PARENT SESSION
Poster Session #45: Elevated CO₂ I.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Soil CO₂ dynamics during five years of Free-Air Carbon Dioxide Enrichment in Duke Forest.

Pippen, Jeff^*,1, Bernhardt, Emily¹, Schlesinger, William¹, ¹ Duke University, Durham

ABSTRACT- As part of the Duke Forest Free-Air CO₂ Enrichment (FACE) experiment, we have examined the impacts of increased forest growth on CO₂ dynamics in soils. Soil respiration (by IRGA and by soda lime methods) and soil pore space CO₂ have been monitored monthly since the experiment was initiated in 1996. The CO₂ fumigation gas contains a unique ¹³C signature so that newly fixed carbon has a distinct label, and we monitored the change in soil ¹³C of CO₂ monthly. As previously reported, elevated CO₂ levels led to increased soil respiration and resulted in higher CO₂ concentrations in soil pore space during the first two years of enrichment. In the following three years, this difference in soil respiration between treatments has declined, with significant differences appearing in only a few months out of each year rather than throughout the growing season. Soil CO₂ concentration differences between ambient and control plots have been dampened in the last three years as a result. Similarly, the 13C of soil CO₂ has stabilized in the enriched plots, it is consistently depleted (~ -30‰) relative to ambient plots (~ -23‰). These observations are consistent with predictions of downregulation of aboveground production in FACE trees.

KEY WORDS: elevated CO₂, soil respiration, FACE, ¹³C