Stable C and N isotope abundances in water-extractable organic matter from air-dried soils as potential indices of microbially utilized organic matter

風乾土壌から水抽出した有機物の炭素・窒素安定同位体比:微生物が利用する有機物の潜在的指標として

永野 博彦*; 安藤 麻里子  ; 田中 草太*; 蓬田 匠   ; 香西 直文   ; 小嵐 淳   

Nagano, Hirohiko*; Atarashi-Andoh, Mariko; Tanaka, Sota*; Yomogida, Takumi; Kozai, Naofumi; Koarashi, Jun

Microbial decomposition of soil organic matter (OM) is crucial in terrestrial carbon cycles; however, analytical approaches to explain the decomposition process in soil have not been completely successful. Forty air-dried soil samples were applied to water extraction and OM analysis. The C and N contents and natural abundances of C and N exhibited positive correlations between the bulk soil OM and water-extractable OM (WEOM). However, the C/N ratio in WEOM showed values around 10, a value similar to that for microbial biomass. The C and N enrichments in WEOM relative to soil OM were negatively and positively correlated, respectively, with the concentrations of organo-mineral complexes and short-range order minerals, which play significant roles in soil OM stabilization in soils. These relationships suggest that the stable isotopic enrichments in WEOM can be a good indicator of the microbial utilization of soil C and N under different substrate availabilities.