Tga. Green et al., DIFFERENCES IN PHOTOSYNTHETIC PERFORMANCE BETWEEN CYANOBACTERIAL AND GREEN ALGAL COMPONENTS OF LICHEN PHOTOSYMBIODEMES MEASURED IN THE FIELD, New phytologist, 125(4), 1993, pp. 723-731
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.