Modeling the effect of abrupt changes in nitrogen availability on lettuce growth, root–shoot partitioning and nitrate concentration

Abstract

A four-compartment lettuce model designed to predict the effects of abrupt changes in nitrogen availability is described. Sensitivity analysis is used to determine the parameters to which the predictions are most sensitive. These parameters are estimated using data from experiments in which nitrogen availability was changed abruptly. The model predicts quite well the main observations associated with interruption of nitrogen supply: reduced shoot growth, increased root-to-shoot ratio (RSR), fast depletion of nitrate, and increased dry matter content. The shoot of plants deprived of nitrogen for 25 days is seven to ten times smaller than the shoot of unstressed plants, while their root-to-shoot ratio is about 12 times larger. Restoring nitrogen supply to previously N-starved plants has opposite effects. A simplified model, obtained by imposing a fixed RSR, gives predictions of shoot fresh mass, dry matter content, nitrate concentration and reduced-N content similar to the predictions of the model with variable RSR, except for extreme cases in which the plants are N-deprived throughout the whole growing period. This indicates that proper modeling of root–shoot partitioning is not essential for predicting the effect of abrupt changes of nitrogen availability on shoot growth and internal plant composition.