Oscillatory Transpiration and CO₂ Exchange of Citrus Leaves at the CO₂ Compensation Concentration

CO 2 and H 2 O vapor exchange were measured by enclosing citrus ( Citrus sinensis cv. Sour Orange) leaves in a temperature controlled transparent leaf chamber. Introduction of dry air into the closed circuit gas flow caused cyclic oscillation in CO 2 and H 2 O vapor exchange. It is suggested that oscillation in the CO 2 exchange at the CO 2 compensation concentration is due to oscillation in non‐stomatal resistance to CO 2 . Three types of oscillation were observed: 3–6 min (peak to peak) in young leaves, 30 min in mature leaves, and 160 min in old leaves.