Antarctic Cryptogams Research Articles

Nitrogen isotope fractionation explains the 15N enrichment of Antarctic cryptogams by volatilized ammonia from penguin and seal colonies

Vegetation near bird and seal rookeries typically has high δ15N signatures and these high values are linked to the enriched δ15N values of rookery soils. However, Antarctic cryptogams are mostly dependent on atmospheric ammonia (NH3) and volatized NH3 from rookeries is severely depleted in δ15N-NH3. So there is an apparent discrepancy between the isotopically depleted source (NH3) and δ15N-enriched vegetation. In this article, we aim to resolve this discrepancy to better understand the mechanisms and processes involved in isotopic changes during nitrogen transfer between Antarctic marine and terrestrial ecosystems. Under laboratory conditions, we quantified whether volatized NH3 affects the isotopic signature of cryptogams. NH3 volatilizing from penguin guano and elephant seal dung was depleted (44–49‰) in δ15N when captured on acidified filters, compared to the source itself. Cryptogams exposed to the volatized NH3 were enriched (18.8–23.9‰) in δ15N. The moss Andreaea regularis gained more nitrogen (0.9%) than the lichen Usnea antarctica (0.4%) from volatilized NH3, indicating a potential difference in atmospheric NH3 acquisition that is consistent with existing field differences in nitrogen concentrations and δ15N between mosses and lichens in general. This study clarifies the δ15N enrichment of cryptogams resulting from one of the most important nitrogen pathways for Antarctic vegetation.

Atmospheric chemistry of mercury in Antarctica and the role of cryptogams to assess deposition patterns in coastal ice-free areas

Mercury in the Antarctic troposphere has a distinct chemistry and challenging long-term measurements are needed for a better understanding of the atmospheric Hg reactions with oxidants and the exchanges of the various mercury forms among air-snow-sea and biota. Antarctic mosses and lichens are reliable biomonitors of airborne metals and in short time they can give useful information about Hg deposition patterns. Data summarized in this review show that although atmospheric Hg concentrations in the Southern Hemisphere are lower than those in the Northern Hemisphere, Antarctic cryptogams accumulate Hg at levels in the same range or higher than those observed for related cryptogam species in the Arctic, suggesting an enhanced deposition of bioavailable Hg in Antarctic coastal ice-free areas.In agreement with the newest findings in the literature, the Hg bioaccumulation in mosses and lichens from a nunatak particularly exposed to strong katabatic winds can be taken as evidence for a Hg contribution to coastal ecosystems by air masses from the Antarctic plateau. Human activities on the continent are mostly concentrated in coastal ice-free areas, and the deposition in these areas of Hg from the marine environment, the plateau and anthropogenic sources raises concern. The use of Antarctic cryptogams as biomonitors will be very useful to map Hg deposition patterns in costal ice-free areas and will contribute to a better understanding of Hg cycling in Antarctica and its environmental fate in terrestrial ecosystems.

Antarctic terrestrial ecosystem and role of pigments in enhanced UV-B radiations

The terrestrial ecosystem of Antarctica are among the most extreme on earth, challenging the communities and making their existence difficult by rapidly increasing annual summer influx of solar ultraviolet radiations (UV-R), extremely cold conditions and lesser availability of nutrients. Spring time ozone depletion is due to release of chlorofluorocarbons in the earth atmosphere and is a serious cause of concern among environmentalists. Antarctic continent is mostly dominated by cryptogamic plants with limited distribution in different parts of the icy continent however; their distribution is mostly confined to Sub-Antarctic region. By the virtue of light requirement, cryptogams are exposed to extreme seasonal fluctuation in photosynthetically active radiation (PAR), and ultraviolet (UV) radiation which are closely associated with photosynthetic pigments in photoautotrophic organisms. Antarctic cryptogams cope up the stress imposed by UV radiation by the development of efficient systems for repairing damage by synthesis of screening compounds such as UV-B absorbing pigments and anthocyanin compounds. A major part of the UV absorbing compounds are appeared to be constitutive in lichens which are usnic acid, perlatolic acid and fumarphotocetraric acid which is particularly induced by UV-B. Secondary metabolites such as phenolics, atranorin, parietin and melanin also enhance the plant defense, by different molecular targets in specific solar irradiance and potential for increased antioxidative protection to UV induced vulnerability.

