EFFECTS OF SALINITY AND NITROGEN ON GROWTH AND WATER RELATIONS IN THE MANGROVE, AVICENNIA MARINA (FORSK.) VIERH

Young plants of Avicennia marina (Forsk.) Vierh, were subjected to a factorial experiment with three concentrations of NaCl (0.1, 0.3, 0.5 M) and three of NH₄ C1 (0.14, 1.4, 14 mg N I^-1 ) in solution culture for three months. Nitrogen and salinity had significant effects on dry matter accumulation in shoots and roots. In general, growth of shoots and roots was significantly greater at 0.1 M NaCl than at 0.3 and 0.5 M NaCl. Added nitrogen at 14 mg N I^-1 significantly increased shoot growth at 0.1 and 0.3 M NaCl. In roots, differences were significant at 0.3 M NaCl and 14 mg N I^-1 . Nitrogen had no significant effect on shoot or root growth at 0.5 M NaCl. At lower salinities there was greater allocation of resources to shoots at 14 mg NI^-1 . Increasing salinity decreased stomatal conductance, tissue water potentials and the concentrations of nitrogen and potassium in tissues. Nitrogen levels had no effect on tissue water potentials. These results are discussed in relation to the effects of salinity and nitrogen on productivity, nutrient uptake and on plant water relations.