Soil Organic C and N Destabilization and Decline Following a Decade of Free-Air CO2 Enrichment (FACE) in Aridland Ecosystems.

Arid and semiarid environments constitute ~40% of the earth's land surface. Ecosystems contained therein are expected to be particularly susceptible to global change factors, largely because the organisms inhabiting them often exist at physiological extremes. As a result, there may be dramatic shifts in the biogeochemistry of soil C and N that may have implications on global climate change and the future productivity of the ecosystem. This study examines shifts in the pool sizes and bioavailability of soil organic C and N in response to a decade of free-air CO2 enrichment (FACE) in the Mojave Desert at the Nevada Desert FACE Facility. Characteristic ground cover in the Mojave includes the perennial evergreen shrub Larrea tridentata, some perennial deciduous shrubs, and areas of bare ground, often colonized by biological soil crusts (interspace). Cover type has a dramatic influence on the soil organic matter dynamics of this ecosystem that also influences the response of soil organic C and N to elevated atmospheric CO2. Soils under the dominant vegetative cover, Larrea tridentata, contained up an order of magnitude more C and N and exhibited much larger shifts in the bioavailability of these pools in response to future atmospheric CO2 concentrations.