A comparison of the impacts of various nitrogen sources on acid-base balance in C3Triticum aestivumL. and C4Zea maysL. plants

Abstract

This work aimed to study the impacts of acquisition and assimilation of various nitrogen sources, i.e. NO 3 - NH 4 + or NH 4 NO 3 , in combination with gaseous NH 3 on plant growth and acid-base balance in higher plants. Plants of C 3 Triticum aestivum L. and C 4 Zea mays L. grown with shoots in ambient air in hydroponic culture solutions with 2 mol m -3 of nitrogen source as NO 3 - , NH 4 + or NH 4 NO 3 for 21 d and 18 d, respectively, had their shoots exposed either to 320 μg m -3 NH 3 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, ΔH + /ΔC, Δ(C-)A/ΔN, and Δ(C-A)/ΔC to analyse influences of different nitrogen sources on acid-base balance in C 3 Triticum aestivum and C 4 Zea mays plants. Root growth in dry weight gain was significantly reduced by treatment with 320 μg m -3 NH 3 in Triticum aestivum and Zea mays growing with different N-forms, whereas leaf growth was not significantly affected by NH 3 . In comparison with C 3 Triticum aestivum, non-fumigated C 4 Zea mays had low ratios of ΔOH - /ΔN in NO 3 - -grown plants and of ΔH + /ΔN in NH 4 + - and NH 4 NO 3 -grown plants. Utilization of NH 3 from the atmosphere reduced both the ΔOH - /ΔN ratios in NO 3 - -grown plants and the ΔH + /ΔN ratio in NH 4 + - and NH 4 NO 3 -grown plants of both species. Furthermore, Zea mays had higher ratios of A(C-A)/AN in NH 4 + - and NH 4 NO 3 -grown plants than Triticum aestivum. This means that C 4 Zea mays had synthesized more organic anion per unit increase in organic N than C 3 Triticum aestivum plants. Within both species, different nitrogen sources altered the ratios of Δ(C-A)/ΔN in the order: NH 4 NO 3 >NH 4 + >NO 3 - . Fumigation with NH 3 increased organic acid synthesis in NO 3 - and NH 4 + -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 C 3 Triticum aestivum and C 4 Zea mays plants growing with different nitrogen sources are discussed.