Modeling diurnal nitrate uptake in young tomato (Lycopersicon esculentum Mill.) plants using a homoeostatic model

A mechanistic predictive model for diurnal nitrate uptake is proposed. It is based on the simple hypothesis of negative feedback uptake regulation by plant nitrate concentration. Nitrate assimilation is considered as a purely photosynthetic process and diurnal changes in plant water content are taken into account. The model parameters are determined from independent experiments set in a growth room. Long-term measurements of plant growth, nitrogen and nitrate accumulations are completed by short-term measurements of net uptake rate, plant nitrate and water contents during a nycthemeral cycle followed by a prolonged period of darkness. The linear and negative relationship between uptake rate and plant nitrate concentration, as used in the model, provides realistic simulations of experimental data. Furthermore, the role of diurnal plant water content changes in nitrate uptake is emphasized.