Dominating the Antarctic environment: bryophytes in a time of change

Polar ecosystems, and particularly Antarctica, are one of the few environs in which bryophytes dominate the flora. Their success in these regions is due to bryophytes’ ability to withstand an array of harsh conditions through their poikilohydric lifestyle. However, the unique conditions that allow bryophytes to proliferate over other forms of vegetation also create considerable limitations to growth and photosynthetic activity. High latitude areas are already experiencing some of the most pronounced and rapid climatic change, especially in the Arctic, the Sub-Antarctic Islands and Maritime Antarctica, and these are predicted to continue over the next century. This climatic change is already impacting the flora of the polar regions both via direct and/or indirect impacts on plant species. Water availability and temperature are undoubtedly the most influential factors that determine bryophyte productivity in the Antarctic, but the ozone hole is also having an impact either directly via increased ultraviolet-B radiation and/or indirectly through the increasing wind speeds associated with ozone depletion. In a time of shifting climate the dominance of bryophytes in these regions may be threatened

Moss species on the move in East Antarctic terrestrial communities

Antarctica has experienced major changes in temperature, wind speed and stratospheric ozone levels over the last 50 years. Whilst West Antarctica and the peninsula showed rapid warming and associated ecosystem change, East Antarctica appeared to be little impacted by climate warming, thus biological changes were predicted to be relatively slow. Detecting the biological effects of Antarctic climate change has also been hindered by the paucity of long-term data sets, particularly for organisms that have been exposed to these changes throughout their lives. We monitored vegetation communities in the Windmill Islands, East Antarctica from 2000 to 2014 and found significant changes in moss species composition. In addition, we have shown that radiocarbon signals preserved along shoots of the dominant Antarctic moss flora can be used to determine accurate growth rates over a period of several decades, allowing us to explore the influence of environmental variables on growth. Carbon stable isotopic measurements suggest that the observed effects of climate variation on growth are mediated through changes in water availability and most likely linked to the more positive phase of the Southern Annular Mode and changing westerly wind patterns. For cold remote locations like Antarctica, where climate records are limited and of relatively short duration, this illustrates that mosses can act as microclimate proxies and have the potential to increase our knowledge of coastal Antarctic climate change

Phytoremediation of hydrocarbon contaminants in sub-Antarctic soils

Accidental fuel spills on sub-Antarctic Macquarie Island have caused considerable contamination. Due to the island‘s high latitude position, its climate, and the fragility of its ecosystems, traditional methods of remediation are unsuitable for onsite clean up. However, if left untreated, even minor to moderate fuel spills could take decades before natural attenuation reduces the petroleum to environmentally acceptable concentrations. Currently, low cost, low disturbance in-situ methods to enhance biodegradation of fuel products, such as nutrient additions and air sparging, are under examination on Macquarie Island. This study investigated the potential of the sub-Antarctic native tussock grass, Poa foliosa, to contribute to such remediation efforts. This species was selected as it is common in areas of contamination and displays criteria which enhance phytoremediation efficiency. Growth trials were conducted with seedlings of P. foliosa in soil artificially spiked with Special Antarctic Blend (SAB) diesel at concentrations of 0, 1 000, 5 000, 10 000, 20 000 or 40 000 mg/kg. Replicate pots, containing single seedlings, were compared with paired unplanted pots at each SAB soil concentration. Pots were kept under controlled conditions (8°C; photoperiod of 8.75/13.25 hours) to simulate the growth environment on Macquarie Island. Plants were harvested destructively at 0, 2, 4 and 8 months. Tolerance of P. foliosa to SAB, and the effects of fuel contaminants on plant health and productivity (biomass production, plant morphology, pigments and photosynthetic health) were assessed. The rate of SAB degradation and the microbial communities within the rhizosphere (total heterotrophs and hydrocarbon degraders) were compared between planted and unplanted treatments. This study found P. foliosa to be highly tolerant across all SAB concentrations tested with respect to biomass, although higher concentrations of 20 000 and 40 000 mg/kg caused slight reductions in leaf length, width and area. Total Petroleum Hydrocarbons (TPH) were degraded 35 - 48% faster in planted soils compared to unplanted soil and were approaching soil background levels within four months. Although P. foliosa significantly stimulated the growth of both total heterotrophs and hydrocarbon degraders at low concentrations of 0 and 1 000 mg/kg, the presence of microbes in the root zone did not appear to be the sole driving force behind TPH degradation. This study provides persuasive evidence that phytoremediation using P. foliosa is a valuable technology in the suite of current in-situ remediation methodologies being adopted at these sites, and may be applicable to the remediation of spills in other cold climate regions

