Dehydration-induced responses of primary photosynthetic processes and spectral reflectance indices in Antarctic Nostoc commune

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 (FPSII) 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 (FPSII) was found at RWC range 80-100%. At the RWC range, FPSII 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 FPSII values, phase II – an increase with desiccation at RWC 80-30%, and phase III – sigmoidal 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)