Article

Cold resistance and metabolic activity of lichens below 0°C

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Abstract

Laboratory measurements show that lichens are extremely tolerant of freezing stress and of low-temperature exposure. Metabolic activity recovered quickly after severe and extended cold treatment. Experimental results demonstrate also that CO2 exchange is already active at around −20°C. The psychrophilic character of polar lichen species is demonstrated by optimum temperatures for net photosynthesis between 0 and 15°C. In situ measurements show that lichens begin photosynthesizing below 0°C if the dry thalli receive fresh snow. The lowest temperature measured in active lichens was −17°C at a continental Antarctic site. The fine structure and the hydration state of photobiont and mycobiont cells were studied by low-temperature scanning electron microscopy (LTSEM) of frozen hydrated specimens. Water potentials of the frozen system are in the range of or even higher than those allowing dry lichens to start photosynthesis by water vapor uptake at +10°C. The great success of lichens in polar and high alpine regions gives evidence of their physiological adaptation to low temperatures. In general lichens are able to persist through glacial periods, but extended snow cover and glaciation are limiting factors.

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... When the environmental temperature is below freezing, lichens usually exist in a dehydrated state and are thus physiologically inactive (11). However, lichens can survive in a fully hydrated, physiologically active state at temperatures below -20°C (18), due to the presence of secondary substances, such as trehalose or antifreeze proteins, which prevent freezing (35). ...
... Although freeze-thaw cycles occur in the environment, especially at high altitudes and latitudes, the algae remain in a liquid, supercooled state. Contrastingly, lichen thalli are able to cope with a wide range of temperature and moisture conditions; furthermore they are also capable of withstanding numerous hydration/dehydration cycles, sometimes at temperatures well above zero (18). ...
... Contrary to snow algae, the lichens must cope with much lower temperatures and a much wider range of temperatures with rapid diurnal and seasonal changes, especially in exposed areas. Decreasing the supercooling point in lichen phycobionts will provide protection against freezing and allow photosynthesis to continue even at sub-zero temperatures (18). On the other hand, the supercooling temperatures of intact lichen thalli are high due to ice nucleation activity of mycobionts, providing a method of increasing uptake of atmospheric water vapour (2). ...
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Differences in the level of cold acclimation and cryoprotection estimated as ice nucleation activity in snow algae (Chlamydomonas cf. nivalis and Chloromonas nivalis), lichen symbiotic algae (Trebouxia asymmetrica, Trebouxia erici and Trebouxia glomerata), and a mesophilic strain (Chlamydomonas reinhardti) were evaluated. Ice nucleation activity was measured using the freezing droplet method. Measurements were performed using suspensions of cells of A 750 (absorbance at 750 nm) ~ 1, 0.1, 0.01 and 0.001 dilutions for each strain. The algae had lower ice nucleation activity, with the exception of Chloromonas nivalis contaminated by bacteria. The supercooling points of the snow algae were higher than those of lichen photobionts. The supercooling points of both, mesophilic and snow Chlamydomonas strains were similar. The lower freezing temperatures of the lichen algae may reflect either the more extreme and more variable environmental conditions of the original localities or the different cellular structure of the strains examined.
... When examined in more detail, samples without lichens had almost the same or lower enzymatic activity, as an indication of the low biological activity uniformly distributed on the stone surfaces (Table 1) [27]. On the other hand, enzymatic activity values ranging from 20.55 to 1134.90 µg fluorescein/g in the samples with lichens referred to the variety of physiological states of the lichens, which could have been related with the type of partners in this symbiotic living form, their adaptation capacity to changing environmental conditions [28], the type of stone [28,29] and their locations on these substrates as well ( Table 2). ...
... When examined in more detail, samples without lichens had almost the same or lower enzymatic activity, as an indication of the low biological activity uniformly distributed on the stone surfaces (Table 1) [27]. On the other hand, enzymatic activity values ranging from 20.55 to 1134.90 µg fluorescein/g in the samples with lichens referred to the variety of physiological states of the lichens, which could have been related with the type of partners in this symbiotic living form, their adaptation capacity to changing environmental conditions [28], the type of stone [28,29] and their locations on these substrates as well ( Table 2). ...
Article
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Stones of historical monuments exposed to the open air deteriorate over the course of time depending on physical, chemical, and biological factors acting in co-association. Among the biological factors, microorganisms play a key role in the deterioration process of stones. Detecting the level of microbial activity on stones is an essential step in diagnostic and monitoring studies of stone biodeterioration, and aids in controlling the performance of treatments applied to the stones. Therefore, this study aimed to develop a practical and rapid method for the determination of microbial activity on historical stones and use this method on the Mount Nemrut monuments (MNMs) (Adiyaman, Turkey). For that purpose, the fluorescein diacetate (FDA) hydrolysis method, frequently employed for soil environments, was adapted for the estimation and assessment of total microbial activity to understand whether microorganisms posed a potential risk for the biodeterioration of the limestones and sandstones of the MNMs. The traditional plate count method was also applied simultaneously to the same stone samples to compare and assist in the interpretation of the results of the FDA hydrolysis method, which relies on the quantitative determination of bacterial and fungal colonies in nutrient agar and malt extract agar medium, respectively. The results of the FDA hydrolysis and plate count methods showed consistency. The total microbial activity determined by the FDA hydrolysis method was low for both types of stone samples. In addition, the plate count method showed low bacterial and fungal counts on all of the samples. This revealed that microbial activity did not play an important role in the stone deterioration process on the MNMs, although different lichen species were frequently observed on both the sandstones and the limestones. Hence, further investigation must be undertaken for determination of their long-term behavior and effects on the stones of the MNMs. On the other hand, the results of the FDA hydrolysis and plate count methods showed correlation. Lower bacterial counts were observed when lower enzymatic activity was observed in the stone samples, and likewise, higher bacterial counts were observed when higher enzymatic activity was observed. Consequently, the application of the FDA hydrolysis method was determined to be reliable for the estimation of total microbial activity on historical stones. The method had obvious advantages in terms of its rapid measurement rate and sensitivity, even on small samples.
... This indicates that Psora becomes inactive when the soil surface freezes, but at the same time is able of exploiting melted water from ice early in the morning after sunrise. This suggests an interesting mixed adaptation pattern for crustose lichens in some semi-arid areas that are not exposed very often to extreme cold situations as is the case of this study (see Table S2 for detailed information regarding microclimatic lichen surface temperatures during the winter; see also Kappen 1988;Kappen et al. 1996). Although this mixed pattern mentioned deserves detailed comparative analyses, it seems to be different to previous studies involving cold-adapted lichens, that can show clearly lower temperature values during activity (Schroeter et al. 1994) and optimal physiological status between 0 °C and − 3 °C (Marečková et al. 2019;Raggio et al. 2016;Schroeter et al. 2011). ...
... This indicates that Psora becomes inactive when the soil surface freezes, but at the same time is able of exploiting melted water from ice early in the morning after sunrise. This suggests an interesting mixed adaptation pattern for crustose lichens in some semi-arid areas that are not exposed very often to extreme cold situations as is the case of this study (see Table S2 for detailed information regarding microclimatic lichen surface temperatures during the winter; see also Kappen 1988;Kappen et al. 1996). Although this mixed pattern mentioned deserves detailed comparative analyses, it seems to be different to previous studies involving cold-adapted lichens, that can show clearly lower temperature values during activity (Schroeter et al. 1994) and optimal physiological status between 0 °C and − 3 °C (Marečková et al. 2019;Raggio et al. 2016;Schroeter et al. 2011). ...
Article
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Purpose Biocrust communities, which are important regulators of multiple ecosystem functions in drylands, are highly sensitive to climate change. There is growing evidence of the negative impacts of warming on the performance of biocrust constituents like lichens in the field. Here, we aim to understand the physiological basis behind this pattern. Methods Using a unique manipulative climate change experiment, we monitored every 30 minutes and for 9 months the chlorophyll a fluorescence and microclimatic conditions (lichen surface temperature, relative moisture and photosynthetically active radiation) of Psora decipiens , a key biocrust constituent in drylands worldwide. This long-term monitoring resulted in 11,847 records at the thallus-level, which allowed us to evaluate the impacts of ~2.3 °C simulated warming treatment on the physiology of Psora at an unprecedented level of detail. Results Simulated warming and the associated decrease in relative moisture promoted by this treatment negatively impacted the physiology of Psora , especially during the diurnal period of the spring, when conditions are warmer and drier. These impacts were driven by a mechanism based on the reduction of the length of the periods allowing net photosynthesis, and by declines in Yield and Fv/Fm under simulated warming. Conclusion Our study reveals the physiological basis explaining observed negative impacts of ongoing global warming on biocrust-forming lichens in the field. The functional response observed could limit the growth and cover of biocrust-forming lichens in drylands in the long-term, negatively impacting in key soil attributes such as biogeochemical cycles, water balance, biological activity and ability of controlling erosion.
... Growth and metabolic processes in lichens such as photosynthesis largely depend on climate and moisture conditions (Aubert et al., 2007;Boddy, 2016;Kappen et al., 1996;Watkinson, 2016). Lichens can survive desiccation periods in a state of dormancy, and can be re-hydrated and activated easily by rain, snowmelt, dew or humidity, with restoration of metabolic activity (Aubert et al., 2007;Honegger, 1993;Kappen et al., 1996). ...
... Growth and metabolic processes in lichens such as photosynthesis largely depend on climate and moisture conditions (Aubert et al., 2007;Boddy, 2016;Kappen et al., 1996;Watkinson, 2016). Lichens can survive desiccation periods in a state of dormancy, and can be re-hydrated and activated easily by rain, snowmelt, dew or humidity, with restoration of metabolic activity (Aubert et al., 2007;Honegger, 1993;Kappen et al., 1996). Growth rates are relatively fast in humid regions and mild temperatures, (e.g., temperate rain forests), whereas they are much slower in dry, continental Arctic, Antarctic and Alpine environments (Armstrong and Bradwell, 2011;Easton, 1994;Sancho et al., 2019;Scotter, 1963;Vasander 1981). ...
Article
Lichens have been widely used as a biomonitoring tool to record the distribution and concentration of airborne radioactivity and pollutants such as metals. There are limitations, however: although pollutants can be preserved in lichen tissues for long periods of time, not all radioactive and inert elements behave similarly. The chemical species of elements at the source, once captured, and the mode of storage within lichens play a role in this biomonitoring tool. Lichens are a symbiotic association of an algal or cyanobacterial partner (photobiont) with a fungal host (mycobiont). Lichens grow independently of the host substrates, including rocks, soils, trees and human-made structures. Lacking a root system, lichen nutrient or contaminant uptake is mostly through direct atmospheric inputs, mainly as wet and dry deposition. As lichens grow in a large variety of environments and are resilient in harsh climates, they are adapted to capture and retain nutrients from airborne sources. The context of this review partially relates to future deployment of small modular reactors (SMRs) and mining in remote areas of Canada. SMRs have been identified as a future source of energy (electricity and heat) for remote off-grid mines, potentially replacing diesel fuel generation facilities. For licensing purposes, SMR deployment and mine development requires capabilities to monitor background contaminants (natural radioactivity and metals) before, during and after deployment, including for decommissioning and removal. Key aspects reviewed herein include: (1) how lichens have been used in the past to monitor radioactivity; (2) radiocontaminants capture and storage in lichens; (3) longevity of radiocontaminant storage in lichen tissues; and (4) limitations of lichens use for monitoring radiocontaminants and selected metals.
