Microbes in soil can degrade insoluble inorganic and organic phosphorus, which are components of the soil phosphorus cycle and play an important role in plant growth. Pinus massoniana is a pioneer tree species used for afforestation in southern China and grows in poor, acidic soil. A shortage of available phosphorus in soil limits the growth of P. massoniana. To alleviate this situation, it is necessary to improve soil fertility. A fungal strain (JP-NJ2) with the ability to solubilize phosphate was isolated from the P. massoniana rhizosphere. The ability of JP-NJ2 to solubilize inorganic and organic phosphorus and promote the growth of P. massoniana was evaluated. It showed that JP-NJ2 could grow in NBRIP inorganic phosphate (AlPO4, FePO4·4H2O, and Ca3[PO4]2) fermentation broths, with the highest phosphorus concentration (1.93 mg/mL) and phosphate-solubilizing rate (43.7%) for AlPO4 and in Monkina organic phosphate fermentation broth with a phosphorus concentration of 0.153 mg/mL. The phosphate-solubilizing capability in inorganic and organic fermentation broths was negatively correlated with pH. JP-NJ2-produced acids at a total concentration of 4.7 g/L, which included gluconic (2.3 g/L), oxalic (1.1 g/L), lactic (0.7 g/L), and malonic (0.5 g/L) acids. It prioritized extracellular acidic phosphatase and combined with phytase to solubilize organic phosphates. The fungal suspension and extracellular metabolites from phosphate-solubilizing fungi promoted the shoot length of P. massoniana seedlings by 97.7% and 59.5%, respectively, while increased the root crown diameter by 46.8% and 27.7%. JP-NJ2 was identified as Penicillium guanacastense based on its morphology and phylogenetic analyses of five genes/regions (ITS, ben A, cmd, cox1, and tef). This is the first report on P. guanacastense isolated from pine tree rhizosphere soil in China and its high phosphate-solubilization capability, which promoted the growth of P. massoniana. P. guanacastense JP-NJ2 has potential use as a biological fertilizer in forestry and farming.