Establishing the response of Eastern Antarctic soil microbiomes to a changing climate.

Much is known about the existential threat of climate change to plants and animals. But by comparison, we know very little about how microorganisms will be affected by climate change. And until recently, our knowledge of microorganisms in Antarctica was non-existent, where the effects of climate change are arguably the most profound. The goal of this project was to understand what the effects of environmental change would be on microbes living in soils in the Windmill Islands region of eastern Antarctica. We were able to carry out an expedition to Casey Station in Eastern Antarctica in 2019 to obtain critical soils requited to test whether projections made on soils sampled 14 years earlier, about the disappearance of microbes thriving solely on chemicals in the atmosphere were correct. We adapted a modelling tool, called Gradient Forest, and we used this on soil microbial communities (over 17000 species) against 41 environmental parameters measured in soils sampled 14 years earlier. The model suggested that as the Antarctic desert gets less arid and becomes wetter, the changing conditions favour photosynthetic microbes, or phototrophs – the ones that convert light into energy in the same way plants do – over trace gas chemosynthetic bacteria, which feed on low levels of hydrogen gas present in the atmosphere. We predicted at about 10 to 12 per cent moisture in the soil, we’d get a shift from those chemotrophs to the phototrophs, which is exactly what we found.

This potential increase in soils moisture explains why the chemosynthetic microbes had diminished in numbers, as these rare “air eating” bacteria prefer dry nutrient poor environments. We predicted that there will be more phototrophs like algae and cyanobacteria as soil moisture increases. Possible effects of this shift in microbe population could have a knock-on effect on the Antarctic ecosystem. Atmospheric chemosynthetic bacteria – or chemotrophs – play a major role in carbon sequestration by removing hydrogen, carbon monoxide and carbon dioxide from the atmosphere and storing it in organic compounds. We still don’t even really know exactly what these microbes are doing – most of them haven’t even been cultured in the lab. So we think it’s important to monitor changes to the abundance of these novel bacteria as it could have significant effects on climate and environment.

It is vital that we get back to the Windmill Islands. Better understanding of such threshold tipping points, as identified here, will aid conservation efforts and it is crucial that long-term monitoring of these sites is established for the protection of Antarctic desert ecosystems.