Carbon Dioxide Exchange in Lichens : RELATIONSHIP BETWEEN NET PHOTOSYNTHETIC RATE AND CO(2) CONCENTRATION.

The relationship between net photosynthesis and CO(2) concentration was investigated for four species of lichen using an infrared gas analyzer operating in a closed loop system. All species showed a linear relationship at low CO(2) levels (100 microliters per liter) with CO(2) saturation levels being in excess of 400 microliters per liter. Detailed studies of Sticta latifrons showed a strong influence of thallus water content which resulted in the net photosynthetic response at high water contents still being nearly linear at 1000 microliters per liter CO(2). Very low CO(2) compensation values (5 microliters per liter) were obtained under some conditions but the value varied between thalli and with thallus water content. The results differ from previous studies which reported low CO(2) saturation levels (200 microliters per liter) and no apparent effect of water content. It is suggested that some of these differences may result from the use of a discrete sampling injection infrared gas analyzer system in the earlier studies and an assessment is made of the influence of nonsaturating CO(2) levels, lack of cuvette ventilation, and data presentation for this technique.