through a mass balance of carbon among the fractions. The depth profiles of 14C abundances showed that bomb-derived 14C has been penetrated into the first 16 cm mineral soil at least, whereas a significant amount of it has been still preserved as the acid-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 can not provide a representative indicator as a source or a sink of carbon in soil, particularly on annual to decadal timescales.