CARBON BALANCE OF TROPICAL TREE SEEDLINGS - A COMPARISON OF 2 SPECIES

Seedlings of contrasting tropical tree species were grown at two levels of photon flux, and two levels of nutrient supply. The CO, exchanges of plant organs were measured, in an attempt to account for the overall carbon balance of the plants in terms of the photosynthesis and respiration of their constituent parts (buds, stems, roots and leaves that were recently fully expanded, mature and senescing). On a per plant basis the buds and leaves dominated the carbon balance. High photon flux and high nutrient supply increased the respiration rate. The relative importance of leaves of different age in whole plant photosynthetic production and respiration was different in the two species and was affected by the light regime. Maintenance respiration of both species was about the same (0.036-0.050 g CO2 g(-1) d(-1)) but the pioneer species Trema displayed a much higher rate of growth respiration than did Milicia.