Modelling of reserve carbohydrate dynamics, regrowth and nodulation in a N-2-fixing tree managed by periodic prunings

We used a modified transport resistance approach to model legume tree growt h, nodulation and dynamics of reserve carbohydrates after pruning. The mode l distributes growth between roots and shoots applying the transport resist ance approach. Within shoots, growth is divided into leaves, branches and s tems applying the pipe model theory. The model also accounts for the metabo lic differences of principal N sources, nitrate, ammonium and atmospheric d initrogen, in a mechanistic way. We compared the simulation results with me asured biomass dynamics of Gliricidia sepium (Jacq,) Walp. (Papilionaceae: Robinieae) under humid and subhumid tropical conditions. Comparison showed that the biomass production predicted by the model is close to measured val ues. Total N-2 fixation is also similar to measured values. Qualitatively t he model increases the proportion of N-2 fixation if roots acquire less min eral N, In the present study the general form of the model is discussed and compared,vith similar models. The results encourage the use of this approa ch for studying biomass dynamics of legume trees under the scheme of period ic prunings, Also, it shows that process-based models have potential in the simulation of trees disturbed by prunings, herbivory or similar factors.