Solar Radiation Affects Modern Tree-Ring δ13C: Observations at a Cool-Temperate Forest in Japan

Tree-ring δ13C of shoots in two deciduous tree species (Acer rufinerve and Clerodendrum trichotomum) at the cool-temperate forest in Japan showed similar trends with time for four years. The variation of tree-ring δ13C positively correlated with the total solar radiation during the growing season, although it did not always correlate with other climatic parameters. Tree-ring δ13C of a tree-core from 1982 to 1993 in A. rufinerve also correlated strongly with the total solar radiation. We conclude that solar radiation most probably affected the tree-ring δ13C in this moist cool temperate forest, because increasing solar radiation can cause Ci (intercellular CO2 partial pressure) to decrease, consequently increasing δ13C.