Antarctic terrestrial ecosystems are cold, dry, low nutrient environments, with large temperature fluctuations and paradoxically low levels of water availability. These extreme environments are dominated by microorganisms (viruses, archaea, eubacteria, .fungi and microsporidia, alveolata, stramenopila, rhodophyta, green algae and protists), which can either tolerate or are adapted to exploit unfavourable growth conditions. However, climate change is altering the growth environment in Antarctica, and so selection pressures on these microorganisms are changing which, in turn, might affect microbial activity in key processes such as biogeochemical cycling. Although the direct effect of a change in, for example, temperature, is known for very Jew Antarctic microorganisms, molecular techniques (to monitor population structure) and genomic techniques (to identify specific gene function) are starting to give us an insight into what the potential effects of climate change might be at the cellular level. The key to how microorganisms respond to such change depends upon the rate and magnitude of the change along with the physiological capability of microorganisms to adapt or tolerate those changes. Here we will examine a number of case studies in which the effects of factors such as temperature, nutrient availability, grazing, salinity, seasonal cycle and carbon dioxide concentration have each been demonstrated to affect bacterial community structure in polar and alpine ecosystems. The results suggest that the spatial distribution of genetic variation and, hence, comparative rates of evolution, colonization and extinction are particularly important when considering the response of microbial communities to climate change.
Keywords: temperature, nutrient availability, grazing, salinity, seasonal cycle, carbon dioxide concentration, microbial community structure
Climate change is defined as a significant change in the long-term average weather, on a time-scale between decades to millions of years. More recently, however, particularly in the media, it has referred more specifically to changes in the modern climate. The Intergovernmental Panel on Climate Change has stated that warming of the climate system is now unequivocal, and that this is evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global sea level. Moreover, the rate and absolute magnitude of climate change is expected to be greater than that inferred for at least the last four million years (25). There is also growing evidence to suggest that climate change is a result of anthropogenic activities, including the release of greenhouse gases. Of particular concern, is that warming would continue at 0.1[degrees]C per decade even if human activity were to continue at levels set at the turn of the millenium (IPCC Fourth Assessment Report: Climate Change 2007). However, the results of climate change show extreme regional variation. Whilst global warming is known to occur in the Antarctic, plateau stations at the Vostok and South Pole bases have shown no significant differences in average temperature over the last 50 years. In contrast, the Antarctic Peninsula (Figure 1) is one of the most rapidly warming regions on Earth (Table 1). It has experienced increases of 3[degrees]C in mean annual temperature and 6[degrees]C in mean winter temperature over the same period (41). The latter equates to 10 times the mean global rate of increase. Elsewhere, the rate of heat transfer from the Antarctic circumpolar current (ACC) has also increased with a 0.6[degrees]C increase in the upper 300m of shelf water over the last 10 years (8). In the Southern Ocean, data show an increase in mid-depth water temperatures, such that over a 30-year period, waters within the ACC have warmed by around 0.17[degrees]C. …