Carbon Dioxide Exchange in Lichens

Abstract

The relationship between net photosynthesis and CO2 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 CO2 levels (100 microliters per liter) with CO2 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 CO2. Very low CO2 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 CO2 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 CO2 levels, lack of cuvette ventilation, and data presentation for this technique.Studies of photosynthesis in lichens have been made by a variety of techniques including the measurement of "C uptake (6-8), changes in gas volume both by manometry (17), a cartesian diver system (16), and 02 concentration with an 02 electrode (2).Most of these methods have the disadvantage that the lichens are subjected to highly unnatural conditions, such as immersion in buffer solutions and exposure to CO2 and 02 concentrations, which differ markedly from ambient levels. The results of '4C uptake experiments also present interpretation difficulties as the gross photosynthetic rate of lichens is substantially greater than the net photosynthetic rate. More recently, most studies of the rates of CO2 exchange have used an infrared gas analyzer system, sometimes with an adaptation of a flow-through cell (9) to allow simultaneous determination of CO2 exchange and water content.However, the low resistance to water loss common to all lichens (3), coupled with the close interdependence of gas exchange rates and thallus water content, led to the use of low flow rates and, in some instances, this resulted in substantial systematic errors (see Larson and Kershaw (13) for discussion).Several authors (1, 4, 13) have described independently a method of adapting IRGA2 for use as discrete sample analyzers whereby small volumes of gas samples (1-3 ml) can be injected, via a carrier gas, directly into the analysis tube of an IRGA. The 'This investigation was supported by equipment grants to TGAG and a University Grants Committee postgraduate studentship to WPS from the University Grants Committee. 2Abbreviation: IRGA, infrared gas analyzer; NPR, net photosynthetic rate. maximum deflection of the IRGA is found to be proportional to the quantity of CO2 injected, thus, for constant injection volume, it is proportional to the CO2 concentration of the injected gas.Recently, thi...

An assessment of the relationship between chlorophyll a fluorescence and CO 2 gas exchange from field measurements on a moss and lichen

“…7B). These results are surprising since, bearing in mind the results from higher plants (Harbinson et al 1990;, a linear relationship might well be expected for lichens because they often show little evidence of photorespiration, can have very low CO 2 compensation values and can have CO 2 concentrating mechanisms (Snelgar and Green 1980;Green and Snelgar 1981;Badger et al 1993;Palmqvist et al 1994).…”

Physiology of Photosynthetic Organisms Within Biological Soil Crusts: Their Adaptation, Flexibility, and Plasticity

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