Organisms in the Atacama Desert soil are remarkably diverse

A new study shows that resilient and remarkably diverse populations of organisms can persist in the soil despite harsh and extremely dry conditions. An international team led by researchers from the University of Cologne, has examined tiny nematodes in the Chilean Atacama Desert. Along with the polar regions, the Atacama Desert is considered one among these most arid regions in the world. Lack of rainfall, high salt content in the soil, and extreme temperature fluctuations make it one of the most hostile places on earth. The interdisciplinary team with researchers from the fields of zoology, ecology and botany demonstrated the strategies used by different nematodes to survive under these conditions. The study "Geographic distribution of nematodes in the Atacama is associated with elevation, climate gradients and parthenogenesis" was published in Nature Communications and sheds new light on the links between patterns of biodiversity and the environmental parameters that define a landscape.

Nematodes are one of the most common soil organisms with a large number of species. They play a central role within the ecosystem because they regulate bacteria populations, contribute to the nutrient cycle, and are important indicators of soil condition. Their versatility is also evident in their ability to adapt: nematodes survive in the deep sea, in Arctic regions, and even in extremely salty soils.

“Soils are important for the performance of an ecosystem, for example for carbon storage and nutrient supply. This is why understanding the organisms, i.e. not microbes, but multicellular animals, that live there is so important,” says Dr Philipp Schiffer from the University of Cologne’s Institute of Zoology and one of the authors of the study. “Data on soils in extreme ecosystems such as the Atacama Desert is still scarce.”

The research team is part of the Collaborative Research Centre 1211 “Earth - Evolution at the Dry Limit”, which has been working in the Atacama for many years. For this study, they selected six regions of the Atacama with different conditions for the analysis, including more humid highlands with vegetation, saline regions with high UV radiation, and foggy oases that boast a surprising variety of plants given the prevailing conditions. They took samples from sand dunes, salt lakes, river beds and mountains, and evaluated them in relation to biodiversity, reproduction strategies and the population structure of the nematodes.

The results reveal significant differences: in higher altitudes, the soil contains types of nematodes that reproduce asexually. This supports a previously unconfirmed theory that asexuality is advantageous under extreme conditions. The variety in terms of types also correlates to the water profile: as precipitation increases, so does biodiversity. Differences in temperature are also a decisive factor for the composition of the populations.

The results of the study show that resilient soil ecosystems can exist despite extreme conditions and in very remote locations. This indicates that biodiversity in other arid regions may be higher than previously assumed. On the other hand, the findings also provide warning signals: “In some of the examined regions, simplified food webs indicate that these ecosystems are already damaged and may therefore be more susceptible to disruptions.”

“In light of increasing global aridity, which is affecting more and more regions worldwide, these results are becoming increasingly relevant. Understanding how organisms adapt in extreme environments and which environmental parameters cause them to spread can help to improve estimation of the ecological consequences of climate change”, says Schiffer.

The results suggest that macroecological patterns such as precipitation gradient or the significant role of altitude can be identified in regions with extreme conditions and also at the genetic level. The study thus represents an important step toward better assessing the responses of soil organisms to environmental changes worldwide.

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