DIFFERENCES IN PHOTOSYNTHETIC PERFORMANCE BETWEEN CYANOBACTERIAL AND GREEN ALGAL COMPONENTS OF LICHEN PHOTOSYMBIODEMES MEASURED IN THE FIELD

Photosymbiodemes are lichens which contain a single mycobiont but have cyanobacteria and green algae as primary photobionts in different par ts of the thallus. Members of a photosymbiodeme can be found as separa te, free-living lichen species. The photosynthesis of the components o f two Pseudocyphellaria photosymbiodemes were studied in the natural f orest environment in New Zealand. It was found that the green algal co mponent had a large photosynthetic advantage when thallus water conten ts were low and the thalli were in equilibrium with atmospheric humidi ty. The cyanobacterial components were at an advantage when thallus wa ter contents were very high. The environment in which photosymbiodemes are found, forest margins in high humidity areas, seems to provide th e correct combination of thallus water contents so that neither compon ent has a major advantage. The photosymbiodemes appear to be models, p reserved by the special habitat and showing a possible early stage in the evolution before the definite separation of ecologically specializ ed green algal and cyanobacterial species.