Effects of elevated ozone on the contribution of nitrogen rhizodeposition by spring wheat to different soil N pools

Background and aims Elevated ozone (O-3) decreases nitrogen derived from rhizodeposition (NdfR). However, the changes in the partitioning of NdfR in soil N pools due to O-3 remain unclear. The aims of this study were to investigate the contribution of NdfR to different soil N pools and its response to elevated O-3 conditions. Methods Spring wheat was labeled with N-15-urea using a split-root technique under ambient (similar to 40 ppb) and elevated O-3 treatments (60 +/- 5 ppb and 110 +/- 5 ppb) in open-top chambers. Mineral-N, microbial biomass (MB)-N and fixed ammonium (FA)-N in rhizospheric soils were analyzed. Results N rhizodeposition contributed 12-33% of mineral N, 10-14% of FA-N and 6-16% of MB-N under ambient O-3. Elevated O-3 significantly decreased mineral-(15)NdfR and increased FA-(15)NdfR but had no significant influence on MB-(15)NdfR. The decrease in mineral-NdfR was likely due to the decrease in rhizodeposition inputs and the increase in FA-NdfR. Conclusions Our results showed that elevated O-3 altered the contribution of NdfR to soil N pools. The present study increases our understanding of the dynamics of NdfR and the changes in soil N cycling induced by projected future O-3 levels.