Journal
TREES-STRUCTURE AND FUNCTION
Volume 23, Issue 4, Pages 801-811Publisher
SPRINGER HEIDELBERG
DOI: 10.1007/s00468-009-0321-4
Keywords
Oxygen isotope; Temperature; Tree ring
Categories
Funding
- EC
- State Secretariat for Education and Research [01.0499-3, FP6-2004GLOBAL-017008-2]
- SNF [200021_121838/1]
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Stable isotopic ratios integrate ecosystem variability while reflecting change in both environmental and biological processes. At sites, where climate does not strongly limit tree growth, co-occurring trees may display large discrepancies in stable oxygen isotopic ratios (delta O-18) due to the interplay between biological processes (competition for light and nutrients, individual tree physiology, etc.) and climate. For a better quantification of the isotope variability within and among trees, the climatic and/or individual tree effects on seasonal delta O-18 variations in precipitation, soil water, leaf water and leaf organic material (whole leaf, cellulose and starch) and annual delta O-18 variations in tree-ring cellulose for Fagus sylvatica (Fs), Quercus robur (Qr), Carpinus betulus (Cb) and Pinus sylvestris (Ps) were studied in a mature temperate forest in Switzerland, using a mixed linear regression model technique. Furthermore, the influence of environmental factors on delta O-18 was assessed by means of three common isotope fractionation models. Our statistical analysis showed that except for Ps, a greater portion of delta O-18 variance in leaf compounds can be explained by individual tree effects, compared to temperature. Concerning tree-ring cellulose, only Fs and Ps show a significant temperature signal (maximum 12% of the variance explained), while the individual tree effect significantly explains delta O-18 for all species for a period of 38 years. Large species differences resulted in a limited ability of the isotope fractionation models to predict measured values. Overall, we conclude that in a diverse mixed forest stand, individual tree responses reduce the potential extraction of a temperature signal from delta O-18.
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