© 2007 Heron Publishing—Victoria, Canada
Carbohydrate reserves as a competing sink: evidence from tapping rubber trees
U. Silpi (1), A. Lacointe (2), P. Kasempsap (3), S. Thanysawanyangkura (1), P. Chantuma (4), E. Gohet (1,5), N. Musigamart (1), A. Clément (6), T. Améglio (2) and P. Thaler (1,7,8)
1. DORAS Center, Kasetsart University, 10900 Bangkok, Thailand / 2. INRA, UMR PIAF, Site de Crouelle, 60039 Clermont-Ferrand, France / 3. Department of Horticulture, Faculty of Agriculture, Kasetsart University, 10900 Bangkok, Thailand / 4. Chachoengsao Rubber Research Center, RRIT-DOA, Sanam Chai Ket, Thailand / 5. Cirad, UPR Systèmes de pérennes, 34000 Montpellier, France / 6. Cirad, UPR Modélisation intégrative, 34000 Montpellier, France / 7. Cirad, UPR Ecosystèmes de plantation, 34000 Montpellier, France / 8. Corresponding author (thaler@cirad.fr) / Received March 28, 2006; accepted June 24, 2006; published online March 1, 2007
Summary
Carbohydrate reserve storage in trees is usually considered a passive function, essentially buffering temporary discrepancies
between carbon availability and demand in the annual cycle. Recently, however, the concept has emerged that storage might
be a process that competes with other active sinks for assimilate. We tested the validity of this concept in Hevea brasiliensis Müll. Arg. (rubber) trees, a species in which carbon availability can be manipulated by tapping, which induces latex regeneration,
a high carbon-cost activity. The annual dynamics of carbohydrate reserves were followed during three situations of decreasing
carbon availability: control (no tapping), tapped and tapped with Ethephon stimulation. In untapped control trees, starch
and sucrose were the main carbohydrate compounds. Total nonstructural carbohydrates (TNC), particularly starch, were depleted
following bud break and re-foliation, resulting in an acropetal gradient of decreasing starch concentration in the stem wood.
During the vegetative season, TNC concentration increased. At the end of the vegetative season, there were almost no differences
in TNC concentration along the trunk. In tapped trees, the vertical gradient of starch concentration was locally disturbed
by the presence of the tapping cut. However, the main effect of tapping was a dramatic increase in TNC concentration, particularly
starch, throughout the trunk and in the root. The difference in TNC concentration between tapped and untapped trees was highest
when latex production was highest (October); the difference was noticeable even in areas of the trees that are unlikely to
be directly involved in latex regeneration, and it was enhanced by Ethephon stimulation, which is known to increase latex
metabolism and flow duration. Thus, contrary to what could be expected if reserves serve as a passive buffer, a decrease in
carbohydrate availability resulted in a net increase in carbohydrate reserves at the trunk scale. Such behavior supports the
view that trees tend to adjust the amount of carbohydrate reserves stored to the level of metabolic demand, at the possible
expense of growth.
Keywords:
Hevea brasiliensis, latex yield, resource partition, seasonal dynamics, starch, storage, sugar.
