Articles
MODELLING THE IMPACT OF LEAF SENESCENCE ON NITROGEN PARTITIONING IN SYCAMORE (ACER PSEUDOPLATANUS L.) SEEDLINGS.
It is recognized that spring leaf growth of deciduous trees depends largely upon the nitrogen (N) supply of the previous year, through the remobilization of N stored during the winter.
Modelling the growth, nitrogen uptake by the root system and the N partitioning within the tree, including the withdrawal from senescing leaves, would enable us to translate our mechanistic understanding of the processes into a framework for mature trees and extend the model from one season to several years.
The withdrawal of N during leaf senescence has still not been included in a model describing the distribution of nitrogen within a plant during a growing season.
This limits the use of modelling to the current year’s growth.
In a previous study, a model was used to predict N allocation within trees up to the onset of leaf senescence (Habib et al., 1990). A major limitation in extending the model to include leaf N withdrawal during canopy senescence was that sink needs were considered as driving forces in N partitioning.
In order to be able to model nitrogen withdrawal from senescing leaves, a negative growth rate (i.e. a decrease in leaf mass) can be used to allocate nitrogen back from leaves to other tissues.
This is illustrated here with data from sycamore seedling experiments (Millard and Proe, 1991).