Résumé
Transitory carbohydrate storage plays a vital physiological role in functioning of woody plants and may serve as indicator of source/sink relationship. Contrary to temperate trees, little work has been done on this subject for tropical, perennial trees. The objectives were to describe the nature, the distribution and the quantity of carbohydrate reserves and to study their seasonal variations in relation with vegetative growth, fruit production and climate. The study was carried out on Riau Estate (Sumatra Island, Indonesia) on thirty-two, 9 years old oil palm trees, representative of a large population and felled on 4 sampling dates between October 2002 and February 2004. The experimental design comprised two treatments (control and 'leaf-pruning' i.e. removing leaves except the 17 youngest), replicated four times. Accumulation zones were identified by sampling and measurement of dry mass and sugars concentrations for all vegetative organs: stem, fronds, roots, persistent leaves bases, and meristem. Non-structural carbohydrates represented 20% of total dry vegetative biomass. Plants contained large quantities of glucose (53% of total carbohydrates), sucrose and starch (20% each) and little fructose. Reserves were predominantly located in the stem. Glucose concentration decreased from bottom to top and from centre to periphery of the stem, whereas sucrose showed reverse gradients. Starch was nearly absent in the lower parts of the stem but attained a concentration of 150 mg g-1 at the top. Monosaccharides concentration was high, and sucrose and starch concentration low, at the end of the dry period (October, when fruit production was high). At the end of the rainy season (February), fruit production and glucose concentration were low. Leaf pruning decreased sugar concentrations at the beginning of the experiment in most plant parts and then this difference disappeared (October 2003 and February 2004). No significant effects of pruning treatment were observed on fruit production. The results indicated that oil palm is one of the rare species using glucose as transitory reserve sugar. Further studies on the agro-ecological and physiological function of these reserves are in progress. (Résumé d'auteur)