Soil phosphorus sorption capacity dictates the effect of elevated CO2 on soil and plant critical phosphorus levels for wheat growth

Background: Rising atmospheric CO2 concentrations can increase crop yields; however, it is poorly understood if plants require higher phosphorus (P) inputs to support increased production. In addition, soils with contrasting P-sorption capacities may alter plant response to elevated CO2. Aims: We examined the effect of elevated CO2 on the critical concentrations of soil available P and shoot P for plant growth in soils with contrasting P-sorption capacities. Methods: Response curves to P applications were generated for wheat (Triticum aestivum L.) grown in a low P-sorption Sodosol and a high P-sorption Ferrosol. Plants were grown for 5 weeks under ambient (400 ppm) and elevated (800 ppm) CO2 concentrations at nine P application rates. The concentrations of plant P and soil P extracted using Olsen, Bray and Resin methods were analysed. Results: Elevated CO2 increased biomass production in both soils. Plants grown in the Ferrosol but not in the Sodosol required higher P inputs to achieve maximum biomass production in response to elevated CO2. Elevated CO2 increased the critical Olsen-P but decreased the critical Bray-P concentrations for shoot biomass production in the Ferrosol. Elevated CO2 decreased the critical P concentration in shoots of plants grown in the Sodosol but not in the Ferrosol. Conclusions: The effect of P fertilisation on plant response to elevated CO2 depends on soil type. Elevated CO2 also potentially alters P acquisition mechanisms of plants, which requires adjustment of the critical P concentration in shoot and in soil depending on soil P-sorption capacity and the analytical method used to assess P availability.