Verification of a mathematical growth model of Phragmites australis using field data from two Scottish lochs

A growth model of Phragmites australis was verified using two independent s ets of published field data. The model simulates the growth pattern of a we ll-established, monospecific stand of P. australis in die absence of geneti c diversity and environmental stresses of mainly nutrient and water deficie ncy. The model formulated using first order differential equations was comb ined with plant phenology and comprises five subroutines in which photosynt hetically active radiation, shoot, root, rhizome and new rhizome biomass ar e calculated. Using the model, experimental results were reproduced within reasonable limits having concordance correlation coefficients of more than 0.75 for 70% of the output parameters, which was the main objective of the study. The modelled efficiencies of PAR were 7.15% and 3.09%, as opposed to 7.7% and 2.53% in experimental estimations, for Loch of Forfar and Loch of Balgavies, respectively. Production and seasonal fluxes of dry matter of P . australis in Scottish lochs were estimated using the modelled quantities for the 1975 growing season in g m(-2). They showed that 31% and 37% of tot al net photosynthate translocated to rhizomes before shoot senescence began in Loch of Forfar and Loch of Balgavies, respectively. Also in both lochs approximately 45% of total downward translocation came from accumulated sho ot dry matter during senescence, while the rest came from photosynthesis be fore the shoots started to senesce.