Dynamics of fungal species related to nitrogen transformation and their network patterns during cattle manure-corn straw with biochar composting

Fungi are reputed to play a significant role in the composting matrix as decomposers of recalcitrant organic materials like cellulose and lignin. However, information on the fungi communities' roles in nitrogen transformation under a compost-biochar mixture is scarce. This study investigated shifts in fungal species mediating N transformation and their network patterns in cattle manure-corn straw (CMCS) and CMCS plus biochar (CMCB) composting using high-throughput sequencing data. The results revealed that the addition of biochar altered fungal richness and diversity and significantly influenced their compositions during composting. Biochar also altered the compost fungal network patterns; CMCS had a more complex network with higher positive links than CMCB, suggesting stable niche overlap. The consistent agreement of multivariate analyses (redundancy, network, regression, Mantel and path analyses) indicated that Ciliophora_sp in CMCS and unclassified_norank_Pleosporales in CMCB were the key fungal species mediating total N transformation, whereas Scedosporium_prolificans in CMCS and unclassified_Microascaceae in CMCB were identified as major predictive indices determining NO3--N transformation. Also, Coprinopsis cinerea and Penicillium oxalicum were the predictive factors for NH4+-N transformation in CMCS and CMCB during composting. These results indicated that the effects of biochar on N conversions in composting could be unraveled using multivariate analyses on fungi community evolution, network patterns, and metabolism.