... Some cold-adapted species photosynthesis at -20˚C with water vapor obtained from snow. Photosynthetic activity can be high by at 0˚C (Kappen et al., 1996;Kappen et al., 1997). On the other hand, most plants containing cyanobacterial lichens need liquid water for the photosynthesis (Richardson et al., 2002). ...
Article
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A strong species of lichens was sorted out to expose the extreme conditions which will be encountered by interplanetary space, followed our previous work of fungal and moss spores. Caloplaca flavovirescens was the most resistant lichen among 10 kinds (9 species) of the lichens examined against temperature fluctuations in vacuum, UV irradiation and cosmic ion irradiation (examined 3 species). The survival rate decreased about 24% by the thermal cycle treatment under vacuum (<1Pa) for 6 weeks under the condition of temperature fluctuations between −80˚C and 80˚C once every 90 min. The rate after one year is extrapolated to be 4.7% (cultivation method) and 7.1% (fluorescent method) under the supposition of the exponential decrease of survival rate continue for a long period of time. The growth rates did not decrease after the temperature fluctuations between −60˚C and 60˚C with the same periodicity. The survival rate of the lichen was decreased by 5% at 1,413mJ/cm 2 of UV-C (254nm) irradiation. The survival rate of the lichen was decreased by about 20% after 335Gy irradiation of helium beam, and the 10% survival rate (D10) was calculated for 1,640 Gy from the extrapolation of regression equation. This amount will be equivalent to 130-1,300 year irradiation at the outer environment of ISS. The reduction rate of carbon beam seems somewhat larger than that of helium beam. As far as these factors concerned, C. flavovirescens inside the container which prevent UV, will survive for several years at the ISS outer environment.
... Although both species belong to the same family, molecular phylogenetic studies indicate that they are not closely related within the Umbilicariaceae (Miadlikowska et al. 2006Miadlikowska et al. , 2014). The two species have almost identical physiological niche responses to light and temperature (Kappen et al. 1996Kappen et al. , 1997 Hestmark et al. 1997), and very similar population dynamics (Hestmark 1997bHestmark , c, 2000 Sletvold & Hestmark 1999; Ramstad & Hestmark 2000). In contrast to U. spodochroa, L. pustulata reproduces mainly through isidia, that is, packages of fungal hyphae and algae produced as coralloid or tree-like structures on the upper surface of the thallus (Fig. 2). ...
Article
The identity and phylogenetic placement of photobionts associated with two lichen-forming fungi, Umbilicaria spodochroa and Lasallia pustulata were examined. These lichens commonly grow together in high abundance on coastal cliffs in Norway, Sweden and Finland. The mycobiont of U. spodochroa reproduces sexually through ascospores, and must find a suitable algal partner in the environment to re-establish the lichen symbiosis. Lasallia pustulata reproduces mainly vegetatively using symbiotic propagules (isidia) containing both symbiotic partners (photobiont and mycobiont). Based on DNA sequences of the internal transcribed spacer region (ITS) we detected seven haplotypes of the green-algal genus Trebouxia in 19 pairs of adjacent thalli of U. spodochroa and L. pustulata from five coastal localities in Norway. As expected, U. spodochroa associated with a higher diversity of photobionts (seven haplotypes) than the mostly asexually reproducing L. pustulata (four haplotypes). The latter was associated with the same haplotype in 15 of the 19 thalli sampled. Nine of the lichen pairs examined share the same algal haplotype, supporting the hypothesis that the mycobiont of U. spodochroa might associate with the photobiont ‘pirated’ from the abundant isidia produced by L. pustulata that are often scattered on the cliff surfaces. Up to six haplotypes of Trebouxia were found within a single sampling site, indicating a low level of specificity of both mycobionts for their algal partner. Most photobiont strains associated with species of Umbilicaria and Lasallia, including samples from this study, represent phylogenetically closely related taxa of Trebouxia grouped within a small number of main clades (Trebouxia sp., T. simplex/T. jamesii, and T. incrustata+T. gigantea). Three of the photobiont haplotypes were found only in U. spodochroa thalli.
... The first unambiguous indication of microbial SZA came from Antarctic studies of the cryptoendolithic lichens (Lange and Kappen 1972;Kappen and Friedmann 1983;Kappen 1988Kappen , 1993Schroeter et al. 1992;Friedmann et al. 1993;Kappen et al. 1996Kappen et al. , 1998. Lichens are composite organisms consisting of a fungus (the mycobiont) and a photosynthetic partner (the photobiont or phycobiont) growing together in a symbiotic relationship. ...
Article
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Cold adaptation is usually interpreted as ability of microorganisms to grow at temperature around zero or recover from deep freezing. This chapter focuses on a recently discovered physiological phenomenon of microbial growth and metabolism in a frozen environment cooled down to-20 °C and deeper. Still, there are numerous controversies about subzero activity (SZA); therefore, the chapter starts from extensive introduction into the SZA phenomenon beyond the yeasts' taxonomic boundary. Critical review of available techniques for SZA detection resulted in a precautionary note that some reports based on account of frozen soil respiration or methane generation could be considerably overestimated. More reliable measurements of SZA are obtained by using methods based on direct microscopy and uptake of labelled gaseous substrates, e.g. 14CO2. Two types of below-zero habitats are recognized: homogeneous icy environment (polar sea ice, glaciers, snow) where microbial cells can survive in supercooled liquid veins and permanently frozen soils and sediments containing buried organic matter and allowing slow gas exchange through aeration micropores. Fungi including yeasts are the most successful colonizers of the second type of habitats. Solid-state frozen enrichment culture, phylogenetic survey of soils, round-year seasonal community dynamics and specific inhibitors of protein synthesis-all indicate that fungi have a competitive advantage over prokaryotic organisms in frozen soils. None of the known molecular mechanisms of cold adaptation, e.g. membrane structure, heat-and cold-stress proteins, cold-adapted enzymes, could be uniquely attributed to fungi. Instead, the author discusses wide opportunities given to all fungi by bigger cell size and colonization of frozen heterogeneous environments via mycelial or pseudomycelial growth. © Springer-Verlag Berlin Heidelberg 2014. All rights are reserved.
... Similarly, Bjerke et al. (2004) found that in Flavocetraria nivalis, the concentration of usnic acid was highest at the sites with the lowest temperatures. Tundra lichens are typically metabolically active at near-zero or subzero temperatures (Kappen et al., 1996). Thus, Flavocetraria nivalis, a common tundra lichen, is most likely metabolically ...
Article
Lichens, obligate symbiotic associations between a fungus and an alga and/or cyanobacterium, produce an impressive diversity of secondary metabolites. These secondary compounds are derived from three fungal metabolic pathways-acetyl polymalonyl, mevalonic acid, and shikimic acid pathways. Lichen phenols are unique and are produced mainly by the acetyl-polymalonyl pathway and occasionally by the shikimic acid pathway. Lichen phenolic compounds have several potential pharmaceutical applications based on antibiotic, anticancer, antioxidant, and anti-viral properties. In addition, some lichen phenolics serve as "sun screen" effectively regulating the quality and quantity of light available to the algal partner (photobiont). The production and diversity of phenolics in lichens is influenced by various environmental factors such as light, UV radiation, temperature, elevation, geographic and seasonal variation, as well as culture-related conditions. Although phenolics in lichens are produced by a fungal pathway, the photobiont plays a significant role in terms of providing the "raw materials" for assembling the phenolic compounds. Research concerning the positive and negative effects of environmental parameters on the phenolic content of lichens has yielded contradictory results. These environmentally mediated differences may be attributed to the fact lichen phenolics are produced by different pathways regulated by variable gene groups which could potentially yield different responses under the same environmental conditions.
... Lichens are highly resistant to extreme temperatures, a feature that substantially supports the success of these organisms in cold environments such as the ice-free areas of the Antarctic continent and the adjacent islands Lange 1970, 1972;Kappen 1973;Schlensog et al. 2003). While lichens are often highly resistant to temperature extremes in the anabiotic state, photosynthetic activity of polar lichens has been detected at subzero temperatures (Kappen et al. 1996). ...
Article
Lichens as symbiotic associations consisting of a fungus (the mycobiont) and a photosynthetic partner (the photobiont) dominate the terrestrial vegetation of continental Antarctica. The photobiont provides carbon nutrition for the fungus. Therefore, performance and protection of photosystem II is a key factor of lichen survival. Potentials and limitations of photobiont physiology require intense investigation to extend the knowledge on adaptation mechanisms in the lichen symbiosis and to clarify to which extent photobionts benefit from symbiosis. Isolated photobionts and entire lichen thalli have been examined. The contribution of the photobiont concerning adaptation mechanisms to the light regime and temperature conditions was examined by chlorophyll a fluorescence and pigment analysis focusing on the foliose lichen Umbilicaria decussata from North Victoria Land, continental Antarctica. No photoinhibition has been observed in the entire lichen thallus. In the isolated photobionts, photoinhibition was clearly temperature dependent. For the first time, melanin in U. decussata thalli has been proved. Though the isolated photobiont is capable of excess light protection, the results clearly show that photoprotection is significantly increased in the symbiotic state. The closely related photobiont of Pleopsidium chlorophanum, a lichen lacking melanin, showed a higher potential of carotenoid-based excess light tolerance. This fact discriminates the two photobionts of the same Trebouxia clade. Based on the results, it can be concluded that the successful adaptation of lichens to continental Antarctic conditions is in part based on the physiological potential of the photobionts. The findings provide information on the success of symbiotic life in extreme environments.
... Some Antarctic lichen species may survive extremely harsh environmental conditions, desiccation stress and frost [1][2][3]. They perform active photosynthesis below 0 • C [4,5], below ice nucleation of their cellular fluids [6], and can hydrate from gaseous phase to the hydration level sufficient to initiate active photosynthetic activity, e.g. Usnea aurantiaco-atra (Jacq.) ...
Article
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Hydration kinetics, sorption isotherm, and proton free induction decays are measured for Leptogium puberulum Hue thalli hydrated from gaseous phase. Very tightly, tightly and loosely bound water fraction are distinguished. The hydration dependence of mobile NMR signal component is non-linear and fitted well by rational function, which suggest the presence of water soluble solid (presumably carbohydrate) fraction in thallus structures of L. puberulum.
... It is well comparable to the evidence from a wide variety of organisms (mainly lichens) investigated by a chlorophyll fluorescence approach, see e.g. Kappen et al. 1995, Kappen et al. 1996, Barták et al. 2005, Barták et al. 2007 However, differences in Φ PSII courses were found between the studied organisms. Whereas the diurnal courses of Φ PSII were more or less within the same range in biological soil crust, they varied in a lichen. ...
Article
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In polar ecosystems, primary producers have to cope with a very harsh climate that limits the time available for growth and biomass production. In this study, diurnal measurement of photosynthetic processes in biological soil crust and a lichen were carried out in Petuniabukta, Spitsbergen. For field measurements, a method of induced fluorescence of chlorophyll was used. Measurements of photosynthetic activity were taken as repetitive measurements of effective quantum yield of photosystem II (Φ PSII). The short-term field measurements were carried out for 10 days in summer 2014. Φ PSII was recorded each 5 minutes as well as microclimatic data (air temperature, air humidity , photosynthetically active radiation-PAR). The microclimatic parameters were recorded by a datalogger. In general, physiological activity of both biological soil crust and a lichen showed daily courses. Tested lichen was Cladonia rangiferina and the most dominant species in biological soil crust was Nostoc sp. Typically, most of Φ PSII values ranged 0.6 – 0.7 in both model organisms. The results have shown that photosynthetic activity was strongly correlated with all observed abiotic factors in both study objects. Particularly important was the relation found between PAR and Φ PSII in biological soil crust. When the biological soil crust was exposed to high PAR doses of irradiation (about 2300 µmol m-2 s-1) photoinhibition of primary processes of photosynthesis was observed as Φ PSII decrease, while photosynthetic activity of lichen remained at same level. Furthermore, it has been demonstrated increasing that in situ photosynthetic activity increased in both biological soil crust and lichen with a decrease in temperature.
