Elevated atmospheric carbon dioxide and O3 differentially alter nitrogen acquisition in Peanut

Elevated atmospheric CO2 and ozone (O3) may affect productivity of legumes in part by altering symbiotic N2 fixation. To investigate this possibility, measurements of plant biomass, N levels and natural 15N abundance ({delta}15N) were used to examine the effects of elevated CO2 and O3 on N acquisition in field-grown peanut (Arachis hypogaea L.) using open-top chambers. Seasonal 12-h daily average CO2 treatment concentrations were 376, 550, and 730 µmol mol–1. Carbon dioxide treatments were applied in reciprocal combinations with seasonal 12-h daily average O3 concentrations of 21, 49, and 79 nmol mol–1. At mid-vegetative growth, elevated CO2 significantly reduced leaf N concentrations by up to 44%, but not {delta}15N values. Elevated O3 did not significantly affect N concentrations or {delta}15N values. At harvest, plant N concentrations were similar among treatments except for a 14% reduction in the highest-level CO2–O3 treatment. Plant N accumulation varied in proportion with treatment effects on biomass production, which was increased with elevated CO2 when averaged over the O3 treatments and suppressed by high-level O3 at ambient CO2. Elevated CO2 reduced plant {delta}15N values in low- and mid-level O3 treatments while mid- and high-level O3 increased them at ambient CO2. The changes in {delta}15N values suggested that N2 fixation activity was stimulated with elevated CO2 and inhibited by elevated O3. Elevated CO2 ameliorated detrimental O3 effects to varying extents depending on the concentrations of the two gases. These results indicated that interactions between CO2 and O3 on plant physiology can alter N acquisition processes, with impacts on peanut productivity likely dependent in part on these changes.

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