Foliar nutrient resorption in two Mojave Desert shrubs exposed to Free-Air CO 2 Enrichment (FACE)

Foliar nutrient resorption enables plants to sequester resources that might otherwise become unavailable. Future atmospheric CO2 concentrations may increase growth, nutrient demand and nutrient resorption, leading to lower quality leaf litter. During dry, average and wet rainfall years we examined resorption efficiency and proficiency of macro- and micronutrients in Ambrosia dumosa and Lycium pallidum growing under ambient or elevated [CO2]. Resorption efficiencies did not significantly differ between [CO2] in either species during any year. However, Ambrosia N and P resorption efficiencies in both [CO2] were significantly greater in the dry year, as was Lycium N at both [CO2] and P at elevated [CO2]. Resorption in Ambrosia was more proficient for Mn under elevated [CO2] in the dry year and N in the wet year, while P resorption in Lycium was more proficient at elevated [CO2] in the average rainfall year. Significant differences between years always revealed lower N and P litter content in the dry vs. wet year. The most significant result was greater retention of macronutrients in a dry year. The hypothesis that elevated [CO2] will lower leaf litter quality was not supported, as precipitation inputs had a stronger effect on nutrient resorption in these desert shrubs than [CO2].