Bio-cementation boosts organic carbon sequestration in coastal saline soils via aggregation, humification, and chemoautotrophs enrichment.

Formation of soil aggregates is crucial for coastal saline soils, as it improves the physicochemical characteristics of soil, and significantly influences the stability of soil organic carbon (SOC) and soil ecological functions. Applying organic fertilizer is a common way to improve these soils, but its exclusive use often exacerbates soil carbon emissions. This study evaluated the effects of microbially induced carbonate precipitation (MICP), an environmentally benign bio-cementation technique, combined with organic fertilizer application (the MICPOF group) on SOC transformation and sequestration in coastal saline soils through a 90-day greenhouse incubation experiment. After 90 days of incubation, compared with the control group (CK), MICPOF significantly improved soil properties: it increased the mean weight diameter (MWD) of aggregates by 79.43 %, reduced exchangeable sodium (E-Na) by 15.36 % and raised mineral-associated organic carbon (MAOC) by 24.95 %. All these effects outperformed those of the OF group (organic fertilizer application alone). Notably, cumulative CO2 emissions in MICPOF were about 26 % and 44 % lower than in CK and OF, respectively. Analysis of the SOC composition demonstrated that bio-cementation promoted humification and increased the abundance of biorefractory substances, including lignin, tannins, and aromatic compounds. Metagenomic analysis further indicated that MICPOF elevated the abundance of chemoautotrophic microorganisms (e.g., Muriiphilus and Sulfurivermis). Functional genes related to the Calvin cycle, a key carbon sequestration pathway, were 39.37 % and 29.11 % more abundant in MICPOF than in CK and OF, respectively. These findings demonstrate that bio-cementation is a highly effective strategy for reclaiming coastal saline soils and substantially enhancing their carbon sequestration potential.