The process is primarily mediated by plants which absorb carbon dioxide from the atmosphere during photosynthesis; some of this carbon is eventually stored as soil organic carbon. (nativeenergy.com)
Much the same happens in forest soils, which absorb carbon from trees and release CO2 as microorganisms break down plant matter. (newscientist.com)
Plants absorb carbon dioxide from the atmosphere and convert it to organic carbon during photosynthesis. (scientificamerican.com)