Development of oxygen isotope chronology of tropical trees

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K14943
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Forest science
• Research Institution: Kyoto University
• Principal Investigator: OKADA NAOKI 京都大学, 地球環境学堂, 准教授 (40335302)
• Research Collaborator: OHASHI Shinta ; NAKAI Wataru ; Amir Affan Abdul Azim ; Venin Teera
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 酸素同位体 / 熱帯樹木 / 年輪 / 降水

Outline of Final Research Achievements

Many tropical trees do not form visible annual rings, but even such trees show cyclic changes of stable oxygen isotope ratio in xylem along radius, which changes are considered to be formed annually. These cyclic variation is caused by seasonal variation of oxygen isotope ratio of rain water, which is absorbed via roots and incorporated into plant tissue through photosynthesis. Seasonal variation of oxygen isotope ratio in xylem is more conspicuous in the trees growing in seasonal tropics than those growing in wet tropics.Radial changes in oxygen isotope ratio in xylem are similar in a tree individual, but are variations among trees of a species. Radial changes in oxygen isotope ratio in xylem of different species growing in a site showed seasonal trends but their patterns were slightly different.

Free Research Field

樹木生理学

Academic Significance and Societal Importance of the Research Achievements

熱帯樹木の酸素同位体比（δ18O）は温帯樹木と同様に季節変化を示すこと明らかとなり、この変化は年輪に相当するものと考えられた。したがって、木部の酸素同位体比の変化を解析することによって、熱帯では研究の進んでいない樹木年輪研究の発展につながるものと考えられる。この研究を発展させていけば、過去の気象観測データの少ない熱帯地域における古気候の解明や、熱帯樹木の成長動態の解析につながり、森林管理や将来予測に資するものと考えられる。