Metabolic recovery of continental antarctic cryptogams after winter

The activation of metabolism after the winter period was investigated in several mosses and lichens in continental Antarctica. Thalli that were still in their over-wintering inactive state in early spring were sprayed artificially and the time-dependent activation of photosystem II (PSII), carbon fixation and respiration was determined using gas exchange and chlorophyll a fluorescence techniques. The investigated lichens recovered PSII activity almost completely within the first few minutes and gross photosynthesis was fully reactivated within a few hours. In contrast, photosynthesis took much longer to recover in mosses, which could indicate a general difference between the green-algal symbionts in lichens and moss chloroplasts. Only small and quickly reversible increased rates of respiration were observed for the foliose lichen Umbilicaria aprina from a more xeric habitat. In contrast, species occurring near persistent meltwater, such as the moss Bryum subrotundifolium and the lichen Physcia caesia, had highly increased respiration rates that were maintained for several days after activation. Calculation of the carbon balances indicated that the activation pattern strongly dictated the length of time before a carbon gain was achieved. It appears that the differences in recovery reflect the water relations of the main growth period in summer.

Effects of physical factors on photosynthesis by the Antarctic liverwort Marchantia berteroana

Effects of irradiance, temperature and water availability on respiration and photosynthesis in a maritime Antarctic liverwort, Marchantia berteroana, were investigated. Carbon dioxide exchange was measured using an infra-red gas analysis system under controlled conditions. The relationships between respiration, photosynthesis, irradiance and temperature were modelled. Application of these models to year-round micro-climate data provided an estimate of yearly net productivity of 823 (SE=75) mg C⋅g-1 ash-free dry weight. year-1; this is somewhat higher than figures obtained for other Antarctic cryptogams. Desiccation had a highly adverse affect on Marchantia. Photosynthetic capacity was reduced below a water content of 12 g⋅g-1 afdw, and there was only a limited recovery (ca. 10%) after dehydration. Freezing also caused a great reduction in photosynthesis, although the model suggested that photosynthesis at sub-zero temperatures is likely. It is suggested that seasonality in the photosynthetic capacity and the survival of sub-zero temperatures might be important. It is concluded that Marchantia is a relatively productive Antarctic cryptogam that may dominate favourable areas, but that its low tolerance of environmental stress, particularly desiccation, limits its distribution to relatively mild habitats.

13C NMR analysis of Antarctic cryptogam extracts

Water soluble compounds were extracted from the dominant cryptogams of the Windmill Islands, Wilkes Land, and compared with standard polyols, sugars and amino acids using 13C nuclear magnetic resonance (NMR) spectroscopy. Previous findings for sugars and polyols from gas liquid chromatorgraphy were validated and extended. Arabitol, ribitol and mannitol were confirmed as the major soluble carbohydrate compounds in all lichen species examined. Sucrose, fructose and glucose, but no polyols were detected in two species of moss. Sorbitol was confirmed as a major component of the algae Prasiola crispa and Schizogonium murale. Mesotaenium bergrenii was confirmed to contain sucrose and glucose. No significant quantities of sugars or polyols or any other compound were found in extracts of the red snow alga Chloromonas sp.1. Amino acids were detected in the majority of cryptogam samples and were particularly abundant in the algae P. crispa and S. murale. In the latter species the total identified acids ranged from 13.5–66mg g-1 dry weight. In addition to the common amino acid components of proteins, betaine and γ-amino-butyric acid were detected, the latter being particularly abundant, being found widely in the moss, lichen and algae. Several unknown carbohydrates were characterized. Usnea sphacelata, U. antarctica and Pseudephebe minuscula contained a deoxy-hexitol, Grimmia antarctici contained resonance peaks consistent with a trisaccharide containing a sucrose moiety and Umbilicaria decussata possibly contained a glucose-arabitol dimer. 13C NMR was confirmed as a powerful tool for the characterization of low molecular weight constituents of Antarctic cryptogams.

