Concentration of Carbon Dioxide inside Leaves

Abstract

DURING photosynthesis, the concentration of carbon dioxide in the intercellular spaces of a leaf, [CO₂]_int, determines the flux of carbon dioxide into the leaf if stomatal apertures and external concentration remain constant. Previously [CO₂]_int has not been estimated during photosynthesis but has been equated with the external concentration at which photosynthesis ceased. Our object was to estimate [CO₂]_int during active photosynthesis. Gabrielsen¹ found the minimum to which many plants would reduce the concentration of carbon dioxide in a closed system to be 100 p.p.m. by volume and concluded that [CO₂]_int was also 100 p.p.m. Heath² arrived at the same conclusion. He drew air through leaves with porometers, varied the flow-rate and carbon dioxide concentration in the incoming air, and measured the carbon dioxide in the air leaving the leaf. Regardless of the rate of flow of air or concentration of carbon dioxide, the exhausted air contained about 100 p.p.m. carbon dioxide. Similar results were obtained by passing air over leaves at slow flow-rates.