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 fine root dynamics in a Mojave Desert ecosystem: a FACE study.

Phillips, Donald^*,1, Tingey, David¹, Johnson, Mark¹, Catricala, Christina², Hoyman, Toni², ¹ U.S. Environmental Protection Agency, Corvallis, OR² Dynamac International, Inc., Corvallis, OR

ABSTRACT- We studied elevated CO₂ effects on fine root dynamics at the Nevada Desert FACE (Free-Air- CO₂ -Enrichment ) Facility (NDFF). We installed 28 minirhizotron tubes under Larrea and Ambrosia shrubs and along transects in each of three ambient CO₂ and three 550-ppm CO₂ plots. We monitored fine root length production, turnover, and standing crop monthly in 1998-1999. Peak production occurred in April-May, with peak standing crop a month later and peak turnover during the summer. Rainfall in 1998 was ~3.5x normal, with profuse winter annual germination and growth. In contrast, 1999 had half the normal rainfall, with little winter precipitation and no winter annuals. 1999 peak standing crop was ~60% of that for 1998, reflecting poorer soil moisture conditions for root growth and the lack of annuals. There were no consistent CO2-treatment differences in fine root standing crop, production, or turnover except in Transect tubes, where standing crop was consistently lower in the elevated CO₂ treatment, with significant differences in June-July 1998, and February-June and October 1999. Other studies at NDFF have found increased perennial aboveground biomass and decreased leaf conductance under CO₂ enrichment. Higher water use efficiency and decreased conductance in elevated CO₂ may allow sufficient water uptake with smaller amounts of fine roots per unit aboveground biomass. For elevated CO₂ there was a tendency for deepening of root systems under Larrea during the wet year but not the dry year.

KEY WORDS: CO₂ , FACE, roots, desert