HR: 15:00h
AN: B33A-05    [Abstracts]
TI: Atmospheric CO2 and N cycling: An ecosystem scale 15N tracer experiment
AU: * Hofmockel, K S
EM: khof@umich.edu
AF: Duke University, Nicholas School of the Environment and Earth Sciences, Durham, NC 27708, United States
AU: * Hofmockel, K S
EM: khof@umich.edu
AF: University of Michigan, School of Natural Resources and Environment, Ann Arbor, MI 48109-1115, United States
AU: Gallet-Budynek, A S
EM: agallet@bu.edu
AF: Boston University, CAS Biology 5 Cummington Street, Boston, MA 02215, United States
AU: Currie, W S
EM: wcurrie@umich.edu
AF: University of Michigan, School of Natural Resources and Environment, Ann Arbor, MI 48109-1115, United States
AU: Jackson, R B
EM: jackson@duke.edu
AF: Duke University, Nicholas School of the Environment and Earth Sciences, Durham, NC 27708, United States
AU: Finzi, A C
EM: afinzi@bu.edu
AF: Boston University, CAS Biology 5 Cummington Street, Boston, MA 02215, United States
AB: A major question in C sequestration science is whether N availability will limit long-term biological sequestration of atmospheric CO2. At the Duke Forest Free Air CO2 Enrichment (FACE) site, increased net primary productivity was sustained over a decade of experimental CO2 fumigation. Additional N was assimilated to support increased growth under elevated CO2, but the source of this additional N remains unknown. We used an ecosystem scale 15N tracer experiment to identify additional N resources. Isotopically labeled NH4NO3 was applied to the forest floor in May 2003. The forest plots were then sampled for isotope recovery in plant and soil pools for three subsequent growing seasons (September 2003, 2004, 2005). Results indicate that despite higher N uptake under elevated CO2, the total recovery of 15N in trees was similar under ambient and elevated CO2. At the same time, the concentration of 15N in the pine canopy was significantly lower under elevated compared to ambient CO2. This suggests that trees growing under elevated CO2 assimilate an additional, unlabelled source of N, causing the canopy 15N signature to be depleted relative to leaves growing under ambient conditions. Recovery of the 15N tracer decreased with soil depth, indicating that additional N uptake may be derived from roots exploiting unlabelled mineral resources deeper in the soil profile.
DE: 0428 Carbon cycling (4806)
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0469 Nitrogen cycling
SC: Biogeosciences [B]
MN: 2007 Joint Assembly