HR: 17:15h
AN: B14B-06    [Abstracts]
TI: The Contribution of the Long-term Carbon Pool to Nighttime Foliage Respiration as Revealed by a Year-long C-13 Labeling Experiment
AU: * Smith, M
EM: mattsmith@ocean.fsu.edu
AF: Department of Oceanography, Florida State University, Tallahassee, Fl 32306-4320 United States
AU: Mortazavi, B
EM: mortazavi@ocean.fsu.edu
AF: Department of Oceanography, Florida State University, Tallahassee, Fl 32306-4320 United States
AU: Chanton, J
EM: jchanton@mailer.fsu.edu
AF: Department of Oceanography, Florida State University, Tallahassee, Fl 32306-4320 United States
AB: Slash pine (Pinus elliottii) saplings were placed in a CO2 enrichment (~500 ppm above ambient) facility for an entire year, starting in June of 2004. The CO2 used for the enrichment, with an isotopic signature of -48‰, allowed us to track the fate of the labeled photosynthate during nighttime respiration experiments once the saplings were removed from the enrichment facility. A set of saplings subject to similar environmental conditions, but not subject to CO2 enrichment, served as controls. Nighttime respiration experiments for the labeled saplings were measured by two methods. The first procedure consisted in determining the isotopic signature of nighttime integrated (sunset to sunrise) foliage respired CO2, while the second procedure consisted in determining the pre-dawn signal. The nighttime integrated signal was determined by enclosing the entire foliage of four labeled saplings in a non-destructive manner in a 300-liter airtight chamber. Initial and final samples were collected at sunset and sunrise for CO2 concentration and 13C determination and a mass balance equation was used to determine the 13C of respired CO2. In the second procedure foliage from four labeled saplings were collected just prior to dawn and placed in a leaf-chamber. Sequential CO2 samples evolved in darkness over a 15 min period were collected for CO2 concentration and 13C determination from which a Keeling plot was constructed to determine the isotopic signature of foliage respired CO2. The isotopic signature of pre-dawn foliage respired CO2 for the control plants was also determined with an identical leaf-chamber system. Immediately after removal from the enrichment facility, the 13C of foliage respired CO2 had a pre-dawn signature of -40.2‰ and a nighttime integrated signal of -44.1‰, while the control plants had a dCf value of -25.8‰ signature. Monitoring of dCf during a 35-day period revealed a non-linear approach in dCf of the labeled plants towards the control dCf values, with the steepest change measured during the initial 10 days following exposure to ambient CO2. Three days following exposure to ambient CO2 nearly 90% of nighttime respired CO2 consisted of labeled carbon. The contribution of the labeled pool to nighttime foliage respiration declined to 5% at day 35 following exposure to ambient CO2. These results indicate the presence of a carbon pool with a residence time much longer than that previously reported which contributes to nighttime foliage respiration. Future attempts in relating dCf to environmental variables will need to consider the presence of this older carbon pool and its contribution to foliage respiration.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0490 Trace gases
SC: Biogeosciences [B]
MN: Fall Meeting 2005