Seasonality of δ18O in needles and wood of Picea abies

The temporal variability in delta(18) O of organic matter (delta(18) O-org ) 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 delta(18) O (delta(18) O-wso ), air humidity, temperature and global radiation. Measured delta(18) O-org was compared with values calculated with the Dongmann model extended by a dampening factor (f (org) ) and a biochemical fractionation parameter (epsilon(org) ). The short-term variations in delta(18) O-org of current-year spruce needles could be explained by the delta(18) O-wso in the topsoil layer (r (2) = 0.43). The difference in delta(18) O-org between the years was influenced by differences in humidity. A highly significant agreement between measured and modeled delta(18) O-org was achieved with f (org) = 0.2, yet the dampening was not as strong (0.66), if only the delta(18) O-org during needle development was considered. The temporal delta(18) O-org signal of current-year needles correlated with the corresponding early- or late-wood delta(18) O, 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.