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.

Net ecosystem CO₂ fluxes in chaparral when grown under elevated and reduced atmospheric CO₂.

Cheng, Yufu^*,1, Oechel, Walter¹, Hastings, Steve¹, Bryant, Pablo¹, Qian, Yonghai¹, ¹ Global Change Research Group, San Diego, CA, USA

ABSTRACT- Ecosystem carbon dioxide flux was studied between 1997 and 2001 under six different CO₂ concentrations using CO₂ LT (CO₂ controlled, naturally Lit, Temperature controlled) null balance chambers and Free Air CO₂ Enrichment (FACE) in southern California chaparral dominated by Adenostoma faciculatum H. & A. For the null balance system, the carbon flux was measured automatically providing replicated in situ ecosystem level measurements at the 6 different CO₂ concentrations from 250 to 750 ppm, with 100 ppm in increment. The annual net ecosystem carbon flux under different CO₂ treatments was calculated from daily carbon flux values. There was a significant CO₂ effect (p=0.049) and year effect (p=0.000) for annual NEE (net ecosystem exchange) from 1997 to 2000. The effects of elevated CO₂ showed a strong seasonal pattern. In the FACE, a Clapp cuvette was used for measuring the carbon flux at elevated CO₂ (treated by 550 ppm CO₂) and ambient on a monthly basis. The effect of elevated CO₂ also showed different patterns in the dry and wet seasons. During the growing season (April-July), the ecosystem under FACE treatment showed less efflux than its control (P=0.033), while during the non-growing season, it showed higher source (P=0.041).

Key words: carbon dioxide flux, elevated CO₂, chaparral