The effect of whole-soil warming on the bioenergetic signature of soil organic carbon

The stability of soil organic carbon (SOC) governs the carbon resistance to decomposition. Thereby, its response to warming is a key determinant of SOC dynamics under warming. However, SOC stability is an ecosystem property regulated by complex mechanisms, which complicates its quantification. Recent insights suggest that SOC stabilization mechanisms collectively contribute to microbial energy limitation. Accordingly, the bioenergetic perspective provides promising approaches for quantifying SOC stability under warming. Here, based on an 8-year whole-soil warming experiment in an alpine meadow on the Tibetan Plateau, we assess warming (+4℃) effects on the bioenergetic signature of SOC across depth (0-100 cm). We find that the activation energy (E_a, representing potential microbial energy investment) increases with depth, whereas the energy density (E_d,representing potential microbial energy gain) declines. This depth-dependent pattern implies that greater energy limitation may contribute to higher SOC stability in subsoil than in topsoil. Moreover, we find that whole-soil warming decreases E_a across depth while has no significant effect on E_d. The reduction of E_a suggests that warming may lower the energy barrier of decomposition reactions. Overall, our results demonstrate that warming will alleviate microbial energy limitation and thereby may threaten SOC storage.