Ecological and physiological investigations in continental Antarctic cryptogams

Microclimate and CO2 exchange of the lichen Usnea sphacelata were measured during summen on a hill near Casey Station, Bailey Peninsula, Wilkes Land, Antarctica. Within a period of 52 days (November 10 until December 31, 1985), 8 diurnal courses of net photosynthesis were measured in naturally snow-covered lichen thalli, and 9 diurnal courses in thalli experimentally sprayed with melt water. Photosynthetic performance of a light-form of Usnea sphacelata was compared with that of a shade-form. Net photosynthesis was reversibly depressed in snow-covered lichen thalli of both forms when irradiance was higher than 600 μmol m−2 s−1 photosynthetic active radiation (PAR), the depression persisting several hours after a period of strong light. These responses suggest photoinhibition. Models of photosynthesis were established for the light-form by non-linear regressions with field data from water-sprayed thalli (Model W) and field data measured in snow-covered lichens (SNO I, SNO II). Model SNO I is based on median values of photosynthetic rates and SNO II on maximum values for each light/temperature combination. Photosynthetic rates were calculated using model W; the results showed values approximately three times higher than measured in the field with naturally moistened thalli. Photosynthetic rates according to model SNO II fitted the data of naturally moistened lichens measured during the day, before strong light (> 600 μmol m−2s−1 PAR) caused reversible decrease of net photosynthesis. Model SNO I fitted the data measured during and after a phase of strong irradiance. Model SNO I demonstrated that light stress was highest at temperatures below 2 °C. This study has shown that long-term calculation of the photosynthetic productivity must take into account decreases in net photosynthesis rate caused by strong light, as well as effects of water content and temperature. For the investigated period of the austral summer, a carbon production of 3.44 gm−2 was estimated for U. sphacelata.

Ecological and physiological investigations in continental Antarctic cryptogams II. Moisture relations and photosynthesis of lichens near Casey Station, Wilkes Land

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.

Ecological and Physiological Investigations in Continental Antarctic Cryptogams: I. Vegetation Pattern and its Relation to Snow Cover on a Hill Near Casey Station, Wilkes Land

Summary The vegetation of the summit region of a small ice:free hill in the inner part of the east-Antarctic Bailey Peninsula, Windmill Islands, was recorded by 105 releves along various transects. It was analysed by the Braun-Blanquet phytosociological method, by a divisive polythetic procedure and tested by an ordination analysis. An epipetric Usnea sphacelata- and a Rinodina olivaceobrunnea -moss turf community were described as distinct communities and additionally a transient community. The vegetation is highly dependent on the extension and duration of a shallow snow cover, because snow is the main water source for the poikilohydrous cryptogams. This was shown by recording regularly the changes of snow cover in 5 quadrats of the summit region. The photophilous, wind- exposed vegetation of this hill resembles ecologically that of high arctic and alpine regions. The dominance of Neuropogon species is characteristic of the Antarctic and also the Andine region, in equivalent arctic-alpine communities Umbilicaria species are the most prominent element. The epibryic and epigeic Rinodina olivaceobrunnea -moss turf community has no identical counterpart in the arctic and alpine region.

Summer and Winter Concentrations of Sodium, Potassium and Calcium in Some Maritime Antarctic Cryptogams

SUMMARY discussed. (2) The concentrations of total Na, K and Ca were determined for fifteen species of moss, one species of liverwort, one species of alga and nine species of lichen growing in a wide range of habitats. (3) In all species examined the concentration of Na was considerably higher in summer than in winter, the difference being least in the lichens. Species occupying wet habitats or habitats near the shore had the highest Na concentrations (up to 0 53% of dry weight). There was a strong correlation between Na content in the plants and the distance both vertically and horizontally from the sea. (4) Potassium concentrations were higher than those of Na, but the concentration in summer was frequently less than that in winter, particularly in those mosses and lichens growing in relatively dry rock habitats. As with Na, the higher K concentrations appeared to be correlated with increased moisture availability, with the highest K values (up to 1 41% of dry weight) in species growing on wet rocks. (5) The concentrations of Ca varied considerably and showed little conformity in fluctuation in all groups of species. The highest concentrations of the element (up to 2.29% of dry weight) were in species associated with mineral substrata and a high Ca content. There was a strong correlation between the Ca concentration in the plant material and the pH of the substratum. (6) The difference between summer and winter concentrations of the three cations suggests the probability of an annual cycle of mineral elements within the plants, with relatively high spring to early summer levels and winter minima. However, this cycle may not be complementary with the seasonal trends in soil elements. (7) The mineral-ion concentration within the plants varied considerably, not so much in relation to species but to environment, and to some extent to growth form which is strongly correlated with environment. Different species associated with a particular habitat tended to have similar concentrations of specific mineral elements, whereas the same species growing in a variety of habitats tended to have a range of mineral-ion concentrations. (8) The simple mechanism of uptake and storage of mineral-ions in these non-vascular species is considered to be a response to the moisture regime of the habitat and to the concentration of the elements in the substratum or in precipitation. The concentrations within the plants tend to be proportional to those occurring in the substratum, although some degree of accumulation, despite the absence of specialized storage tissues, is suspected.