[M-IS14] 生物地球化学

[MIS14-16] 北東アジアの乾燥地生態系における窒素同位体比を用いた窒素循環過程と植物窒素源の推定

*田中(小田) あゆみ¹、遠藤 いず貴²、大手 信人³、矢野 翠⁴、眞壁 明子⁵、木庭 啓介⁶、Undarmaa Jamsran⁷、山中 典和⁸、吉川 賢⁹ (1.森林総合研究所、2.兵庫県立大学、3.京都大学情報学研究科、4.農業環境変動研究センター、5.海洋研究開発機構、6.京都大学生態学研究センター、7.モンゴル生命科学大学、8.鳥取大学乾燥地研究センター、9.岡山大学地域総合研究センター)

キーワード：窒素同位体比、窒素循環、乾燥地生態系

Nitrogen (N) is one of most restricted nutrient for plant growth in the dryland ecosystems; it is still unclear the mechanisms of plants nutrients absorption from the dry soil. The N isotope ratio (δ¹⁵N) of organic and inorganic N reflects N cycle and it also used for estimation of plant N source by comparison with δ¹⁵N value in the plants. To better understand the N cycle and plant N uptake in the dryland ecosystem, we analyzed N content and δ¹⁵N value of soils and plant foliage in the Mongolian Gobi steppe. We established four typical vegetation plots based on the dominant plant species and topographical conditions; river bottom with halophyte species, riverbank with a large perennial grass community, the upper slope with an isolate grass communities and flat plain with annual forbs. We sampled soil from five depth of the vertical soil layer from the vegetation plots and measured extracted dissolved organic and inorganic N content and δ¹⁵N values. We also measured above- and belowground length, N content (N%) and δ¹⁵N values. The plants root mostly distributed in the 10-15 cm depth soil layer. The soil inorganic N concentration was extremely limited expect under the large grass communities. The δ¹⁵N values of soil nitrate were corresponded with the perennial grass species, while in the other species often had higher δ¹⁵N values than soil nitrogen source. From these results, indicated that N cycle in the dryland ecosystems significantly varied with aboveground vegetation and nitrate was one of N source of perennial grass species. For the other plant species dissolved organic N which had higher δ¹⁵N values may have some role for N source in the dryland ecosystem.