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.