[M-IS14] 生物地球化学

[MIS14-P06] ¹⁵N₂O添加培養による土壌N₂O還元ポテンシャル直接評価法の確立

*新宮原 諒¹、中島 泰弘²、鵜野 光²、伊藤 虹児¹、島田 紘明¹、南澤 究³、和穎 朗太¹ (1.農研機構 農業環境研究部門、2.農研機構 高度分析研究センター、3.東北大学大学院生命科学研究科)

キーワード：総N2O還元速度、窒素同位体トレーサー、培養実験、土壌、純粋培養系

N₂O reduction is a key biogeochemical process for mitigating N₂O emission from soil. This process is the final step of denitrification and commonly quantified using the acetylene inhibition technique or ¹⁵NO₃⁻ amendment. Recently, significant N₂O production from NH₄⁺ via nitrification was reported. In addition, recent microbiological studies showed the presence of clade II nosZ bacteria, non-denitrifying N₂O reducers catalyzing reduction of N₂O but not NO₂⁻ nor NO. Thus, quantifying N₂O reduction directly is becoming more critical. Several research groups developed the ¹⁵N₂O pool dilution technique (Clough et al., 2006; Yang et al., 2011; Wen et al., 2016), which added ¹⁵N-labelled N₂O to the soil, determined the gross N₂O production from the decrease in the ¹⁵N/¹⁴N ratio of N₂O, and calculated the gross N₂O reduction from the difference between the gross and net N₂O productions. Here, we tested the applicability of a more direct method by amending the ¹⁵N₂O tracer and analyzing the ¹⁵N/¹⁴N ratio of N₂ to determine the ¹⁵N₂ production and thereby N₂O reduction potential. First, we validated ¹⁵N mass balance in the incubation experiment using pure cultures of denitrifying bacteria. Second, we applied the method to soil samples collected from the upland agricultural field and adjacent forest by the incubation under controlled moisture condition in vials. In this presentation, we will discuss the validity and applicability of this method to determine gross N₂O reduction potential toward mechanistic understanding of N₂O dynamics in soil.