Lichen photosynthesis in relation to CO₂ concentration

Photosynthetic CO₂ dependencies were measured for six lichen species, representing a variety of morphologies and collected from widely different habitats. All curves exhibited a linear increase in photosynthesis with increasing CO₂ concentrations at the lower range of CO₂ values, but little photosynthetic variation with increasing CO₂ concentrations at the upper range of CO₂ values. Half maximal CO₂ concentration estimates varied from 147-440 μl CO₂·l¹, but had broadly overlapping confidence intervals. We conclude that lichen CO₂ dependencies are basically similar to those reported for higher plants and discuss the reasons why widely varying results have previously been published.