Nematode predation modulates the energetic dynamics of soil micro-food webs with consequences for soil multifunctionality

Energy fluxes driven by predation are crucial to the relationships between biodiversity and ecosystem functioning in soils. However, there is little empirical evidence connecting these fluxes within soil micro-food webs to soil multifunctionality. Here, we initially used a long-term field experiment to investigate the extent to which nematode predation influences energy fluxes in soil micro-food webs and, in turn, impacts soil multifunctionality. Based on our analysis of body mass-scaled metabolic rates for 70 organismal groups, we estimated that nematodes require roughly three orders of magnitude more energy per individual than bacteria. In the field, we found nematode addition to increase multitrophic diversity and to strengthen interactions between bacteria-feeding nematodes and bacteria. This resulted in multitrophic energy fluxes that were 5.9–169.4 % greater than in soil lacking nematode additions. Specifically, nematode addition reinforced the bacterial energy channel, resulting in greater energy transfer from basal resources to bacteria and subsequently to protists and bacterivorous or omnivorous-predatory nematodes, which altered energy composition and reduced energy flow uniformity. Moreover, our results revealed that elevated multitrophic diversity and shifts in the energetic structure of soil micro-food webs mediated the enhancement in soil multifunctionality. Lastly, a complementary ¹³C-tracer microcosm experiment validated selective predation by nematodes on bacterial taxa (e.g., Mesorhizobium and Paenibacillus ), as shown by significant positive correlations between ¹³C-labeled bacteria and ¹³C-enriched nematodes that explain the trophic transfer observed in nematode addition field treatments. Taken together, this study demonstrates that selective predation by nematodes reorganizes energy flow within soil micro-food webs, offering mechanistic evidence that predator-driven shifts in energy flow underpin biodiversity-function relationships in agricultural soils.