Diatomite-mediated humification and fungal community succession during composting

Organic-matter degradation and humification degree are key determinants of compost quality. In this study, we used pig manure and wheat straw to investigate the effects of diatomite on organic-component degradation, humification, and fungal community succession. In a 40-day aerobic composting experiment, we compared a control treatment with treatments supplemented with 4% and 8% diatomite. The results indicated that diatomite significantly accelerated organic-matter degradation and humification, with 8% diatomite increasing organic matter and lignin degradation by 9.05% and 9.27%, respectively. Based on linear interpolation of the HA/FA ratio dynamics, it was estimated that the maturity threshold (a ratio of humic acid to fulvic acid > 1.6) was reached 5–7 days earlier in the group subjected to 8% diatomite treatment relative to the control. Fungal community analysis revealed that the 8% diatomite treatment effectively alleviated fungal suppression under high-temperature conditions. By the maturation phase, fungal richness and diversity in the group subjected to the 8% diatomite treatment reached 1.8 and 2.6 times that of the control, respectively, significantly promoting the colonization and recovery of thermophilic Ascomycota, including Mycothermus and Aspergillus. Diatomite shifted fungal interactions from competition to symbiotic cooperation centered on Mycothermus, with partial least squares path modeling confirming fungal composition was a primary regulator of humification. This study demonstrates that 8% diatomite enhances composting efficiency and humification quality by optimizing fungal community structure and function, offering a theoretical and practical basis for the use of agricultural waste resources.