Succession of micro-food webs and their role in lignocellulose degradation during pepper stalk composting.

Abtract. Multitrophic interactions among bacteria, fungi, protists, and nematodes play vital roles in organic matter decomposition in soil ecosystems, yet their contributions during composting remain poorly understood. Improving our understanding of these cross-trophic dynamics is essential for optimizing microbial regulation in composting systems. In this study, we investigated the community dynamics and interactions of these trophic groups throughout the aerobic composting of pepper stalks and evaluated their collective influence on lignocellulose degradation. Bacteria expanded rapidly in the early phase, dominating organic matter decomposition, but declined during maturation. Fungi remained low in abundance, with Aspergillus transiently dominating the thermophilic stage. Phagotrophic protists shifted from Colpodella to stress-tolerant Oxytrichidae, while nematodes, which were absent at peak temperature, recovered later, shifting from Rhabditella to Panagrolaimus. Pronounced temporal shifts in community composition and diversity were observed. Co-occurrence network analysis showed increasing interaction complexity over time, with bacterial and fungal taxa dominating lignocellulose-associated modules. Protists and nematodes exerted top-down effects via trophic cascades, indirectly enhancing microbial activity. Structural equation modeling confirmed that food web complexity mediated the indirect effects of community structure on lignocellulose degradation. These findings provide novel insights into compost multitrophic dynamics and highlight the ecological importance of cross-trophic interactions in optimizing decomposition efficiency.