Organic-mineral amendments enhance soil carbon accumulation and rice biomass in coastal salinized soil by regulating fungal necromass carbon and microbial communities

Introduction Coastal soil salinization impairs soil structure and microbial functionality, thereby hindering soil organic carbon (SOC) accumulation and constraining rice productivity. Organic amendments offer a promising route for reclaiming such degradedsoil; however, the mechanisms by which they modulate soil carbon transformation dynamics and rhizosphere microbial communities to improve rice productivity remain poorly resolved. Methods To address this gap, we conducted a pot experiment on coastal saline soil with four treatments: (i) conventional chemical fertilizer (NPK), (ii) NPK combined with attapulgite (ATG), (iii) NPK + ATG + composted straw/swine manure (ATG.SM), and (iv) NPK + ATG + woody peat (ATG.WP). Results Results showed that, compared with NPK, ATG.WP significantly mitigated soil salinity, as indicated by 26.0%, 25.8%, and 9.3% reductions in electrical conductivity (EC), total salt content (TSC), and sodium adsorption ratio (SAR), respectively, alongside a 12.2% increase in soil Ca 2+ and elevated rice biomass. ATG.WP also significantly increased SOC, particulate organic C (POC), microbial biomass C (MBC), total amino sugars, fungal necromass C (FNC), the fungal-to-bacterial necromass C ratio (F/B), and C management index (CMI) ( p < 0.05). Activities of cellobiohydrolase (CBH) and b-glucosidase (bG) enzymes were 163.8% and 81.5% higher under ATG.WP than under NPK. Correlation analysis revealed that rice biomass was negatively correlated with soil salinity indicators but positively correlated with multiple soil C components and C-cycling enzyme activities. Metagenomics analysis further demonstrated that ATG.WP selectively enriched beneficial bacterial phyla (e.g., Pseudomonadota, Chloroflexota, Acidobacteriota), while concurrently suppressed fungal taxa such as Ascomycota and Chytridiomycota. Random forest modeling identified FNC and POC as the primary predictors of SOC accumulation, and structural equation modeling (SEM) revealed that organic-mineral amendments enhanced SOC accumulation by alleviating saline stress, stimulating fungal necromass C production, and recruiting specialized bacterial consortia that chemically stabilize the labile C component. Discussion Collectively, these findings demonstrate that co-application of woody peat and attapulgite is an effective organic-mineral strategy for reclaiming coastal saline paddy soil, operating through a fungal-dominated microbial carbon pump that drives stable SOC accumulation.