A Simulation Model for Decomposition in Grasslands

Abstract

A model has been developed to simulate the dynamics of decomposers and substrates in grasslands. Substrates represented are humic material, feces, and dead plant and animal remains. Except for humic material, substrates are further divided into a rapidly and a slowly decomposing fraction. The proportion of rapidly decomposing material in a substrate is predicted from its initial nitrogen content. The belowground portion of the system is divided into layers because temperature and soil water, the most important driving variables for the model, vary with depth. Decomposition rates are predicted from temperature, water tension, and inorganic nitrogen concentration. Taxonomic groups of decomposers are not distinguished, but distinction is made between active and inactive states, which differ in respiration rate, in death rate, and in that only active decomposers assimilate substrate. The model's predictions compare favorably to data on CO 2 evolution and to litter bag experiments, but not to ATP estimates of active microbial biomass. The model indicates a profound influence of depth on decomposition rates and on decomposer biomass dynamics, growth yield, and secondary productivity.