PARENT SESSION
Poster Session 9: Arid Lands and Deserts
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Effects of elevated atmospheric CO2 on soil respiration in a Mojave Desert ecosystem.

de Soyza, Amrita^*,1, Nowak, Robert¹, Knight, Eric², Babcock, Derek¹, Smith-Longozo, Vickie¹, ¹ University of Nevada - Reno, Reno, Nevada² University of Nevada - Las Vegas, Las Vegas, Nevada

ABSTRACT- Worldwide, increasing levels of atmospheric CO₂ are a potential threat to ecosystem function and stability. At the Nevada Desert Free Atmospheric CO₂ Enrichment (FACE) Facility located on the Nevada Test Site, 60 miles North of Las Vegas, Nevada we are studying the potential effects of higher than ambient levels of atmospheric CO₂ (550 ppm) on the functioning of a Mojave Desert community dominated by Larrea tridentata. For this study on soil CO₂ efflux we used three 425 x 94 mm ID plexiglass soil respiration cuvettes in each of the three elevated CO₂ plots and their control (ambient CO₂) plots. This static system drew a continuous stream of air through the cuvettes from which CO₂ concentrations were measured every six minutes using LI6262 infra-red gas analyzers. Cuvettes were positioned in three micro-sites (under an evergreen shrub canopy –Larrea tridentata, under a deciduous shrub canopy – Ambrosia dumosa, and inter-space areas) in each of the three elevated CO₂ plots and the three ambient CO₂ plots. Measurements during 2003 – 2004, with average precipitation, indicated that CO₂ efflux from the soil was greatest during spring – early summer. Soil respiration was also greater under plant canopies, particularly in soil under L. tridentata canopies, and atmospheric CO₂ enhancement also increased soil respiration rates. The occurrence of rain also increased soil respiration, particularly in elevated CO₂ plots and much of this increase occurred during the early morning and nighttime – suggesting that daytime soil respiration rates had reached maximal rates under prevailing environmental conditions. These results support the contention that soil respiration rates are spatially and temporally fragmented, and that any increase in net photosynthesis in the presence of elevated atmospheric CO₂ may be offset by increased CO₂ evolution due to increased soil respiration.

Key words: soil respiration, elevated CO2