Reduced phosphorus availability in paddy soils under atmospheric CO₂ enrichment

Phosphorus is an essential element for plant metabolism and growth, but its future supply under elevated levels of atmospheric CO₂ remains uncertain. Here we present measurements of phosphorus concentration from two long-term (15 and 9 years) rice free air carbon dioxide enrichment experiments. Although no changes were observed in the initial year of the experiments, by the end of the experiments soil available phosphorus had declined by more than 20% (26.9% and 21.0% for 15 and 9 years, respectively). We suggest that the reduction can be explained by the production of soil organic phosphorus that is not in a readily plant-available form, as well as by increased removal through crop harvest. Our findings further suggest that increased transfers of plant available phosphorus from biological, biochemical and chemical phosphorus under anthropogenic changes are insufficient to compensate for reductions to plant available phosphorus under long-term exposure to elevated CO₂. We estimate that reductions to rice yields could be particularly acute in low-income countries under future CO₂ scenarios without the input of additional phosphorus fertilizers to compensate, despite the potentially reduced global risk for phosphorus pollution.