... It can be concluded that the measured impairment of QY (Fv/Fm) after cold UVC-exposure is due to the UVC-exposure itself. Lichens from cold environments as Antarctica are known to have low temperature optima, can take up water directly from snow, are able to prevent ice nucleation in intracellular spaces and thus can retain positive net photosynthesis at subzero temperatures down to −17°C (Kieft & Ahmadjian 1989;Kappen et al. 1996;Kappen 2000;Pannewitz et al. 2002). As the ice and sample temperatures in the present exposure experiment range below that limit, it can be assumed that the PBs are (photosynthatically) inactive during the irradiation period. ...
Article
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Several investigations on lichen photobionts (PBs) after exposure to simulated or real-space parameters consistently reported high viability and recovery of photosynthetic activity. These studies focused on PBs within lichen thalli, mostly exposed in a metabolically inactive state. In contrast, a recent study exposed isolated and metabolically active PBs to the non-terrestrial stressor UVC 254 nm and found strong impairment of photosynthetic activity and photo-protective mechanisms (Meeßen et al. in 2014b). Under space and Mars conditions, UVC is accompanied by other stressors as extreme desiccation and low temperatures. The present study exposed the PBs of Buellia frigida and Circinaria gyrosa , to UVC in combination with desiccation and subzero temperatures to gain better insight into the combined stressors' effect and the PBs' inherent potential of resistance. These effects were examined by chlorophyll a fluorescence which is a good indicator of photosynthetic activity (Lüttge & Büdel in 2010) and widely used to test the viability of PBs after (simulated) space exposure. The present results reveal fast recovery of photosynthetic activity after desiccation and subzero temperatures. Moreover, they demonstrate that desiccation and cold confer an additional protective effect on the investigated PBs and attenuate the PBs' reaction to another stressor – even if it is a non-terrestrial one such as UVC. Besides other protective mechanisms (anhydrobiosis, morphological–anatomical traits and secondary lichen compounds), these findings may help to explain the high resistance of lichens observed in astrobiological studies.
... Some cold-adapted species photosynthesis at -20˚C with water vapor obtained from snow. Photosynthetic activity can be high by at 0˚C (Kappen et al., 1996;Kappen et al., 1997). On the other hand, most plants containing cyanobacterial lichens need liquid water for the photosynthesis (Richardson et al., 2002). ...
... They are among the most successful organisms in extreme environments such as cold arctic and alpine environments where few other plants can grow (e.g. Schroeter et al. 1994;Kappen et al. 1996). Lichens also show a high diversity as eipiphytes and thus may benefit from high diversity of trees and shrubs with species-specific bark chemistry, texture and stability (Kessler 2000;Bruun et al. 2006;Grytnes et al. 2006). ...
... Antarctic lichens are extremophilic organisms very resistant on desiccation stress and cold [1][2][3]. They perform active photosynthesis below 0 • C [4,5] and below ice nucleation of their cellular fluids [6]. An important mechanism of freezing resistance is the ice crystallite growth in extracellular spaces accompanied by simultaneous drastic decrease in hydration of intracellular spaces, thus the explanation of the molecular mechanisms of drought resistance and the mechanisms of cold resistance may be common. ...
Article
Hydration courses and proton free induction decays are recorded at 30 MHz for Usnea antarctica thalli hydrated from gaseous phase. NMR data combined with gravimetry allow one to distinguish two fractions of tightly bound water, and loosely bound/free water pool. No water fraction "sealed" in thallus structures is present in U. antarctica.
... Some cold-adapted species photosynthesis at -20˚C with water vapor obtained from snow. Photosynthetic activity can be high by at 0˚C (Kappen et al., 1996;Kappen et al., 1997). On the other hand, most plants containing cyanobacterial lichens need liquid water for the photosynthesis (Richardson et al., 2002). ...
... They are among the most successful organisms in extreme environments such as cold arctic and alpine environments where few other plants can grow (e.g. Schroeter et al. 1994;Kappen et al. 1996). Lichens also show a high diversity as eipiphytes and thus may benefit from high diversity of trees and shrubs with species-specific bark chemistry, texture and stability (Kessler 2000;). ...
... Additionally, they frequently produce high amounts of secondary lichen compounds (Huneck & Yoshimura 1996) which may provide protection against ultraviolet (UV) irradiation and/or excess photosynthetically active radiation (Solhaug & Gauslaa 1996;Nybakken et al. 2004;Kranner et al. 2005). These adaptive traits enable the lichen symbiosis to colonize all biomes on Earth and adapt to the harsh environmental conditions of extreme habitats such as deserts, alpine and polar regions (aridity, cold, freeze-thaw cycles, high insolation) where they occasionally form the dominant vegetation (Kappen et al. 1996;Kappen & Schroeter 1997;Kappen 2000;Sadowsky & Ott 2012). Owing to these adaptions, lichens found some attention in astrobiological research (de Vera et al. 2003(de Vera et al. , 2004a(de Vera et al. , 2008de la Torre et al. 2007de la Torre et al. , 2010aSancho et al. 2007;Stöffler et al. 2007;Horneck et al. 2008; Raggio et al. 2011;Onofri et al. 2012;Sánchez et al. 2014) and were supposed to be astrobiological model organisms (Sancho et al. 2008). ...
Article
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The lichen Xanthoria elegans has been exposed to space conditions and simulated Mars-analogue conditions in the lichen and fungi experiment (LIFE) on the International Space Station (ISS). After several simulations and short space exposure experiments such as BIOPAN, this was the first long-term exposure of eukaryotic organisms to the hostile space conditions of the low Earth orbit (LEO). The biological samples were integrated in the EXPOSE-E facility and exposed for 1.5 years outside the ISS to the combined impact of insolation, ultraviolet (UV)-irradiation, cosmic radiation, temperatures and vacuum conditions of LEO space. Additionally, a subset of X. elegans samples was exposed to simulated Martian environmental conditions by applying Mars-analogue atmosphere and suitable solar radiation filters. After their return to Earth the viability of the lichen samples was ascertained by viability analysis of LIVE/DEAD staining and confocal laser-scanning microscopy, but also by analyses of chlorophyll a fluorescence. According to the LIVE/DEAD staining results, the lichen photobiont showed an average viability rate of 71%, whereas the even more resistant lichen mycobiont showed a rate of 84%. Post-exposure viability rates did not significantly vary among the applied exposure conditions. This remarkable viability is discussed in the context of particular protective mechanisms of lichens such as anhydrobiosis and UV-screening pigments.
... Lichens are highly resistant to extreme temperatures, a feature that substantially supports the success of these organisms in cold environments such as the ice-free areas of the Antarctic continent and the adjacent islands Lange 1970, 1972;Kappen 1973;Schlensog et al. 2003). While lichens are often highly resistant to temperature extremes in the anabiotic state, photosynthetic activity of polar lichens has been detected at subzero temperatures (Kappen et al. 1996). ...
Conference Paper
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The flora of continental Antarctica is dominated by lichens. These symbiotic associations consist of a fungus (the mycobiont) and a green alga or cyanobacterium (the photobiont) essential for carbon nutrition of the symbiotic organisms. Lichen thalli occur in crustose and more complex growth forms. In non-crustose species (macrolichens) of continental Antarctic habitats, green algal photobionts of the genusTrebouxia clade S are the most widespread. In the study presented, the role of the photobionts concerning stress tolerance was examined byphysiological experiments with isolated photobionts and entire lichen thalli. The study has been performed in situ and under laboratory conditions with lichens from North Victoria Land, continental Antarctica. Photobionts were isolated from lichens collected at North Victoria Land, Coal Nunatak (Alexander Island) and Rothera Point (Antarctic Peninsula), as well as from a European site (Gotland, South Sweden) for comparison. The physiological response of the various isolated Trebouxia photobionts to desiccation/rehydration, freezing/thawing and high light intensities indicates a habitat-specific stress physiology. The photobionts of endemic Antarctic lichens showed peculiar resistance towards the applied stressors. While desiccation and high light intensities caused long-term reduction of the studied photobionts’ vitality, freezing could easily be tolerated. The results will improveknowledge on a) the role of adaptations on the photobiont level in the physiology of lichen thalli, and b) the physiological prerequisites of lichens for the successful colonization of the terrestrial Antarctic biome. The novel comparative approach of the study presented will give fundamental information on the physiology of lichens, additionally providing a baseline for the recognition and interpretation of the consequences of environmental change in future decades.
... Long before space exposure experiments with lichens, many lichen species were found to be extraordinarily resistant to temperature fluctuations and to desiccation stress (Lange 1953) and their physiological adaptations to harsh environments were studied thoroughly; from the coldest polar areas to the deserts with the highest temperatures. In Antarctic lichens, gas exchange was measured down to about −20°C and positive net photosynthesis take place even at −17°C (Kappen et al. 1996), while extended desert areas are covered by lichen vegetation in regions where the average annual precipitation is lower than 13 mm (Lange et al. 2007). Owing to their extremotolerant character, they were considered as suitable candidates for astrobiological exposure experiments in Low Earth Orbit (LEO, unshielded solar UVR (UV > 170 nm), cosmic radiation, temperature fluctuations from −23°C to +60°C and vacuum of *10 − 6 Pa), which cause extreme desiccation, thermal stress as well as molecular and cellular damages by cosmic and solar radiation. ...
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Many experiments were carried out in order to evaluate the survival capacity of extremotolerant lichens when facing harsh conditions, including those of outer space or of simulated Martian environment. For further progress, a deeper study on the physiological mechanisms is needed that confer the unexpected levels of resistance detected on these symbiotic organisms. In this work, the response of the lichenized green algae Trebouxia sp. (a predominant lichen photobiont) to increasing doses of UV-C radiation is studied. UV-C (one of the most lethal factors to be found in space together with vacuum and cosmic-ionizing radiation with high atomic number and energy (HZE) particles) has been applied in the present experiments up to a maximum dose analogue to 67 days in Low Earth Orbit (LEO). For that purpose we selected two extremotolerant and space-tested lichen species in which Trebouxia sp. is the photosynthetic partner: the crustose lichen Rhizocarpon geographicum and the fruticose lichen Circinaria gyrosa. In order to evaluate the effect of the physiological state of the lichen thallus (active when wet and dormant when dry) and of protective structures (cortex and photoprotective pigments) on the resistance of the photobiont to UV-C, four different experimental conditions were tested: (1) dry intact samples, (2) wet intact samples, (3) dry samples without cortex/acetone-rinsed and (4) wet samples without cortex/acetone-rinsed. After irradiation and a 72 hours period of recovery, the influence of UV-C on the two lichen’s photobiont under each experimental approach was assessed by two complimentary methods: (1) By determining the photosystem II (PSII) activity in three successive 24 hours intervals (Mini-PAMfluorometer) to investigate the overall state of the photosynthetic process and the resilience of Trebouxia sp. (2) By performing high performance liquid chromatography (HPLC)-quantification of four essential photosynthetic pigments (chlorophyll a, chlorophyll b, β-carotene and lutein) of one sample of each species and dose. Results indicate that the physiological state of the thallus is the most important factor impairing the tolerance of Trebouxia sp. to UV-C radiation in both lichen species. Desiccated thalli were demonstrated to be more resistant to UV-C. No clear influence of UV-C radiation on the carotenoid content was detected. Comparing the respective doses applied, the individuals of R. geographicum are more sensitive than C. gyrosa.
