Stomatal and boundary-layer conductances in an Amazonian terra firme rain forest.
Diurnal measurements of stomatal conductance (gs) and boundary-layer conductance (ga) were made using a diffusion porometer from a 40-m tower in the Reserva Florestal Ducke, near Manaus, Brazil, in 3 periods: Sep.-Oct. 1983, Jul.-Aug. 1984 and Mar.-Apr. 1985, which covered a range of soil water conditions. The canopy species measured were Piptadenia suaveolens, Licania micrantha, Bocoa viridiflora, Naucleopsis glabra, Enterolobium schomburgkii, Eschweilera fracta, Gustavia angusta and Rinorea racemosa; understorey species were 2 palms (Scheelea sp. and Astrocaryum sp.). Maximum gs values were observed near the top of the 40-m canopy, declining towards the forest floor; ga values also decreased but a slight maximum occurred 20 m above ground. Values of gs were correlated negatively with specific humidity deficit, and positively with solar radiation. Lowest gs values occurred at the same time as lowest soil water potentials.