Multitrophic energy flux in soil micro-food webs: the primacy of functional diversity across primary and secondary forest succession

• Total energy flux and biomass showed complex, stage-specific patterns. • Mature forests in secondary succession exhibited higher energy use efficiency. • Secondary succession accelerated the bacterial-to-fungal energy channel transition. • Functional diversity was a strong predictor of total energy flux. Forest restoration is a cornerstone strategy for combating global biodiversity loss and restoring degraded ecosystem functions. Energy fluxes within ecological communities serve as the link between multitrophic biodiversity and ecosystem functioning. However, the long-term impacts of forest restoration involving primary and secondary succession on the recovery of belowground food web energy fluxes and functions remain poorly understood. Here, we conducted comprehensive biotic and abiotic surveys in primary (glacial retreat) and secondary (post-logging) successional trajectories on the eastern Qinghai-Tibet Plateau. By integrating biomass spectra with metabolic theory, we quantified energy fluxes through key functional guilds (bacterivores, fungivores, herbivores, and omnivores-predators) to analyze the energetic and functional development of soil micro-food webs across both successional trajectories. While total energy flux and biomass showed limited directional shifts across both successional trajectories, community maintenance costs of mature forests in secondary succession decreased by up to 53.2%, reflecting a marked improvement in energy use efficiency. Relative to primary succession, biotic legacies and residual organic matter in secondary succession accelerated the classic shift from bacterial- to fungal-dominated energy channels. Crucially, functional diversity dominated total energy flux prediction in primary succession, whereas taxonomic and functional diversity both acted as positive predictors in secondary succession. These findings underscore the context-dependent role of biodiversity in driving belowground energy dynamics and highlight the need to incorporate functional traits into restoration strategies aimed at enhancing ecosystem functions.