Photosynthetic characteristics of lichens of genus Umbilicaria from SW
Greenland (Nuuk area) in reponse to thallus dehydration
Barták, M.1, Hansen, E.S.2, Hazdrová, J.1 , Skácelová, K. 1, Trnková, K.1, Prošek, P.3
1 Department of Experimental Biology, Laboratory of Photosynthetic Processes, Faculty of Science,
Masaryk University, Kamenice 5, Brno, Czech Republic
2 Natural History Museum of Denmark, Gothersgade 130, 1123 København, Denmark
3Department of Geography, Faculty of Science, Masaryk University, Kotlářská 2, Brno, Czech Republic
Acknowledgements
The authors are grateful to the
CzechPolar infrastructure for providing laboratory facilities
Introduction
It is well etablished that lichens, typical poikilohydric organisms, are capable to perform
photosynthesis under a wide range of water loss from their thalli. However, species-specific
response of their photosynthesis, particular processes in photosystem II (PS II) of symbiotic
algae, to dehydration is not fully understood. In our study, we used three different approaches to
assess photosynthetic process in Antarctic lichens Umbilicaria arctica  and Umbilicaria hyperborea
to evaluate desiccation-induced changes to structure and function of photosynthetic apparatus.
(1) Evaluation of effective quantum yield of photosynthetic processes in PS II in response to
decreasing water potential
(2) Assesment of spectral reflectance indices PRI, NDVI
(3) Analysis of fast induction kinetics of chlorophyll fluorescence (OJIP)
U. hyperborea
A
Spectral indices NDVI, PRI
During gradual dehydration of lichen thalli, two commonly used indices, NDVI and PRI, were measured
at each WP. Normalized difference vegetation index (NDVI) was measured by PlantPen NDVI 300 (Photon
System Instruments, Czech Republic), while photosyntetic reflectance index (PRI) was measured by
PlantPen PRI 200 (Photon System Instruments, Czech Republic). Both instruments use particular
spectral reflectances (at below-specified wavelengths) for calculation of the indices using the
below equations.
NDVI = (R740 – R660)/(R740 + R660)
PRI = (R570-R531)/(R570+R531)
Material and Methods
Sample collection
Thalli of foliose epilithic lichens Umbilicaria arctica and U.hyperborea were collected
on the rocks at several locations in the neighbourhood of Nuuk, and transported to
the Czech Republic where kept in dry state in dark at 5 oC before experiments. After
48 h rehydration, simultaneous measurements of
Photosynthetic parameters
Effective quantum yield
Lichen thalli were let to follow natural desiccation. The water potential (WP) was measured
simultaneously with several photosynthetic characteristics (see below). During gradual dehydration,
changes in WP were measured each 30 min, by a dew point water potential meter (WP4T; Decagon
Devices, USA), together with effective quantum yield of photosynthetic processes in PSII (a
fluorometer, PAM 2000, Germany) using saturation pulse method.
Fast fluorescence kinetics (OJIP)
were measured by a FluorPen FP 100 (Photon System Instruments, Czech Republic). This method
measures and records a polyphasic rise of fluorescence during the first 3 s after (of sample
exposition to continuous light. On the curve resulting from such measurement (OJIP), four typical
chlorophyll fluorescence levels can be distinguished. They represent points O, J, I and P, numeric
value of which reflects processes of light absorption and efficiency of energy flow through
photosystem II and plastoquinone pool
Conclusions
•In our study, U.arctica showed higher YieldPSII and less sensitivity to dehydration than
U.hyperborea in the WP range of -5 to -20 MPa.
•
•PRI in U.arctica and U.hyperborea exhibited curvi- linear increase with dehydration. The relation
of PRI to WP was,however, species-specific.
•
•NDVI, a vigor indicator, decreased with dehydration in both species, however, due to generally
black color of U. hyperborea, the NDVI values were lower throughout all range of dehydrationin the
species.
•
•OJIPs recorded in fully hydrated thalli showed typical polyphasic curves with peak chlorophyll
fluorescence level "P„ found at 150-300 ms followed by a dip "D„. With more pronounced dehydration,
OJIPs exhibited a decrease in chlorophyll fluorescence signal and photosynthetic parameters derived
from OJIPS.
•
•The results presented in this study indicated a high degreeof tolerance of the two Umbilicaria
species to partial dehydration stress. However, interspecific differences in photosynthetic
parameters were apparent in response to thalli dehydration.
Fig. 4 Viability od Trebouxia cells (microscopic study)
img08 razitko_01_scan SV103968 SV103978 Sample3_073925 greenland_map znak200_mu-1
Nuuk
Umbilicaria hyperborea
Umbilicaria arctica
NDVI spectrometer
PRI spectrometer
OJIP fluorometer
Results
.
Umbilicaria hyperborea
Umbilicaria arctica
NDVI
in response to dehydration
Umbilicaria hyperborea
Umbilicaria arctica
in response
to dehydration
Effective
quantum
yield
D
P
I
J
O
Control
Control
After photoinhibition (60 min, 2000 micromol m-2 s-1)
After photoinhibition (60 min, 3000 micromol m-2 s-1)
After 60 min recovery
After 60 min recovery
Strong photoinhibition
OJIPs
Extremely strong photoinhibition
OJIPs