A comparison of the impacts of various nitrogen sources on acid-base balance in C3 Triticum aestivum L. and C4 Zea mays L. plants

Abstract

This work aimed to study the impacts of acquisition and assimilation of various nitrogen sources, i.e. NO3, NH4/+ or NH4NO3, in combination with gaseous NH3 on plant growth and acid-base balance in higher plants. Plants of C3 Triticum aestivum L. and C4 Zea mays L. grown with shoots in ambient air in hydroponic culture solutions with 2 mol m-3 of nitrogen source as NO3/-, NH4/+ or NH4NO3 for 21 d and 18 d, respectively, had their shoots exposed either to 320 μg m-3 NH3 or to ambient air for 7 d. Variations in plant growth (leaves, stubble and roots), and OH- and H+ extrusions as well as the relative increases in nitrogen, carbon and carboxylate were determined. These data were computed as ΔH+/ΔN, DH+/ΔC, Δ(C-A)/ΔN, and Δ(C-A)/ΔC to analyse influences of different nitrogen sources on acid-base balance in C3 Triticum aestivum and C4 Zea mays plants. Root growth in dry weight gain was significantly reduced by treatment with 320 μg m-3 NH3 in Triticum aestivum and Zea mays growing with different N-forms, whereas leaf growth was not significantly affected by NH3. In comparison with C3 Triticum aestivum, non-fumigated C4 Zea mays had low ratios of ΔOH-/ΔN in NO3/- -grown plants and of ΔH+/ΔN in NH4/+ -and NH4NO3-grown plants. Utilization of NH3 from the atmosphere reduced both the ΔOH-/ΔN ratios in NO3/- -grown plants and the ΔH+/ΔN ratio in NH4/+- and NH4NO3-grown plants of both species. Furthermore, Zea mays had higher ratios of Δ(C-A)/ΔN in NH4/+ -and NH4NO3-grown plants than Triticum aestivum. This means that C4 Zea mays had synthesized more organic anion per unit increase in organic N than C3 Triticum aestivum plants. Within both species, different nitrogen sources altered the ratios of Δ(C-A)/ΔN in the order: NH4NO3>NH4/+>NO3/-. Fumigation with NH3 increased organic acid synthesis in NO3/- -and NH4/+grown plants of Triticum aestivum, whereas it decreased organic acid synthesis in Zea mays plants under the same conditions. Furthermore, these differences in acid-base regulation between C3 Triticum aestivum and C4 Zea mays plants growing with different nitrogen sources are discussed.