... The strategy of living in certain specific habitats-especially fissures and cracks-is probably adaptive behavior to protect against desiccation and high UV-fluxes, where just a small amount of scattered photosynthetically active radiation (PAR) can reach the organisms, thus allowing photosynthesis ( Fig. 1e and f showing environmental data which were taken in parallel to data of photosynthetic activity of the lichen in niche areas what is shown in Fig. 5a expressed by the column "field conditions: niche site"). The lichen can also resist both temperatures ⪡0 1C, and low water activity (Fig. 1f), as do many species of polar lichens, which remain metabolically active at À17 to À 20 1C and can absorb small amounts of liquid water in a snow-and ice-rich environment (Kappen et al., 1996). Extremophilic organisms from various Earth environments have been previously exposed to simulated Martian environmental conditions to study their survival rates and survival strategies (Morozova et al., 2007;Schuerger et al., 2003;Osman et al., 2008;Diaz and Schulze-Makuch, 2006). ...
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Extremophilic microorganisms like lichens and cyanobacteria were collected from tropic deserts and from polar and alpine habitats because of their occurrence in intensely irradiated, very dry and/or cold environments which are supposed to be as close as possible to Martian surface conditions. The collected species were exposed during different experiments either to real space conditions on space exposure platforms like BIOPAN and EXPOSE-E on the International Space Station or to Mars simulation conditions in a Mars simulation chamber. Some of these species were also exposed to both of the extreme environmental conditions. It is a technical challenge to perform Mars simulation experiments with long duration exposure times on microorganisms - the so called extremophiles. One of the challenges is, to take care of measuring and monitoring all environmental parameters including measurements of metabolic activity of the investigated microorganisms. But the first performed one month experiment on the Antarctic lichen Pleopsidium chlorophanum in the Mars simulation facility at the Institute of Planetary Research at the DLR Berlin was successful and shows remarkable results on the adaptation capacity of photosynthetic activity within the simulation time of 34 days. This result will be a starting point to revise the previously analyzed simulation experiments on other lichen species and cyanobacteria and to start new "long duration" experiment series with other polar microorganisms. The outcome of this work might be relevant to classify Mars as a habitable planet by a new experimental and biological approach.
... It is important to note that for the initiation of the life cycle a macroscopic body of liquid water is not necessary. We know thatAntarctic lichens start photosynthesizing at −18 • C below the snow because enough molecules of water leave the surface of the snow cavity and enter the cells at this low temperature (Kappen et al., 1996). Also, liquid water at the micro-and nanoscale is markedly different from macroscopic water. ...
Chapter
Several major breakthroughs have helped contribute to the emerging field of astrobiology. Focusing on these developments, this fascinating book explores some of the most important problems in this field. It examines how planetary systems formed, and how water and the biomolecules necessary for life were produced. It then focuses on how life may have originated and evolved on Earth. Building on these two themes, the final section takes the reader on a search for life elsewhere in the Solar System. It presents the latest results of missions to Mars and Titan, and explores the possibilities of life in the ice-covered ocean of Europa. This interdisciplinary book is an enjoyable overview of this exciting field for students and researchers in astrophysics, planetary science, geosciences, biochemistry, and evolutionary biology. Colour versions of some of the figures are available at www.cambridge.org/9780521875486.
... Les lichens sont de fait répandus à travers toutes les régions du monde et ils représentent environ 8% de la couverture terrestre (Larson, 1987), s'installant dans des cours d'eau, au niveau de l'estran, dans des déserts arides mais également dans des régions polaires (où certaines espèces peuvent résister à des températures extrêmes de -40°C) ( Figure 9). La photosynthèse des lichens antarctiques est toujours effectuée à des températures avoisinant -20°C avec un record de -24°C atteint chez Cladonia alcicornis (Kappen et al., 1996;Lange, 1966;Lange and Kappen, 1972). Divers lichens antarctiques hydratés ont pu supporter 12 heures passées dans l'azote liquide sans dommages (Kappen, 1993). ...
Thesis
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Les lichens, organismes symbiotiques associant un champignon et un partenaire photosynthétique (algue verte et/ou cyanobactérie), sont caractérisés par la biosynthèse de métabolites secondaires uniques dotés de bioactivités variées. Pour valoriser au mieux cette ressource privilégiée, des méthodes innovantes de spectrométrie de masse ont été développées dans le but de minimiser la préparation de l’échantillon et la durée des analyses. Deux techniques de spectrométrie de masse ont été évaluées en ce sens : le DART-MS et le LDI-MS. L’apport de chacune de ces deux méthodes a pu être établi sur un large panel de lichens, représentant une part importante de l’espace chimique couvert par ces organismes. Il a été démontré que des profils chimiques complets pouvaient être obtenus respectivement à partir de thalles lichéniques et d’extraits acétoniques totaux. Compte tenu de la très large utilisation de la CCM pour l’analyse chimique de lichens, les possibilités offertes par le couplage de la CCM à l’ionisation electrospray ont également été explorées. Une seconde partie de ces travaux avait pour but de cartographier la distribution des métabolites secondaires au sein du thalle lichénique. À ces fins, des analyses d’imagerie LDI ont été réalisées sur une coupe transversale d’un lichen crustacé modèle : Ophioparma ventosa. Ce lichen a été étudié en phytochimie pour identifier six napthopyranones à partir des apothécies dont quatre nouvelles structures. Les principaux métabolites de ce lichen ont pu être imagés par LDI-MSI avec une résolution spatiale de 50 μm environ. Une corrélation entre la distribution des molécules et leur rôle écologique présumé permet d’avancer des hypothèses d’écologie chimique. Des approches conjointes reliant histolocalisation et étude génétique des partenaires de la symbiose ont été entreprises. La recherche des gènes de la biosynthèse de la mycosporine sérinol chez les symbiontes isolés de Lichina pygmaea par microdissection capture laser a été initiée en ce sens. D’autres approches innovantes comme l’analyse cristallographique par diffraction de poudre par les rayons X sont également abordées dans ce document articulé autour de six publications issues de ce travail et de deux articles en cours de soumission.
... Elevated level of carotenoids, lutein and neoxanthin, found in several Antarctic lichens helps them to protect from antioxidative stress, frequently accompanying other types of stresses (Strzalka et al. 2011). The unique symbiosis of mycobiont and photobionts makes lichens advantageous over higher plants in harsh climatic conditions, but it results in slow and retarded growth, as species of Usnea and Umbilicaria grow only up to 20 cm in Antarctica and Antarctic maritime, respectively (Kappen et al. 1996b). However, in spite of limitations of retarded and slow growth rate, it is evident that lichens achieved evolutionary success populating very hostile areas of the planet. ...
Chapter
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The poikilohydrous nature of lichens provides them the ability to resist low temperature, deep dehydration and deficit in light irradiance. The process of water uptake can be correlated with the resistance for dehydration below water percolation threshold (fractal exponent characteristic for approximately two-dimensional lattice). Gaseous phase hydration kinetics presents tightly bound water and mobile loosely bound water fractions, differentiated in hydration/dehydration rate and in proximity to thallus surfaces.
... Arctic lichens may have a positive net primary photosynthesis balance at low temperatures (many studies by K.A. Kershaw and co-workers, e.g. Larson & Kershaw 1975, Kershaw 1985, even under snow and ice, and survive extremely low temperatures and levels of water content (Kappen et al. 1996, Sommerkorn 2000. ...
Chapter
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Fungi are one of the most species-rich groups of organisms in the Arctic. While the occurrence, distribution and ecology for lichenized fungi (lichens)1 are reasonably well known, less is known about non-lichenized fungi (normally just called fungi), including lichenicolous fungi (fungi living on lichens)2 and in particular, microfungi3. The known number of fungal species in the Arctic is presently about 4,350, of which 2,600 are macrofungi4 and 1,750 are lichens, the rest are microfungi. The fungi have largely a cryptic life form and have therefore not been exhaustively inventoried. Hence, total fungal-species richness in the Arctic may exceed 13,000. Local species richness is typically high and can be very high, e.g. about 50 lichen species on less than 1 m2. Most species appear to be present throughout the Arctic, and they also occur in alpine habitats outside the Arctic, particularly in the northern hemisphere. Few fungi are endemic to the Arctic. Of the lichens, 143 species are listed as Arctic endemics, but it is likely that the major part will prove to be synonyms of other species. Fungi are pivotal in Arctic terrestrial food-webs. Mycorrhizal, saprotrophic5 and pathogenic fungi drive nutrient and energy cycling, and lichens are important for primary production. Reindeer lichens Cladonia subgenus Cladina spp. form dominant vegetation types in many areas and function as keystone species. As for other inconspicuous organism groups, it is obviously desirable to gain a better knowledge of the identity, occurrence and functions of fungal species, and particularly the large number of unrecorded species (mainly microfungi). An evaluation of the conservation status of Arctic fungi is feasible, and the mapping of rare and endemic species is necessary. Enhanced monitoring and functional research would enable more accurate prediction of how fungal diversity and the ecosystem functions of fungi will develop with climate change. Effects of climate change on diversity of Arctic fungi are predicted to be gradual but radical over time, due to changes in vascular plant flora and vegetation, especially the expansion of shrubs. Most fungal species associate with living or dead parts of specific vascular plants and will respond directly to changing composition, abundance and location of the vegetation. Similarly, terricolous6 lichen communities will be affected by increased competition from vascular plants. The changing vegetation will transform the fungal diversity and thereby affect ecosystem services provided by fungi, such as plant’s uptake of nutrients, decomposition and long-term carbon sequestration in soil, although unknown how and to what degree. The conservation status of Arctic fungi is predicted to scarcely be affected within the next decades but greatly changed over the long term.
... However, freezing and the associated loss in water potential does not necessarily exclude photosynthesis in lichens. In Antarctic lichens, photosynthesis [22,25] and Φ PSII [16] has been measured at temperatures as low as −17°C. However, Lobaria species with higher temperature optima for growth [3] and with very low growth rates in winter [27] likely have higher temperature thresholds for photosynthesis. ...
Article
Lichens are considered freezing tolerant, although few species have been tested. Growth, a robust measure of fitness integrating processes in all partners of a lichen thallus, has not yet been used as a viability measure after freezing. We compared relative growth rates (RGR) after freezing with short-term viability measures of photo- and mycobiont functions in the coastal Lobaria virens and the widespread L. pulmonaria to test the hypothesis that low temperature shapes the coastal distribution of L. virens. Hydrated thalli from sympatric populations were subjected to freezing at -10, -20 and -40 °C for 5 h. The rate of cooling and subsequent warming was 5 °C h-1. Short-term viability measures of photobiont (maximal photosystem II efficiency, effective PSII yield) and mycobiont viability (conductivity index), as well as subsequent RGR, were assessed. The exotherms showed that L. virens froze at -3 °C; L. pulmonaria, at -4 °C. Freezing significantly impaired short-term viability measures of both photo- and mycobiont, particularly in the coastal species. Lobaria pulmonaria grew 2.1 times faster than L. virens, but the short-term damage after one freezing event did not affect the long-term RGR in any species. Thereby, short-term responses were impaired by freezing, long-term responses were not. While the lacking RGR-responses to freezing suggest that freezing tolerance does not shape the coastal distribution of L. virens, the significant reported adverse short-term effects in L. virens may be aggravated by repeated freezing-thawing cycles in cold winters. In such a perspective, repeated freezing may eventually lead to reduced long-term fitness in L. virens.
