Mechanism of fungi in regulating phosphorus turnover in upland soils

Fungi promote soil phosphorus cycling, but their effects on soil phosphorus conversion and crop growth under excessive phosphorus application conditions are unclear. We examined the role of three fungi with different phosphorus solubility characteristics (Talaromyces purpureogenus F24, Emericellopsis pallida F27, and Mortierella sp. F34) in a pot experiment with corn under long-term excessive phosphorus application. There were five treatments, including no phosphorus fertilizer control (CK), no inoculation with phosphorus fertilizer (CKP, with a phosphorus application rate of 100 mg·kg^-1, the same below), and inoculation with F24, F27, and F34 fungi with phosphorus fertilizer. We explored the effects of fungal inoculation on corn growth, soil phosphorus, and rhizosphere soil bacterial community. The results showed that: 1) CKP treatment significantly reduced phosphorus content in maize roots, while fungal inoculation significantly increased the leaf SPAD value and root dry weight of maize. Compared with CKP treatment, the inoculation treatment significantly increased total phosphorus content in maize roots, with the F24+phosphate fertilizer treatment showing the largest increase of 33.9%. 2) The proportion of soil calcium bound inorganic phosphorus components increased by 28.5%, 30.9%, and 27.8% respectively after inoculation with F24, F27, and F34 plus phosphorus fertilizer treatment, and the proportion of iron aluminum bound organic phosphorus components increased by 37.4%, 26.8%, and 32.8% respectively. 3) The inoculation of F27 effectively enriched the nitrogen fixing bacteria Serratia and Aminobacter in the rhizosphere soil, while the ino-culation of F34 significantly increased the relative abundance of Bacillus bacteria. The inoculation of F24 significantly enriched the bacteria of Oligoflexus and Crocinitomix; Network analysis shows that the complexity and number of nodes in the microbial network of moderately utilized phosphorus were significantly higher than those in the easily and difficultly utilized phosphorus networks. In summary, adding phosphorus solubilizing fungi to dryland soils with excessive phosphorus application could promote maize phosphorus absorption, activate the utilization of occluded soil phosphorus, and effectively improve the rhizosphere soil microenvironment.