Capability of Penicillium oxalicum y2 to release phosphate from different insoluble phosphorus sources and soil

Due to insufficient amount of soluble phosphate and poor persistence of traditional chemical phosphate fertilizers in agricultural soils, the eco-friendly and sustainable phosphorus sources for crops are urgently required. The efficient phosphate-releasing fungal strain designated y2 was isolated and identified by the internal transcribed spacer of rDNA as Penicillium oxalicum y2. When lecithin, Ca₃(PO₄)₂, or ground phosphate rock were separately used as sole phosphorus source, different phosphate-releasing modes were observed. The strain y2 was able to release as high as 2090 mg/L soluble phosphate within 12 days of incubation with Ca₃(PO₄)₂ as sole phosphorus source. In the culture solution, high concentration of oxalic, citric, and malic acids and high phosphatase activity were detected. The organic acids contributed to solubilizing inorganic phosphate sources, while phosphatase was in charge of the mineralization of organic phosphorus lecithin. Afterwards, the fungus culture was applied to the soil with rape growing. During 50 days of incubation, the soil's available phosphate concentration increased by three times compared with the control, the dry weight of rape increased by 78.73%, and the root length increased by 38.79%. The results illustrated that P. oxalicum y2 possessed both abilities of solubilizing inorganic phosphorus and mineralizing organic phosphorus, which have great potential application in providing biofertilizer for modern agriculture.