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

Effects of elevated CO2 on desert shrub litter production at the Nevada Desert FACE Facility.

Zitzer, Stephen^*,1, Arnone, John², Billings, Sharon³, Fenstermaker, Lynn², Nowak, Robert¹, Smith, Stanley⁴, Weahterly, Heather², ¹ University Nevada Reno, Reno, NV² Desert Research Institute, Las Vegas, NV³ University of Arkansas Fayetteville, Fayettville, AR⁴ University Nevada Las Vegas, Las Vegas, NV

ABSTRACT- Desert ecosystems are predicted to have large increases in productivity due to rising atmospheric CO₂. Various studies at the Nevada Desert FACE Facility (NDFF) assessing the growth responses of the dominant vegetation to elevated (550 L/L) CO₂ have shown the response varies from <0% to +80%. In order to integrate total productivity across all species, in March 1998 we began measuring litter accumulation beneath Ambrosia dumosa, Larrea tridentata, Lycium andersonii and L. pallidum, which contribute 80% to aboveground perennial biomass at NDFF. Paired trays (25 x 25 cm) were placed beneath three individuals of each species in 9 circular plots (12.5 m diameter). Three plots were fumigated with elevated CO₂. Litter was collected at 4-8 week intervals, oven-dried at 60°C, separated into leaf, wood and reproductive tissues and weighed. After four years, total cumulative litter production (gm^-3 canopy volume) was positively correlated with rainfall and for all species combined was 25% greater under elevated CO₂ . Larrea litter production was 42% greater under elevated CO₂ followed by L. andersonii (29%), Ambrosia (14%) and L. pallidum (10%). Contributions of leaves, wood and reproductive tissues to litter were species dependent, with L. pallidum having significantly more leaf litter under elevated than ambient CO₂ (71% and 52%, respectively), while total allocation to reproductive tissues was reduced by 42 % for L. pallidum. Conversely, under elevated CO₂ Larrea, L. andersonii and Ambrosia litter contained 63%, 48% and 16% more reproductive tissue, respectively. Based on greater litter production and shifts in relative contributions of leaf, wood, and reproductive structures to litter under elevated CO₂, nutrient cycles are likely to be impacted by rising atmospheric CO₂. Furthermore, if species-specific allocation to reproductive structures continues to be greater under elevated CO₂, long-term community structure may shift towards a greater dominance of Larrea and L. andersonii compared to current species frequencies.

KEY WORDS: elevated CO2, litter, shrubs, mojave desert