Global Distribution and Influencing Factors of Plant-Available Phosphorus in (Semi-)Natural Soils

Phosphorus (P) is frequently a limiting nutrient for plant growth in natural ecosystems. Determining plant-available P concentration in soil is essential for pinpointing areas where P availability might restrict plant growth and terrestrial carbon sequestration. However, the worldwide distribution and factors influencing plant-available P in (semi-)natural soils are not well understood. Here, we have developed a comprehensive global database that compiles plant-available P measurements using five prevalent analytical methods: Olsen, Bray-1, Mehlich III, Colwell, and AB-DTPA. The data set encompasses 6,253 plant-available P measurements in (semi-)natural soils (under natural ecosystems and >10 years since anthropogenic activities) at 3,353 globally distributed sites. Leveraging this extensive database, we initially examined the global distribution and influencing factors of plant-available soil P. Subsequently, we utilized a random forest model to delineate a detailed global map of plant-available soil P patterns. Globally, plant-available P varied over four orders of magnitude, from 0.01 to 99.2 mg kg⁻¹. The variation was best explained by parent material types and total soil P concentration. Random forest predicted plant-available P increased significantly with latitude in both hemispheres, though with large longitudinal variations. Global stock of plant-available P was estimated to be 0.73 Pg and 1.59 Pg at 0–30 cm and 30–100 cm soil depths. Our analysis provides insight into the underlying drivers of plant-available P in (semi-)natural soils, presents a spatially explicit assessment of plant-available soil P, which can provide a basis for assessing, predicting, and understanding global patterns of terrestrial P limitation and the functioning of the Earth system.