DIFFERENTIAL EFFECTS OF LIGHT ON PHOTOSYNTHESIS AND NITROGEN METABOLISM IN CHLORELLA PYRENOIDOSA.

A series of investigations was conducted to examine some of the differential effects of light on the photosynthetic reduction of carbon dioxide and on nitrogen metabolism in the unicellular alga, Chlorella pyrenoidosa. Nitrite uptake in the presence of, and in the absence of, carbon dioxide was measured. Similar measurements were made of nitrate uptake. Light intensities above the saturation level for photosynthesis reduced the rate of nitrite uptake but did not appear to affect the uptake of either carbon dioxide or nitrate. The rate of nitrite uptake at 20 m2.sq. cm. was approximately 50 of that at 8 mw.sq. cm., while over this same range of intensities the uptake of carbon dioxide and nitrate remained constant. At light intensities below the saturation level for photosynthesis, nitrate appeared to compete with carbon dioxide for light energy. In short-term experiments the assimilatory CO2NO3 ratio at 0.50 mw.sq. cm. was one-third that observed at 8 mw.sq. cm., indicating that under these conditions nitrate uptake had priority over carbon dioxide assimilation. Author