Acidic compost tea reduces fungal diversity but improves community structure and P availability in calcareous cotton fields

Acidic compost tea (CT) can provide nutrients for cotton in calcareous (alkaline) soil and improve soil properties; however, the responses of fungi to rhizosphere nutrient conditions and physicochemical properties remain unclear. In this study, the responses of phosphorus (P) morphology and fungal community structure and function to CT in cotton rhizosphere soil were examined. The results indicated that the contents of water P, NaHCO₃-P, and NaOH-P in rhizosphere soil as well as the absorption and accumulation of nutrients by cotton were significantly increased following CT application. The diversity of rhizosphere fungi decreased; however, the species formed a more complex and stable community. Moreover, the relative abundance of oligotrophic species, such as Basidiomycota, decreased. Random forest distribution and Mantel tests revealed that the main driving factors in the compositional change of the fungal species were soil pH and the increasing proportion of labile P (water P and NaHCO₃-P) and moderately labile P (NaOH-P and HCl-P), which directly affected the abundance of species with varying nutrient modes. A structural equation model revealed that the primary factor for dry matter accumulation and yield increase in cotton was increased P availability. This study revealed the changes in P morphology and fungal community in rhizosphere soil in response to CT and factors contributing to these changes as well as evaluated the relationship between efficient utilization of P in calcareous soil and rhizosphere fungal microecology.