Background and aims <p>Increasing salinity and sodicity threaten soil fertility and crop yield worldwide and the accumulation of soil organic carbon (SOC) is a vital guarantee for soil improvement. However, there is still a gap in understanding how microbes influence the accumulation of SOC in saline-sodic land reclamation (converting saline-sodic land into cultivated land).</p> Methods <p>Herein, we conducted a survey of microbes in saline-sodic (solonetz) and cultivated soil collected from the Songnen Plain, and analyzed the impact of distribution patterns of niche breadth, microbial composition and multitrophic networks on SOC.</p> Results <p>Results showed saline-sodic land reclamation (reducing pH and EC) significantly increased SOC, niche breadth and microbial diversity of bacteria, fungi and protists. Microbes with significant narrow niche breadth (specialists), which associated over 85% underground connections especially negative connections, were extremely important of both network connectivity and SOC accumulation. SEM revealed that weakened negative connectivity and increased network complexity of specialists promoted the accumulation of SOC in saline-sodic land reclamation. Specialists explained 72.4% of the variance of SOC, higher than 61.3% of the whole community.</p> Conclusions <p>We demonstrated that specialists with high taxonomic diversity could facilitate SOC accumulation in saline-sodic land reclamation by strengthen multitrophic interactions. Our findings enhance the understanding of the effect of saline-sodic land reclamation on soil properties and microbial community and highlight the importance of integrating specialists into models of SOC accumulation, and these findings provide theoretical support for promoting SOC content in saline-sodic land reclamation.</p>