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

Net ecosystem CO₂ exchange in Mojave Desert shrublands during the eighth year of exposure to elevated CO₂.

Jasoni, Richard^*,1, Smith, Stan², Arnone, John¹, ¹ Desert Research Institute, Reno, NV, USA² University of Nevada - Las Vegas, Las Vegas, NV, USA

ABSTRACT- Arid ecosystems, which occupy about 35% of the Earth's terrestrial surface area, are believed to be among the most responsive to elevated [CO₂]. Net ecosystem CO₂ exchange (NEE) was measured in the eighth year of CO₂ enrichment at the Nevada Desert FACE Facility between the months of December 2003 - December 2004. Mean daily NEE (24 h) (micromol CO₂ m^-2 s^-1) of ecosystems exposed to elevated atmospheric CO₂ were similar to those maintained at current ambient CO₂ levels. Mean daily NEE varied seasonally across both CO₂ treatments, increasing from about 0.1 micromol CO₂ m^-2 s^-1 in December 2003 to a maximum of 0.5 to 0.6 micromol CO₂ m^-2 s^-1 in early spring. Maximum NEE in ecosystems exposed to elevated CO₂ occurred one month earlier than it did in ecosystems exposed to ambient CO₂, with declines in both treatments to lowest seasonal levels by early October, but then increasing to near peak levels in late October, November, and December. Photosynthesis in the autotrophic crust community (lichens, mosses, and free-living cyanobacteria) following rains were probably responsible for the high NEEs observed in late October, November, and December when vascular plant photosynthesis was low. Both CO₂ treatments were net CO₂ sinks in 2004, but exposure to elevated CO₂ reduced CO₂ sink strength by 30% (positive NEP = 127 ± 17 g C m^-2 yr^-1 ambient CO₂ and 90 ± 11 g C m^-2 yr^-1 elevated CO₂, P=0.011). Thus, the decrease in C sequestration seen in our study under elevated CO₂ - along with the extensive coverage of arid and semi-arid ecosystems globally (ca. 35% of the Earth's terrestrial surface) -points to a significant drop in global C sequestration potential in the next several decades due to responses of heretofore overlooked dryland ecosystems.

Key words: NEE, NEP, ET, CO₂