... Besides the existence of an energy source, the presence of water in solid, gaseous or liquid form is one of the main characteristics for habitability. It is known that a number of organisms are able to be physiologically active in presence of the different states of water's aggregation ( (Kappen et al., 1996), (de Vera et al., 2013), (Stevenson et al., 2014)) and particular at values of relative humidity between 60% and 100%. But even largely below 60% relative humidity also some bacteria and archaea are even able to grow (Stevenson et al., 2014). ...
Article
The Finnish Meteorological Institute (FMI) provides a relative humidity measurement sensor (HS) for NASA's Mars 2020 rover. The sensor is a part of the Mars Environmental Dynamic Analyzer (MEDA), a suite of environmental sensors provided by Spain's Centro de Astrobiología. The main scientific goal of the humidity sensor is to measure the relative humidity of the Martian atmosphere near the surface and to complement previous Mars mission atmospheric measurements for a better understanding of Martian atmospheric conditions and the hydrological cycle. Relative humidity has been measured from the surface of Mars previously by Phoenix and Curiosity. Compared to the relative humidity sensor on board Curiosity, the MEDA HS is based on a new version of the polymeric capacitive humidity sensor heads developed by Vaisala. Calibration of humidity devices for Mars conditions is challenging and new methods have been developed for MEDA HS. Calibration and test campaigns have been performed at the FMI, at University of Michigan and the German Aerospace Center (DLR) in Berlin to achieve the best possible calibration. The accuracy of HS and uncertainty of the calibration has been also analysed in detail with VTT Technical Research Centre of Finland. Assessment of sensor performance after landing on Mars confirms that the calibration has been successful, and the HS is delivering high quality data for the science community.
... The lichen symbiosis is characterised by an anatomical structure formed by the mycobiont which serves as protection for the photobiont against excessive loss of water, temperature extremes and high irradiation (Nash 1996;Schlensog and Schroeter 2000;Harańczyk et al. 2012;Meeßen et al. 2013). The thallus structure creates a micro-environment for the photobiont which allows physiological activity even under hostile external environmental conditions (Honegger 2009) such as occur frequently in Antarctica (Kappen et al. 1996). ...
Article
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The vegetation of many terrestrial habitats across Antarctica is dominated by poikilohydric symbiotic lichens. Terrestrial habitats generally are characterised by extended exposure to desiccation and high irradiation. Physiological adaptation mechanisms of the algal partner (photobiont) are key factors in the successful colonisation of lichens of locations under severe environmental conditions. This study focused on isolated photobionts of the genus Trebouxia, from the continental Antarctic lichens Buellia frigida, Pleopsidium chlorophanum, the maritime Antarctic lichen Umbilicaria antarctica, and the Swedish lichen Fulgensia bracteata from a moderate temperate ecosystem at sea level. The photosystems PS II and PS I and the ratio of linear to cyclic electron transport were studied to elucidate adaptation mechanisms in the physiology of the photobionts in response to desiccation and light stress. The photobionts of the Antarctic lichens demonstrated striking tolerance to the stress conditions studied. Although the photobionts of U. antarctica and P. chlorophanum were genetically identical based on non-coding internally transcribed spacer (ITS), their physiological responses were clearly different, possibly indicating ecotypic differentiation. The photobiont of F. bracteata showed clearly different responses to those of the Antarctic photobionts. The response differences of the photobionts studied point to fundamental differences in life history strategies.
... Arctic lichens may have a positive net primary photosynthesis balance at low temperatures (many studies by K.A. Kershaw and co-workers, e.g. Larson & Kershaw 1975, Kershaw 1985, even under snow and ice, and survive extremely low temperatures and levels of water content (Kappen et al. 1996, Sommerkorn 2000. ...
Chapter
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... They are characterized by a unique and evolutionary successful mode of life. Lichen organisms colonize all biomes on Earth and are dominant in severe ecological niches, especially in polar regions (Kappen et al., 1996;Kappen and Schroeter, 1997;Kappen, 2000;Sadowsky and Ott, 2012). They have a broad range of morphological, anatomical, and physiological adaptations, and secondary metabolites (Henssen and Jahns, 1974;de Vera et al., 2003de Vera et al., , 2004ade Vera et al., , 2004bde Vera et al., , 2008de Vera et al., , 2014de la Torre Noetzel et al., 2007;Sancho et al., 2007;Stöffler et al., 2007;Horneck et al., 2008;de la Torre et al., 2010;Raggio et al., 2011;Sánchez et al., 2012Sánchez et al., , 2014Backhaus et al., 2014;Meeßen et al., 2014b). ...
Article
The lichen Buellia frigida was exposed to space and simulated Mars analog conditions in the Biology and Mars Experiment (BIOMEX) project operated outside the International Space Station (ISS) for 1.5 years. To determine the effects of the Low Earth Orbit (LEO) conditions on the lichen symbionts, a LIVE/DEAD staining analysis test was performed. After return from the ISS, the lichen symbionts demonstrated mortality rates of up to 100% for the algal symbiont and up to 97.8% for the fungal symbiont. In contrast, the lichen symbiont controls exhibited mortality rates of 10.3% up to 31.9% for the algal symbiont and 14.5% for the fungal symbiont. The results performed in the BIOMEX Mars simulation experiment on the ISS indicate that the potential for survival and the resistance of the lichen B. frigida to LEO conditions are very low. It is unlikely that Mars could be inhabited by this lichen, even for a limited amount of time, or even not habitable planet for the tested lichen symbionts.
... Moreover, a similar range of critical temperature (about -20°C) is reported in the studies related to the net photosynthesis activity (e.g. Kappen et al. 1996). ...
Article
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Antarctic regions involve a great variety of habitats characterized by environmental stressors and life forms of autotrophic organisms with unique survival and functioning mechanisms. Lichens and mosses from these regions, similarly to high altitude alpine locations, have evolved physiological adaptations to perform photosynthesis at subzero temperatures. In this study we applied linear cooling technique in order to analyze interspecific differences in primary photosynthetic processes in Antarctic species affected by low and subzero temperature stress. We exposed Sanionia uncinata, Rhizoplaca aspidophora, Ochrolechia frigida, Cladonia sp., Himantormia lugubris and Umbilicaria decussata to the cooling from 20 to-35°C at a constant rate of 2°C min-1. Fluorometric parameters were measured during the cooling experiments: F V /F M-potential yield of photosynthetic processes in photosystem II, and F 0-minimal chlorophyll fluorescence. All the species showed S-curves for F V /F M in response to decreasing temperature and interspecific differences in the parameters of S-curve equation. Critical temperature for F V /F M was found-35°C for U. decussata, while the other species ranged between-16 to-20°C. The changes of F 0 with thallus temperature decrease were species-specific. F 0 decrease followed by an increase was found with cooling from 20 to-20°C, and from-20 to-35°C, respectively, in the majority of cases. These results suggest that the experimental moss and lichen species from Antarctica have a high resistance to freezing temperatures. The underlying physiological mechanisms are constitutive features of Antarctic lichens and mosses. They are a crucial part of the adaptation and short-term acclimatory changes in ecophysiological performance of the organisms in harsh polar environments.
... Measurements of surface temperature (soil temperature in 0 cm depth) show temperatures well above 0 • C during daytime in winter (mostly between 12:00 and 18:00; see Fig. A2). Plants may photosynthesize until below −3 • C, at least they do so in Antarctic tussock grass (Bate and Smith, 1983), and lichens may photosynthesize under even colder conditions (Kappen et al., 1996). In summary, we suggest that the CO 2 uptake during winter daytime represents a physiologically meaningful signal rather than an artifact from the SSH effect. ...
Article
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The Tibetan alpine steppe ecosystem covers an area of roughly 800 000 km2 and contains up to 3.3 % soil organic carbon in the uppermost 30 cm, summing up to 1.93 Pg C for the Tibet Autonomous Region only (472 037 km2). With temperatures rising 2 to 3 times faster than the global average, these carbon stocks are at risk of loss due to enhanced soil respiration. The remote location and the harsh environmental conditions on the Tibetan Plateau (TP) make it challenging to derive accurate data on the ecosystem–atmosphere exchange of carbon dioxide (CO2) and water vapor (H2O). Here, we provide the first multiyear data set of CO2 and H2O fluxes from the central Tibetan alpine steppe ecosystem, measured in situ using the eddy covariance technique. The calculated fluxes were rigorously quality checked and carefully corrected for a drift in concentration measurements. The gas analyzer self-heating effect during cold conditions was evaluated using the standard correction procedure and newly revised formulations (Burba et al., 2008; Frank and Massman, 2020). A wind field analysis was conducted to identify influences of adjacent buildings on the turbulence regime and to exclude the disturbed fluxes from subsequent computations. The presented CO2 fluxes were additionally gap filled using a standardized approach. The very low net carbon uptake across the 15-year data set highlights the special vulnerability of the Tibetan alpine steppe ecosystem to become a source of CO2 due to global warming. The data are freely available at https://doi.org/10.5281/zenodo.3733202 (Nieberding et al., 2020a) and https://doi.org/10.11888/Meteoro.tpdc.270333 (Nieberding et al., 2020b) and may help us to better understand the role of the Tibetan alpine steppe in the global carbon–climate feedback.
... They are characterized by a unique and evolutionarily successful mode of life. Lichen organisms colonize all biomes on Earth and are dominant in severe ecological niches, especially in polar regions (Kappen et al., 1996;Kappen and Schroeter, 1997;Kappen, 2000;Sadowsky and Ott, 2012). They have a broad range of morphological, anatomical, and physiological adaptations, and secondary metabolites (Henssen and Jahns, 1974;de Vera et al., 2003de Vera et al., , 2004ade Vera et al., , 2004bde Vera et al., , 2008de Vera et al., , 2014de la Torre Noetzel et al., 2007;Sancho et al., 2007;Stöffler et al., 2007;Horneck et al., 2008;de la Torre et al., 2010;Raggio et al., 2011;Sánchez et al., 2012Sánchez et al., , 2014Backhaus et al., 2014;Meeßen et al., 2014b). ...
Article
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As part of the ESA space experiment BIOMEX (Biology and Mars Experiment) the lichen Buellia frigida has been exposed to space and simulated Mars analogue conditions on the expose facility EXPOSE-R2 placed outside the Russian Zvezda module on the International Space Station (ISS) for 1.5 years. Randomly Amplified Polymorphic DNA (RAPD) technique has been carried out to study the effect of space conditions on the DNA integrity as well as to assess DNA damage. The RAPD profiles of the space exposed lichen samples demonstrate conspicuous changes compared to the control profiles. For the survival of cells and entire organisms the DNA integrity is an essential prerequisite. The results of the study presented indicate a minor resistance potential of the lichen Buellia frigida towards Low Earth Orbit and Mars analogue conditions effecting the survival potential and the resistance of the symbiotic organism.
... For instance, hot springs were found at Mt. Erebus, Antarctica, to be inhabited by specific cyanobacteria (Broady, 1984;Soo et al., 2009). The oxyphotosynthetic microorganisms terrestrially can perform photosynthesis at a temperature range from −20°C in the photobionts of antarctic lichens (Kappen et al., 1986;Kappen et al., 1996) to +70°C in thermophilic unicellular cyanobacteria (Allewalt et al., 2006). Polar microorganism especially adapt well to low-temperature environments and are predicted to be able to survive the Martian environment, as has been demonstrated by terrestrial ground simulations as well as by exposure experiments to a near space environment in low Earth orbit on the International Space Station (de Vera et al., 2004;Olsson-Francis et al., 2009;Cockell et al., 2011;Onofri et al., 2012;de Vera et al., 2014;Brandt et al., 2015). ...
