Ecosystem processes in semiarid grasslands. I. Primary production and water use of two communities possessing different photosynthetic pathways

Abstract

Above- and below-ground productivity and estimated evapotranspiration rates of a C3 native grassland and a sown C4 buffel grassland community growing on sandy red earth soils at Charleville were studied over a 12-month period. Resistance to water vapour transfer from leaves of both species was measured in the field and glasshouse. Although buffel grass had the highest maximum above-ground growth rate in summer, the most striking difference between the two communities was the much greater standing root crop and root production of the C4 community. Above-ground growth rates were very low in winter, and the differences in rates between communities were small. Over the summer growing period the water use efficiency of the C3 community was about 60% the value for the C4 community. Leaf resistance of the latter species was found to be greater under conditions of limiting and non-limiting water supply. The role of external factors influencing the distribution of these grasslands, as well as the agronomic implications of the study, are discussed.