Greater soil carbon and nitrogen in a Mojave Desert ecosystem after 10 years exposure to elevated CO2

Abstract

We investigated patterns and possible mechanisms in the greater soil organic carbon (SOC) and total nitrogen (N) after 10 years exposure to elevated atmospheric CO2 concentration ([CO2]) at the Nevada Desert FACE Facility, USA, reported by Evans et al. (2014). Differences in SOC under elevated and ambient [CO2] depended on cover types, and most evident in soils under deciduous shrubs. Greater SOC was observed in soils close to the surface as well as 0.4 to 0.8 m suggesting elevated [CO2] stimulated production of aboveground litter, root litter, and rhizodeposition. Greater total N under elevated [CO2] was most evident under deciduous shrubs as well as plant interspace that had extensive coverage of biological soil crusts. Greater total N in the top soil profile under elevated [CO2] was accompanied with reduced δ15N by 0.4‰, suggesting elevated [CO2] stimulated N2-fixation and/or reduced N loss. We conclude that, in arid ecosystems under elevated [CO2], shrubs play a major role in determining C sink capacity in desert soils, and N limitation for vascular plants is unlikely to occur due to sustained net N supply.