Biochar-influenced solubilization and mineralization mechanisms of phosphorus in saline-sodic soils

Abstract

Biochar, due to its distinct physicochemical properties, holds significant potential for the remediation of saline-sodic soils and enhancing phosphorus (P) bioavailability. However, the underlying mechanisms remain incompletely understood. This study conducted a two-year field experiment applying four different rates of straw biochar (0 t/ha, 30 t/ha, 60 t/ha, and 120 t/ha) to saline-sodic soils to investigate how biochar enhances P availability. The results indicated that biochar application reduced soil pH by 6.43%–13.17% and electrical conductivity by 55.87%–77.55%. Compared to the control (no biochar), total nitrogen and soil organic carbon increased by 1.15–2.77-fold and 2.16–4.40-fold, respectively. Furthermore, biochar significantly increased microbial species abundance, particularly in bacteria (Rokubacteriales, RB41, 67_14, Vicinamibacteraceae), which changed to a more pronounced degree than fungi, indicating the possible substantial role of them over fungi for P cycling. Biochar also upregulated genes involved in phosphate uptake and P transport. Two key mechanisms were identified: (1) improvement of soil physicochemical properties and influence on metabolite abundance, which elevates CaCl₂-P concentrations (on average by 97.38%); and (2) enhancement of phosphatase content that promotes organic P mineralization by bacteria and upregulates genes (e.g., phoR and pstS) to increase available P (on average by 21.52%). This study clarifies the mechanisms by which biochar regulates P cycling in saline-sodic ecosystems, providing a scientific basis for sustainable soil remediation and enhancing the understanding of nutrient dynamics in degraded environments.