Palygorskite enhances microbial necromass carbon accumulation and drives heavy metal immobilization during chicken manure composting

Microbial necromass carbon (MNC) is a critical component of stable organic matter in compost. However, its role in shaping compost microbial communities and influencing heavy metals (HMs), as well as the effect of palygorskite amendment on MNC and HMs, remains unclear. This study investigated MNC accumulation in chicken manure compost, assessed its impact on microbial communities and HM bioavailability, and evaluated the effects of 5 %, 10 %, and 15 % palygorskite additions. Results showed that palygorskite significantly increased the MNC proportion in total organic carbon, with the 15 % palygorskite enhancing 7.2 % compared to CK. This was primarily due to enhanced bacterial necromass carbon (BNC), which contributed 39.6 %–48.6 % of total MNC. Thermal stress and nutrient limitation were key drivers of MNC accumulation. Fungal necromass carbon (FNC), the dominant MNC component, was positively correlated with compost maturity indices. Palygorskite also markedly reduced HM bioavailability, increasing the passivation rates of Cd, Cu, and Zn by 4.3 %–24.4 %, 10.2 %–11.3 %, and 5.4 %–16.1 %, respectively. Structural equation modeling identified palygorskite, MNC, and pH as the main factors controlling HM bioavailability, explaining up to 83 % of the variation. However, the contribution of MNC to HM immobilization declined as palygorskite addition increased. This study clarifies the relationship between microbial necromass and HMs, highlighting the dual role of palygorskite in stabilizing MNC and reducing HM toxicity.