Physiological Plasticity as a Strategy to Cope with Harsh Climatic Conditions: Ecophysiological Meta-Analysis of the Cosmopolitan Moss Ceratodon purpureus in the Southern Hemisphere.

Determining the physiological tolerance ranges of species is necessary to comprehend the limits of their responsiveness under strong abiotic pressures. For this purpose, the cosmopolitan moss Ceratodon purpureus (Hedw.) Brid. is a good model due to its wide geographical distribution throughout different biomes and habitats. In order to disentangle how this species copes with stresses such as extreme temperatures and high radiation, we designed a meta-analysis by including the main photosynthetic traits obtained by gas exchange measurements in three contrasting habitats from the Southern Hemisphere. Our findings highlight that traits such as respiration homeostasis, modulation of the photosynthetic efficiency, adjustment of the optimal temperature, and switching between shade and sun-adapted forms, which are crucial in determining the responsiveness of this species. In fact, these ecophysiological traits are in concordance with the climatic particularities of each habitat. Furthermore, the photosynthetic trends found in our study point out how different Livingston Island (Maritime Antarctica) and Granite Harbour (Continental Antarctica) are for plant life, while the population from the Succulent Karoo Desert (South Africa) shares traits with both Antarctic regions. Altogether, the study highlights the high resilience of C. purpureus under abrupt climate changes and opens new perspectives about the wide spectrum of physiological responses of cryptogams to cope with climate change scenarios.

La vegetación antártica, centinela del cambio climático / Antarctic vegetation, a sentinel to climate change

La Antártida es el continente más frío, seco, alto y ventoso; aquí, los líquenes y musgos crecen donde es más cálido, húmedo, bajo y protegido. En general, la productividad vegetal depende estrechamente de la longitud del periodo en el cual el agua líquida está disponible, por ello los vegetales se ven confinados a lugares con microclima excepcionalmente favorable. Es está fuerte relación entre microclima y disponibilidad de agua líquida y productividad /crecimiento, lo que hace a este ecosistema potencialmente tan útil para la monitorización del cambio climático global, especialmente en lo que se refiere al incremento de temperatura. Incluso un pequeño aumento de temperatura puede suponer un marcado incremento en el área afectada por estos periodos cálidos produciendo alteraciones en las comunidades vegetales. Es cada vez más claro que existen dos Antártidas, la Península y el continente. Se diferencian en el factor que controla la distribución de la biodiversidad vegetal. En la Península Antártica la temperatura sería el factor determinante y en el continente lo sería la disponibilidad de agua líquida. También el stress por radiación parece limitado a la zona continental. Se han llevado a cabo diferentes intentos de usar líquenes como monitores de cambio climático en regiones polares. La prístina Antártida ofrece una oportunidad única de estudiar el efecto del cambio climático a lo largo de gradientes latitudinales que se extienden entre 62º y 87º S. (AU)

Antarctica is the coldest, driest, highest and windiest continent; the lichens and mosses grow where it is more warm, wet, low and protected. Overall productivity is strongly influenced by the length of period when water is available and the plants become, therefore, increasingly confined to areas of exceptionally good microclimate. It is this strong link between microclimate, water availability and productivity/growth that makes the system so potentially useful for monitoring global climate change, especially temperature increase. Even a small increase in temperature will markedly alter the areas over which such warm periods occur and bring with it a marked community shift. It is becoming clear that there are two Antarcticas, the Peninsula and the main continent. These differ in the controls on biodiversity distribution, there is a probably water unlimited but temperature-determined biodiversity cline in the Peninsula compared to a, water controlled, temperature-independent, fragmented vegetation in the continent. The reverse diel pattern of activity with the presence of very high light stress also seems to be confined to the continent. Several attempts have been made to use lichens as monitors of climate change especially in alpine and polar regions. The pristine Antarctica offers a unique opportunity to study the effects of climate change along a latitudinal gradient that extends between 62º and 87º S. Both lichen species diversity and thallus growth rate seem to show significant correlations to mean annual temperature and precipitation for gradients across the continent as well as to short time climate oscillation in the Antarctic Peninsula. Competition interactions appear to be small so that individual thalli develop in balance with environmental conditions and, as a result, can indicate the trends in productivity for discrete time intervals over long periods of time in a climate warming scenario. (AU)

La vegetación antártica, centinela del cambio climático / Antarctic vegetation, a sentinel to climate change

La Antártida es el continente más frío, seco, alto y ventoso; aquí, los líquenes y musgos crecen donde es más cálido, húmedo, bajo y protegido. En general, la productividad vegetal depende estrechamente de la longitud del periodo en el cual el agua líquida está disponible, por ello los vegetales se ven confinados a lugares con microclima excepcionalmente favorable. Es está fuerte relación entre microclima y disponibilidad de agua líquida y productividad /crecimiento, lo que hace a este ecosistema potencialmente tan útil para la monitorización del cambio climático global, especialmente en lo que se refiere al incremento de temperatura. Incluso un pequeño aumento de temperatura puede suponer un marcado incremento en el área afectada por estos periodos cálidos produciendo alteraciones en las comunidades vegetales. Es cada vez más claro que existen dos Antártidas, la Península y el continente. Se diferencian en el factor que controla la distribución de la biodiversidad vegetal. En la Península Antártica la temperatura sería el factor determinante y en el continente lo sería la disponibilidad de agua líquida. También el stress por radiación parece limitado a la zona continental. Se han llevado a cabo diferentes intentos de usar líquenes como monitores de cambio climático en regiones polares. La prístina Antártida ofrece una oportunidad única de estudiar el efecto del cambio climático a lo largo de gradientes latitudinales que se extienden entre 62º y 87º S. Tanto la diversidad de especies liquénicas, como sus tasas de crecimiento muestran correlaciones significativas con la temperatura y la precipitación anual a través del continente así como con las oscilaciones climáticas de periodo corto sucedidas en la Península Antártica. Las interacciones competitivas parecen ser pequeñas, de modo que cada individuo se desarrolla en equilibrio con las condiciones ambientales y, como resultado, puede indicar las tendencias en la productividad para intervalos temporales discretos dentro de un escenario de cambio climático. "Es todo aquí tan imponente, tan gigantescas todas las formas que las palabras no alcanzan a describirlo acertadamente. Nosotros cuatro somos los primeros seres humanos a quienes les ha sido dado asombrarse ante estas maravillas de la naturaleza y se nos antoja, a veces, que habrá de pasar largo tiempo antes de que otros pongan el pie en estos remotos parajes" (Diario de Shackleton, 4 de Diciembre de 1908)"

