HR: 17:00h
AN: B14B-05    [Abstracts]
TI: Influence of 13C-enriched Foliage Respired CO2 on 13C of Ecosystem-respired CO2 Estimated From Mid-canopy CO2 Sampled During Several Hours After Sunset
AU: * Mortazavi, B
EM: mortazavi@ocean.fsu.edu
AF: Florida State University Dept of Oceanography, W. Call St. OSB, Tallahassee, FL 32306-4320
AU: Chanton, J
EM: chanton@ocean.fsu.edu
AF: Florida State University Dept of Oceanography, W. Call St. OSB, Tallahassee, FL 32306-4320
AU: Smith, M
EM: mattsmith@ocean.fsu.edu
AF: Florida State University Dept of Oceanography, W. Call St. OSB, Tallahassee, FL 32306-4320
AB: Nighttime CO2 concentration and 13C isotopic ratio were measured in the summer and fall of 2004 by two approaches at a Biosphere Atmosphere Stable Isotope Network (BASIN) network site in Florida, USA. The site is a naturally regenerated pine ecosystem dominated by longleaf and slash pine. The first approach consisted in making measurements at multiple heights within the canopy from ground level to top of the canopy just prior to dawn. The second approach consisted in making measurements at mid- canopy at different times from 1 hour after sunset till 2 am. For each method a Keeling plot was used to estimate the isotopic composition of respired CO2 (dCr). dCr values determined with the time-series were enriched relative to those determined from multiple heights just prior to dawn. The 13C of slash pine foliage respired CO2 (dCf) was also measured at temperatures ranging from 6.6 to 30 °C. dCf was enriched initially after dark by as much as 9° and then declined, reaching constant values after a few hours. Maximum enrichment in dCf was measured at the lowest temperature and the decline in dCf towards constant values took longer at lower temperatures. The influence of 13C enriched and temporally variable nighttime foliage respired CO2 accounts for the enriched time-series dCr. A model constrained by field and experimental data was used to determine the impact of the non-constancy of dCf on the linearity and intercept of dCr Keeling plots determined from CO2 samples collected during several hours at mid-canopy height. For the months examined, results indicate that (i) Keeling plots determined from mid-canopy heights were linear despite the addition of temporally variable dCf (range: 5 °) and (ii) the enrichment in the Keeling intercepts determined from samples collected during several hours at mid-canopy compared to those determined from multiple heights were consistent with the addition of 13C enriched foliage respired CO2. A common approach that specifies the time (pre-dawn) and spatial distribution (multiple heights) for CO2 collection is required for inter-comparison of dCr to be valid.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 4870 Stable isotopes (0454, 1041)
SC: Biogeosciences [B]
MN: Fall Meeting 2005