Diversity and ecology of autotrophic terrestrial life forms on rock and soil in the Antarctic Dry Valleys

Investigation area

The McMurdo Dry Valleys are amongst the driest regions of the earth. Water availability is limited by very low precipitation, always in the form of snow. Liquid water only occurs with direct sunlight, resulting in melting of snow/ice. However, extremely low relative air humidity and strong, almost permanent winds increase the rapid loss of water by sublimation into air.

Investigation sites were selected according to latitudinal, altitudinal and coastal distance gradients (fig.1).

So far, five expeditions have been performed with the support of Antarctica New Zealand and the DFG (2003, 2007, 2008, 2009, 2009-2010).



Fig. 1: Map with all localities visited so far (courtesy of USGS).

Results

Diversity

Several microbial autotrophic life forms have been found: endolithic biofilms composed of mainly cyanobacteria (17 species), sometimes with additional green algae (5 species; fig. 2), and biological soil crusts composed of green algal lichens (4-5 species), few mosses (5 species), intermingled with green algae (5 species) and black fungal hyphae (fig. 3).



Fig. 2: Antarctic endolithic communities; from left to right: in granite, in Beacon sandstone, in calcite, the unicellular cyanobacterium Chroococcidiopsis.



Fig. 3: Biological soil crust types mainly dominated by green algal lichens; from left to right: Caloplaca citrine, Taylor Valley; Acarospora gwynneii, Diamond Hill; Lecanora expectans, Garwood Valley.



Biomass

Endolithic communities, dominated by cyanobacteria, were present in most granitic rocks and sandstones of all investigated regions. The biomass reached from 0.07 to 168 g total carbon/m². The chlorophylla content varied from 1.8 – 109 mg Chla/m². Biological soil crusts were discovered so far at the Darwin Glacier area and in the Garwood Valley. They reached a biomass of 1.7 g organic carbon/m² (17.9 g total carbon/m²). The chlorophyll a+b content varied from 120 – 229 mg Chla+b/m².

Water

Our investigations clearly showed that condensation of water on rock surfaces via dew point reduction is a frequent and important source of water besides melts water from snowfall for endolithic cyanobacterial communities. Radiocarbon dating of the age of endolithic communities along the above mentioned gradients revealed that the age of the endolithic communities was positively correlated with increasing altitude. Given the case, that with increasing altitude frost events and duration is much more frequent than at lower altitudes, water availability directly correlates with altitude (results of the dissertation of Fritz Bicker, not published yet).

Photosynthesis

Chlorophyll fluorescence measurements of the activity of photosystem II in the field showed, that most endolithic communities were active due to the presence of water condensation, even when there was no precipitation for 3-4 weeks or longer (Büdel et al 2008). First CO₂-gas exchange measurements on biological soil crusts in the field and in the laboratory showed that the crusts need a high amount of water to perform positive net photosynthesis compared with crusts from other geographical regions. They reach their optimum at low temperatures and are active even below zero. Characteristic seems to be a high ratio of net photosynthesis/respiration.

Scientists

Burkhard Büdel, Hans Reichenberger, Claudia Colesie, Fritz Bicker
Plant Ecology and Systematics
TU Kaiserslautern

Research areas

Taylor Valley, Garwood Valley, Miers Valley, Diamond Hill region, Nussbaum Riegel, Lake Fryxell, Antarctica

Publications

Büdel B, Bendix J, Bicker F, Green TGA, 2008. Dewfall as a water source frequently activates the endolithic cyanobacterial communities in the granites of Taylor Valley, Antarctica. Journal of Phycology 44, 1415-1424.

Büdel B, Schulz B, Reichen-Berger H, Bicker F, Green TGA, 2009. Cryptoendolithic cyanobacteria from calcite marble rock ridges, Taylor Valley, Antarctica. Algological Studies 129, 61-69.

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Research funding organisation

German Research Foundation (DFG) and Antarctica New Zealand (AntNZ)

Project number: BU 666/11
Funding period: 2008 - 2011