Article
Bio-monitoring of mercury (Hg) in air using transplanted and in-situ lichens was conducted at three locations in Slovenia: (I) the town of Idrija in the area of the former Hg mine, where Hg contamination is well known; (II) Anhovo, a settlement with a cement production plant, which is a source of Hg pollution, and (III) Pokljuka, a part of a national park. Lichens from Pokljuka were transplanted to different sites and sampled four times—once per season, from January 2020 to February 2021. Lichens were set on tree branches, fences, and under cover, allowing them to be exposed to different environmental conditions (e.g., light and rain). The in-situ lichens were sampled at the beginning and the end of the sampling period. The highest concentrations were in the Idrija area, which was consistent with previous research. Significant mass-dependent fractionation has been observed in transplanted lichens during summer period. The δ²⁰²Hg changed from −3.0‰ in winter to −1.0‰ in summer and dropped again to the same value in winter the following year. This trend was observed in all samples, except those from the most polluted Idrija sampling site, which was in the vicinity of the former Hg ore-smelting plant. This was likely due to large amounts of Hg originating from polluted soil close to the former smelting plant with a distinct isotopic fingerprint in this local area. The Δ¹⁹⁹Hg in transplanted lichens ranged from −0.5‰ to −0.1‰ and showed no seasonal trends. These findings imply that seasonality, particularly in summer months, may affect the isotopic fractionation of Hg and should be considered in the sampling design and data interpretation. This trend was thus described in lichens for the first time. The mechanism behind such change is not yet fully understood.
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Diese erste Rote Liste und Checkliste der Flechten, flechtenbewohnenden und flechtenähnlichen Pilze Bayerns umfasst 2.054 Taxa, davon 1.624 Flechten, 399 flechtenbewohnende Pilze und 31 flechtenähnliche Pilze. Sie wurde aufgrund intensiver Recherchen in der Literatur erstellt, die in einem elektronischen Supplement nachvollziehbar niedergelegt sind. Insgesamt kommen von den drei Artengruppen 1.417 Taxa (1.163 Flechten/236 flechten-bewohnende/18 flechtenähnliche Pilze) in der alpinen Region sowie 1.691 (1.341/323/27) in der kontinentalen Region vor. 909 Taxa (44 %) sind als Rote-Liste-Arten der Kategorien 0, 1, 2, 3 und G ausgestorben oder gefährdet (in der alpinen Region 31 %, in der kontinentalen Region 48 %). Dazu treten als „extrem seltene“ Arten in der Kategorie „R“ 395 Taxa (19 %) hinzu – in der alpinen Region 21 %, in der kontinentalen Region 13 %. In der kontinentalen Region mit der intensiveren Flächennutzung finden sich prozentual mehr gefährdete Arten als in der alpinen Region. Da-gegen finden sich in den Alpen besonders viele extrem seltene Arten. Die bayerischen Flechtenbestände waren in den letzten 200 Jahren (dem Zeitraum, zu dem Angaben zu den Beständen vorliegen), etlichen Belastungen ausgesetzt: Die Industrialisierung führte zu erhöhten Schwefeldioxyd-Konzentrationen in der Luft, die aber Ende des 20. Jahr-hunderts durch verstärkte Anstrengungen in der Luftreinhaltung wieder signifikant verringert werden konnten. Neuordnung und Intensivierung der Landwirtschaft vernichtete vor allem in der Zeit nach 1950 zahlreiche Lebensräume in der offenen Landschaft, während in der Forst-wirtschaft bereits ab Mitte des 19. Jahrhunderts Nadelholzmonokulturen in den Wäldern zu massiven Diversitätsverlusten führten. Seit etwa 40 Jahren bedroht zunehmend eine steigende Eutrophierung (vor allem durch Stickstoffverbindungen aus Industrie, Verkehr und Landwirtschaft) umfassend die Flechten und ihre Lebensräume, vor allem indem sie Höhere Pflan-zen und konkurrenzkräftige Moose fördert. Dringend notwendig zum Schutz der Flechtenflora ist • eine Reduktion der Eutrophierung, • die Wiederherstellung eines Netzes von Kleinstrukturen in der Landschaft, • das weitere Zurückdrängen der Nadelholz-Monokulturen, • die Einrichtung von Altholzinseln in den Wäldern, • die Wiederherstellung von Flechten-Kiefernwäldern sowie • gezielte Artenhilfsmaßnahmen, wie die Übertragung von Flechten in renaturierte Biotope.
Chapter
Die kalten, polnahen waldfreien Regionen der Erde teilen sich in die feuchten und vegetationsreichen Tundren und die äußerst trockenen und kalten, vegetationsarmen polaren Wüsten. Die polaren Wüsten befinden sich vollständig, die Tundren überwiegend im Bereich des kontinuierlichen Permafrosts. In der Arktis sind die Kältewüsten auf die äußersten Nordspitzen Grönlands, die nordkanadischen und sibirischen Inseln sowie die Inseln der Barentssee beschränkt.
Article
Data on the respiratory activity of 12 species of Antarctic lichens are presented. It is found that the respiration of foliose lichens is more intensive than the respiration of fruticose lichens. The O2 uptake rate correlates positively with the nitrogen content in the biomass of thalli and depends on temperature. The thalli O2 uptake rate increased 2.2–2.4 times with a temperature increase from 5 to 15°C. The reaction of respiration upon a further rise in temperature is species-specific. The decrease in the temperature coefficient of respiration (Q10) with a temperature increase to 35°C is most pronounced in the endemic species Usnea aurantiacoatra, which is well-adapted to Antarctic conditions. The calculations show that, in summer, lichens are able to lose an amount of substrate equivalent to 0.8–1.4% of the thallus dry biomass in respiration daily. The total respiration cost of the lichen maintenance under snow during the winter can reach of 30–35% from their biomass. These results extend our knowledge on Antarctic lichens, and rediction their response to climatic change.
Article
In the past 2 years, as in 1991–92 (Progress in Botany 55, p. 288), there has been a strong increase in taxonomic knowledge of lichenized fungi. At least 25 new genera were proposed, several reintroduced with a new circumscription, and over 370 new species described. Again, the new species were predominantly discovered in the best-known area of the world, with the highest density of workers. More than one third were discovered in the temperate and cool areas of the nothern hemisphere. Slightly lower numbers originate from the tropics and the southern temperate to cold zone. In addition, over 50 new species of lichenicolous fungi were described, mostly from the temperate northern hemisphere. These figures illustrate that the taxonomic exploration of this group is in full progress, and suggest that probably many more species are to be discovered.
Article
The CO2 exchange of two fruticose alpine lichen species was compared with respect to their thallus water content, light, temperature and moisture in the field and in the laboratory. Maximum net photosynthesis in both lichens was similar in the field, but in the laboratory Cetraria islandica had higher net CO2 uptake rates than Flavocetraria nivalis. The light compensation point of Cetraria islandica was lower than those of Flavocetraria nivalis and increased with increasing temperature. The upper temperature compensation point was higher in Cetraria islandica than in Flavocetraria nivalis. Both lichens had similar moisture compensation point in the field and in the laboratory. The maximal and minimal thallus water content was lower in Cetraria islandica in comparison with Flavocetraria nivalis. In the field hydration is the most important factor which determines the pattern of CO2 exchange. CO2 exchange was detected during the daytime and no nocturnal respiration was recorded. Total period of NP was ca. 52 % and ca. 45 % of time the lichens were inactive. Less but still positiVe NP was found when the lichens were frozen respectively when air temperature was far below the freezing point.
Chapter
Photosynthesis in lichens is intimately linked to the photosynthetic capacities of the photobiont, i.e. autotrophic algae and cyanobacteria, that form the lichen association together with a fungal partner. Lichen photosynthesis in nature is also affected by a complex mixture of internal and external factors. Intrathalline locatization of photobiont cells, structure of photobiont layer, functional photobiont-mycobiont interlink, and physico-chemical properties of the fungal part of thallus are considered important internal characteristics affecting photosynthesis and utilization of photosynthetic products in lichens. In this chapter, a brief introduction into the anatomy and morphology is provided from a view point of function. Special attention is given to cellular structure of photobionts, and especially to the chloroplast of unicellular alga Trebouxia, the most abundant symbiotic alga in lichen association. Since lichens are typical poikilohydric organism with no active control of their hydration status, the photosynthetic responses of lichens to full, partial and severely limited water supply are described. In addition the protective mechanisms activated during thallus desiccation are discussed. Several aspects of lichen photosynthesis including light-response curves, photoinhibition, activation of photoprotective mechanisms and reactive oxygen species-induced changes in the amount and activity of antioxidative substances are reviewed. Lichens can photosynthesize over a wide temperature range, including subzero temperature. The photobiont also exhibits response depending on nitrogen availability and exposure to heavy metals.
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The effect of freezing‐thawing alternation on lichen photosynthesis is yet unknown in China. To study the responses of photosynthetic activity (indicated by net photosynthetic rate, Pn) to freezing‐thawing cycles and their relationships with water conditions, two species of lichens from Mt. Wulingshan of North China, Flavopunctelia soredica and Peltigera elisabethae, were subjected to 5 freezing‐thawing cycles under two thallus water conditions (wet‐freezing treatment group: thallus water content > 200% dry weight; dry‐freezing group: thallus water content < 20%). The results show that Pn of F. soredica under dry‐freeze decreased to 21% as compared with the control after 5 freezing‐thawing cycles, and decreased to negative values after 3 wet‐freezing cycles. Pn of P. elisabethae decreased to negative values after 5 wet‐freezing and dry‐freezing cycles. The linear regression analysis between relative Pn and freezing‐thawing cycles shows that the slope absolute values decrease in order of wet‐freezing F. soredica (58.06) > wet‐freezing P. elisabethae (41.01) > dry‐freezing P. elisabethae (32.27) > dry‐freezing F. soredica (11.44). These results indicate that the photosynthetic activity of both lichens is inhibited by freezing‐thawing alternation, and the inhibition extent is dependent on species and thallus water conditions. The increase of water content can intensify the inhibition effects. The difference of photosynthetic response to freezing‐thawing cycles between the two lichens may be due to the physiological adaption to different microclimate conditions. P. elisabethae inhabits the shady and moist habitats, while F. soredica occupies more open and drier habitats. F. soredica has higher tolerance to dry and low temperature than P. elisabethae, and its adaptation ability to wet and cold is weaker. Global climate change may have negative effects on the photosynthesis and distribution of lichens through the impacts of alteration of spatio‐temporal patterns of
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Several individual-based perspectives on lichen population structure and dynamics are explored. The possibility of relating measurements of ecophysiological performance to population processes and structure is discussed with reference to recent studies. Individual variation-the stuff of which populations are made This Festschrift celebrates the unique and extraordinary performance of an individual. While most humans have no problem perceiving that all humans are not created equal, and do not in fact have the same opportunities for`Lifefor`Life, Liberty and the Pursuit of Happiness (and Research)', this inequality has only recently been recog nized to be the norm also for lichens. The somewhat uneasy feeling that something significant had been overlooked was eminently caught in the title of a paper by Larson (1984): `Thallus size as a complicating factor in the physiological ecology of lichens'. Larson showed that the physiological performance of some species is size-dependent, in others size-independent, and you cannot predict which from a priori principles. You have to perform the measurements on each and every species, and on quite a number of different individuals to ascertain the range of variation (cf. also Larson 1979). This means a lot of work. It also implies that thètypical individual' so favoured in many physiological, mo r-phological, anatomical and chemical studies, is a very dubious entity indeed.
