| |
|---|---|
 (476Kb)
|
41,107,000 Yen (FY1995 13,530,000 Yen)
(1) Diurnal changes of photosynthesis in leaves of four tree species at the canopy.
Measurements of photosynthesis and stomatal conductance were conducted with leaves of four tropical tree species, Neobalanocarpus heimii, Xanthophyllium amoneum, Ptychopyxis caput-medusae and Dipterocarpus sublamellatus, at the canopy in the lowland forest at Pasoh, Malaysia. A canopy walkway was used to access to the canopy level in the crown of 30-40m tall individuals. The diurnal changes of net photosynthesis and stomatal conductance were determined two consecutive days. The most significant difference of the environmental factors between the two days was vapor pressure difference. The diurnal patterns of net photosynthesis were different between the two days and between the four species examined in the present measurement, though photosynthetic rates of these four species were quite low. Photosynthetic rates increased with in creasing PFD(photon flux density) before noon and then declined. This diurnal pattern of net photosynthesis was typical for D. sublamellatus and N. heimii. The responsibility of net photosynthesis to PFD was not clear in N. heimii, probably because of the low stomatal conductance in day time caused by the water deficit. The close to proportional relationship between stomatal conductance and net photosynthesis and similar slopes of the relationship could be detected except for D. sublamellatus on the day 1.
(2) Photosynthesis and morphological characteristics of Elateriospermum tapos at different insertion levels.
Measurements of photosynthesis and characteristics in Elateriospermum tapos grown in the lowland forest at Pasoh, Malaysia were conducted on leaves attached at various height from 34m of the canopy level to 16m using a canopy walkway. Photosynthetic rates and stomatal conductance were measured at 34, 26, 21 and 16m from the ground with a portable photosynthesis system and steady state porometer, respectively. Beside of these measurements, leaves were collected to measure the morphological characteristics from the same levels and seedlings(ca. 1m in height).
The relative PFD was 28% at 34m, 14% at 26m, 8% at 21m, 4% at 16m and 2% at 1m. Leaf sizes increased with lowering height and were almost double of leaves of seedlings suggesting that the difference in leaf characteristics is mainly induced by the differences of PFD at the different levels.
The measured photosynthetic rates were related to the incident PFD. The apparent quantum use efficiencies in leaves at lower levels (16 and 21m) and higher levels (25 and 34m) were ca. 0.05 and 0.03, respectively. These results indicate that those leaves attached below the canopy have the photosynthetic characteristics of shade leaves.
Allometry, Forest Canopy, Photosynthesis, Stomatal Conductance