Aromatic carbon from low-temperature biochar enhances bacterial phosphorus solubilization under saline-alkaline stress.

Co-applying biochar with phosphate-solubilizing bacteria (PSB) holds promise for ameliorating severely degraded ecosystem productivity due to low phosphorus (P) bioavailability in saline-alkaline soils. However, their interaction on how biochar reshapes microbial metabolism function remains poorly understood. Here, low/high-temperature biochar (BC300 and BC700) were utilized to explore the possible mechanism on biochar derived carbon-driven cell's metabolic characteristics in terms of P-solubilization optimization. Specifically, BC300 at 15,000 mg/L was prominent in P-solubilization level over 37.0% of the control rather than BC700 (decreased by 21.4%). Consistent with this divergence, BC300 exhibited significantly higher DOC (108.9 vs. 21.5 mg/L) and SUVA254 values (4.3 vs. 0.9) than BC700. Metabolic-transcriptomic revealed up-regulated the PhoR/PhoB two-component system, enhancement of aromatic amino acid metabolism alongside suppressed ribosome biosynthesis and citrate cycle in BC300. Further detection on targeted LC-MS confirmed a 12.8-fold increase in extracellular maleic acid (28,571.2 ng/mL). Meanwhile, BC300 also improved stress defense supported by increase in extracellular polymeric substances and superoxide dismutase activity. Collectively, these findings suggest the pivotal role of low-temperature biochar in modulating microbial metabolic response to phosphorus deficiency under saltine-alkaline stress, which is possibly associated with aromatic-rich DOC that drives organic acid overflow and stress defense, thereby sustaining efficient P-solubilization.