Document: STE-3-34-72

Litter accumulation beneath Mojave Desert shrubs exposed to predicted 21st century atmospheric CO₂ levels using Free Air CO₂ Enrichment (FACE).

STEPHEN, Z.F.* ¹, J.COLEMAN ², R.NOWAK ¹, JSEEMANN ¹ and S.D.SMITH ³

University of Nevada Reno ¹
Desert Research Institute ²
University of Nevada Las Vegas ³

Abstract:
Deserts are predicted to have the largest relative increases in primary productivity due to rising atmospheric CO₂. Therefore, we began continuous exposure of an undisturbed Mojave Desert plant community to 550 ppm CO₂ using FACE (Free Air Carbon Dioxide Enrichment) technology in April 1997. Perennial cover in our study plots was dominated by Larrea tridentata , an evergreen shrub, and the deciduous shrubs Ambrosia dumosa, Lycium andersonii and Lycium pallidum accounting for 64% of total perennial cover. Our experimental design consisted of 9 circular 23 m diameter plots, 3 fumigated with 550 ppm CO₂, 3 controls fumigated with ambient CO₂ and 3 controls with no fumigation. Paired litter trays, (25 by 25 cm) were placed beneath 3 shrub canopies per species per plot in spring 1998. Litter was collected at 4-8 week intervals. For 1998, a wet year (309 mm rainfall), litter accumulation for all species under elevated CO₂ was significantly greater than under ambient CO_2, (161.5 + 16.2 and 128.0 + 9.3 g m^-3 canopy volume< respectively). In contrast, 1999 was a dry year (107 mm rainfall) and litter for all species under elevated CO₂ was not significantly greater than under ambient CO₂, (57.0 + 10.7 and 42.9 + 5.7 g m^-3 canopy volume< respectively). Larrea had significantly greater litter accumulation under elevated CO₂ during the wet year, (244.8 + 21.0 g m^-3) than L. pallidum (158.2 + 5.9), Ambrosia (119.8 + 11.3) and L. andersonii (81.4 + 6.2), which were not significantly different. Litter accumulation during the dry year was reduced by 50, 70, 77 and 91% for Larrea, L. andersonii, Ambrosia and L. pallidum , respectively, and the percent decrease was similar under both CO₂ levels. Litter quality varied greatly relative to proportions of leaf, wood and seeds. Increased litter accumulation under desert shrubs due to elevated CO₂ may represent a significant carbon sink under predicted levels of increasing atmospheric CO₂.

Keywords: plant litter desert shrubs elevated CO₂

This abstract is being presented at: 10:30 AM in session:
Poster Session #18: Elevated CO₂.