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Latitudinal gradient of C4 grass contribution to Black Soil organic carbon and correlation between δ13C and the melanic index in Japanese forest stands
- Ishizuka, Shigehiro, Kawamuro, Kimiyasu, Imaya, Akihiro, Torii, Atsushi, Morisada, Kazuhito
- Biogeochemistry 2014 v.118 no.1-3 pp. 339-355
- C3 plants, C4 plants, carbon, climate, color, forest stands, forests, grasses, grasslands, humus, land use, latitude, organic matter, pollen, polluted soils, soil organic carbon, soil profiles, stable isotopes, temperature, tephra, Japan
- Black Soil in Japanese forests is believed to have formed under grasslands, on the basis of pollen and stable carbon isotopic analyses. Carbon stable isotope ratios (δ¹³C) have indicated that the δ¹³C value widely ranged from −25 to −17 ‰ in various land-use soils. We measured the δ¹³C of soil organic carbon (SOC) in Black Soil in forests from northern (43°N) to southern (31°N) Japan. The δ¹³C values in topmost soils were contaminated by carbon from current C₃vegetation. Excluding these soils, the average contribution ratio of C₄grass in Black Soils was estimated to be ~44.6 % of SOC by mass balance calculation from the δ¹³C of SOC. The proportion of C₄plants supplying soil carbon was smaller at higher latitudes, this indicating that the δ¹³C values of SOC were affected by the competitiveness of C₄grass and C₃plants which might depend on the temperature. The melanic index, which is an index of humus properties and divides the humus into “Type A” (≤1.7) and other humus (>1.7), correlates negatively with δ¹³C values. This result indicates that C₄grass played an important role in generating the dark-colored organic matter in Japanese Black Soils. The δ¹³C values of soil profiles with key tephra are therefore potentially useful for the study of past climate dynamics and vegetation responses.