PARENT SESSION
Oral Session #58: Elevated CO₂. Presiding: A. Finzi.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Madison Ballroom C.

Three years of shrub productivity under natural wet and dry cycles at the Nevada Desert FACE Facility.

Housman, David¹, Huxman, Travis^1,2, Smith, Stan¹, ^{1 2}

ABSTRACT- We measured shoot productivity of the dominant shrubs at the Nevada Desert FACE Facility over a three-year period (1998-2000) in order to determine the effect of elevated atmospheric CO₂ on aboveground primary production in an intact Mojave Desert ecosystem. Three shoots per plant on three plants per CO₂ treatment ring (3 ambient and 3 elevated rings - totaling 27 shoots per species) were tagged for three deciduous shrubs (Ambrosia dumosa, Krameria erecta, and Lycium pallidum) and an evergreen shrub (Larrea tridentata) prior to the active growing season. Shoot growth was monitored via a fixed mark on each tagged stem from which cumulative shoot lengths were measured. These lengths were converted to a measure of cumulative shoot biomass based on regressions made from onplot harvests. Using a repeated measures ANOVA, with [CO₂], time, and their interaction as factors, we found elevated CO₂-grown Larrea significantly increased production over ambient-grown Larrea in the wet year of 1998. Elevated CO₂-grown Ambrosia and Krameria also showed trends towards greater shoot biomass in 1998, but these were not statistically significant. In the dry years 1999 and 2000, shoot productivity was low and biomass did not significantly differ between CO₂ treatments for any species. These results suggest that predicted future levels of atmospheric CO₂ will stimulate production of desert shrubs, but only during years with adequate rainfall.

KEY WORDS: Elevated CO₂ , Plant Growth, Mojave Desert, FACE