PHOTOSYNTHESIS AND GROWTH OF SEEDLINGS OF TWO TREE SPECIES FROM SOUTHEAST ASIA AT DIFFERENT LIGHT REGIMES

摘要

Seedlings of two tropical tree species, Intsia palembanica Mig (Caesalpiniaceae) and Hopea odorata Roxb. (Dipterocarpaceae) were grown for 8 months in a greenhouse at different light regimes (full light and under a green tissue transmitting 20% of daylight). At the end of the experiment light response curves of plants from the two treatment groups were measured. This served as a basis for calculating photosynthetic capacity (Pn_(max)), dark respiration (R_D), light saturation point (I_S), light compensation point (I_C), and quantum efficiency (pi). After measuring photosynthesis the chlorophyll (Chl) content and the ratio ChlA/Chl B (Chla/b) in the leaves were analysed. Transpiration rate (E), leaf conductance for water vapour (LC) and water use efficiency (WUE) were also noted. Finally the plants were harvested and total biomass (DW), leaf number (n) and area (LA), specific leaf area (SLA) and shoot/root ratio (S/R) were estimated. Plants of H. odorata show higher biomass values under full light treatment. In both species leaf number, leaf area, and specific leaf area are greater under shade treatment. The shoot/root ratio of I palembanica is indifferent to differential light treatment. The shoot/root ratio of H. odorata shows a significant decrease under full light. H. odorata showed a decrease in Pn_(max) and I_S and an increase in WUE in response to shading, which is typical of shade-adapted plants. I palembanica under full light treatment showed a decrease in Pn_(max) and I_S as well as in Chl, LC, and WUE. Strong radiation causes photoinhibi-tion in this species. This is largely due to the small root system these plants develop irrespectively of light environment and the low water uptake resulting from this. As a consequence the plants suffer water stress under full light even when they are watered well.