Elevated CO 2 increases nitrogen rhizodeposition and microbial immobilization of root‐derived nitrogen

Summary•  With this study, we aimed to determine how elevated CO 2 affects rhizodeposition and the cycling of rhizodeposited nitrogen (N) in the soil under C 3 and C 4 plants. In addition, we examined how cultivated genotypes of wheat ( Triticum turgidum ) and maize ( Zea mays ) responded to elevated CO 2 in comparison with their wild relatives. •  By constructing an N‐transfer experiment we could directly assess cycling of the rhizodeposited N and trace the fate of rhizodeposited N in the soil and in receiver plants. •  Biomass production, rhizodeposition and cycling of root‐borne N in maize genotypes were not affected by elevated CO 2 . Elevated CO 2 stimulated above‐ and below‐ground biomass production of the wheat genotypes on average by 38%, and increased rhizodeposition and immobilization of root‐derived N on average by 30%. Concurrently, elevated CO 2 reduced mineral 15 N and re‐uptake of the root‐derived N by 50% in wheat. •  This study shows that elevated CO 2 may enhance N limitation by increasing N rhizodeposition and subsequent immobilization of the root‐derived N.