Antarctica is the coldest, driest, highest and windiest continent; the lichens and mosses grow where it is more warm, wet, low and protected. Overall productivity is strongly influenced by the length of period when water is available and the plants become, therefore, increasingly confined to areas of exceptionally good microclimate. It is this strong link between microclimate, water availability and productivity/growth that makes the system so potentially useful for monitoring global climate change, especially temperature increase. Even a small increase in temperature will markedly alter the areas over which such warm periods occur and bring with it a marked community shift. It is becoming clear that there are two Antarcticas, the Peninsula and the main continent. These differ in the controls on biodiversity distribution, there is a probably water unlimited but temperature-determined biodiversity cline in the Peninsula compared to a, water controlled, temperature-independent, fragmented vegetation in the continent. The reverse diel pattern of activity with the presence of very high light stress also seems to be confined to the continent. Several attempts have been made to use lichens as monitors of climate change especially in alpine and polar regions. The pristine Antarctica offers a unique opportunity to study the effects of climate change along a latitudinal gradient that extends between 62º and 87º S. Both lichen species diversity and thallus growth rate seem to show significant correlations to mean annual temperature and precipitation for gradients across the continent as well as to short time climate oscillation in the Antarctic Peninsula. Competition interactions appear to be small so that individual thalli develop in balance with environmental conditions and, as a result, can indicate the trends in productivity for discrete time intervals over long periods of time in a climate warming scenario

Lichen Vitality After a Space Flight on Board the EXPOSE-R2 Facility Outside the International Space Station: Results of the Biology and Mars Experiment.

As part of the Biology and Mars Experiment (BIOMEX; ILSRA 2009-0834), samples of the lichen Circinaria gyrosa were placed on the exposure platform EXPOSE-R2, on the International Space Station (ISS) and exposed to space and to a Mars-simulated environment for 18 months (2014-2016) to study: (1) resistance to space and Mars-like conditions and (2) biomarkers for use in future space missions (Exo-Mars). When the experiment returned (June 2016), initial analysis showed rapid recovery of photosystem II activity in the samples exposed exclusively to space vacuum and a Mars-like atmosphere. Significantly reduced recovery levels were observed in Sun-exposed samples, and electron and fluorescence microscopy (transmission electron microscope and field emission scanning electron microscope) data indicated that this was attributable to the combined effects of space radiation and space vacuum, as unirradiated samples exhibited less marked morphological changes compared with Sun-exposed samples. Polymerase chain reaction analyses confirmed that there was DNA damage in lichen exposed to harsh space and Mars-like environmental conditions, with ultraviolet radiation combined with space vacuum causing the most damage. These findings contribute to the characterization of space- and Mars-resistant organisms that are relevant to Mars habitability.

Cellular Responses of the Lichen Circinaria gyrosa in Mars-Like Conditions.

Lichens are extremely resistant organisms that colonize harsh climatic areas, some of them defined as "Mars-analog sites." There still remain many unsolved questions as to how lichens survive under such extreme conditions. Several studies have been performed to test the resistance of various lichen species under space and in simulated Mars-like conditions. The results led to the proposal that Circinaria gyrosa (Lecanoromycetes, Ascomycota) is one of the most durable astrobiological model lichens. However, although C. gyrosa has been exposed to Mars-like environmental conditions while in a latent state, it has not been exposed in its physiologically active mode. We hypothesize that the astrobiological test system "Circinaria gyrosa," could be able to be physiologically active and to survive under Mars-like conditions in a simulation chamber, based on previous studies performed at dessicated-dormant stage under simulated Mars-like conditions, that showed a complete recover of the PSII activity (Sánchez et al., 2012). Epifluorescence and confocal laser scanning microscopy (CLSM) showed that living algal cells were more abundant in samples exposed to niche conditions, which simulated the conditions in micro-fissures and micro-caves close to the surface that have limited scattered or time-dependent light exposure, than in samples exposed to full UV radiation. The medulla was not structurally affected, suggesting that the niche exposure conditions did not disturb the lichen thalli structure and morphology as revealed by field emission scanning electron microscopy (FESEM). In addition, changes in the lichen thalli chemical composition were determined by analytical pyrolysis. The chromatograms resulting from analytical pyrolysis at 500°C revealed that lichen samples exposed to niche conditions and full UV radiation consisted primarily of glycosidic compounds, lipids, and sterols, which are typical constituents of the cell walls. However, specific differences could be detected and used as markers of the UV-induced damage to the lichen membranes. Based on its viability responses after rehydration, our study shows that the test lichen survived the 30-day incubation in the Mars chamber particularly under niche conditions. However, the photobiont was not able to photosynthesize under the Mars-like conditions, which indicates that the surface of Mars is not a habitable place for C. gyrosa.