Mechanism of Combined Improvement of Saline‐Alkali Soil by Artificial Humic Acid and Microbial Inoculant

To address the widespread constraints imposed by saline‐alkaline soils on agricultural production worldwide, the combined reclamation and carbon cycle regulation effects of artificial humic acid (AHA) and a multifunctional microbial inoculant were evaluated through pot experiments. Results demonstrated that co‐application of AHA (4 g·kg −1 ) and the inoculant (1 g·kg −1 ) significantly improved soil physicochemical properties: soil pH decreased by 11.0%, while EC and Na + content were reduced by 20.7% and 38.6%, respectively. Soil urease and catalase activities increased by 100% and 25%. This combined treatment increased crop yield by 64.2%. Microbial analysis indicated elevated bacterial alpha‐ and beta‐diversity in the treatment group, accompanied by significant community restructuring, characterized by the enrichment of functional taxa and a reduction in halotolerant groups. Furthermore, soil carbon metabolism was reconfigured: the Calvin cycle and reductive acetyl‐CoA pathway were suppressed, while anaerobic carbon fixation pathways, such as the reductive tricarboxylic acid cycle and the 3‐hydroxypropionate bicycle were promoted. In terms of carbon degradation, enzymatic systems for starch and lignin decomposition were preferentially activated, whereas cellulase activity was transiently inhibited. These findings elucidate the key mechanisms underlying the combined improvement of saline‐alkaline soils and carbon cycle regulation by AHA and microbial inoculant, providing a theoretical foundation for sustainable management of saline‐alkaline lands globally and advancing the understanding of nutrient‐microbe‐carbon cycle interactions in saline‐alkaline environments.