A short version of the ammonium-nitrate interaction model

The performance of the complex ammonium-nitrate interaction model (ANIM) of Flynn el al. (Philos. Trans. R. Soc., 352, 1997) is compared with that of a simplified version (SHANIM) in which the internal pools of inorganic nitrogen (N) and the enzymes of nitrate-nitrite reduction and glutamine synthetase are absent. Although SHANIM is incapable of simulating cell size-linked processes such as the accumulation of inorganic N and the uncoupling of inorganic N transport from assimilation, it offers a good compromise for those needing a simplified modelling solution. The general close agreement between ANIM and SHANIM simulations (usually differing in the details of nutrient transport by phasing of a few hours even in a light-dark cycle) is due to the retention of two major features of ANIM, namely nutrient history-linked transport rates for nitrate and ammonium and regulation of transport by an organic product of N assimilation (glutamine).