Effects of elevated carbon dioxide on green leaf tissue and leaf litter quality in an intact Mojave Desert ecosystem

The effects of elevated carbon dioxide (CO 2 ) on plant litter are critical determinants of ecosystem feedback to changing atmospheric CO 2 concentrations. We measured concentrations of nitrogen (N) and carbon (C) and calculated C : N ratios of green leaves of two desert perennial shrubs, and the same quality parameters plus lignin and cellulose content of leaf litter from four shrub species exposed to elevated CO 2 (FACE technology; Hendrey & Kimball, 1994 ) for 3 years in an intact Mojave Desert ecosystem. Shrubs tested were Larrea tridentata , Lycium pallidum , Lycium andersonii and Ambrosia dumosa . We calculated resorption efficiency from green tissue and leaf litter N data and measured lignin and cellulose content in litter in the last year study. Green leaves of L. tridentata grown under elevated CO 2 had significantly lower N concentrations and higher C : N ratios than shrubs grown in ambient conditions in 1999 ( P < 0.05). Lycium pallidum green leaves grown under elevated CO 2 had significantly lower N concentrations and higher C : N ratios than shrubs grown under ambient conditions in 2000 ( P < 0.05). There was no CO 2 effect on C content of either species. We found no effect of CO 2 on N or C content, C : N ratios, or lignin or cellulose concentrations in leaf litter of L. tridentata , L. pallidum , L. andersonii , or A. dumosa . There was no significant effect of CO 2 on estimates of shrub resorption efficiency. There was a seasonal effect on green tissue and litter tissue quality for L. tridentata , with lower tissue N content in summer than in spring or winter months. These data suggest that any productivity increases with elevated CO 2 in desert ecosystems may not be limited by lower leaf litter quality and that resorption efficiency calculations are best performed on an individual leaf basis.