Responses of primary photosynthetic processes to repetitive rehydration differ in two representatives of Svalbard moss flora

Global warming in polar regions brings a risk of more frequent and long-lasting dry periods due to warmer and windier climate during polar summers. Mosses are well adapted to desiccation-rehydration events and they have evolved remarkable constitutive and inducible mechanisms of desiccation tolerance. In our study, Sanionia uncinata and Racomitrium lanuginosum were collected in Svalbard and used for laboratory-based repetitive 32-h-lasting rehydration cycles with continuous monitoring of restoration of their primary photosynthetic processes measured by chlorophyll fluorescence parameters. Immediately after the addition of water to dry thalli, potential quantum yield of PSII (FV/FM) was about 50% of its maximum reached after 32 h of rehydration. In a course of time of rehydration, both species showed an increase in FV/FM and effective quantum yield (FPSII) following a S-curve relationship. Non-photochemical quenching did not show clear trend with the rehydration time, It differed between the two species and showed both decrease and increase with the time of rehydration. Relative chlorophyll fluorescence decrease (RFd), which is considered a vitality indicator, increase with the time of rehydration showing similar trends in the first and the third cycle of rehydration. The results indicate that both Sanionia uncinata and Racomitrium lanuginosum are resistant to desiccation since FV/FM and FPSII recovered fully after 32 h of rehydration and there we only minor differences in the two parameters between the first and third rehydration cycle

Biometrical analysis and thallus morphology characteristics of Placopsis antarctica from King George Island, Antarctica ( Short Communication )

Placopsis antarctica is an ornithocoprophilous lichen that has been for a long time confused with P. contortuplicata I. M. Lamb. In our study, we focused on morphological characteristics of P. antarctica thalli. We report biometrical data on dominant morphological structures of P. antarctica thallus: cephalodia, marginal lobes, sorediate pits and soralia. Thalli of P. antarctica were collected at the King George Island, Antarctica and analyzed in a laboratory using a digital microscopy approach. Central cephalodium was found rather elliptic then round-shaped. Mean length/width was found 2.424/1.720 mm. Marginal lobes were found wider at the apex (1.415 mm) than basal part (0.495 mm). Side cephalodia were smaller, their mean length/width was found 1.034/0.610 mm

The effect of shock freezing on physiological properties and consequent growth of Antarctic filamentous (Stigeoclonium sp.) and coccal alga (Diplosphaera chodatii) on agar plates

In this study, we investigated the effects of shock freezing on physiological properties and consequent growth of in the Antarctic alga Stigeoclonium sp. and comparative coccal alga Diplosphaera chodatii on agar plates. Culture of algae grown in liquid medium were used to study subzero temperatures on the species resistance to shock freezing. Then, microalgae were frozen in liquid nitrogen and inoculated on BBM agar after thawing. Physiological status of algae was evaluated by chlorophyll fluorescence parameters during 28 days. The results showed that interspecific differences existed in their tolerance to shock freezing, as well as their consequent growth rate on agars. Direct effects of freezing in liquid nitrogen was demonstrated in chlorophyll fluorescence parameters recorded immediately after thawing the samples (in liquid medium). In spite of the fact that majority of cells was destroyed by shock freezing, the potential of photochemical processes in PS II (FV/FM) remained constant in D. chodatii. It may indicate high resistance of the species to freezing/thawing cycles and a capability of the surviving cells, core chlorophylls in PS II respectively, to perform photosynthetic processes related to PS II. Contrastingly, Stigeoclonium sp. showed a shock freezing-dependent decrease in FV/FM. When shock-frozen, thawed and inoculated on agar plates, the culture of D. chodatii, and Stigeoclonium sp. showed cultivation time-dependent increase in chlorophyll fluorescence parameters (FV/FM, FS)

The effect of upper cortex absence on spectral reflectance indices in Antarctic lichens during thallus dehydration

