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Biochar application is perceived as a promising agricultural technology, but risk evaluation on the soil ecosystem has focused exclusively on soil microbes, whether microfood-web is likewise influenced by biochar remains unclear. We carried out a pot experiment planted with rapeseed for 2 years to test how biochar application (0, 20, 60 t ha−1), with or without nitrogen (N) fertilizer (0, 60, 120 t ha−1), affected soil microbes and microfauna (protists and nematodes). We observed that a high amount of biochar (60 t ha−1) increased crop productivity, microbial activity, and biomass carbon (C) and N, as well as the abundance of flagellates (protists), but decreased the abundances of bacterivorous, fungivorous, and herbivorous nematodes as well as the abundance of amoebae (protists). High biochar addition rates also shifted nematode community composition toward a fungivore dominance, and favored herbivores by decreasing the ratio of microbivorous to herbivorous nematodes. However, N fertilizer and its interaction with biochar generally had no effect on microbial activity and biomass as well as the abundance of protist and nematode. A structural equation model revealed that the effects of biochar on soil biota were largely direct, which might depend on biochar properties (e.g., pore size and alkalinity), whereas indirect effects, mediated by crop, soil pH, soil moisture, and polycyclic aromatic hydrocarbon (PAH) concentration, generally had no effect on soil biota. We conclude that biochar is a suitable soil amendment for increasing crop growth, but its detrimental effect on multitrophic levels of soil fauna calls for an identification of the optimal application rate and size fraction that could minimize potential negative effects on certain soil communities. [ABSTRACT FROM AUTHOR]

Energy dynamics within ecological communities are important in delivering ecosystem services. However, it remains elusive how the energy fluxes within soil food webs respond to agricultural fertilization regimes. Here, we studied the effects of long-term organic amendments and mineral fertilizers on the energetic structure of soil nematodes from a food-web perspective. We replicated our experiment in a rice paddy and in an upland maize cropping system. Results showed that the abundance of most trophic groups was higher in organically amended soils compared with mineral fertilizer treatments in both systems. Organic amendments, but not mineral fertilizers, increased the energy flux of total nematodes and most trophic groups compared with the no-fertilizer treatment. Furthermore, organic amendments increased the relative allocation of energy flux to microbivores but decreased the relative allocation to herbivores, supporting a higher flow uniformity than mineral fertilizers. We further found that organic amendments favored a higher total energy flux by supporting a greater nematode diversity, while sustained a higher flow uniformity by altering nematode community composition. Taken together, the result provides the evidence that a complex and species-rich community could transfer more energy to support ecosystem services. A broader perspective on linkages of biodiversity and energy dynamics spanning multitrophic groups is crucial for sustainable management, particularly in the light of non-random species loss under future environmental change. [Display omitted] • Organic amendments increased total energy flux and flow uniformity. • High flow uniformity resulted from increasing relative energy flux of microbivores. • Energy fluxes and flow uniformity were positively linked with nematode diversity. • Effect of diversity decline on energy loss was stronger in paddy than upland fields. [ABSTRACT FROM AUTHOR]

Livestock grazing can affect both above- and below-ground communities, however, the effects of grazing intensity on vertical distribution of root traits and their associations with belowground food webs are still unclear. Based on a 5-year grazing intensity experiment (i.e., no grazing, moderate grazing and heavy grazing) in a Tibetan plateau meadow, we investigated how grazing-induced changes in root traits affected soil biota (microbes and nematodes) from the surface (0–10 cm) and subsurface soils (10–20 cm). Our results showed that moderate grazing increased nematode abundance and structure complexity of the soil micro-food webs compared to no and heavy grazing, and predominantly increased herbivores and fungivores regardless of soil layers. Shifts in herbivores and fungivores were mainly driven by root quantity and quality, emphasizing the stronger bottom-up effects on the lower trophic levels of nematodes. Grazing decreased the number of omnivores-predators in the surface soil compared to no grazing, which therefore weakened predation pressure on soil nematodes lower in the trophic structure, including root herbivores, while that effect was far less pronounced in the subsurface soil. Our study demonstrated that changes in root quantity and quality were highly associated with the complexity of the soil micro-food webs under grazing scenarios. These findings warranted the ideas that combined aboveground herbivore-root-soil micro-food webs as an ecological holo is essential for sustainable management of grassland. [Display omitted] • Structure complexity of soil micro-food webs showed hump-shaped responses to grazing intensity. • The carbon\nitrogen ratio of plant root was decreased by grazing compared to no grazing scenarios. • Moderate grazing strengthened the herbivory and fungal pathways of nematode community. • The abundance of herbivores and fungivores were positively correlated with plant root quantity and quality. [ABSTRACT FROM AUTHOR]