Long-term free-air-CO-enrichment increases carbon distribution in the stable fraction in the deep layer of non-clay soils.

Elevated CO (eCO) in the atmosphere can increase plant C input into soils. However, in dryland cropping systems, it remains unclear how eCO may alter soil organic C content and stability in relation to potential changes in microbial community composition and whether these changes may depend on soil type and depth. Using an eight-year free-air-CO-enrichment (SoilFACE) system, this study addressed these questions in three farming soils including a sandy Calcarosol, a clay Vertosol and a silt loam Chromosol at depths of 0-40 cm.