© 2005 Heron Publishing—Victoria, Canada
Long-term trends in cellulose δ13 C and water-use efficiency of tropical Cedrela and Swietenia from Brazil
Peter Hietz (1, 2), Wolfgang Wanek (3) and Oliver Dünisch (4)
1. Institute of Botany, University of Natural Resources and Applied Life Sciences (BOKU), Gregor Mendel-Str. 33, 1180 Vienna,
Austria / 2. Corresponding author (peter.hietz@boku.ac.at) / 3. Institute of Ecology and Conservation Biology, University of Vienna, Althanstr 14, 1090 Vienna, Austria / 4. Biozentrum Klein Flottbek, University of Hamburg, Ohnhorststr. 18, 22609 Hamburg, Germany / Received June 15, 2004; accepted October 23, 2004; published online April 1, 2005
Summary
Elevated CO2 concentrations ([CO2]) affect plant water relations and photosynthesis, and the increase in atmospheric [CO2] over the past 100–200 years has been related to changes in stomatal density and the carbon isotope ratio (δ13C) in tree rings and leaves from herbarium specimens. Because many tropical trees do not produce annual growth rings and their
wood is therefore difficult to date, no trends in δ13C of tropical trees have been reported. Wood from Cedrela odorata L. (tropical cedar) and Swietenia macrophylla King (bigleaf mahogany), which do produce annual rings, was collected from a primary rain forest in Aripuanã, Brazil (10°09′
S, 59°26′ W). We measured wood cellulose δ13C in 10-year growth increments from 37 Cedrela trees (between 11 and 151 years old in 2001) and 16 Swietenia trees (48–126 years old). A comparison of δ13C in cellulose of trees from different decades and of trees of different cambial ages showed that the amount of δ13C was largely related to the decade the wood was produced in, and not, or only to a minor extent, to tree age. Cellulose δ13C decreased from –26.0 to –27.3‰ in Cedrela and from –25.7 to –27.1‰ in Swietenia, with the largest changes occurring during the past 50 years. Based on these data and the trends in atmospheric [CO2] and δ13CO2, we calculated that the internal [CO2] increased from about 220 to 260 ppm and that intrinsic water-use efficiency increased by 34% in Cedrela and by 52% in Swietenia. This may have implications for the water cycle and may explain the trend toward increased tree growth and turnover observed
in some tropical forests.
Keywords:
carbon isotope discrimination, Cedrela odorata, cellulose extraction, dendrochronology, elevated CO2, Swietenia macrophylla, tropical trees.
