A Model of Production and Turnover of Roots in Shortgrass Prairie

Abstract

A mathematical model was constructed to simulate various aboveground and belowground compartments of the producer subsystem for a shortgrass prairie. Simulated aboveground compartments are live shoots, recent and old dead shoots, litter and crowns. Major belowground compartments are live and dead juvenile roots, non-suberized, and suberized roots. The rooting depth is divided into 6 layers and all of the belowground compartments are simulated for each layer. Driving variables in the model are: daily rainfall, daily maximum and minimum air temperatures, long-term monthly average cloud cover, relative humidity and wind speed. The major processes linking the state variables are net photosynthesis; translocation to crowns and roots; death of shoots, crowns and roots; production of litter; aging of roots; respiration of crowns and roots; and decomposition of litter, crowns and roots. Results obtained from the model were compared with observed biomass from 1974 and 1975. In general, the model output compared favorably with observed data; the model tended to overestimate crown and shoot production. A sensitivity analysis of the model shows that above- and belowground production are most sensitive to the translocation parameter, the photosynthesis rate and root respiration. CO2 evolution from soil is relatively insensitive to direct changes in primary production but sensitive to decomposition and root respiration rates.