Simulation model of a laboratory-grown phreatophytic woody legume

A mechanistic model was developed to simulate growth of mesquite Prosopis glandulosa Torr. trees under a phreatic (groundwater) moisture regime. Experimental data obtained in a greenhouse reproducing the phreatic environment (2 m soil columns with 10 cm of water-saturated soil at the bottom) were used to parameterize three submodels predicting carbon (C), nitrogen (N) and water dynamics in leaves, branches, roots and root nodules. In the column simulation model (COLSIM), photosynthesis was driven by air temperature and soil salinity. Water availability was nonlimiting. Nitrogen was absorbed by the roots from inorganic soil N and also fixed by root nodules. Comparison of the simulation with results from the greenhouse experiment showed that the model accurately reproduced shoot biomass and nitrogen content dynamics up to three years with or without a high soil salinity content. Root biomass was underestimated when soil salinity was high because the model did not account for the increased allocation of C to roots under conditions of high salinity. Observed annual cycles of water uptake during the three-year run were not reproduced because the model did not include a phenological function which apparently drives these cycles.