Effect of Inorganic Nitrogen lons on Photosynthesis and Carbon Dioxide Compensation Concentration of Themeda triandra and Zea mays*

Vacuum infiltration of nitrate and ammonium ions into nitrogen-starved leaf tissue of Themeda triandra and Zea mays increased the carbon dioxide compensation point well in excess of the level normally associated with C4 photosynthetic pathway plants. The net photosynthetic rate was stimulated by the nitrate ions and but slightly inhibited by the ammonium ions. These effects were immediate. The ions increased the Themeda triandra carbon dioxide compensation point and had no effect on that of Zea mays when these plants were grown on fertilized soil. The dark respiration rates of nitrogen-starved Themeda triandra leaves were unaffected by the infiltration of inorganic nitrogen ions. The results suggest that photosynthesis and photorespiration are directly influenced by inorganic nitrogen ions.