Moss δ13C: implications for subantarctic palaeohydrological reconstructions

Southern Ocean Islands, despite their equitable oceanic climates, have recently experienced a number of pronounced climate variations. Shifts in water availability in this region are of concern; however, methods of measuring water availability are currently inadequate. Recent advances using stable carbon isotopes (δ13C) in Antarctic mosses to record long-term variations in water availability suggest that this technique might be applicable in other locations where conditions are cold enough to produce meaningful moss growth for reconstructions. Verification of this technique at each new location is essential, however, due to disparity between species and climates. Here, variations in δ13CBULK with growth water availability were measured in three moss species on subantarctic Macquarie Island. We found these subantarctic mosses showed no difference in δ13CBULK signatures between growth water environments and displayed more negative δ13CBULK ranges than those from East Antarctica, suggesting that climatic differences override the microclimate signal. Despite significant differences in leaf cell morphology there was no variation in δ13CBULK between these subantarctic species. It may be that these species are unsuitable as biological proxies due to their growth form being less dense than the turf forming Antarctic species. This underlines the need to carryout preliminary research into moss carbon isotope fractionation for each new region, and for each species, where palaeohydrological reconstructions are planned – a step that is often not given appropriate consideration in palaeo-research

Phytoremediation of hydrocarbon contaminants in subantarctic soils: an effective management option

Accidental fuel spills on world heritage subantarctic Macquarie Island have caused considerable contamination. Due to the island\u27s high latitude position, its climate, and its fragile ecosystem, traditional methods of remediation are unsuitable for on-site clean up. We investigated the tolerance of a subantarctic native tussock grass, Poa foliosa (Hook. f.), to Special Antarctic Blend (SAB) diesel fuel and its potential to reduce SAB fuel contamination via phytoremediation. Toxicity of SAB fuel to P. foliosa was assessed in an 8 month laboratory growth trial under growth conditions which simulated the island\u27s environment. Single seedlings were planted into 1 L pots of soil spiked with SAB fuel at concentrations of 1000, 5 000, 10 000, 2000 and 40 000 mg/kg (plus control). Plants were harvested at 0, 2, 4 and 8 months and a range of plant productivity endpoints were measured (biomass production, plant morphology and photosynthetic efficiency). Poa foliosa was highly tolerant across all SAB fuel concentrations tested with respect to biomass, although higher concentrations of 20 000 and 40 000 mg SAB/kg soil caused slight reductions in leaf length, width and area. To assess the phytoremediation potential of P. foliosa (to 10 000 mg/kg), soil from the planted pots was compared with that from paired unplanted pots at each SAB fuel concentration. The effect of the plant on SAB fuel concentrations and the associated microbial communities found within the soil (total heterotrophs and hydrocarbon degraders) were compared between planted and unplanted treatments at the 0, 2, 4 and 8 month harvest periods. The presence of plants resulted in significantly less SAB fuel in soils at 2 months and a return to background concentration by 8 months. Microbes did not appear to be the sole driving force behind the observed hydrocarbon loss. This study provides evidence that phytoremediation using P. foliosa is a valuable remediation option for use at Macquarie Island, and may be applicable to the management of fuel spills in other cold climate regions

Photoprotection enhanced by red cell wall pigments in three East Antarctic mosses

Background: Antarctic bryophytes (mosses and liverworts) are resilient to physiologically extreme environmental conditions including elevated levels of ultraviolet (UV) radiation due to depletion of stratospheric ozone. Many Antarctic bryophytes synthesise UV-B-absorbing compounds (UVAC) that are localised in their cells and cell walls, a location that is rarely investigated for UVAC in plants. This study compares the concentrations and localisation of intracellular and cell wall UVAC in Antarctic Ceratodon purpureus, Bryum pseudotriquetrum and Schistidium antarctici from the Windmill Islands, East Antarctica. Results: Multiple stresses, including desiccation and naturally high UV and visible light, seemed to enhance the incorporation of total UVAC including red pigments in the cell walls of all three Antarctic species analysed. The red growth form of C. purpureus had significantly higher levels of cell wall bound and lower intracellular UVAC concentrations than its nearby green form. Microscopic and spectroscopic analyses showed that the red colouration in this species was associated with the cell wall and that these red cell walls contained less pectin and phenolic esters than the green form. All three moss species showed a natural increase in cell wall UVAC content during the growing season and a decline in these compounds in new tissue grown under less stressful conditions in the laboratory. Conclusions: UVAC and red pigments are tightly bound to the cell wall and likely have a long-term protective role in Antarctic bryophytes. Although the identity of these red pigments remains unknown, our study demonstrates the importance of investigating cell wall UVAC in plants and contributes to our current understanding of UV-protective strategies employed by particular Antarctic bryophytes. Studies such as these provide clues to how these plants survive in such extreme habitats and are helpful in predicting future survival of the species studied

Photoprotection enhanced by red cell wall pigments in three East Antarctic mosses

