PARENT SESSION
Oral Session # 12: Biogeochemistry I: Carbon Dioxide Cycling.
Presiding: D Markewitz
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 204.

Soil carbon sequestration and turnover after six years of CO₂ enrichment at the Duke Forest.

Lichter, John¹, Barron, Stacy ¹, Finzi, Adrien², Schlesinger, William³, ¹ Bowdoin College, Brunswick, ME, USA² Boston University, Boston, MA, USA³ Duke University, Durham, NC, USA

ABSTRACT- After three years of CO₂ fumigation at the Duke Forest Free-air CO2 Enrichment (FACE) experiment, a significant accumulation of carbon associated with the elevated CO₂ treatment was detected in the forest floor, but not in the mineral soil. Now after six years, the forest floor under the elevated CO₂ treatment has continued to accumulate carbon at a steady rate of 57 gC m-2 yr-1 greater than the control. However, there are still no detectable changes in the carbon content of the mineral soil. Increased carbon inputs to the forest floor associated with CO₂-enhanced primary productivity do not entirely account for the increase in forest-floor carbon storage, suggesting that the rate of decomposition may be declining under the treatment. Estimates of decomposition based on measured carbon pools and inputs are consistent with reduced decomposition under the treatment (Ambient CO₂: k = 0.345 (+0.020); Elevated CO₂: k = 0.273 (+0.012); n = 3, p = 0.036). Although there is no indication of a change in litter chemistry, decomposition rates may decline if microbial activity is constrained by nutrient availability. Our data suggest that the CO₂-induced growth enhancement at the Duke Forest FACE experiment will begin to attenuate as nitrogen availability becomes progressively more limiting with declining decomposition.

Key words: decomposition , elevated CO₂, nitrogen limitation