Modelling Nitrogen Uptake in Ingestad Units Using Michaelis-Menten Kinetics

The concept of nutrient flux density was developed to grow plants at a controlled and stable relative growth rate whilst maintaining a constant internal concentration of a limiting nutrient. The method requires frequent and exponentially increasing additions of nutrients to replenish uptake. In developing this approach there has been little reference to Michaelis-Menten-like nutrient uptake kinetics for characterising uptake by roots. This paper applies a simple model of nitrogen-limited plant growth using Michaelis-Menten uptake kinetics to data from previously published experiments based on the nutrient flux density approach. It is shown that the model can indeed reproduce key features of experiments: (1) plant relative growth rate equals nitrogen relative addition rate up to a limit; (2) when nitrogen uptake kinetic parameters are within the range reported in the literature, this limiting growth rate agrees with that observed; and (3) solution nitrogen concentrations are consistent with those published. We suggest that the understanding of nutrient uptake and utilisation by plants could be advanced by jointly considering these two approaches.