EFFECT OF NITROGEN NUTRITION ON PHOTOSYNTHESIS AND GROWTH IN C4-PANICUM SPECIES

The growth and photosynthetic responses to high and low N nutrition were measured in 2 NADP-malic enzyme and 4 NAD-malic enzyme C4 subtype Panicum species to evaluate whether differences in C4 photosynthetic biochemistry result in differences in the N requirement for growth. All species had lower biomass production, photosynthesis rates, and shoot N concentrations at low N, and no consistent differences between the C4 subtypes were apparent. The assimilation rates (biomass accumulated over the period of growth) for the NADP-malic enzyme species were higher than the NAD-malic enzyme species at high N but not at low N. When assimilation rates were evaluated on a shoot N basis a higher N-use-efficiency was found for the NADP-malic enzyme species at high N. Thus the NADP-malic enzyme Panicum species had a greater amount of growth for a given shoot N concentration, but only above a certain level of shoot N concentrations.