Phosphorus supply enhances the response of legumes to elevated CO 2 (FACE) in a phosphorus-deficient vertisol

Background & aims: Understanding the mechanism of how phosphorus (P) regulates the response of legumes to elevated CO 2 (eCO 2) is important for developing P management strategies to cope with increasing atmospheric CO 2 concentration. This study aimed to explore this mechanism by investigating interactive effects of CO 2 and P supply on root morphology, nodulation and soil P fractions in the rhizosphere. Methods: A column experiment was conducted under ambient (350 ppm) (aCO 2) and eCO 2 (550 ppm) in a free air CO 2 enrichment (FACE) system. Chickpea and field pea were grown in a P-deficient Vertisol with P addition of 0-16 mg P kg -1. Results: Increasing P supply increased plant growth and total P uptake with the increase being greater under eCO 2 than under aCO 2. Elevated CO 2 increased root biomass and length, on average, by 16 % and 14 %, respectively. Nodule biomass increased by 46 % in response to eCO 2 at 16 mg P kg -1, but was not affected by eCO 2 at no P supply. Total P uptake was correlated with root length while N uptake correlated with nodule number and biomass regardless of CO 2 level. Elevated CO 2 increased the NaOH-extractable organic P by 92 % when 16 mg P kg -1 was applied. Conclusion: The increase in P and N uptake and nodule number under eCO 2 resulted from the increased biomass production, rather than from changes in specific root-absorbing capability or specific nodule function. Elevated CO 2 appears to enhance P immobilization in the rhizosphere. © 2012 Springer Science+Business Media B.V.