Seasonality of δ¹⁸O in needles and wood of<i>Picea abies</i>

Abstract

• The temporal variability in δ18O of organic matter (δ18Oorg) in needles and in early- and late-wood of mature spruce trees (Picea abies) was related to changes in climate under field conditions, including soil water δ18O (δ18Owso), air humidity, temperature and global radiation. • Measured δ18Oorg was compared with values calculated with the Dongmann model extended by a dampening factor (forg) and a biochemical fractionation parameter (ɛorg). • The short-term variations in δ18Oorg of current-year spruce needles could be explained by the δ18Owso in the topsoil layer (r2 = 0.43). The difference in δ18Oorg between the years was influenced by differences in humidity. A highly significant agreement between measured and modeled δ18Oorg was achieved with forg = 0.2, yet the dampening was not as strong (0.66), if only the δ18Oorg during needle development was considered. The temporal δ18Oorg signal of current-year needles correlated with the corresponding early- or late-wood δ18O, although strongly dampened in the tree rings. • These results show that the short-term climate is much more strongly reflected in the seasonal oxygen isotope signal of current-year needle organic matter than early- and late-wood. Yet the temporal variations in both tissues, leaf and wood are the same, showing how precisely the isotopic pattern is translated to the tree rings.