Effects of NaCl on growth and nitrogen fixation and assimilation of inoculated and KNO3 fertilized Vicia faba L. and Pisum sativum L. plants

Faba bean (Vicia faba L. var. minor cv. Alborea) and pea (Pisum sativum I,. cv. Lincoln) plants, inoculated with Rhizobium leguminosarum biovar. vicia e strain GRA19, were treated with salt (100 mM NaCl) and/or nitrate (8 mM K NO3) to test whether plants grown with inorganic-nitrogen are more tolerant to salinity than plants entirely reliant upon fixed nitrogen. According to the growth inhibition recorded, pea plants dependent on dinitrogen fixatio n proved more tolerant to salt stress than those N-fertilized, in contrast to results obtained for faba bean plants. This study therefore confirms tha t plants dependent on nitrogen fixation are not always more sensitive to sa linity than are N-fertilized plants. Nitrate addition did not reduce the sp ecific nitrogenase activity in pea, but did in faba bean. However, nodulati on was inhibited in both legumes. The specific nitrogenase activity was mor e affected by salt treatment in N-fertilized plants for both legumes. The a ctivity of the enzymes mediating ammonium assimilation in nodules (GS, NADH -GOGAT) was inhibited by salt stress both in N-fixing and in N-fertilized p ea and faba bean plants. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.