WATER CHARACTERISTICS AND SUCCESSIONAL POSITION OF 3 TREE SPECIES IN FRENCH GUYANA IN THE DRY SEASON - TREMA-MICRANTHA, GOUPIA-GLABRA, EPERUA-GRANDIFLORA

Predawn water potential, minimum water potential and maximum stomatal conductance were measured in 2 pioneer species (Trema micrantha and Goupia glabra) and a forest tree (Eperua grandiflora) during the 2 dry spells in 1987 at Cayenne. 1987 was a very dry year but cannot be considered as exceptional. Trema growth was spontaneous, Goupia was grown from transplanted wild seedlings and Eperua was directly sown. All were about 3-y-old. Results show marked differences between the 2 pioneer species. Trema maintains a high water potential and transpiration (but a decresed foliar area) while Goupia endures a low water potential and closes its stomata. Eperua appears intermediate. Laboratory measurements show a dry matter content, a turgescence lost point, a sublethal RWC and a wilting RWC increasing from Trema to Goupia and from Goupia to Eperua. Osmotic potential is lower for Eperua and transpiration speed higher for Trema than for the other 2 species respectively. All in all there is a general behavioural gradient from a large water expenditure in the early successional species to a tighter water control in the late successional species. The main reason for these differences may be found in the root morphologies.