The Seasonal Contribution of C"3 and C"4 Plant Species to Primary Production in a Mixed Prairie

Abstract
A Mixed Prairie in the Northern Great Plains (South Dakota, USA) was studied to determine the floristic composition, according to C3 and C4 types, of the seasonal contribution to aboveground production. Twenty—seven of the 305 species present in the Ordway Prairia possessed Kranz anatomy and are assumed to be C4. Thirty—six percent (19) of the grasses were C4 whereas 4. Dicots were often weedy and fugitive or introduced species. C3 plants possessed a mean °13C value of —26.7%, C4 plants a value of —12.9%. The biomass of lowland and upland communities possessed low °13C values in spring. These values increased significantly in the upland community in midsummer to —20.0% indicating a shift to C4 activity. In fall the biomass °13C values were again low in both communities indicating a return to C3 activity. These data show a clear seasonal displacement in production activity of C3 and C4 grasses in the Mixed Prairie. A general discussion of the evolution and significance of photosynthetic pathways is included.