A MECHANISTIC AND DYNAMIC MODEL OF CARBON ALLOCATION IN WALNUT (Juglans regia L.) SEEDLINGS

A deterministic and dynamic model of carbon allocation in walnut seedlings is described briefly. The plant is modelled as a network of nodal organs acting as net sources or sinks for carbohydrates. In a sink organ the demand for carbon is the sum of 4 elementary demands: maintenance respiration, structural growth, growth-associated respiration and carbon storage. The organs of the plant are assumed to be in potentially exponential growth phase. The supply of carbon readily accessible to the organs is the store of soluble sugars present in a local reservoir. Carbon flows through the network according to the source/sink activities of the organs. Two carbon sources of different 13C isotopic ratio are used as known inputs: variable exportation of soluble sugars from the kernel, and gross photosynthesis. The outputs are the predicted fluxes of carbon within the seedling: carbohydrate allocation to the growing organs, starch accumulation, respiration and 13C composition of these different fractions. Data for the precise time course of the carbon content and chemical/isotopic composition of the kernel and growing organs (roots, stem, leaves), and gas exchange rates during the first 55 days after sowing were used to calibrate and validate the model. After optimisation of the parameter values, the model provided an accurate description of experimental observations in the seed-plant system during the critical transition from heterotrophy to autotrophy, especially C allocation and partitioning between storage, structural growth and respiration in each organ. The results suggest that the growth of the young plant is supply-limited, except at the earliest stages. As a consequence, intense competition for carbohydrates dominates the relations among organs at that time. It is suggested that similar principles could valuably be applied to describe carbon allocation within elder trees.
Additional index words : Pspice, germination, competition between organs.

IV International Walnut Symposium

F.A. Daudet, A. Lacointe, A.J. Escobar-Gutiérrez, P. Maillard, E. Deléens

Juglans regia L., walnut seedling, model, carbohydrates, allocation

https://doi.org/10.17660/ActaHortic.2001.544.28