The relationship between the stable carbon isotope composition of needle bulk material, starch, and tree rings in Picea abies.

We investigated the relationship between the δC signal in current-year and 1-year-old needle bulk material, starch extracts, and early- or late-wood in mature spruce trees (Picea abies) to identify the modifying influence of climatic conditions on the different δC signals. Seasonal patterns of δC were determined in total bulk needle material from 1998 to 2000, and in acid soluble starch extracts in 1999 and 2000, and δC values of early- and late-wood were measured for the years 1991-2000. δC of bulk needle material was most enriched in spring with a trend towards depletion in the course of the season. Current-year needles showed a more distinct seasonal pattern in δC compared to 1-year-old needles. Seasonal trends in bulk material and starch were similar, but the highly enriched signal in spring could not be fully explained by the influence of the δC values of starch (weighted with the corresponding starch amounts). δC of starch in 1-year-old needles, and to a lesser extent of current-year needles, correlated with δC of early-wood, indicating a transfer of the isotopic signal. In addition, early-wood δC corresponded weakly to winter precipitation. In the summer, δC of total bulk needle material and starch showed no relation to the late-wood δC signature. Late-wood δC, however, related to global radiation, relative humidity and temperature, with more enriched values corresponding to warmer and drier conditions. We conclude that the signature of early-wood is determined more by biochemical fractionation, e.g. during starch formation, than by climatic conditions, which exert only a minor influence and are reflected in the isotopic signal of late-wood.