Composting steers biochar from toxicity to tolerance in earthworms

Résumé fourni par la source

The earthworm intestine acts as a highly sensitive environmental interface, offering critical insights into the ecotoxicological impacts of soil amendments. This study investigates the detoxification efficacy of composting on manure-derived biochar and its implications for sustainable soil management. We exposed earthworms ( Pheretima guillelmi ) to soil amended with pig manure biochar (B2: 2% and B5: 5% w/w) and composting-modified biochar (MB2: 2% and MB5: 5% w/w) for 14 days in an OECD-guided microcosm. Using integrated transcriptomics, metabolomics, and histopathological analyses, we mapped multi-level organ responses to these materials. Unmodified biochar induced severe, dose-dependent toxicity. B5 treatment resulted in 23.3% mortality and profound intestinal damage, including epithelial thinning and gross structural deformation. Transcriptomics revealed massive gene dysregulation (11, 223 differentially expressed genes in B5), characterized by excessive immune-inflammatory responses (e.g., NOD-like receptor and TNF pathways) and triggered cell death programs. Concurrently, metabolomics showed critical disruption of metabolic homeostasis, specifically within the renin-angiotensin signaling system (Rich Factor [RF]=0.18), glycerophospholipid metabolism, and nucleotide synthesis. Composting modification fundamentally reversed this toxicity. Earthworms in MB2 and MB5 treatments achieved 100% survival and maintained pristine intestinal histoarchitecture. Multi-omics integration demonstrated that composting-modified biochar only elicited a mild, controlled innate immune response. Furthermore, it actively stimulated pro-survival mechanisms, including PI3K-Akt signaling (RF=0.25), and sustained core amino acid and nucleotide metabolic networks. This transition from toxicity-driven metabolic collapse to adaptive physiological tolerance correlates closely with a reduction in reactive functional groups achieved during the composting process. These findings firmly establish the earthworm intestine as a robust molecular bioindicator, highlight the severe ecological risks of raw manure biochar, and prove composting is a highly effective detoxification strategy for safe carbon sequestration and soil enhancement.

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