Abstract
In the southeast Asian lowland dipterocarp forest of Peninsular Malaysia (Pasoh Forest Reserve), upper canopy tree species with heterobaric leaves show severe midday depression of net assimilation rate (A) accelerated by patchy stomatal closure, although it is still unclear whether it always happens or not. We added the in situ observations at various meteorological conditions over the last decade to evaluate the frequency and environmental conditions of patchy stomatal closure in Dipterocarpus sublamellatus Foxw., an emergent tree with heterobaric leaves through leaf-gas exchange measurements combined with numerical simulations and chlorophyll fluorescence imaging. Our observation revealed that on days with moderate leaf temperature (<35 °C) and vapor pressure deficit (VPD), which consist four of nine measurement days during 2003−2015, uniform stomatal behavior could explain observed A during the day. The patterns of stomatal behavior shifted from ‘uniform’ to ‘patchy’ even within a day depending on increases in leaf temperature and VPD according to irradiation of sunlight. However, it did not return from ‘patchy’ to ‘uniform’ once patchy stomatal closure happened in a day.
