We examined the effects of elevated CO2 on soil nitrogen (N) dynamics in the Mojave Desert by measuring plant N isotope composition (δ15N), soil microbial biomass N, soil respiration, resin-available N, and C and N dynamics during soil incubations. With elevated CO2, foliage of Larrea tridentata and Krameria erecta had mean δ15N 2.1 and 1.1? higher with elevated CO2, respectively, and elevated CO2 increased microbial biomass N in dry soils under a perennial grass (6.8 ¿ 1.4 versus 3.7 ¿ 0.3 ¿g/g). Elevated CO2 significantly increased cumulative resin-available N in the field by 12%, driven by available soil moisture. Rates of soil respiration with elevated CO2 were sporadically higher under Pleuraphis and Larrea. Soils under shrubs had greater potential net N mineralization (102.6 ¿ 24.2 ¿g/g) than soils under grasses and in plant interspaces (40.0 ¿ 9.69 ¿g/g). Rates of recalcitrant N turnover in soil incubations were related to soil substrate availability. Results indicate that shifts in soil microbial structure and/or activity may occur with elevated CO2 and may result in increases in plant-available N when soil moisture is available.