Biochar and halophyte litter synergistically enhance recalcitrant organic carbon fractions in coastal salt-affected soil via lignin phenols and microbial necromass carbon

Biochar shows promise for remediating coastal salt‑affected soils and supporting potential carbon sequestration, yet its role in the halophyte litter detritusphere, particularly regarding lignin phenols and microbial necromass C (MNC), remains unclear. Herein, we conducted a 370-day microcosm experiment with coastal salt-affected soil from the Yellow River Delta under two moisture conditions (75% and 125% of maximum water-holding capacity) to evaluate how corn straw biochar (CBC) affects lignin phenols and MNC accumulation in the halophyte Suaeda salsa litter detritusphere. Results showed that CBC and litter inputs were stronger drivers of lignin phenol and MNC accumulation than moisture conditions. Litter input significantly increased the contents of lignin phenols and MNC by 32.80–33.36% and 0.78–14.36%, whereas CBC alone decreased lignin phenol content by 12.18–12.87%, but enhanced MNC accumulation by 15.36–42.22%. Compared with litter alone, CBC addition with litter significantly increased lignin phenols, bacterial necromass carbon (BNC), and MNC by 22.43–41.15%, 165.21–233.48%, and 25.09–53.82% under both moisture conditions. Mechanistically, CBC addition with litter alleviated salinity/sodicity stress and improved nutrient availability, enriching decomposition-associated taxa ( Preussia , Talaromyces ) and taxa associated with BNC accumulation ( Thiobacillus , Thioalkalispira ). Concurrently, CBC was associated with greater aggregate stability and organo‑mineral associations, patterns that may favor the retention of lignin-derived residues and microbial necromass. These findings inform biochar as a nature-based strategy for sustainable management of coastal salt‑affected soils and carbon sequestration.