Distributional and ecophysiological study on the Antarctic lichens species pair Usnea antarctica/Usnea aurantiaco-atra

A geospatial dataset of lichen key attributes in the Earth's three poles

In the Antarctic, Arctic, and Tibetan Plateau-recognized as the Earth's three poles characterized by extremely harsh environments-lichens prevail in the ecosystem and play crucial roles as pioneer species. Despite their importance, studies investigating the spatial distribution patterns of lichen attributes are scarce due to a lack of appropriate datasets. To bridge this gap and enhance our understanding of the growth preferences of lichens in these areas, here we present a geospatial dataset encompassing key attributes of lichens, such as color type and growth form, for over 2800 lichen species and 170,000 in-situ lichen records. The dataset facilitates the creation of the first spatial distribution map illustrating the variation of lichen attributes across different latitudes and longitudes. This can serve as a foundational resource for studies on the relationship between lichen types and their growing environment, which is a vital scientific question in the ecology domain. Additionally, it can contribute to the development of specialized remote sensing technique tailored for lichen monitoring, which is currently lacking.

Floristic Similarities between the Lichen Flora of Both Sides of the Drake Passage: A Biogeographical Approach

This paper analyses the lichen flora of Navarino Island (Tierra del Fuego, Cape Horn Region, Chile), identifying species shared with the South Shetland Islands (Antarctic Peninsula). In this common flora, species are grouped by their biogeographic origin (Antarctic-subantarctic endemic, austral, bipolar, and cosmopolitan), their habitat on Navarino Island (coastal, forest, and alpine), their morphotype (crustaceous, foliaceous, fruticulose, and cladonioid), and the substrate from which they were collected (epiphytic, terricolous and humicolous, and saxicolous). A total of 124 species have been recognised as common on both sides of the Drake Passage, predominantly bipolar, crustaceous, and saxicolous species, and with an alpine distribution on Navarino Island. The most interesting fact is that more than 30% of the flora is shared between the southern tip of South America and the western Antarctic Peninsula, which is an indication of the existence of a meridian flow of propagules capable of crossing the Antarctic polar front.

Climate change leads to higher NPP at the end of the century in the Antarctic Tundra: Response patterns through the lens of lichens

Poikilohydric autotrophs are the main colonizers of the permanent ice-free areas in the Antarctic tundra biome. Global climate warming and the small human footprint in this ecosystem make it especially vulnerable to abrupt changes. Elucidating the effects of climate change on the Antarctic ecosystem is challenging because it mainly comprises poikilohydric species, which are greatly influenced by microtopographic factors. In the present study, we investigated the potential effects of climate change on the metabolic activity and net primary photosynthesis (NPP) in the widespread lichen species Usnea aurantiaco-atra. Long-term monitoring of chlorophyll a fluorescence in the field was combined with photosynthetic performance measurements in laboratory experiments in order to establish the daily response patterns under biotic and abiotic factors at micro- and macro-scales. Our findings suggest that macroclimate is a poor predictor of NPP, thereby indicating that microclimate is the main driver due to the strong effects of microtopographic factors on cryptogams. Metabolic activity is also crucial for estimating the NPP, which is highly dependent on the type, distribution, and duration of the hydration sources available throughout the year. Under RCP 4.5 and RCP 8.5, metabolic activity will increase slightly compared with that at present due to the increased precipitation events predicted in MIROC5. Temperature is highlighted as the main driver for NPP projections, and thus climate warming will lead to an average increase in NPP of 167-171% at the end of the century. However, small changes in other drivers such as light and relative humidity may strongly modify the metabolic activity patterns of poikilohydric autotrophs, and thus their NPP. Species with similar physiological response ranges to the species investigated in the present study are expected to behave in a similar manner provided that liquid water is available.

