A CARBON BALANCE MODEL OF PEACH-TREE GROWTH AND DEVELOPMENT FOR STUDYING THE PRUNING RESPONSE

We modeled tree responses to pruning on the basis of growth rules esta blished on unpruned trees and a simple principle governing root-shoot interactions. The model, which integrates architectural and ecophysiol ogical approaches, distinguishes four types of anatomical organs in a tree: rootstock, main axis, secondary axes and new roots. Tree structu re is described by the position of secondary axes on the main axis. Th e main processes considered are plastochronal activity, branching, ass imilate production, respiration and assimilate partitioning. Growth an d development rules were based on measurements of two unpruned trees. The model was used to simulate growth of peach trees (Prunus persica ( L.) Batsch) in their first growing season. Assuming that the equilibri um between roots and shoots tends to be restored after pruning, the re sponse to removal of the main axis above the twentieth internode in mi d-July was simulated and compared to the response measured in three pr uned trees. The model fit the unpruned tree data reasonably well and p redicted the main traits of tree behavior after pruning. Dry matter gr owth of the secondary axes of pruned trees was increased so that shoot seasonal carbon balance was hardly modified by pruning. Rhythmicity o f growth was enhanced by pruning, and might result from variations ind uced in the root:shoot ratio. Variation in pruning severity had greate r effects than Variation in pruning date. A sensitivity analysis indic ated that: (1) root-shoot partitioning was a critical process of the m odel; (2) tree growth was mainly dependent on assimilate availability; and (3) tree shape was highly dependent on the branching process.