Abstract:Soil organic phosphorus (Po) is an important phosphorus pool in soils. The forms, contents and bioavailability of Po change significantly with pedogenesis, which affects soil P supply, nutrient balance and ecosystem productivity. However, compared with inorganic phosphorus (Pi), previous studies paid less attention to Po, which was mainly attributed to the difficulty in the extraction, analysis and identification of different Po speciation. In recent years, the solution 31P nuclear magnetic resonance (31P NMR) spectroscopy was increasingly applied in pedology for characterizing Po compounds, providing a new way for quantitative analysis of Po forms and contents. This significantly improved our understanding of the transformation process of Po during long-term terrestrial ecosystem evolution. This paper systematically summarized the forms and properties of soil Po, and described the principle and procedures of solution 31P NMR spectroscopy for characterizing soil Pospeciation. Then we reviewed the evolution trends and controls of different Pospeciation during natural pedogenesis, and put forward several questions that need to be resolved in the future. Future research priorities include (i) determining the rates, pathways and thresholds of soil Po transformation during long-term soil evolution; (ii) elucidating the coupling relationship between Po and other nutrients such as C and N at different stages of soil evolution and the mechanisms of fixation and release of soil Po; and (iii) building a quantitative model of Po evolution in different types of soils. Providing solutions to the above questions can improve our understanding of the phosphorus biogeochemical cycle in Earth’s Critical Zone and provide a theoretical basis for nutrient management and regulation at different stages of soil evolution, and would promote sustainable utilization of soil resources.