Dynamic modeling of the growth of Phragmites australis: model description

Abstract

A dynamic model was developed to simulate the growth dynamics of a monospecific stand of Phragmites australis in freshwater ecosystems. Five state variables (biomass of shoots, inflorescence, roots, old rhizomes and new rhizomes) were selected to illustrate the growth of P. australis. Growth was described using mathematical relationships. The net growth of the plant stand was the integral effect of photosynthesis, respiration, mortality and assimilate translocation between shoots and below-ground plant organs. Below-ground biomass (i.e. rhizome and root biomass) before the growth commencement, daily total global radiation and daily mean air temperature were input data. The model is capable of simulating the seasonal variation of above-ground biomass (shoots, stems, leaves and panicles), leaf area index, rhizome, new rhizome, root biomass and shoot height with correlation coefficients close to 1.0 for most of the parameters. The model estimated the conversion efficiency of photosynthetically active radiation varying from 3.76 to 7.19% from northern temperate regions to warmer southern temperate regions. The carbon budget was constructed using the modelled predictions. Analysis of annual net production and fluxes showed that irrespective of the varying climatic conditions, the percentage of annual fluxes of an event, as a proportion of the total photosynthetic production remained almost same. The respiration of shoots, as well as rhizomes and roots, was shown to consume a considerable amount of photosynthetic production: 25% by shoot respiration and 40% by rhizome and root respiration.