Dissolved organic carbon dynamics in a cool temperate forest soil; Clues from C and C signatures

炭素同位体を利用した安比ブナ林土壌における溶存有機炭素の動態研究

中西 貴宏  ; 小嵐 淳   ; 安藤 麻里子  ; 平井 敬三*

Nakanishi, Takahiro; Koarashi, Jun; Atarashi-Andoh, Mariko; Hirai, Keizo*

森林土壌において、溶存有機炭素は、鉛直移動に伴う有害物質の輸送,土壌への炭素固定,微生物活動の栄養源など、重要な役割を担っている。本研究では、水抽出溶存有機炭素(WEOC)の炭素同位体組成(C・C)から、岩手県安比ブナ林での溶存有機炭素の動態を推定した。Cの結果より、土壌から生物利用性有機物(糖類,アミノ酸など)が優先的に分解されてWEOCが生成されていることが明らかになった。このことは、親水性有機物と疎水性有機物へのカラム分画実験の結果からも示唆された。また、Cの結果より、WEOCの滞留時間が土壌有機物に比べてずっと短い(数十年以内)ことが明らかになった。

Dissolved organic carbon (DOC) is an important constituent in forest soils, because it affects soil formation and transport of heavy metals, is a source of C for microbes, and contributes to soil organic carbon (SOC) accumulation. In this study, we measured C and C in water extractable organic carbon (WEOC) to investigate the dynamics of DOC at Appi, a cool temperate deciduous forest in Japan. The C values of WEOC were slightly higher than those of SOC. Such enrichment in C indicated that WEOC production, which was coupled with the microbial activity, mainly used a C-enriched SOC fraction (including sugars, amino acids, etc.) of the total SOC. Indeed, hydrophilic fractions were enriched in C compared to the total WEOC. Hydrophilic fractions are considered more biologically available for decomposition. The result of C indicated that WEOC consists mainly of C-enriched, labile, hydrophilic organic materials with faster turnover times (several decades).