Influence of tree shade on plant water status, gas exchange, and water use efficiency of Panicum maximum Jacq. and Themeda triandya Forsk. in a Kenya savanna

Abstract

A study of net co. assimilation rate and water vapour exchange of panicum maximum that grows predominantly beneath savanna tree canopies, and Themeda triandra that grows primarily in adjacent open grassland sites, was carried out on both sites in Nairobi National Park. Panicum maximum exhibited less water stress, had lower stomatal conductance and transpiration, and had higher water use efficiency than T. triandra under tree canopies. This indicated that P. maximum should accumulate more biomass with less water loss than Z. triandra under tree canopies, as both grasses had similar rates of net co, assimilation in the shade. More grazing selection pressure for p. maximum thai T. triandra in the open grassland may also help to explain why p. maximum is more dominant in shaded habitats; whereas, T. triandra dominates open habitats. Key words: grasses, photosynthesis, net assimilation rate