Effects of elevated atmospheric CO₂ on dissolution of geological fluorapatite in water and soil

Most of phosphorus (P) is present as insoluble phosphorus-bearing minerals or organic forms in soil. Geological fluorapatite (FAp) is the dominant mineral-weathering source of P. In this study, FAp was added into water and soil under elevated CO₂ to investigate the pathway of P release. Two types of soils (an acidic soil from subtropical China and a saline-alkali soil from Tibet Plateau, China) with similar total P content were studied. In the solution, increased CO₂ in air enhanced the dissolution of FAp, i.e., from 0.04 to 1.18ppm for P and from 2.48 to 13.61ppm for Ca. In addition, release of Ca and P from FAp reached the maximum (2.14ppm for P and 13.84ppm for Ca) under the combination of elevated CO₂ and NaCl due to the increasing ion exchange. Consistent with the results from the solution, CO₂ elevation promoted P release more significantly (triple) in the saline-alkali soil than in the acidic soil. Therefore, saline-alkali soils in Tibet Plateau would be an important reservoir of available P under the global CO₂ rise. This study sheds the light on understanding the geological cycle of phosphorus.