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Permafrost and ice are important components of cryogenic planets and other bodies, which are abundant in the universe. Earth is one of many planets of the cold type. Earth's permafrost and ice provide an opportunity to test hypotheses that could be applied in the search for possible ecosystems and potential life on extraterrestrial cryogenic planets. Permafrost sediments in polar and alpine regions are natural ecosystems with a unique feature of low‐temperature preservation of the biological material and its genetic information. Therefore, permafrost studies allow reconstruction of the events that occurred in the Cenozoic and the prediction of possible life that might have been preserved before the effect of anthropogenic factors on these ecosystems, and could be found within ice or permafrost on other cryogenic planets.
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Comparison of different harvesting and preparation pathways showed that low-temperature SEM is an adequate method to conserve the stomatal aperture for SEM. Both critical point drying and freeze drying cause considerable artefacts. Exposure to site-relevant concentrations of ozone led to reduced width of the stomatal aperture. Moreover, unetchable droplet-like exudates were found on the outer face of mesophyll cells of leaves where the trees had been exposed to ozone. These exudates were later followed by collapsed mesophyll cells and ended in necrotic zones before premature leaf loss.
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Free and perturbed water (9) within lichen thalli can be localized with low-temperature scanning electron microscopy after freeze-fracturing and etching. A high water content was found in the outer parts of medullary hyphal cell walls of fully water saturated Teloschistes lacunosus, probably indicating an apoplastic water transport to the photobiont cells. In Cetraria islandica, free water was only found within cavities of the hydrophilous cortex. Free water was never detected within the medulla. In water-vapor hydrated thalli, a relationship between air humidity and turgescence of photobionts was found. However, at low air humidity, when photobiont cells were completely collapsed, the plasmalemma were tightly fitted to the cell wall.
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A dedicated cryopreparation system, the SCU 020 (Balzers), is introduced and described in detail for use in low-temperature scanning electron microscopy (LTSEM). The basic unit consists of two parts: (i) a high-vacuum preparation chamber equipped with a cold-stage, motor-driven fracturing microtome, planar magnetron (PM) sputter source, quartz-crystal thin-film monitor, Meissner cold trap, and turbo molecular pump stand; and (ii) a second part (separated from the first by a sliding, high-vacuum valve) residing in the SEM chamber. This is equipped with an anti-contamination cold trap, a fully movable goniometer cold stage (having motor drives for x, y, and rotation) and replaces the SEM's original stage (Raith). The SCU 020 is entirely self contained allowing independence from, and synchroneity with, the SEM of choice. LTSEM micrographs of specimen (that are fully frozen hydrated or partially freeze-dried) surfaces or fracture faces, without or with various metal coatings, can be examined over a broad temperature range (-150 to +50°C). This is made possible by the combined application of the two, independently controlled, cold stages and the on-line, high-vacuum, specimen cryo transfer between them. In-situ etching is simple and straightforward. Intramembranous particles and membrane fracture steps, typically imaged in transmission electron microscopy (TEM), are resolved by PM sputtering with platinum at low specimen temperature and high-resolution LTSEM in a field emission microscope.
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Structural alterations of the photobiont and mycobiont cells of lichens have been related to CO2-gas exchange during experiments involving water vapour uptake and desiccation of liquid-water-saturated thalli. Increasing water vapour uptake of air dry lichens led to a gradual unfolding of the photobiont cells in Lobaria pulmonaria, Pseudevernia furfuracea, Ramalina maciformis and Teloschistes lacunosus as studied by low-temperature scanning electron microscopy. The data indicated that globular, probably turgid, cells and also slightly infolded or even heavily collapsed cells contributed to positive net photosynthesis, which was reached after water vapour uptake by the four species studied. During desiccation of fully water-saturated thalli of L. pulmonaria, extrathalline water films gradually evaporated before maximum values of CO2-gas exchange were measured and before photobiont cells started to shrivel. In contrast, in P. furfuracea the CO2-gas exchange maximum was reached when a considerable percentage of photobiont cells had already collapsed and while other parts of the thalli were still covered with liquid water. Further desiccation led to cavitation of the cortical cells in both species, this occurring at water contents at which net photosynthesis was still positive.
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The energy and pitch angle distributions of inverted-V electron precipitation fluxes predominantly determined from Atmosphere Explorer satellite observations are shown to be in general agreement with acceleration by a parallel electrostatic potential. The characteristics of secondary electrons are examined, and the effects of beam plasma instabilities on these electrons are discussed. It is found that plasma sheet electrons are continuously accelerated to form inverted-V structures in the premidnight hemisphere, independent of substorm phase. The acceleration processes are probably related to large scale, electrostatic wave turbulence observed at altitudes of a few thousands km. It is suggested that narrow bursts of intense electron precipitation possess characteristics which may cause auroral arcs in the atmosphere.
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A detailed study is presented of simultaneous density and electric field fluctuation spectra over a large-scale length range seen in association with large structured convective plasma flows, field-aligned currents, and particle precipitation at high latitudes. The data were obtained for two Dynamics Explorer 2 orbits at two different altitudes within the F region and the topside ionosphere. The observations are compared with results of nonlinear simulations of shear flow-driven instabilities and predictions based on two-dimensional turbulence arguments, with particular reference to the Kelvin-Helmholtz process.
Article
Eight coastal Californian and Baja Californian lichens, four each with Trentepohlia and Trebouxia phycobionts, were studied under hydrated conditions to determine their response to a series of 6-hour cold treatments ranging from − 5 to − 78°C. All lichens with Trentepohlia exhibited significant reductions in net photosynthesis following − 20°C treatments and one species was so affected following − 12°C treatments. For all four of these Trentepohlia-containing species net photosynthesis was depressed to negative values following − 28°C treatments, and this response was associated with a significant decrease in total chlorophyll. In contrast, such a major response did not occur in the lichens with Trebouxia until the − 46°C treatment was applied. For the latter lichens a slight depression in net photosynthesis occurred following the − 28°C treatment in the Ramalina menziesii specimens, but no such decline occurred in the Niebla species. From these results and previous publications it is inferred that lichens in general from the Roccellaceae, a familiy characterized by species with Trentepohlia, are more susceptible to frost than lichens with Trebouxia. The results help explain coastal lichen distribution patterns in western North America in particular and the world-wide tropical and subtropical distribution pattern of the Roccellaceae in general.
Chapter
This chapter illustrates the physiological and morphological responses of lichens to extreme environmental stresses, which include drought and desiccation, wetness, temperature, humidity, visible or ionizing radiation, gamma irradiation, radioactive materials, and mechanical influences. The drought resistance of lichen is directly correlated to the intensity of desiccation (relative humidity) and to the length of the desiccation period. The stimulation of respiration after desiccation stress causes considerable loss of carbohydrates. Photosynthesis increases spontaneously with water vapor intake at a relative humidity below 100%. Further, the desiccation resistance varies according to species. The comparative analyses of resistance to submersion shown by terrestrial and aquatic lichens clearly demonstrate the ecological importance of the moisture regime for the distribution of lichens. The life of lichen is characterized by rapid changes between active and inactive states. These changes can be optimally profitable if they allow for sufficient time (continuation) and intensity of metabolism, thus, producing biomass. Their resistance allows lichens to persist under environmental stress either in the active state (plasmatic tolerance) or by diminishing the stress in the anabiotic, desiccated state, which is made possible by their poikilohydric nature (constitutional resistance). Lichen can respond to adverse conditions by morphological adjustments, by pigmentation of the thallus, and by changes in the symbiotic state. Erratic lichens in deserts and steppes indicate the ability to be translocated to more favorable environments.
Article
The intensities of photosynthesis and respiration of three montane mosses were determined at winter low temperatures. The experiments were carried out under outdoor light and at air temperature, the exposure lasting 4-5 hours. The lowest temperature for CO2 assimilation in Brachythecium geheebii and Camptothecium philippeanum was -9° C; for Isothecium viviparum it was about -8° C. In the dark respiration also occurred at -14° C. The minimum temperatures for CO2 assimilation by the tested mosses in winter are somewhat lower than those for evergreen trees and nearer to the minimum temperatures for lichens.
Article
Photosynthetic activity and structural changes at subzero temperatures were monitored in the foliose lichen Umbilicaria aprina Nyl. from continental Antarctica. Carbon dioxide gas exchange measurements revealed that net photosynthesis and dark respiration occurred at subzero temperatures regardless of whether a lichen thallus saturated with liquid water was exposed to subzero temperatures, or if a dry thallus was re‐hydrated only from snow at subzero temperatures. When water‐saturated thalli of U. aprina were slowly cooled at subzero temperatures ice nucleation activity could be detected at — 5·4 °C, indicating extracellular freezing of water. Using low‐temperature scanning electron microscopy (LTSEM) it was demonstrated that extracellular ice formation leads to cytorrhysis in the photobiont cells and to cavitation in the mycobiont cells. Both processes were reversible if the lichen thallus was re‐warmed. When dry lichen thalli were covered with snow at subzero temperatures a substantial re‐hydration from snow could be observed in LTSEM micrographs and measured gravimetrically. The final thallus water content was strongly dependent on the temperature regime and gave water contents between 20% d. wt at — 21 °C and 56% d. wt at —4·5 °C after 16 h exposure. Carbon dioxide gas exchange measurements revealed that metabolic activity was initiated during re‐hydration from snow at subzero temperatures. It is proposed that water uptake from snow at subzero temperatures occurs in the gaseous phase and depends only on the temperature‐related differences in water potential between the cell contents and the surrounding atmosphere in equilibrium with snow. Photosynthetic activity and re‐hydration from snow at subzero temperatures are of great ecological importance for primary production in extreme environments such as Antarctica where metabolic activity is severely limited by water availability and low temperatures.
Article
Comparisons have been made of the shape of algal cells in the lichen Parmelia sulcata which was subjected to controlled desiccation regimes inducing substantial water loss. The spherical appearance of algal cells obtained by conventional techniques for transmission electron microscopy (TEM) was shown by low temperature scanning electron microscopy (LTSEM) to be the consequence of rapid rehydration during fixation. Collapse of the walls of algal cells and fungal hyphae in the medulla and algal layer when desiccated were observed with LTSEM and shown to be reversible on rehydration. Desiccation‐induced contraction of cortical fungal protoplasts was detected with LTSEM. Fixation with osmium vapour only before TEM demonstrated a similar contraction of algal protoplasts.
Article
In polar ecosystems primary producers have to cope with the very limited living conditions of the harsh climate. Vascular plants in the Northern Hemisphere extend to the northem-most edges of the continents, but only two taxa are present as far south as the Antarctic Peninsula region in the Southern Hemisphere. Lower plants, lichens in particular, become more important with increasing latitudes and form the dominant element of the Antarctic vegetation. Based on recent investigations and literature, this paper discusses to what extent lichens are better adapted to snow and ice than vascular plants. Vascular plants in high latitudes have high freezing tolerances but are photosynthetically inactive in winter (e.g., evergreen coniferous species), while lichens in a highly freezing-tolerant stage can be active and productive under winter conditions. Vascular plants can be active under snow but have no photosynthesis if the tissue is frozen. Recent in situ measurements indicate that lichens are able to photosynthesize at temperatures below - 10°C, apparently in the frozen state. It was also found that photosynthetic CO2 exchange of dry thalli can be activated by snow during frost. Water uptake during winter was also recorded for coniferous trees at the arctic timberline. This uptake may reduce water stress in conifers but apparently has no relevance for metabolic activity. Water uptake from snow and metabolic activity at - 10°C are possible for lichens because they are able to photo- synthesize at water potentials lower than -20 MPa. Although lichens are adapted to be active in snow at low temperatures, strong light on clear days may inhibit the photosynthetic apparatus.
