PARENT SESSION
Oral Session #58: Elevated CO₂. Presiding: A. Finzi.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Madison Ballroom C.

Elevated CO₂ increases net ecosystem CO₂ uptake in a Florida scrub-oak ecosystem .

Hymus, Graham¹, Johnson, David¹, Dijkstra, Paul¹, Hinkle, C Ross², Drake, Bert¹, ^{1 2}

ABSTRACT- We report measurements of net ecosystem CO₂ exchange (NEE) made in open-top chambers (OTCs), modified to work as an open gas exchange system. After fire, in May 1996, 16 large OTCs were sited within the scrub-oak ecosystem of coastal central Florida. Since then the ecosystem has regenerated in OTCs maintained at either current ambient, or elevated (ambient + 350 mol-1 CO₂) atmospheric CO₂ concentration. Elevated CO₂ stimulated light saturated and light-limited NEE throughout the study. This was primarily a consequence of increased photosynthesis per unit leaf area and increased leaf area. However, there were clear seasonal effects on the magnitude of the stimulation. Water availability, leaf age and effects of elevated CO₂ on rates of leaf fall and leaf area may be important mediators of the CO₂ effect, collectively accounting for much of it. At night, NEE was unaffected by elevated CO₂ for the first two years of the experiment, likely due to large respiratory fluxes from belowground root biomass and soil carbon established pre burn. Since then respiratory losses of carbon have been higher in elevated CO₂ by an amount consistent with the increased plant biomass. We interpret this as evidence of the increasing importance of respiration derived from plant biomass regenerated post burn. These findings have important implications for carbon uptake, carbon storage and fuel loads in this fire dependent ecosystem.

KEY WORDS: elevated co2, net ecosystem co2 exchange, open-top chambers, fire