Physiological Aspects of Rainforest Regeneration

Abstract

SUMMARYSyzygium fioribundum, a rainforest climax species and Solatium mauritianmn, a rainforest pioneer, were raised in sand cultures containing NO3" or NH4+ under various shade regimes. Optimum growth of Syzygium occurred with NHj"*" and of Solamim with NO^". Ammonium appeared toxic for Solatium at low light intensity.Shoot-root ratios of Syzygiutn 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 oi Syzygiutn 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 Syzygiutti. GDH and GS are both active in the leaves of this species. High GDH and low GS activity in both leaves and roots of Solanutn suggests that GDH is the main NHj^ assimilating enzyme in this species.

Inorganic nitrogen assimilation in plants of Austrlian rainforest communities

“…The presence of glutamine synthetase in all of the rainforest speeies examined here differs from the more restricted distribution reported earlier by Chandler (1981b). The low levels of ehloroplastie glutamine synthetase in leaves of some of the under-storey species contrasts with observations made on autotrophic herbaeeous species, where leaves invariably exhibit aetivity of the ehloroplastie isoform (McNally et al 1983).…”

“…3* Physiiil, PUint, 74. I1SS However, Chandler (1981a) found no effect of irradianee on the amount of glutamine synthetase present in leaves of the climax species Waterhoiisia floribunda.…”

“…B. Hyland (syn. Syzygium florihundum) exhibited greater growth on ammonium ions than on nitrate ions (Chandler 1981a).…”

Biochemical aspects of inorganic nitrogen assimilation by woody plants

“…Not surprisingly, woody plant species exhibit differences in their capacities to utilize nitrate and ammonium ions (see e.g., Chandler, 1981 These differences relate in part at least to the prevalent form of available nitrogen in their ecological niche.…”

Aspects of Rainforest Regeneration

“…A similar adaptation was noted for S. fioribundum (Chandler, 1981). Given the high levels of NH4''" in many rainforest soils (Tanner, 1977) and the apparent adaptation of rainforest plants to growth on ammonium nutrient solutions, the hypothesis (see Hewitt and Smith, 1975) that most species grow better with nitrate than with ammonium-N needs closer examination with regard to a complex rainforest ecosystem.…”