日本地球惑星科学連合2016年大会

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セッション記号 H (地球人間圏科学) » H-TT 計測技術・研究手法

[H-TT21] 環境トレーサビリティー手法の開発と適用

2016年5月24日(火) 13:45 〜 15:15 101A (1F)

コンビーナ:*陀安 一郎(総合地球環境学研究所)、中野 孝教(大学共同利用機関法人 人間文化研究機構 総合地球環境学研究所)、座長:陀安 一郎(総合地球環境学研究所)

13:45 〜 14:00

[HTT21-07] 日本の森林土壌における窒素安定同位体比の変動様式について

*木庭 啓介1平塚 敏2浦川 梨恵子3仁科 一哉6磯部 一夫7柴田 英昭4大手 信人5 (1.京都大学生態学研究センター、2.東京農工大学農学部、3.アジア大気汚染研究センター、4.北海道大学北方生物圏フィールド科学センター、5.京都大学大学院情報学研究科、6.国立環境研究所、7.東京大学大学院農学生命科学研究科)

キーワード:安定同位体、森林土壌、窒素循環

Natural abundance of 15N of bulk soil N has been investigated in many studies with emphasis on soil N decomposition, N loss, and chronosequence of N dynamics in forests. δ15N of bulk soil N generally increases with soil depths, which is considered as a consequence of the loss of 15N-delpleted N via leaching and gaseous loss both coupled with N mineralization and nitrification as well as the incorporation of 15N-enriched N into bulk soil N via microbial biomass. However, the details on how 15N of bulk soil N can be discriminated during these processes are not clear.
We analyzed the δ15N of bulk soil N collected in the GRENE (Green Network of Excellence) environmental information project and the ReSIN (Regional and comparative Soil Incubation study on Nitrogen dynamics in forest ecosystems) project (Urakawa et al. 2014, 2016). Mineral forest soils were collected in each watershed from five soil profiles with different soil depths down to 40 or 50cm depth. We used a modified EA-IRMS in TUAT with higher sensitivity to measure the δ15N of bulk soil N with low N concentrations. We analyzed the soil samples (488 samples from 32 watersheds) with higher N concentration than ca. 0.1% (with less than 8mg sample weight to run) to reduce the risk of incomplete combustion.
δ15N of bulk soil N ranged from -3.2 to +10.2 permill with N concentrations ranging from 0.1 to 1.3%. Isotopic fractionation factors for bulk soil N, estimated from the relationship between N concentrations and δ15N values, ranged from 0.6 to 7.2 permill. The differences in mycorrhizal association of plants would influence the isotopic fractionation factor (Hobbie and Ouimette 2009), although we found no significant relationships between mycorrhizal associations (ECM, AM) and the isotopic fractionation factors. Climate factors such as MAT and MAP suggested as the factors affecting δ15N of bulk soil N (Amundson et al. 2003) were not significantly correlated with δ15N of bulk soil N. In the presentation we will discuss the possible factors influencing δ15N of bulk soil N and isotopic fractionation factors in the forest watersheds.