Long-term atmospheric carbon dioxide enrichment decreases soil phosphorus availability in a grazed temperate pasture

•Elevated CO2 negatively affected soil P availability in a grazed temperate pasture.•Long-term CO2 enrichment decreased labile P while increased organic P forms.•Organic P accumulation was related to microbial activity and higher root biomass and turnover.•Adsorption on reactive mineral surfaces could have increased organic P accumulation. Elevated atmospheric carbon dioxide (eCO2) associated with climate change increases plant production and soil nutrient transformations. However, changes in soil phosphorus (P) availability and dynamics are unclear. We used the long-term New Zealand Free Air CO2 Enrichment (FACE) experiment to quantify changes in P availability and soil P fractions as well as chemical and biological parameters in response to ambient and elevated CO2 (up to 500 ppm) concentrations. Results revealed that labile and moderately labile soil inorganic P decreased in response to eCO2, while organic P increased. Accumulation of organic P was related to enhanced biological activity, increased inputs of organic P from root detritus, and immobilization on reactive mineral surfaces. The findings of this study confirmed that elevated CO2 had a major impact on the dynamics and bioavailability of soil P under grazed pasture, which may be further impacted by continued climate change.