PHYSIOLOGICAL ASPECTS OF RAINFOREST REGENERATION

Abstract

SUMMARY Syzygium floribundum, a rainforest climax species and Solarium mauritianum, a rainforest pioneer, were raised in sand cultures containing NO3− or NH4+ under various shade regimes. Optimum growth of Syzygium occurred with NH4+ and of Solatium with NO3−. Ammonium appeared toxic for Solatium at low light intensity.Shoot‐root ratios of Syzygium were remarkably constant irrespective of light intensity but ammonium promoted greater leaf production. Conversely, Solatium shoot‐root ratios were not affected by nutrients but increased dramatically at low light intensity.Leaves of Syzygium exhibited high levels of glutamate dehydrogenase (GDH) activity which decreased with increasing light intensity. Roots of Syzygium exhibited low GDH activity. This, together with high glutamine synthetase (GS) activity in the roots, suggests that GS is the main ammonium assimilating enzyme in the roots of Syzygium. GDH and GS are both active in the leaves of this species. High GDH and low GS activity in both leaves and roots of Solatium suggests that GDH is the main NH4+ assimilating enzyme in this species.