Elevated CO2 increases nitrogen rhizodeposition and microbial immobilization of root-derived nitrogen

With this study, we aimed to determine how elevated CO2 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 CO2 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 CO2. Elevated CO2 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 CO2 reduced mineral N-15 and re-uptake of the root-derived N by 50% in wheat. This study shows that elevated CO2 may enhance N limitation by increasing N rhizodeposition and subsequent immobilization of the root-derived N.