Enhanced rice phosphorus use efficiency under elevated atmospheric CO2 and its drivers

Soil phosphorus (P) is the second most important nutrient for rice growth and development, but its use efficiency (PUE) is still very low. Meanwhile, the elevated atmospheric carbon dioxide (CO₂) concentration during recent decades has increased the biomass and rice yield globally, but its impact on the PUE of rice is still not well understood. Therefore, this study aims to explore the effect of elevated CO₂ on PUE of rice and its underlying mechanisms, based on the evidence from two-years field free-air CO₂ enhancement (FACE) experiment and the results from a global meta-analysis, we use the open-top chamber (OTC) to explore its underlying mechanism. Results showed that compared to atmospheric CO₂ (ACO₂), elevated CO₂ (ECO₂) has significantly increased the PUE of rice, with a magnitude of 16.6 %. The effects of elevated CO₂ on PUE was higher for Japonica rice than that for Indica rice. These findings were also confirmed by the results from a global meta-analysis. Results based on OTC experiments showed that the aboveground biomass (AGB) of rice increased by 27.8 % and the soil available P increased by 20.3 % with elevated CO₂., two possible drivers accounting for the positive CO₂ effect on rice PUE were investigated, of which one was the enhanced aboveground biomass and the other one was the enhanced soil phosphatase and available P content, both could increase the P accumulation of rice under elevated CO₂ conditions. Further analysis showed that these two factors jointly controlled the elevated PUE at elevated CO₂ conditions, of which the contribution from enhanced aboveground biomass was larger. These findings thus suggested that elevated CO₂ will promote the absorption of P and accelerate the P cycles in rice soils. Our results also could provide important benefits for forming management strategies to balance the contradiction between increasing demand for food and limited P fertilizer resources in the context of climate change.