Oecologia

, Volume 98, Issue 2, pp 212–220

In situ photosynthetic differentiation of the green algal and the cyanobacterial photobiont in the crustose lichen Placopsis contortuplicata

  • B. Schroeter
Original Paper

DOI: 10.1007/BF00341474

Cite this article as:
Schroeter, B. Oecologia (1994) 98: 212. doi:10.1007/BF00341474

Abstract

In situ photosynthetic activity in the green algal and the cyanobacterial photobionts of Placopsis contortuplicata was monitored within the same thallus using chlorophyll a fluorescence methods. It proved possible to show that the response to hydration of the green algal and the cyanobacterial photobionts is different within the same thallus. Measurements of the photochemical efficiency of PS II, Fv/Fm, reveal that in the dry lichen thallus photosynthetic activity could be induced in the green algal photobiont by water vapour uptake, in the cyanobacterial photobiont only if it was hydrated with liquid water. However, rates of apparent electron flow through PS II as well as rates of CO2 gas exchange were suboptimal after hydration with water vapour alone and maximum rates could only be observed when the thallus was saturated with liquid water. The differences in the waterrelated photosynthetic performance and different light response curves of apparent electron transport rate through PS II indicate that the two photobionts act highly independently of each other. It was shown that the cyanobacteria from the cephalodia in P. contortuplicata act as photobiont. The rate of electron flow through PS II was found to be saturated at 1500 μmol photon m−2 s−1, despite a considerable increase of non-photochemical quenching in the green algal photobiont which is lacking in the cyanobacterial photobiont. No evidence of photoinhibition could be found in either photobiont. Pronounced competition between the green algal and the cyanobacterial thallus can be observed in the natural habitat, indicating that the symbiosis in P. contortuplicata should be regarded as a very variable adaptation to the extreme environmental conditions in the maritime Antarctic.

Key words

AntarcticaChlorophyll a fluorescenceCyanobacterial photobiontGreen algal photobiont Lichen

Abbreviations

DR

dark respiration

ETR

apparent rate of electron flow of PS II (=ΔF/Fm′×PFD)

ΔF

difference in yield of fluorescence and maximal Fm′ and steady state Fs under ambient light

Fo

minimum level of fluorescence yield in dark-adapted state

Fo′

minimum level of fluorescence yield after transient darkening and far-red illumination

Fm

maximum level of dark-adapted fluorescence yield

Fm′

maximum yield of fluorescence under ambient light

Fs

yield of fluorescence at steady state

Fv

difference in minimum fluorescence and maximum fluorescence in dark-adapted state

NP

net photosynthesis

NPQ

coefficient for non-photochemical quenching

PAR

photosynthetically active radiation (400–700 nm)

PFD

photon flux density in PAR

PS II

photosystem II

qN

coefficient for non-photochemical quenching

qP

coefficient for photochemical quenching

Copyright information

© Springer Verlag 1994

Authors and Affiliations

  • B. Schroeter
    • 1
  1. 1.Botanisches InstitutUniversität KielRielGermany