EFFECTS OF CLIPPING AND FOUR LEVELS OF NITROGEN ON THE GAS EXCHANGE,GROWTH, AND PRODUCTION OF TWO EAST AFRICAN GRAMINOIDS

Kyllinga nervosa and Themeda triandra plants were subjected to different clipping and nitrogen availability regimes. Following an extended period of growth under these conditions, total biomass, gas exchange and several morphological parameters were measured. Kyllinga nervosa showed compensatory growth to moderate levels of clipping whereas any clipping reduced the total biomass of T. triandra. Unclipped plants of either species were unable to respond to increased levels of nitrogen. Clipped plants responded in an ambiguous fashion, with increased allocation to offtake (material removed by clipping) in both species. Total biomass of K. nervosa was highest at 15 mM nitrogen levels which are equivalent to field levels. Both photosynthesis and respiration rates were unaffected by nitrogen treatments. Photosynthesis was significantly reduced by the most severe clipping regime of K. nervosa, but was unaffected by clipping of T. triandra.