This study investigates the bioenergetic control of soil carbon dynamics across depth. By combining radiocarbon and thermal analyses with long-term incubations, the researchers demonstrate that bioenergetic constraints of decomposers drive the depth-dependency of soil carbon dynamics. Slow subsoil carbon dynamics are linked to low energy density and high activation energy of decomposition, resulting in an unfavorable energy return on investment for decomposers. Rhizosphere priming, accelerated decomposition induced by roots, alleviates this energy limitation. Subsoil carbon persistence stems from poor energy quality and insufficient energy supply by sparse deep roots. These findings highlight the bioenergetic control of SOC persistence and suggest that increased plant rooting depth due to global change could destabilize millennia-old subsoil carbon.

Ludovic Henneron, Jérôme Balesdent, Gaël Alvarez, Pierre Barré, François Baudin, Isabelle Basile-Doelsch, Lauric Cécillon, Alejandro Fernandez-Martinez, Christine Hatté, Sébastien Fontaine