Two states in the U.S. were selected: Colorado and Florida, which are extremely different in terms of ecoregion, climate zone, topography and other ecological conditions.2.1 ColoradoColorado is a U.S. state that encompasses most of the Southern Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains (Fig. 1). Colorado is the 8th most extensive (size: 269,601 km2). Colorado is noted for its vivid landscape of1 INTRODUCTIONSoil organic carbon (SOC) sequestration has received much attention recently as the concentration of CO2 rises in the atmosphere, intensifying climate change. Considering global issues of significance, such as food security, land degradation, and global climate change, more emphasis is needed on maintaining soil’s natural condition under the impact of disturbances and human activities (Grunwald et al., 2011). Characterizing organic carbon (C) pools across large regions is critical to understanding the dynamics of soil C in the context of climate change.