Energetic and functional development of soil food webs along secondary succession

1. As ecosystems develop, aboveground biomass and belowground organic matter accumulate, while energy turnover declines. This trend is largely supported by vegetation studies, but remains unexplored for soil food webs that channel the majority of energy in terrestrial ecosystems. 2. Here, we tested whether successional theory applies to soil food webs across size-based compartments, ranging from microfauna (nematodes) to macrofauna (soil arthropods and earthworms), along a secondary succession in southwestern China, using an energy-flux approach. To assess whether forest restoration by planting follows natural succession, we also compared spruce and larch plantations with secondary birch forest of the same successional stage. 3. Supporting expectations of reduced energy turnover, the results showed an increasing animal biomass-to-energy flux ratio and a functional shift from herbivory-dominated (green) to detritivory-dominated (brown) energy channelling along succession. Soil food web compartments showed contrasting trends: macro-food webs shifted towards bacterial energy channels with decreasing predation, while micro-food webs maintained similar bacterial/fungal energy flux ratios and tended towards increasing predation. The larch plantation supported lower animal biomass than the secondary birch forest, whereas the spruce plantation did not differ. We further found that energy flux correlated positively with microbial biomass and soil animal diversity, but negatively with litter biomass during succession. 4. Overall, we expand successional theory by revealing the transformations in energy use and pathways within soil food webs along secondary succession, thereby advancing understanding of ecosystem functioning and guiding ecosystem restoration. Our results further suggest that tree plantations do not necessarily replicate the belowground development of natural succession, which should be considered in ecosystem restoration.