A DEMOGRAPHIC-MODEL OF ASSIMILATION AND ALLOCATION OF CARBON AND NITROGEN IN GRAPEVINES

A dynamic crop model is presented for grapevine (Vitis vinifera L.) dry matter and nitrogen (N) assimilation and allocation with distributed developmental times and age structures of the plant subunits. The model forms a basis for future analyses in the vineyard ecosystem. A flowchart of the daily computations is presented and the corresponding mathematical structure is described. In the model, the plant is divided into annual populations of fruit, leaves, shoots and roots which develop on a perennial frame. In general, these populations are age-structured and have the attributes of numbers, dry matter and N mass, and their dynamics are simulated as a time-invariant distributed delay process with attrition. Growth occurs per degree-day above the developmental threshold of 10-degrees-C. The seasonal N dynamics is the net result of the processes of new tissue formation with high N concentrations and the constant proportional export of N from ageing parts to reserves. The latter process commences immediately after tissue formation. The mean concentration of N in a population of plant subunits is determined by the ratio between young N-rich zones and ageing N-exporting tissues. Simulations were used to assess the patterns and magnitudes of photoassimilate allocation to the three sinks: maintenance respiration, reproductive growth and vegetative growth. In summer, roughly one-third of the assimilate available daily is allocated to each.