A Model of Production and Turnover of Roots in Shortgrass Prairie

(1) A mathematical model was constructed to simulate various above-ground and below-ground compartments of the producer subsystem for a shortgrass prairie. (2) Simulated above-ground compartments are live shoots, recent and old dead shoots, litter, and crowns. Major below-ground compartments are live and dead juvenile roots, non-suberized, and suberized roots. (3) The rooting depth is divided into six layers and all of the below-ground compartments are simulated for each layer. (4) 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. (5) 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. (6) Results obtained from the model were compared with observed biomass from 1974 and 1975. In general, the model output compared favourably with observed data; however, the model tended to overestimate crown and shoot production. (7) A sensitivity analysis of the model shows that above- and below-ground production are most sensitive to the translocation parameter, the photosynthesis rate, and root respiration. CO-2 evolution from soil is relatively insensitive to direct changes in primary production but sensitive to decomposition and root respiration rates.

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