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 μg/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 μg/g) than soils under grasses and in plant interspaces (40.0 ± 9.69 μg/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.