Elevated Atmospheric Carbon Dioxide and O3Differentially Alter Nitrogen Acquisition in Peanut

Elevated atmospheric CO2and ozone (O3) may affect productivity of legumes in part by altering symbiotic N2fixation. To investigate this possibility, measurements of plant biomass, N levels and natural 15N abundance (δ15N) were used to examine the effects of elevated CO2and O3on N acquisition in field‐grown peanut (Arachis hypogaeaL.) using open‐top chambers. Seasonal 12‐h daily average CO2treatment concentrations were 376, 550, and 730 μmol mol−1Carbon dioxide treatments were applied in reciprocal combinations with seasonal 12‐h daily average O3concentrations of 21, 49, and 79 nmol mol−1At mid‐vegetative growth, elevated CO2significantly reduced leaf N concentrations by up to 44%, but not δ15N values. Elevated O3did not significantly affect N concentrations or δ15N values. At harvest, plant N concentrations were similar among treatments except for a 14% reduction in the highest‐level CO2–O3treatment. Plant N accumulation varied in proportion with treatment effects on biomass production, which was increased with elevated CO2when averaged over the O3treatments and suppressed by high‐level O3at ambient CO2Elevated CO2reduced plant δ15N values in low‐ and mid‐level O3treatments while mid‐ and high‐level O3increased them at ambient CO2The changes in δ15N values suggested that N2fixation activity was stimulated with elevated CO2and inhibited by elevated O3Elevated CO2ameliorated detrimental O3effects to varying extents depending on the concentrations of the two gases. These results indicated that interactions between CO2and O3on plant physiology can alter N acquisition processes, with impacts on peanut productivity likely dependent in part on these changes.