Summer activity patterns for a moss and lichen in the maritime Antarctic with respect to altitude

There is considerable scientific interest as to how terrestrial biodiversity in Antarctica might respond, or be expected to respond, to climate change. The two species of vascular plant confined to the Antarctic Peninsula have shown clear gains in density and range extension. However, little information exists for the dominant components of the flora, lichens and bryophytes. One approach has been to look at change in biodiversity using altitude as a proxy for temperature change and previous results for Livingston Island suggested that temperature was the controlling factor. We have extended this study at the same site by using chlorophyll fluorometers to monitor activity and microclimate of the lichen, Usnea aurantiaco-atra, and the moss, Hymenoloma crispulum. We confirmed the same lapse rate in temperature but show that changes in water relations with altitude is probably the main driver. There were differences in water source with U. aurantiaco-atra benefitting from water droplet harvesting and the species performed substantially better at the summit. In contrast, activity duration, chlorophyll fluorescence and photosynthetic modelling all show desiccation to have a large negative impact on the species at the lowest site. We conclude that water relations are the main drivers of biodiversity change along the altitudinal gradient with nutrients, not measured here, as another possible contributor.

Study of Ecophysiological Responses of the Antarctic Fruticose Lichen Cladonia borealis Using the PAM Fluorescence System under Natural and Laboratory Conditions

Antarctic lichens have been used as indicators of climate change for decades, but only a few species have been studied. We assessed the photosynthetic performance of the fruticose lichen Cladonia borealis under natural and laboratory conditions using the PAM fluorescence system. Compared to that of sun-adapted Usnea sp., the photosynthetic performance of C. borealis exhibits shade-adapted lichen features, and its chlorophyll fluorescence does not occur during dry days without rain. To understand its desiccation-rehydration responses, we measured changes in the PSII photochemistry in C. borealis under the average light intensity of dawn light and daylight and the desiccating conditions of its natural microclimate. Interestingly, samples under daylight and rapid-desiccation conditions showed a delayed reduction in Fv'/Fm' and rETRmax, and an increase in Y(II) and Y(NPQ) levels. These results suggest that the photoprotective mechanism of C. borealis depends on sunlight and becomes more efficient with improved desiccation tolerance. Amplicon sequencing revealed that the major photobiont of C. borealis was Asterochloris irregularis, which has not been reported in Antarctica before. Collectively, these results from both field and laboratory could provide a better understanding of specific ecophysiological responses of shade-adapted lichens in the Antarctic region.

Symbiosis at its limits: ecophysiological consequences of lichenization in the genus Prasiola in Antarctica

BACKGROUND AND AIMS

Lichens represent a symbiotic relationship between at least one fungal and one photosynthetic partner. The association between the lichen-forming fungus Mastodia tessellata (Verrucariaceae) and different species of Prasiola (Trebouxiophyceae) has an amphipolar distribution and represents a unique case study for the understanding of lichen symbiosis because of the macroalgal nature of the photobiont, the flexibility of the symbiotic interaction and the co-existence of free-living and lichenized forms in the same microenvironment. In this context, we aimed to (1) characterize the photosynthetic performance of co-occurring populations of free-living and lichenized Prasiola and (2) assess the effect of the symbiosis on water relations in Prasiola, including its tolerance of desiccation and its survival and performance under sub-zero temperatures.

METHODS

Photochemical responses to irradiance, desiccation and freezing temperature and pressure-volume curves of co-existing free-living and lichenized Prasiola thalli were measured in situ in Livingston Island (Maritime Antarctica). Analyses of photosynthetic pigment, glass transition and ice nucleation temperatures, surface hydrophobicity extent and molecular analyses were conducted in the laboratory.

KEY RESULTS

Free-living and lichenized forms of Prasiola were identified as two different species: P. crispa and Prasiola sp., respectively. While lichenization appears to have no effect on the photochemical performance of the alga or its tolerance of desiccation (in the short term), the symbiotic lifestyle involves (1) changes in water relations, (2) a considerable decrease in the net carbon balance and (3) enhanced freezing tolerance.

CONCLUSIONS

Our results support improved tolerance of sub-zero temperature as the main benefit of lichenization for the photobiont, but highlight that lichenization represents a delicate equilibrium between a mutualistic and a less reciprocal relationship. In a warmer climate scenario, the spread of the free-living Prasiola to the detriment of the lichen form would be likely, with unknown consequences for Maritime Antarctic ecosystems.

Antarctic Studies Show Lichens to be Excellent Biomonitors of Climate Change

Lichens have been used as biomonitors for multiple purposes. They are well-known as air pollution indicators around urban and industrial centers. More recently, several attempts have been made to use lichens as monitors of climate change especially in alpine and polar regions. In this paper, we review the value of saxicolous lichens for monitoring environmental changes in Antarctic regions. The pristine Antarctica offers a unique opportunity to study the effects of climate change along a latitudinal gradient that extends between 62° and 87° S. Both lichen species diversity and thallus growth rate seem to show significant correlations to mean annual temperature 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.

