Enhancing soil properties and organic matter transformation in low-fertility reclaimed soil through reed-based exogenous carbon: Exploring the impact of rebuilt microbial community and enzyme activity.

Effective and sustainable management of low-fertility reclaimed soils via reed-based carbon amendments is crucial for environmental nutrient cycling, yet their effects on soil microenvironments and microbial function warrant further exploration. A 60-day incubation experiment evaluated four amendments (reed straw-RS; biochar-RB; biochar-conditioned compost RC1; sediment-biochar co-conditioned compost RC2) at 0%, 5%, 10%, 15% rates on soil properties, organic carbon (C) mineralization, and microbial structure. Results showed that the exogenous carbon addition significantly altered soil physicochemical properties, initially elevating TOC and TN stocks. Following a 60-day incubation, the RC2 treatment exhibited the most pronounced TOC depletion (23.8%, p < 0.05), significantly surpassing losses observed in the RB and RS treatments. Correlation analysis revealed that β-glucosidase and dehydrogenase activities were strongly associated with soil bulk density, TOC, and TN levels. Soil potentially mineralizable C (C₀) differed significantly (p < 0.05), with RC2 exerting the strongest influence on both carbon mineralization kinetics and enzymatic activity. The exogenous carbon inputs generally constrained bacterial diversity, they catalyzed the selective enrichment of specific functional taxa; notably, the RS treatment boosted the relative abundance of Actinobacteriota and Proteobacteria by 26.1% and 4.98%, respectively. Redundancy analysis linked microbial variations to compost treatments, and Cluster of Orthologous Groups (COG) analysis revealed high sensitivity of amino acid transport and metabolism to exogenous C. In conclusion, reed-based amendments improved soil properties and enzyme activities; RS showed a stronger priming effect on C mineralization than RB and composts, with 10% RC2 emerging as a promising amendment.