Biomass char-mediated microbial directed remodeling of habitats and productivity regeneration in arid region salt-affected soils.

Soil salinization constitutes a critical bottleneck for sustainable agricultural development in arid regions. In this study, a coupled remediation system integrating biochar and salt-tolerant functional microbial agents was established for saline soil on the southern margin of the Mu Us Sandy Land, Northwest China. Combining column leaching, static capture, bacterial metabolism, and pot experiments with high-throughput microbial sequencing and DFT/RDG electronic topology analysis, we systematically elucidated the amelioration effect of the coupled system on saline soil and its growth-promoting impacts on buckwheat and Leymus chinensis. Results showed that the optimal biochar application rate was 2 % (w/w), achieving a soil salt removal rate of 65.15 %. This rate reduced the Na/(Ca + Mg) molar ratio from 4.30 to 1.66 (well below the safety threshold of 2.0) and lowered the alkali hazard risk index from 80.0 % to 23.2 %. The coupled system achieved efficient remediation through a tripartite mechanism involving physical adsorption, interfacial interaction, and metabolic remodeling-a synergistic framework that, to our knowledge, has not been systematically reported for saline soil remediation. DFT and RDG analyses demonstrated that -COOH and PO43- form a synergistic trapping network that preferentially immobilizes Ca2+ and Mg2+, where PO43- governed efficient capture through bidentate chelation and strong orbital hybridization, confirming the divalent retention, monovalent displacement molecular mechanism. Chemical adsorption governed the selective immobilization of cations, exhibiting a pronounced charge reinforcement effect. Concurrently, biochar drove metabolic reprogramming of microbial strains, leading to a trinity metabolic phenotype characterized by salt tolerance, soil amelioration, and growth promotion. Under salt stress, the retention of salt-tolerant metabolites was 2.7 times higher than that observed with the strains alone. Pot experiments further confirmed that the coupled system exerted significantly superior growth-promoting effects on buckwheat and Leymus chinensis compared to biochar alone. Relative to the control, the equivalent yield of buckwheat increased by 179.9 %, while that of Leymus chinensis rose by 144.1 %. Notably, this study provides the first comprehensive evidence that biochar-driven metabolic reprogramming enables a flexible functionality without salt, tolerance under stress strategy. Critically, the core innovation lies in shifting from single-technology remediation to a synergistic cascade framework of adsorption-interfacial interaction-metabolic remodeling, filling the gap in understanding biochar-microbe coupling as an integrated functional unit. Collectively, this study clarifies the core mechanisms and optimal application parameters of the coupled system, providing a precise technological paradigm for ecological restoration and agricultural productivity improvement in salinized arid regions of Northwest China.