Rethinking spent mushroom substrate: from lignocellulosic waste to soil–microbiome bioresource for circular agriculture

Abstract

Global mushroom cultivation generates large quantities of spent mushroom substrate (SMS), yet its valorization remains limited by compositional heterogeneity, source-dependent functionality, and poor predictability of soil-microbiome-plant responses. SMS is not a uniform organic residue, but a biologically transformed lignocellulosic matrix shaped by edible fungal species, feedstock composition, cultivation system, post-harvest processing, soil context, and application dose. This review examines SMS from soil-microbiome-plant and circular bioeconomy perspectives, focusing on how fungal transformation of lignocellulosic feedstocks can translate into predictable agricultural and environmental applications. Unlike previous reviews that mainly emphasized disposal, composting, bioenergy, or separate valorization routes, we propose a trait-mechanism-function-application framework. Within this framework, SMS traits include residues, lignocellulose, chitin, nutrients, enzymes, metabolites, protein peptides, and microbial consortia, regulate nutrient release, microbiome succession, biodegradation, adsorption/immobilization, pathogen suppression, and plant immune modulation. These mechanisms underpin applications in soil amendment, disease management, remediation, biochar production, bioenergy, microbial carrier systems, feed valorization, and cascaded biorefineries. Key barriers include inter-batch heterogeneity, incomplete chemotyping, unclear causal mechanisms, unresolved dose–response relationships, inconsistent field performance, safety concerns, and insufficient life cycle (LC) and techno-economic assessment (TEA). This review emphasizes practical solutions, including standardized SMS classification, species- and substrate-specific chemotyping, multi-omics validation, microbiome-resolved assessment, long-term field trials, region-specific utilization framework, and LCA/TEA- guided deployment. By integrating fungal biology, soil ecology, microbiome science, and circular bioprocessing, this review rethinks SMS from a waste-management problem into a mechanism-based biological interface for designing predictable, safe, crop-resilient, low-carbon, and scalable circular agriculture systems.