HR: 16:30h
AN: B32D-03    [PDF]
TI: Refinement of Isotopically Derived Fine Root Lifespans Using A Locally Released Radiocarbon Label in Oak Ridge, TN.
AU: * Gaudinski, J B
EM: gaudinsk@ucsc.edu
AF: University of California Santa Cruz, Department of Environmental Studies, Santa Cruz, CA 95064 United States
AU: * Gaudinski, J B
EM: gaudinsk@ucsc.edu
AF: Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Riley, W J
EM: WJRiley@lbl.gov
AF: Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Torn, M S
EM: mstorn@lbl.gov
AF: Lawrence Berkeley Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 United States
AU: Joslin, J D
EM: jdjoslin@esper.com
AF: Belowground Forest Research, 112 Newcrest Lane, Oak Ridge, TN 37830
AB: Isotopic techniques ($^{13}C$ and $^{14}C$) are relative newcomers among the approaches used to quantify fine root ($<$ 2 mm diameter) dynamics in a field setting. Direct measurements of the isotopic content of root tissues, used as a proxy for root age, have shown that at least some portion of the fine root system lives for 5-10 years or more. In this work we take advantage of a local radiocarbon ($^{14}C$) release in Oak Ridge, TN in summer 1999, to examine (1) the influence of stored C in new root growth and (2) the lifespan of fine roots from a mature, temperate deciduous forest. This release provides a local $^{14}C$ pulse of similar magnitude to the peak of the $^{14}C$ bomb spike. However, since we have been able to make ecosystem wide measurements within one year of the local $^{14}C$ release we have much greater time resolution than we do with the standard bomb-$^{14}C$ technique applied today (which is 1-2 years). We have constructed a new multi-compartment model of root growth and decay, whose structure was developed using data from field sampling at Oak Ridge, TN. Model results, constrained with a $^{14}C$ time series of new root growth, show that fine roots are grown with 10% of their carbon coming from stored C sources. Additionally, a three-year time series of root cores shows that at least two pools are required to account for $^{14}C$ changes in live and dead fine roots. Testing this $^{14}C$ data set with our model shows that the shorter-lived root pool has a turnover time (mean lifetime) of a few months and the longer-lived pool has a turnover time of ~5 years.
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting