Soil nutrient limitation controls trophic cascade effects of micro-food web-derived ecological functions in degraded agroecosystems.

Introduction: Soil nutrient supply drives the ecological functions of soil micro-food webs through bottom-up and top-down mechanisms in degraded agroecosystems. Nutrient limitation responds sensitively to variations in degraded agroecosystems through restoration practices, such as legume intercropping.

Objectives: This study examined the effects of legume intercropping on trophic cascade dynamics through resource supply in degraded purple soil ecosystems.

Methods: A field experiment was conducted with three plantation types: Camellia oleifera monoculture (CK), C. oleifera-Arachis hypogaea (peanut) intercropping (CP), and C. oleifera-Senna tora intercropping (CS). Using soil nutrient limitation as a premise, modified by legume intercropping, we assessed the biodiversity of soil biotic taxa, analysed their community composition, and applied partial least squares path modelling (PLS-PM) to link trophic cascade with ecological functions.

Results: Legume intercropping altered the abundance of biotic taxa, leading to changes in biotic diversity and microbial life strategies. The PLS-PM results indicated that legume intercropping enhanced bacterial diversity by aggravating soil P limitation, which subsequently increased protist consumer diversity and omnivore-predator nematode abundance through a bottom-up effect. Omnivore-predator nematodes and protist consumers indirectly influenced soil P metabolism, down-regulated through bacteria in the top-down effect. We observed high consistency between the untargeted metabolomic analysis and soil nutrient limitations. These findings indicate that soil micro-food web structure and function responded sensitively to legume intercropping in degraded ecosystems.

Conclusion: The results highlight the role of soil nutrient limitation in shaping micro-food webs and suggest that soil P limitation controls the down-regulation of soil P-related ecological functions through bottom-up and top-down effects.