Article
The effect of prolonged frozen storage on patterns of photosynthesis and respiration in the lichen Alectoria ochroleuca (Hoffm.) Massal. has been examined. The results indicate that this plant not only survives long-term exposure to low temperatures but also that its basic photosynthetic and respiratory responses to temperature, light intensity, and thallus moisture content are altered very little by long-term storage at −60 °C. This maintenance not only of absolute viability but also of the more subtle patterns of physiological activity suggests that such storage may be used to hold lichen material for use in multivariate experimental systems which require replicates having identical field pretreatment.
Article
In the second of three field studies on the ecology and physiology of lichens on Clark Peninsula, Wilkes Land, Antarctica, photosynthetic activity due to natural and artificial soaking of lichen thalli was investigated. Gravimetric measurements were used to quantify water uptake by lichens in contact with snow or ice. Quantum flux density under a 15 cm thick layer of snow can reach light saturation for net photosynthesis of Usnea sphacelata at temperatures around 0°C. Measurements with a steady-state CO2 diffusion porometer in the field reveal that, in Usnea antarctica, Umbilicaria decussata, and U. aprina, the optimum water content for net photosynthesis was 75–115 % d.wt. after the thalli were sprayed with water or submerged. The depression of net photosynthesis at super-optimal water content was strong in these species. In naturally soaked Usnea sphacelata this depression was less apparent. The water content resulting from contact with snow is frequently near the optimum for photosynthesis. In lichens of continental Antarctica it seems that super-optimal water contents are the exception rather than the rule.
Article
Field measurements of CO2 exchange were made with an infra-red gas analyser system on lichens at Bailey Peninsula, Wilkes Land, continental Antarctica. It has been demonstrated that Usnea sphacelata, a prominent element of the cryptogamic vegetation of this area, became photosynthetically active at temperatures below 0°C when the thalli were covered by drifted snow. Carbon dioxide uptake was detected down to −10°C. The carbon production during such a ‘frost’ day was considerable for a slow-growing Antarctic lichen. The importance of snow for production in lichens is emphasized. The mechanism of water uptake when the thalli are frozen needs further investigation.
Article
Photosynthetic activity and structural changes at subzero temperatures were monitored in the foliose lichen Umbilicaria aprina Nyl. from continental Antarctica. Carbon dioxide gas exchange measurements revealed that net photosynthesis and dark respiration occurred at subzero temperatures regardless of whether a lichen thallus saturated with liquid water was exposed to subzero temperatures, or if a dry thallus was re-hydrated only from snow at subzero temperatures. When water-saturated thalli of U. aprina were slowly cooled at subzero temperatures ice nucleation activity could be detected at -5.4 degrees C, indicating extracellular freezing of water. Using low-temperature scanning electron microscopy (LTSEM) it was demonstrated that extracellular ice formation leads to cytorrhysis in the photobiont cells and to cavitation in the mycobiont cells. Both processes were reversible if the lichen thallus was re-warmed. When dry lichen thalli were covered with snow at subzero temperatures a substantial re-hydration from snow could be observed in LTSEM micrographs and measured gravimetrically. The final thallus water content was strongly dependent on the temperature regime and gave water contents between 20% d. wt at -21 degrees C and 56% d. wt at -4.5 degrees C after 16 h exposure. Carbon dioxide gas exchange measurements revealed that metabolic activity was initiated during re-hydration from snow at subzero temperatures. It is proposed that water uptake from snow at subzero temperatures occurs in the gaseous phase and depends only on the temperature-related differences in water potential between the cell contents and the surrounding atmosphere in equilibrium with snow. Photosynthetic activity and re-hydration from snow at subzero temperatures are of great ecological importance for primary production in extreme environments such as Antarctica where metabolic activity is severely limited by water availability and low temperatures.
Article
summaryFour species of epiphytic lichens from California with varying responses to salinity were studied to determine the response of CO2 exchange to decreasing water potential (Ψ). Changes in Ψ were induced either by allowing dry thalli to come into equilibrium with atmospheres of defined water vapour pressure, or by osmotic stress through incubation of the thalli in sea salt or sorbitol solutions. In two species the gradual decline of CO2 uptake rates with decreasing Ψ was independent of the method which was used to establish ft (and therefore relatively independent of the bulk water content of the thalli); measurable CO2 fixation occurred in Dendrographa minor Darb. and Ramalina menziesii Tayl. to values of Ψ as low as –38 and – 22 MPa, respectively. Photosynthesis of Evernia prunastri (L.) Ach. responded similarly to low Ψ which was induced either through atmospheric desiccation or osmotic dehydration (sorbitol). However, E. prunastri was much more sensitive to low Ψ when the thallus was treated with NaCl solutions. Photosynthesis in Pseudocyphellaria anthraspis Magn., the only species investigated with a blue-green (cyanobacterial) photobiont, was strictly dependent on wetting of the thallus with water. Net photosynthesis was detectable to – 3−5 MPa in sorbitol and salt solutions, but in moist air of a similar Ψ P. anthraspis showed no CO2 uptake. In all four species, dark respiration was markedly less sensitive to osmotic dehydration in sorbitol or salt solutions than at the same Ψ under atmospheric desiccation. In E. prunastri, salt stress combined with high light resulted in a much more pronounced decrease in the rate of photosynthesis than either salt stress in low light, or high light alone. These species provide a model system to differentiate the effect of atmospheric desiccation and osmotic stress on lichen metabolism, and to study the interaction of drought per se with other stress factors such as salt and high light.
Article
Only a few small areas of the coast of north Victoria Land are free of ice. Such an area is Birthday Ridge, Yule Bay, where a lichen vegetation is developed in the interspaces of granitic rocks of the mountaintop detritus. The largest and most frequent lichen is Usnea sulphurea, growing as a light form at exposed habitats and as a shade form below pebbles. Both forms differ by chlorophyll content and temperature dependency of net photosynthesis, which demonstrates an adaptive response of these forms to their environment. Usnea sulphurea is able to take up water from humid air, but in its natural habitat it is moistened mostly by melting snow. CO2-gas exchange is detectable when the water content of the thalli rises above 30% of the dry weight. A decrease of net photosynthesis at very high water contents (at 6C) is not visible. At a CO2 concentration of the air below 200 ppm the lichens have a negative CO2 balance; net photosynthesis is still not saturated at 370 ppm CO2 in the air under the experimental conditions. Like other antarctic lichens, U. sulphurea is a moderately productive, slowly growing species.
Article
Rates of net CO2 exchange in five sympatric species of Umbilicaria were measured after 10 years at-20C. During that time, the lichens had been at either a high (saturated) or a low (air-dry) water content. The results showed an immediate, return to normal rates of gas exchange for air-dried then frozen U.vellea. Rates returned to normal for air-dried U. deusta within four days. The three other species studied, U. mammulata, U. papulosa and U. muhlenbergii showed intermediate responses. Water saturated then frozen thalli of U. vellea were irreparably damaged after 10 years; even fungal respiration was severely impaired. In U. mammulata, U. papulosa and U. muhlenbergii, photosynthesis was eliminated but fungal respiration rates were not influenced. In contrast to this, water saturated then frozen thalli of U. deusta showed a nearly equal photosynthetic capacity to the original rates following 10 years at -20C. In all cases the magnitude of the effect of the long-term subzero treatment correlated well with the known distribution patterns of the lichens in the field.
Article
The temperature at which freezing was initiated within five lichen species was determined using thermal analysis. All of the species tested froze above −4 °C, indicating the association of heterogeneous ice nucleation active agents effective at warm temperatures. Ice nucleation activity was expressed over a range of tissue moisture contents. The results of the present study confirmed earlier reports that lichen tissues were a source of biological ice nucleation activity. In addition, these studies demonstrated that ice nucleation activity is a characteristic of intact lichen tissues and is expressed under conditions representative of those in nature.
Article
Nearly simultaneous measurements of auroral zone electric fields are obtained by the Dynamics Explorer spacecraft at altitudes below 900 km and above 4,500 km during magnetic conjunctions. The measured electric fields are usually perpendicular to the magnetic field lines. The north-south meridional electric fields are projected to a common altitude by a mapping function which accounts for the convergence of the magnetic field lines. When plotted as a function of invariant latitude, graphs of the projected electric fields measured by both DE-1 and DE-2 show that the large-scale electric field is the same at both altitudes, as expected. Superimposed on the large-scale fields, however, are small-scale features with wavelengths less than 100 km which are larger in magnitude at the higher altitude. Fourier transforms of the electric fields show that the magnitudes depend on wavelength. Outside of the auroral zone the electric field spectrums are nearly identical. But within the auroral zone the high and low altitude electric fields have a ratio which increases with the reciprocal of the wavelength. The small-scale electric field variations are associated with field-aligned currents. These currents are measured with both a plasma instrument and magnetometer on DE-1.
Article
Low-temperature scanning electron microscopy (LTSEM) involves three main operational phases: 1. The specimen is rapidly frozen (“quench-frozen”) after which it is maintained either under vacuum or in a dry, argon atmosphere at a temperature below — 130°C (143K). This is generally considered to be the point above which the recrystallization of pure water will occur (e. g., see Talmon, 1982a, and Read et al., 1983, and references therein). Quench-freezing rapidly transforms freezable cellular and extracellular water into its solid state (ice) and the specimen is considered to be fully frozen-hydrated (FFH). 2. The FFH specimen may be fractured, dissected, or retained intact and, if required, it may be heated (etched) and/or coated. If the sample is etched, variable amounts of water are removed by sublimation and the specimen may then be considered partially freeze-dried (PFD). 3. The sample is observed at low temperature [approx. -175°C (98K)] on a temperature-controlled stage in the scanning electron microscope.
Article
Annual gross productivity of the lichen-dominated cryptoendolithic community was calculated from a computer analysis of photosynthetic response based on laboratory measurements of C02 exchange and three years (1985–1988) of field nanoclimate data. Photosynthetic optimum increased from −3 to 2°C between irradiance levels of 100 and 1500 μmol photons m−2 s−1, while the upper compensation point rose from 1 to 17°C. The mean yearly total time available for metabolic activity (temperature above −10°C and moisture present) was 771.3 h for horizontal rock, 421.5 h for northeast-oriented sloped rock, and 1042.2 h for a small depression in horizontal rock (the characteristic site of occasional lichen apothecia). The calculated mean gross productivity value for a horizontal rock was 1215 mg C m−2 y−1, and net photosynthetic gain was 606 mg C m−2 y−1. Net ecosystem productivity (annual accretion of cellular biomass) estimated from long-term events amounted to only about 3 mg C m−2 y−1. The difference between these two values may represent the long-term metabolic costs of the frequent dehydration-rehydration and freezing-thawing cycles or of overwintering, and may account for the leaching of organic substances to the rock. The yearly gross productivity of the cryptoendolithic microbial community of the entire Ross Desert area was estimated at approximately 120,000–180,000 kg C. Of this, 600–900 kg C is in microbial biomass, and much of the rest is soluble compounds that leach into the rocks and possibly percolate to the valleys, providing a source of organic matter for lakes, rivers, and soils.
Article
In the frigid desert of the Antarctic dry valleys there are no visible life forms on the surface of the soil or rocks. Yet in certain rock types a narrow subsurface zone has a favorable microclimate and is colonized by microorganisms. Dominant are lichens of unusual organization. They survive not by physiological adaptation to lower temperatures, but by changing their mode of growth, being able to grow between the crystals of porous rocks. Their activity results in mobilization of iron compounds and in rock weatherning with a characteristic pattern of exfoliation. This simple ecosystem lacks both higher consumers and predators.
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