Nitrogen form but not elevated CO2 alters plant phosphorus acquisition from sparingly soluble phosphorus sources

Background and aims: Maintaining nutrient supply, including phosphorus (P), is critical to ensure the adaptation of cropping systems to future elevated CO2 (eCO2) environments. There is much speculation about the role of sparingly soluble sources to supply plants with P so we tested the hypothesis that eCO2 increases plant's ability to utilise P from sparingly soluble sources via affecting rhizosphere properties. Methods: Chickpea and wheat were grown for 6 weeks in washed sand supplied with 40 mg P kg-1 as either readily soluble Ca(H2PO4)2 or sparingly soluble AlPO4 (Al-P), FePO4 or hydroxyapatite (HAP). Half plants were exposed to eCO2 (700 ppm) while the others to ambient CO2 (380 ppm). Results: Elevated CO2 increased biomass production of both species but did not influence P concentration in plants, rhizosphere pH or Olsen P. Among the sparingly soluble P sources, HAP resulted in the maximum biomass and total P uptake in wheat and chickpea with wheat acquiring more P. Supply of nitrate, as compared to urea, to wheat decreased the uptake of P from HAP but increased it from Al-P. Conclusion: Elevated CO2 does not specifically affect plant access to P from sparingly soluble P sources. Urea facilitates P acquisition from HAP whereas nitrate facilitates it from Al-P. © 2013 Springer Science+Business Media Dordrecht.