The effects of elevated CO2 and nitrogen availability on rhizosphere priming of soil organic matter under wheat and white lupin

© 2018, Springer International Publishing AG, part of Springer Nature. Background and aims: Plants grown under elevated CO2 (eCO2) demand more nitrogen from soil and invest more labile carbon (C) compounds into below-ground. This would potentially affect microbial decomposition of soil organic C (SOC) in the rhizosphere- namely rhizosphere priming effect (RPE). This study aims to reveal how eCO2 and nitrogen (N) supply affect the RPEs under wheat and white lupin. Methods: Wheat (Triticum aestivum L. cv. Yitpi) and white lupin (Lupinus albus L. cv. Kiev) were grown at two N addition rates under ambient CO2 (400 μmol mol−1) and eCO2 (800 μmol mol−1) for 32 and 52 days in a C4 soil. Rhizosphere priming of SOC was quantified using the stable 13C isotopic tracing technique. Results: Relative to adequate N supply, low N increased the RPEs under both species at Day 32, but decreased the RPEs under wheat while had no effect on RPE under white lupin at Day 52. Elevated CO2 increased the RPE except that under wheat at Day 52. Conclusions: Low N availability in soil increased the RPE probably via stimulated microbial N mining while eCO2 and severe N limitation synergistically decreased the RPE under wheat but not under N2-fixing white lupin.