土壌微生物バイオマスの新たな測定法を約40年ぶりに提案

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2025-05-13 新潟大学

土壌微生物バイオマスの新たな測定法を約40年ぶりに提案

新潟大学の永野博彦助教らの研究チームは、約40年ぶりに土壌微生物バイオマスの新たな測定法「風乾土水抽出法」を提案しました。従来法では劇物クロロホルムの使用や新鮮な土壌が必要でしたが、新手法では室温で乾燥させた土壌から水抽出した有機物(WEOC)を分析し、微生物バイオマスを推定可能です。国内10地点の森林や草地土壌で検証した結果、従来法と高い相関が確認され、毒性物質を使用できない環境でも適用可能です。この手法は、土壌微生物バイオマスの大規模データ構築や地球環境変動予測に貢献が期待されます。

<関連情報>

日本の森林および牧草地の土壌を風乾した水抽出有機物に基づく微生物バイオマスの推定 Estimation of microbial biomass based on water-extractable organic matter from air-dried soils from Japanese forests and pasture

Hirohiko Nagano,Yuki Kanda,Yuri Suzuki,Syuntaro Hiradate,Jun Koarashi,Mariko Atarashi-Andoh & Zhibin Guo
Discover Soil  Published:23 April 2025
DOI:https://doi.org/10.1007/s44378-025-00053-4

Abstract

Water-extractable organic matter (WEOM) obtained from air-dried soil samples can be used to estimate microbial biomass instead of chloroform fumigation extraction (CFE) using fresh, moist soils and toxic solvents. However, the accuracy of such WEOM-based estimates has not been evaluated. We evaluated relationships between WEOM measurements obtained from air-dried soils and microbial biomass measurements obtained through CFE based on 50 soil samples from 10 soil profiles in Japanese forests and pasture. The amount of water-extractable organic carbon (C) obtained from air-dried soils corresponded to 31% of microbial biomass C, demonstrating a strong correlation (squared correlation coefficients (R2) = 0.94, statistical probability (P) < 0.01), whereas the amount of water-extractable total nitrogen (N) (WETN) and microbial biomass N was weakly correlated (R2 = 0.56, P < 0.01). Moreover, the relationships with soil physiochemical properties were similar between WEOC and microbial biomass C (R2 = 1.00, root mean square error (RMSE) = 0.04), whereas those were less similar between WETN and microbial biomass N (R2 = 0.73, RMSE = 0.28). The decoupling of WETN for air-dried soils and microbial biomass N was attributed to differences in the amounts of inorganic N compounds (NO3 and NH4+) in K2SO4 extracts from chloroform-fumigated and unfumigated soils compared to those in water extracts from air-dried soils. These results support our hypothesis that WEOM originates from and is a valid estimate of microbial biomass, particularly for C, offering a solution to the practical difficulties involved in measuring microbial biomass using the CFE. Nevertheless, a caution should be noted that this novel method is still empirical estimation without less mechanistic or process driven explanation. Thus, there is a need to validate this new estimation in other sets of soil samples.

生物環境工学
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