Positive biotic associations of microorganisms promote metabolic efficiency to drive organic carbon stabilization in saline soils

• Microbial positive associations regulate the microbial carbon pump and mineral carbon pump. • Microbial positive associations promote SOC sequestration via metabolic optimization. • Microbial positive associations drive over 72% of global SOC stability variance. • Salt and nitrogen inhibit and promote microbial positive associations, respectively. The stability of soil carbon pools deeply influences global climate changes. Mineral-associated organic carbon (MAOC) as a stable carbon storage formula, plays an important role in soil carbon stability. However, it is still not clear how soil microbial biotic associations govern SOC stabilization by regulating MAOC formation under salinized soil conditions. Here, we collected soil samples from the Yellow River Delta where soil salinization is widely distributed, to reveal the relationship between soil microbial biotic associations and soil carbon stabilization under this special environment. Further, we conducted a global meta-analysis spanning diverse climates and soil types to investigate whether the findings were supported on a global scale. The results showed that positive biotic associations of microorganisms enhanced microbial metabolic efficiency and improved more carbon allocation to microbial biomass and microbial necromass, as evidenced by elevated carbon use efficiency and microbial growth rate, and reduced metabolic quotient. Further, soil minerals interacted with microbial-derived carbon, promoting MAOC formation and improving SOC stability. Meta-analysis validated the exact relationship between soil microbial biotic associations and soil carbon sequestration, and the positive biotic associations could explain over 72–88% of global-scale variance in SOC stability variables. This study highlights the potential of positive biotic associations to reshape microbial metabolic traits, offering novel insights into how microbe–mineral–soil environment interactions influence the formation and stabilization of SOC in saline soils.