A COMPARISON OF THE IMPACTS OF VARIOUS NITROGEN-SOURCES ON ACID-BASE-BALANCE IN C-3 TRITICUM-AESTIVUM L AND C-4 ZEA-MAYS L PLANTS

This work aimed to study the impacts of acquisition and assimilation o f various nitrogen sources, i.e. NO3- NH4+ or NH4NO3, in combination w ith gaseous NH3 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 sh oots in ambient air in hydroponic culture solutions with 2 mol m(-3) o f nitrogen source as NO3-, NH4+ or NH4NO3 for 21 d and 18 d, respectiv ely, had their shoots exposed either to 320 mu g m(-3) NH3 or to ambie nt air for 7 d. Variations in plant growth (leaves, stubble and roots) , and OH- and H+ extrusions as well as the relative increases in nitro gen, carbon and carboxylate were determined, These data were computed as Delta H+/Delta N, Delta H+/Delta C, Delta(C-A)/Delta N, and Delta(C -A)/Delta C to analyse influences of different nitrogen sources on aci d-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 mu g m(-3) NH3 in Triticum aestivum and Zea mays growing with diff erent N-forms, whereas leaf growth was not significantly affected by N H3. In comparison with C-3 Triticum aestivum, non-fumigated C-4 Zea ma ys had low ratios of Delta OH-/Delta N in NO3--grown plants and of Del ta H+/Delta N in NH4+- and NH4NO3-grown plants, Utilization of NH3 fro m the atmosphere reduced both the Delta OH-/Delta N ratios in NO3--gro wn plants and the Delta H+/Delta N ratio in NH4+- and NH4NO3-grown pla nts of both species. Furthermore, Zea mays had higher ratios of Delta( C-A)/Delta N in NH4+- and NH4NO3-grown plants than Triticum aestivum, This means that C-4 Zea mays had synthesized more organic anion per un it increase in organic N than C-3 Triticum aestivum plants, Within bot h species, different nitrogen sources altered the ratios of Delta(C-A) /Delta N in the order: NH4NO3>NH4+>NO3-. Fumigation with NH, increased organic acid synthesis in NO3-- and NH4+-grown plants of Triticum aes tivum, 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 grow ing with different nitrogen sources are discussed.