Litter Production as a Proxy for Aboveground Productivity under Elevated Atmospheric CO₂ at the Nevada Desert FACE Facility

Abstract

Over the past 150 years, atmospheric CO₂ concentration ([CO₂]) has increased from 270 to 378 μmol mol^-1 and is expected to reach ~565 μmol mol^-1 by 2100. In addition to changes to global climate, increasing [CO₂] directly affects autotrophs such as plants, often increasing both photosynthesis and primary productivity. However, biomass accumulation by perennial plants is offset to some degree by biomass shed, which is usually called litter production. Using Free-Air CO₂ Enrichment (FACE) technology at the Nevada Desert FACE Facility (NDFF) in the Mojave Desert of southwestern North America, we examined litter production over 9 years of experimental treatments to determine if litter production changed in concert with aboveground productivity in a desert ecosystem. Results indicate that the evergreen shrub Larrea tridentata was the only species that had significant [CO₂] effects on litter production. These significant effects occurred in two years and when summed over the entire 9-year period of observation. Litter production for the drought-deciduous shrub Ambrosia dumosa under elevated [CO₂] tended to be greater than other treatments in most years and cumulative litter production for Ambrosia was numerically greater for the elevated [CO₂] treatment, but differences were not significant in any one year or when summed over all years. Litter production for other microsites was usually very similar, both within each year and when summed over the 9-year period. These litter production results are consistent with shoot production results, although temporally delayed and, thus, is an appropriate proxy for aboveground productivity response to elevated atmospheric [CO₂].