Photosynthesis and Dry Matter Production in C3 and C4 Pasture Plants, With Special Emphasis on Tropical C3 Legumes and C4 Grasses

Abstract

The nature of C3 and C4 pasture plants is described, and the potential biomass productivity is discussed. Then differences in net annual production and crop growth rates of C3 and C4 pasture plants are analysed in terms of the interception of solar radiation and the efficiency of its conversion to dry matter. Finally, the components of photosynthetic production of tropical C4 grasses and tropical C3 legumes are compared with their growth rates and dry matter yields in the subtropics. The higher crop growth rates of tropical C4 grasses compared with C3 pasture plants, whether they are of temperate or tropical origin, seem to be due mainly to higher leaf net photosynthetic rates and to the absence of photorespiration associated with possession of the C4 pathway. However, light utilization efficiencies are probably also higher in C4 grasses. In addition to these two characteristics, the longer growing season of C4 grasses in the warm conditions of the tropics contributes to their higher net annual production of dry matter. There is a close association between possession of the C4 pathway, higher rates of photosynthesis and growth, and higher dry matter yields when tropical C4 pasture grasses are compared with tropical C3 legumes in a subtropical climate.