Elevated CO2 temporally enhances phosphorus immobilization in the rhizosphere of wheat and chickpea

Aims The efficient management of phosphorus (P) in cropping systems remains a challenge due to climate change. We tested how plant species access P pools in soils of varying P status (Olsen-P 3.2-17.6 mgkg(-1)), under elevated atmosphere CO2 (eCO(2)). Methods Chickpea (Cicer arietinum L.) and wheat (Triticum aestivum L.) plants were grown in rhizoboxes containing Vertosol or Calcarosol soil, with two contrasting P fertilizer histories for each soil, and exposed to ambient (380 ppm) or eCO(2) (700 ppm) for 6 weeks. Results The NaHCO3-extractable inorganic P (Pi) in the rhizosphere was depleted by both wheat and chickpea in all soils, but was not significantly affected by CO2 treatment. However, NaHCO3-extractable organic P (Po) accumulated, especially under eCO(2) in soils with high P status. The NaOH-extractable Po under eCO(2) accumulated only in the Vertosol with high P status. Crop species did not exhibit different eCO(2)-triggered capabilities to access any P pool in either soil, though wheat depleted NaHCO3-Pi and NaOH-Pi in the rhizosphere more than chickpea. Elevated CO2 increased microbial biomass C in the rhizosphere by an average of 21 %. Moreover, the size in Po fractions correlated with microbial C but not with rhizosphere pH or phosphatase activity. Conclusion Elevated CO2 increased microbial biomass in the rhizosphere which in turn temporally immobilized P. This P immobilization was greater in soils with high than low P availability.