Rhizodeposition-induced decomposition increases N availability to wild and cultivated wheat genotypes under elevated CO2

Elevated CO2 may increase nutrient availability in the rhizosphere by stimulating N release from recalcitrant soil organic matter (SOM) pools through enhanced rhizodeposition. We aimed to elucidate how CO2-induced increases in rhizodeposition affect N release from recalcitrant SOM, and how wild versus cultivated genotypes of wheat mediated differential responses in soil N cycling under elevated CO2. To quantify root-derived soil carbon (C) input and release of N from stable SOM pools, plants were grown for I month in microcosms, exposed to C-13 labeling at ambient (392 mu mol mol(-1)) and elevated (792 mu mol mol(-1)) CO2 concentrations, in soil containing N-15 predominantly incorporated into recalcitrant SOM pools. Decomposition of stable soil C increased by 43%, root-derived soil C increased by 59%, and microbial-C-13 was enhanced by 50% under elevated compared to ambient CO2. Concurrently, plant N-15 uptake increased (+7%) under elevated CO2 while N-15 contents in the microbial biomass and mineral N pool decreased. Wild genotypes allocated more C to their roots, while cultivated genotypes allocated more C to their shoots under ambient and elevated CO2. This led to increased stable C decomposition, but not to increased N acquisition for the wild genotypes. Data suggest that increased rhizodeposition under elevated CO2 can stimulate mineralization of N from recalcitrant SOM pools and that contrasting C allocation patterns cannot fully explain plant mediated differential responses in soil N cycling to elevated CO2. Published by Elsevier Ltd.