Abstract
Plant growth and leaf photosynthesis were studied for saplings of two species in the Dipterocarpaceae family planted on open bare ground in the Philippines. The greatest rate of growth in height in the initial 14 months after planting was for Shorea contorta, followed by Dipterocarpus grandiflorus. The light-saturated photosynthetic rate (Pmax) for S. contorta and D. grandiflorus was 9.9 ± 0.29 μmol m-2s-1 and 5.5 ± 0.28 μmol m-2s-1, respectively. Dark respiration and apparent quantum yield efficiency did not differ between them. The daily course of photosynthesis showed the existence of a midday depression in net photosynthesis for S. contorta and D. grandiflorus on open bare ground. When the leaf-to-air vapor pressure difference (L-AirVPD) was abruptly raised to 30 hPa, the decrease in the rate of photosynthesis was the same for potted saplings of S. contorta and D. grandiflorus in the nursery. One reason for the difference in growth between species is thought to be the difference in carbon gain depending on a difference in Pmax between the species in the morning, before the leaves suffer from large L-AirVPD at midday.
