ETUDE DE LA CONDUCTIVITE HYDRAULIQUE DES TRONCS D’HEVEA: CAS D’UNE PLANTATION EN COTE D’IVOIRE. (I) MATERIEL ET METHODES

Jerzy Jan NIZINSKI, Gérard GALAT, Anh GALAT-LUONG

ABSTRACT: The necrosis of the rubber tree is an affection of the stem, being expressed by a deterioration of the cortical tissues on the level of which are located the conducting latex tissues. We studied the water relations in a mature rubber tree plantation (clone PB 260; planted in January 1996), in Côte d’Ivoire (May and September 2004), on «healthy» and on «necrosed» trees: mean height 15.0 m; mean circumference at 1.3 m level 59.6 cm; stand density 333 trees ha^-1; leaf area index 3.2; rooting depths 4 m; field capacity, R_FC=412 mm; permanent wilting point, R_WP=225 mm; available water content, R_AW=187 mm. Measurements of water potential allow us to appreciate resistances along the continuum roots - trunk - leaves: the resistances between the trunk and the leaves are identical for « healthy » trees (0.3± 0.1 cm³ H₂0 s^-1 bars^-1) and « necrosed » trees (0.2 ±0.1 cm³ H₂0 s^-1 bars^-1); on the other hand, concerning the resistances between the roots and the trunk the two types of trees differentiate radically: 0.2±0.1 cm³ H₂0 s^-1 bars^-1 for « healthy » trees and 1.1 ±0.3 cm³ H₂0 s^-1 bars^-1 for « necrosed » trees, it is thus on the level of the junction of grafting that resistance is exceptionally high for « necrosed » trees. The results seem to show a difference in functioning between «healthy» and « necrosed » trees in the regulation of transpiration flux. Measurements were made here in optimum conditions for water availability; these measurements would have to be continued in conditions of water shortage for the plant, we could then provide more contrasting results.

Keywords: Hevea brasiliensis; clone PB 260; Côte d’Ivoire; bark necrosis; transpiration; hydraulic conductance of a stem.

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