Distribution and Chemical Characteristics of Cations in Annual Rings of Japanese Cedar

Abstract

AbstractThe objectives of this study were to investigate the distribution and chemical characteristics of cations in annual rings of Japanese cedar (Cryptomeria japonica D. Don) grown in a healthy stand of an unindustrialized region in Japan and discuss the possibility of using cations in tree‐rings as a chronological index of acidic deposition. Radial distributions of some cations and P at different vertical positions of the stem were analyzed for five trees from the same mountain. Each cation and P in all trees showed a specific distribution in its radial pattern but similar distribution trends were observed at all vertical positions. The cations and P were classified into three groups: (I) constant radial concentrations (Ca2+, Sr2+, Na+, and probably Ba2+), (II) high concentrations in the heartwood and low in the sapwood (Mg2+, K+, Rb+, Cs+), and (III) increasing concentrations in the sapwood (P, Mn2+, Cu2+). The total concentration of cations exceeded the calcium‐binding capacity (CBC) of the wood, and the excess was attributed to K+ in a salt form. The CBC increased from the sapwood/heartwood boundary toward the pith in the heartwood but remained constant in the sapwood. The increase of CBC in the heartwood was consistent with the profile of Mg2+, indicating a transfer of Mg2+ into heartwood and fixation on the acquired binding site. The radial distribution of 90Sr was closely related to the cumulative deposition of fallout from the nuclear weapon tests, but that of 137Cs was unrelated. This suggests immobility of Sr2+ and mobility of Cs+ in the horizontal direction of wood. The conservation of the historical 90Sr/Sr2+ change indicated that no influence of heartwood formation on the chemical environment of Sr2+ in cedar xylem and a possibility of using Sr2+ as a chronological index of nutrient availability. A steady‐state in nutrient availability is speculated for trees growing in this mountain because all of the trees analyzed show constant radial distributions of Sr2+ for decades.