Wheat and white lupin differ in rhizosphere priming of soil organic carbon under elevated CO2

Elevated CO2 (eCO(2)) alters plant rhizosphere processes and soil microbial properties which in turn change the decomposition of native soil organic carbon (SOC), the process termed rhizosphere priming effect (RPE). This study examined the effect of eCO(2) on RPEs of plant species contrasting in root system and exudation. Two C3 species, wheat (Triticum aestivum L. cv. Yitpi) and white lupin (Lupinus albus L. cv. Kiev), were grown under ambient CO2 (400 +/- 15 mu mol mol(-1)) and eCO(2) (800 +/- 30 mu mol mol(-1)) for 34 and 62 days in a C4 soil. The amounts of CO2 derived from SOC and plant roots were quantified. Elevated CO2 increased the RPEs of white lupin by 78% and 47% at days 34 and 62, respectively. It increased microbial respiration (63%) and biomass carbon (43%) in the rhizosphere soil of white lupin at Day 62. In contrast, eCO(2) decreased wheat RPE by 22% and did not affect rhizosphere soil respiration and microbial biomass carbon at Day 62. Moreover, eCO(2) increased the concentration of soluble organic carbon in the rhizosphere of white lupin but not wheat. The enhanced RPE of white lupin but not wheat under eCO(2) had resulted from an increase in root exudation of white lupin.