Phosphate addition regulates microbial wood degradation in a composting environment through phosphorus supply, pH control, and bacterial community restructuring

Dissolved inorganic phosphates (Pi) can function both as a phosphorus source and a pH buffer during composting. However, the effects of Pi additives on wood-dominated composting remain insufficiently understood, particularly regarding how Pi dosage and Pi-mediated pH conditions shape microbial wood degradation and community dynamics. To address this gap, this study used monosodium phosphate and disodium hydrogen phosphate as Pi additives to assess the effects of Pi dosage and the resulting environmental pH on microbial wood degradation in a composting environment. We found that at comparable environmental pH levels, increasing the Pi dosage (from 0.3 to 3.8 mg PO₄-P/g dry mass wood per 14–18 days) significantly increased oxygen consumption and wood mass loss; while with the same Pi dosage, near-neutral environmental pH (6.1–6.8) facilitated more efficient long-term wood degradation than acidic conditions (pH 3.7–5.8). Under high Pi dosage and near-neutral environmental pH, the highest removal of wood dry mass (21.8%), lignin (26.8%), and total carbohydrates (29.7%) was achieved after 60 days, which may be associated with increased bacterial diversity and enrichment in predicted functional potential related to lignin degradation and carbohydrate metabolism. This study provides new evidence that inorganic phosphate salts, applied as the sole exogenous phosphorus source, can simultaneously enhance the degradation of both lignin and carbohydrates in wood-dominated composting environments. Our findings underscore the importance of phosphate regulation and pH control for supporting prolonged microbial activity and effective microbial wood degradation during composting.