Does earthworm stocking density act as an ecological lever to modulate microbial communities, phospho-lipid fatty acid signatures, and mineralization-humification dynamics?

Abstract

Stocking density emerged as the key ecological lever governing how Eisenia fetida and Eudrilus eugeniae transformed municipal solid waste. At lower density (7 worms kg⁻¹), E. fetida achieved maximal carbon stabilization, N mineralization, P and K solubilization through strong humification and a bacteria-dominant microbiome, whereas overcrowding suppressed its efficiency. E. eugeniae performed optimally at moderate densities (10–15 worms kg⁻¹); rapidly depleting labile carbon, increasing humic acids, and sustaining diverse aerobic microbial consortia. Detoxification pathways diverged such that E. fetida primarily immobilized metals via chelation and humic binding, while E. eugeniae stimulated microbial redox transformations that substantially reduced toxic heavy metals. PLFA profiles reinforced species-specific patterns, showing bacterial enrichment under E. fetida and higher fungal-actinomycete abundance under E. eugeniae. Integrating ANN and Sobol sensitivity analysis identified T2 (E. fetida, 7 worms kg⁻¹) and T6 (E. eugeniae, 10 worms kg⁻¹) as optimal regimes, providing robust predictive validation for vermicomposting optimization.