Abstract Background Antarctic bryophytes (mosses and liverworts) are resilient to physiologically extreme environmental conditions including elevated levels of ultraviolet (UV) radiation due to depletion of stratospheric ozone. Many Antarctic bryophytes synthesise UV-B-absorbing compounds (UVAC) that are localised in their cells and cell walls, a location that is rarely investigated for UVAC in plants. This study compares the concentrations and localisation of intracellular and cell wall UVAC in Antarctic Ceratodon purpureus, Bryum pseudotriquetrum and Schistidium antarctici from the Windmill Islands, East Antarctica. Results Multiple stresses, including desiccation and naturally high UV and visible light, seemed to enhance the incorporation of total UVAC including red pigments in the cell walls of all three Antarctic species analysed. The red growth form of C. purpureus had significantly higher levels of cell wall bound and lower intracellular UVAC concentrations than its nearby green form. Microscopic and spectroscopic analyses showed that the red colouration in this species was associated with the cell wall and that these red cell walls contained less pectin and phenolic esters than the green form. All three moss species showed a natural increase in cell wall UVAC content during the growing season and a decline in these compounds in new tissue grown under less stressful conditions in the laboratory. Conclusions UVAC and red pigments are tightly bound to the cell wall and likely have a long-term protective role in Antarctic bryophytes. Although the identity of these red pigments remains unknown, our study demonstrates the importance of investigating cell wall UVAC in plants and contributes to our current understanding of UV-protective strategies employed by particular Antarctic bryophytes. Studies such as these provide clues to how these plants survive in such extreme habitats and are helpful in predicting future survival of the species studied

It is hot in the sun: Antarctic mosses have high temperature optima for photosynthesis despite cold climate

The terrestrial flora of Antarctica’s frozen continent is restricted to sparse ice-free areas and dominated by lichens and bryophytes. These plants frequently battle sub-zero temperatures, extreme winds and reduced water availability; all influencing their ability to survive and grow. Antarctic mosses, however, can have canopy temperatures well above air temperature. At midday, canopy temperatures can exceed 15°C, depending on moss turf water content. In this study, the optimum temperature of photosynthesis was determined for six Antarctic moss species: Bryum pseudotriquetrum, Ceratodon purpureus, Chorisodontium aciphyllum, Polytrichastrum alpinum, Sanionia uncinata, and Schistidium antarctici collected from King George Island (maritime Antarctica) and/or the Windmill Islands, East Antarctica. Both chlorophyll fluorescence and gas exchange showed maximum values of electron transport rate occurred at canopy temperatures higher than 20°C. The optimum temperature for both net assimilation of CO2 and photoprotective heat dissipation of three East Antarctic species was 20–30°C and at temperatures below 10°C, mesophyll conductance did not significantly differ from 0. Maximum mitochondrial respiration rates occurred at temperatures higher than 35°C and were lower by around 80% at 5°C. Despite the extreme cold conditions that Antarctic mosses face over winter, the photosynthetic apparatus appears optimised to warm temperatures. Our estimation of the total carbon balance suggests that survival in this cold environment may rely on a capacity to maximize photosynthesis for brief periods during summer and minimize respiratory carbon losses in cold conditions

It Is Hot in the Sun: Antarctic Mosses Have High Temperature Optima for Photosynthesis Despite Cold Climate

The terrestrial flora of Antarctica's frozen continent is restricted to sparse ice-free areas and dominated by lichens and bryophytes. These plants frequently battle sub-zero temperatures, extreme winds and reduced water availability; all influencing their ability to survive and grow. Antarctic mosses, however, can have canopy temperatures well above air temperature. At midday, canopy temperatures can exceed 15 degrees C, depending on moss turf water content. In this study, the optimum temperature of photosynthesis was determined for six Antarctic moss species:Bryum pseudotriquetrum,Ceratodon purpureus,Chorisodontium aciphyllum,Polytrichastrum alpinum,Sanionia uncinata, andSchistidium antarcticicollected from King George Island (maritime Antarctica) and/or the Windmill Islands, East Antarctica. Both chlorophyll fluorescence and gas exchange showed maximum values of electron transport rate occurred at canopy temperatures higher than 20 degrees C. The optimum temperature for both net assimilation of CO(2)and photoprotective heat dissipation of three East Antarctic species was 20-30 degrees C and at temperatures below 10 degrees C, mesophyll conductance did not significantly differ from 0. Maximum mitochondrial respiration rates occurred at temperatures higher than 35 degrees C and were lower by around 80% at 5 degrees C. Despite the extreme cold conditions that Antarctic mosses face over winter, the photosynthetic apparatus appears optimised to warm temperatures. Our estimation of the total carbon balance suggests that survival in this cold environment may rely on a capacity to maximize photosynthesis for brief periods during summer and minimize respiratory carbon losses in cold conditions