In maritime Antarctica, lichens and mosses represent dominant autotrophs forming community structure of vegetation oases. In our study, we selected 4 most common lichen species (Xanthoria elegans, Rhizoplaca melanophthalma, Leptogium puberulum, Physconia muscigena) and monospecific colony of Nostoc commune typical for James Ross Island (Antarctica) for detailed physiological experiments. We investigated their spectral characteristics in response to hydration status of their thalli. In samples desiccating from fully wet (RWC, relative water content of 100%) to dry state (RWC = 0), photochemical reflectance index (PRI), and normalized difference vegetation index (NDVI) were evaluated for control thalli and those with removed upper cortex. In this way, the effect of presence/absence of the upper cortex on PRI, NDVI was studied. PRI showed either no change or species-specific an increase/decrease with dehydration. Removal of the upper cortex caused both PRI decrease (N. commune, P. muscigena) and increase (R. melanophthalma, L. puberulum). Removal of the upper cortex led to increase in NDVI in all species, typically within the RWC range of 20-100%. Species-specific differences of hydration-response curves of PRI and NDVI are discussed as well as the role of the absence of the upper cortex in the evaluation of spectral characteristics in desiccating lichens

Light regimen-induced variability of photosynthetic pigments and UV-B absorbing compounds in Luzula sylvatica from Arcto-Alpine tundra

The aim of this study was to evaluate the effects of different in situ light regimen on ecophysiological parameters of Luzula sylvatica leaves. Plants of L. sylvatica grown under natural sunny and shade conditions in arcto-alpine tundra were analyzed with respect to their leaf anatomy, content of photosynthetic pigments, UV absorbing compounds and phenanthrenoid compounds. Relationship between chlorophyll concentrations (Chla+b) and SPAD values was determined for sun and shade leaves measured repeatedly within summer and autumn seasons 2019 and 2020. Pooled data showed curvilinear Chla+b to SPAD relationship with the highest Chla+b and SPAD values found for shade leaves. Sun leaves had higher UV-B absorbing compounds contents than shade ones. The HPLC-DAD analysis revealed significant amount of soluble flavonoids in Luzula sylvatica leaves, amongst others the flavone-luteolin and its derivatives (e.g. tentatively identified luteolin-methyl-glucoside and luteolin-glucoside). The accumulation of luteolin based compounds in sun acclimated leaves is also plausible explanation for the higher antioxidant activity determined in sun leaf extraxts. Such response of flavonoid metabolism may help L.S. to cope with excessive-light stress through UV-attenuation mechanism and ROS scavanging. Additionally, phenanthrenoid compounds contents in L. sylvatica leaves were determined. Altogether, 9 phenanthrenoid compounds were identified by HPLC-HRMS. Their content was markedly different (up to the factor of 5) between sun and shade leaves of L.sylvatica

Inhibition of Primary Photosynthesis in Desiccating Antarctic Lichens Differing in Their Photobionts, Thallus Morphology, and Spectral Properties

Five macrolichens of different thallus morphology from Antarctica (King George Island) were used for this ecophysiological study. The effect of thallus desiccation on primary photosynthetic processes was examined. We investigated the lichens' responses to the relative water content (RWC) in their thalli during the transition from a wet (RWC of 100%) to a dry state (RWC of 0%). The slow Kautsky kinetics of chlorophyll fluorescence (ChlF) that was recorded during controlled dehydration (RWC decreased from 100 to 0%) and supplemented with a quenching analysis revealed a polyphasic species-specific response of variable fluorescence. The changes in ChlF at a steady state (Fs), potential and effective quantum yields of photosystem II (F-V/F-M, phi(PSII)), and nonphotochemical quenching (NPQ) reflected a desiccation-induced inhibition of the photosynthetic processes. The dehydration-dependent fall in F-V/F-M and phi(PSII) was species-specific, starting at an RWC range of 22-32%. The critical RWC for phi(PSII) was below 5%. The changes indicated the involvement of protective mechanisms in the chloroplastic apparatus of lichen photobionts at RWCs of below 20%. In both the wet and dry states, the spectral reflectance curves (SRC) (wavelength 400-800 nm) and indices (NDVI, PRI) of the studied lichen species were measured. Black Himantormia lugubris showed no difference in the SRCs between wet and dry state. Other lichens showed a higher reflectance in the dry state compared to the wet state. The lichen morphology and anatomy data, together with the ChlF and spectral reflectance data, are discussed in relation to its potential for ecophysiological studies in Antarctic lichens