[M-IS06] 生物地球化学

[MIS06-09] 窒素負荷量の異なる2林分における樹木と土壌の窒素同位体比

*田中 あゆみ¹、稲垣 善之²、刘 学炎³、矢野 翠⁴、木庭 啓介⁴、平井 敬三¹ (1.森林総合研究所、2.森林総合研究所四国支所、3.中国科学院、4.京都大学生態学研究センター)

キーワード：窒素同位体比、窒素負荷、無機態窒素

Anthropogenic nitrogen (N) deposition on forest site is concerning to modify plant species diversity and soil-to-plant N uptake. The N isotope ratio (δ¹⁵N) of soil and foliage reflects nitrogen cycle in the ecosystem and distinct plant N source. To better understand the effects of N deposition to soil N status and plant N uptake, we analyzed N content and δ¹⁵N of soils and foliage in two different N deposition forests (Mt. Tsukuba: 11.5 kg N ha^-1 year^-1, Katsura: 7.5 kg N ha^-1 year^-1) in Kanto region. We sampled soil from upper and lower position of the two forest site respectively, and measured extracted inorganic N content and isotope ratio. We also analyzed leaf N content (N%) and δ¹⁵N values of 30 woody species with different life forms (canopy and understory species). The soil nitrate concentration in Mt. Tsukuba was 25 fold higher than Katsura, and the δ¹⁵N value was constant through the site (-2.6 ± 0.1‰). While in Katsura, ammonium concentration in soil was high especially in upper slope, but in lower slope dominated nitrate. The foliage N% was high in Mt. Tsukuba than Katsura. The foliage δ¹⁵N value differed significantly among species in Katsura but in Mt. Tsukuba foliage δ¹⁵N value showed steady through species and the value corresponded with soil nitrate δ¹⁵N. From these results, N deposition may lead changing soil N status and alter plant N source and uptake.