Harnessing salt-alkali-tolerant carbon-fixing bacteria to enhance carbon sequestration in saline-alkaline soils

Saline-alkali soils reduce the mineralization of organic carbon by suppressing microbial activity and simultaneously limit carbon input by restricting plant growth, thereby leading to reduced accumulation of soil organic carbon. With climate change exacerbating the expansion of saline-alkali affected areas, developing practical strategies to enhance carbon sequestration in these challenging environments has become critically important. In this study, we isolated and introduced the salt- and alkali-tolerant carbon-fixing bacterium Glutamicibacter halophytocola DA1, which exhibited high carbon fixation efficiency even under saline-alkaline stress. After a 45-day incubation in soil microcosms, soils inoculated with DA1 exhibited substantial increases in soil organic carbon, particularly in mineral-associated organic carbon and particulate organic carbon. Metagenomic analysis revealed that DA1 inoculation enhanced the abundance of autotrophic taxa, such as the phyla Acidobacteriota , Hydrogenedentota , and Pseudomonadota , and the families Myxococcaceae and Polyangiaceae , while also upregulating key genes ( rbcL, rbcS, acsA, porA ) associated with multiple carbon fixation pathways, namely the Calvin–Benson–Bassham cycle, the Wood–Ljungdahl pathway, and the reductive citric acid cycle. Co-occurrence network analysis further showed that DA1 inoculation increased microbial connectivity and complexity, and also shifted interaction patterns, with positive correlations declining and competitive associations becoming more prominent over time. Collectively, these findings demonstrate that inoculating saline-alkali soils with a halotolerant carbon-fixing bacterium enhances carbon sequestration, reshapes microbial communities, and activates multiple complementary carbon fixation pathways. This study highlights microbial bioaugmentation as a promising strategy for restoring degraded saline-alkali soils and mitigating the impacts of global climate change.