HR: 1340h
AN: B33E-1088    [Abstracts]
TI: Size and age of the non structural carbohydrate pool in boreal trees
AU: * Czimczik, C I
EM: czimczik@uci.edu
AF: University of California, Irvine, Department of Earth System Science 2103 Croul Hall, Irvine, CA 92697-3100 United States
AU: Trumbore, S
EM: setrumbo@uci.edu
AF: University of California, Irvine, Department of Earth System Science 2103 Croul Hall, Irvine, CA 92697-3100 United States
AB: Autotrophic respiration of trees is supposed to be closely linked to CO₂ uptake by photosynthesis on a time scale of days. However, several studies have indicated that roots of boreal trees do not respired carbon (C) with a radiocarbon signature Δ¹⁴C similar to that of CO₂ in the atmosphere, but C that is 3-4 years old. Also, estimates of gross primary productivity obtained by eddy covariance flux measurements do often not correlate with tree ring width (growth). Both these findings point to the presences of a large non-structural C (NSC) pool within the tree, mainly sugars and starches. The concentration of NSC in tree tissue is considered a measure of C shortage or surplus for growth. Studies indicate that the NSC pool in trees is usually large and relatively constant throughout the year, not affected by e.g. leaf flushing. While estimates of the size of the NSC pool are available for a number of trees from various ecosystems, estimated of its turnover time are lacking. We tested if our finding that boreal trees respire 3-4 year old C is an artifact resulting from the depletion of the NSC pool in excised roots over time. We incubated roots with a diameter of 2-4 mm while they were still attached to the tree, and excised roots after 3 hours, and 1 to 4 days. We sampled CO₂ for Δ¹⁴C analysis of intact roots, freshly excised roots, and after 1 and 3 days. To obtain an estimate of the NSC pool size and its turnover time in roots of various diameter, we excised and incubated roots of 3 diameters: root hairs with mycorrhizal fungi, 2-4 mm, and 1-2 cm. We followed their respiration over the course of one full day. We will also compare the Δ¹⁴C of respired CO₂ of freshly root hairs to that of the NSC in the roots. To obtain an estimate of the size and turnover of the whole tree NSC pool, we will measure the Δ¹⁴C of NSC in wood. Preliminary results indicate that CO2 fluxes were not correlated to temperature or the initial CO2 concentration in the chamber. While CO2 fluxes of medium and coarse roots remained relatively constant over 4 days, the respiration rates of root hairs declined sharply within the first 24 hours.
DE: 0400 BIOGEOSCIENCES
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0476 Plant ecology (1851)
SC: Biogeosciences [B]
MN: Fall Meeting 2005