Soil microbial activity and N availability with elevated CO2 in Mojave desert soils -: art. no. GB1011

We examined the effects of elevated CO2 on soil nitrogen (N) dynamics in the Mojave Desert by measuring plant N isotope composition (delta(15)N), 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 delta(15)N 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 mug/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 mug/g) than soils under grasses and in plant interspaces (40.0+/-9.69 mug/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.