Soil microbial activity and N availability with elevated CO 2 in Mojave Desert soils

We examined the effects of elevated CO 2 on soil nitrogen (N) dynamics in the Mojave Desert by measuring plant N isotope composition (δ 15 N), soil microbial biomass N, soil respiration, resin‐available N, and C and N dynamics during soil incubations. With elevated CO 2 , foliage of Larrea tridentata and Krameria erecta had mean δ 15 N 2.1 and 1.1‰ higher with elevated CO 2 , respectively, and elevated CO 2 increased microbial biomass N in dry soils under a perennial grass (6.8 ± 1.4 versus 3.7 ± 0.3 μg/g). Elevated CO 2 significantly increased cumulative resin‐available N in the field by 12%, driven by available soil moisture. Rates of soil respiration with elevated CO 2 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 CO 2 and may result in increases in plant‐available N when soil moisture is available.