Can Antarctic lichens acclimatize to changes in temperature?

The Antarctic Peninsula, a tundra biome dominated by lichens and bryophytes, is an ecozone undergoing rapid temperature shifts. Such changes may demand a high physiological plasticity of the local lichen species to maintain their role as key drivers in this pristine habitat. This study examines the response of net photosynthesis and respiration to increasing temperatures for three Antarctic lichen species with different ecological response amplitudes. We hypothesize that negative effects caused by increased temperatures can be mitigated by thermal acclimation of respiration and/or photosynthesis. The fully controlled growth chamber experiment simulated intermediate and extreme temperature increases over the time course of 6 weeks. Results showed that, in contrast to our hypothesis, none of the species was able to down-regulate temperature-driven respiratory losses through thermal acclimation of respiration. Instead, severe effects on photobiont vitality demonstrated that temperatures around 15°C mark the upper limit for the two species restricted to the Antarctic, and when mycobiont demands exceeded the photobiont capacity they could not survive within the lichen thallus. In contrast, the widespread lichen species was able to recover its homoeostasis by rapidly increasing net photosynthesis. We conclude that to understand the complete lichen response, acclimation processes of both symbionts, the photo- and the mycobiont, have to be evaluated separately. As a result, we postulate that any acclimation processes in lichen are species-specific. This, together with the high degree of response variability and sensitivity to temperature in different species that co-occur spatially close, complicates any predictions regarding future community composition in the Antarctic. Nevertheless, our results suggest that species with a broad ecological amplitude may be favoured with on-going changes in temperature.

Elemental content of mosses and lichens from Livingston Island (Antarctica) as determined by instrumental neutron activation analysis (INAA)

The total content of 8 major and 32 trace elements in four species of mosses and two of lichens as well as neighboring soil and rocks collected from different places of the Livingston Island Antarctica was determined by instrumental neutron activation analysis. The main goals of the project consisted of evidencing the possible trace of anthropogenic contamination as well as the influence of altitude on the distribution of considered elements. In the absence of a unanimously accepted descriptor, enrichment factor, geo-accumulation, and pollution load indices with respect to soil and rocks were used. The data, interpreted within the model of a reference plant, were compared with previous studies regarding the same organisms in similar geographic and climatological areas. The experimental results evidenced different capacity of mosses and lichens to retain the considered elements, but within experimental uncertainties, no traces of anthropogenic pollution were found. At the same time, it was found that the content of most of the elements decreased with the altitude.

Sensitivity of photosynthetic processes to freezing temperature in extremophilic lichens evaluated by linear cooling and chlorophyll fluorescence

Extremophilic lichens and their photosynthesizing photobionts from the cold regions of Earth are adapted to perform photosynthesis at subzero temperatures. To evaluate interspecific differences in the critical temperature for primary photochemical processes of photosynthesis, we exposed lichen thalli of Usnea antarctica, Usnea aurantiaco-atra, and Umbilicaria cylindrica to linear cooling from +20 to -50 °C at a constant rate of 2 °C min^-1. Simultaneously, two chlorophyll fluorescence parameters (F_V/F_M - potential yield of photosynthetic processes in photosystem II, Φ_PSII - effective quantum yield of PS II) evaluating a gradual subzero temperature-induced decline in photosynthetic processes were measured by a modulated fluorometer. For the studied species, the response of F_V/F_M and Φ_PSII to declining temperature showed an S-curve shape. The decline in F_V/F_M and Φ_PSII at low temperatures started at -5 and +5 °C, respectively in the majority of cases. The decline was, however, species-specific. U. aurantiaco-atra showed a constant-rate decline of Φ_PSII from the physiological temperature 20 °C. U. antarctica exhibited the first sign of F_V/F_M decline at -12 °C. The critical temperature related to full inhibition of the photosynthetic processes in PSII (F_V/F_M), was found at -20 °C. However, this occurred at -30 °C for U. cylindrica. In an individual sample, the critical temperature for F_V/F_M was typically lower than for Φ_PSII. The method of linear cooling combined with simultaneous measurements of chlorophyll fluorescence parameters proved to be an efficient tool in the estimation of extremophilic species sensitivity/resistance to freezing.