Leaf conductance decreased under free-air CO2 enrichment (FACE) for three perennials in the Nevada desert

A common response of plants to elevated atmospheric CO2 concentration (CO2) is decreased leaf conductance. Consequently, leaf temperature is predicted to increase under elevated CO2. Diurnal patterns of leaf conductance and temperature were measured for three desert perennials, the C-3 shrub Larrea tridentata, C-3 tussock grass Achnatherum hymenoides and C-4 tussock grass Pleuraphis rigida, at the Nevada Desert FACE facility. Measurements were made on ambient and c. 550 mu mol mol(-1) CO2 plots through both a wet and dry year. Reductions in conductance were 35%, 20% and 13% for Pleuraphis, Achnatherum and Larrea, respectively Decreased conductance occurred through out the day only for Pleuraphis. Both C-3 species had smaller CO2 effects during dry periods than wet. Leaf temperature did not differ significantly between elevated and ambient CO2 for any species. Comparisons of blower-control and nonring plots indicated that the FACE apparatus did not confound our results. All three species exhibited decreased leaf conductance under elevated CO2, although reductions were not uniform during the day or among years. Nonetheless, leaf energy balance was only minimally changed for these microphyllous desert perennials.