Lichens are difficult to classify. They are an interaction between a fungus and a photosynthetic species, usually green or blue green algae. The species form a symbiosis, but there is a debate as to what the association between the two species really is. To answer this question, researchers designed a series of experiments. They took advantage of the photosynthetic abilities of an algae to examine the role of association with fungi in the production of sugar, a product of photosynthesis. The carbon in the sugar molecules comes from carbon dioxide (CO2) in the air. Researchers exposed the algae to CO2 molecules containing radioactive carbon. The following experiments were done and the data is graphed (note: all graphs use the same scale).
Algae were grown in culture in the lab and exposed to radioactive CO2. The growth rates and production of sugar containing radioactive carbon are shown in the graphs below.
Algae were grown in the presence of fungi (therefore, this is lichen grown in the laboratory). The lichen was exposed to radioactive CO2. The growth rate of the algae species and the production of sugar containing radioactive carbon are shown in the graphs below.
Lichen were grown under dehydration conditions while exposed to radioactive CO2. The growth rate of the algae and the production of sugar containing radioactive carbon are shown in the graphs below.
|A||There is reduced photosynthesis in the algae.|
|B||There is reduced photosynthesis in the fungus.|
|C||The fungi have been killed.|
|D||There is a decomposition of the algae by the fungus.|
Since there is less sugar production, but not less growth of the algae, it appears that dehydration causes photosynthesis to decrease.