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The authors thank to the infrastructure of the CzechPolar for providing facilities necessary for sample collection, their storage and handling before microscopic study. Help of Gema Gonzales with microscopic analyses is acknowledged. Daniel Nývlt work of this paper has been supported by the project "Employment of Best Young Scientists for International Cooperation Empowerment" (CZ.1.07/2.3.00/30.0037) co-financed from European Social Fund and the state budget of the Czech Republic. The authors also acknowledge the help provided by Jiří Komárek (Třeboň, CZ) in determination of some cyanobacteria.

In this study, we investigated the effects of salt stress (2 mM NaCl) on excitation energy transfer from light harvesting complexes to photosystem II (PS II) in two Antarctic algal species: Klebsormidium sp. and Zygnema sp. Short-term salt stress led to a significant changes in the shape of chlorophyll fluorescence transient (OJIP). Analyses of the polyphasic fluorescence transients (OJIP) showed that the fluorescence yield at the phases J, I and P declined considerably with the time of exposition to salt stress. In both experimental species, OJIP transients reached lowest values of chlorophyll fluorescence signal after 30/60 min. of NaCl exposition. Then, OJIP shape and chlorophyll fluorescence showed species-specific recovery and rised towards original values (about 2/3 of untreated control). Analyses of chlorophyll fluorescence parameters derived from OJIPs showed that salt stress led to a decrease in the maximal efficiency of PS II photochemistry (F V /F M ) in Zygnema sp. but not Klebsormidium sp. The results indicated that the probability of excitation energy transfer before and beyond Q A , and the yield of electron transport beyond Q A is limited by salt-induced stress in Zygnema sp. In addition, salt stress resulted in a decrease in the photosynthetic electron transport per PS II reaction center, but both increase and decrease in the trapping per PS II reaction center was found. Performace index (PI abs ) was affected negatively in Zygnema sp. but possitively Klebsormidium sp. indicating that the latter species was more resistant to salt stress than Zygnema sp.

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In this study, we investigated the relationship between relative water content (RWC) of N. commune colonies recorded during gradual dehydration and (i) normalized difference vegetation index (NDVI), (ii) photochemical reflectance index (PRI), and (iii) primary photochemical processes of photosynthesis, effective quantum yield of photosynthetic processes ( PSII ) in photosystem II particular. PRI increased from -0.05 to 0.02 with RWC decrease from 100% (full hydration) to 0% (dry state). NDVI showed somewhat curvilinear relationship with desiccation with minimum value of 0.25 found at 10% RWC. Negative effect of suprasaturation of N. commune colony with water on effective quantum yield ( PSII ) was found at RWC range 80-100%. At the RWC range,  PSII reached only 50 % of maximum found at RWC of 30%. In general, desiccation-response curve of showed polyphasic character with three main phases (phase I -constant  PSII values, phase II -an increase with desiccation at RWC 80-30%, and phase IIIsigmoidal decrease with desiccation at RWC 0-30%). Non-photochemical quenching (qN) of absorbed light energy showed triphasic dependence on RWC as well. qN showed constant values in the phase I, an increase (phase II), and constant values at severe dehydration (phase III).