Gullies and Moraines Are Islands of Biodiversity in an Arid, Mountain Landscape, Asgard Range, Antarctica.

Adam J Solon,Lara Vimercati,S K Schmidt,John L Darcy,Eli M S Gendron,Pacifica Sommers,Claire Mastrangelo,Dorota L Porazinska

doi:10.3389/fmicb.2021.654135

Abstract

Cold, dry, and nutrient-poor, the McMurdo Dry Valleys of Antarctica are among the most extreme terrestrial environments on Earth. Numerous studies have described microbial communities of low elevation soils and streams below glaciers, while less is known about microbial communities in higher elevation soils above glaciers. We characterized microbial life in four landscape features (habitats) of a mountain in Taylor Valley. These habitats varied significantly in soil moisture and include moist soils of a (1) lateral glacial moraine, (2) gully that terminates at the moraine, and very dry soils on (3) a southeastern slope and (4) dry sites near the gully. Using rRNA gene PCR amplicon sequencing of Bacteria and Archaea (16S SSU) and eukaryotes (18S SSU), we found that all habitat types harbored significantly different bacterial and eukaryotic communities and that these differences were most apparent when comparing habitats that had macroscopically visible soil crusts (gully and moraine) to habitats with no visible crusts (near gully and slope). These differences were driven by a relative predominance of Actinobacteria and a Colpodella sp. in non-crust habitats, and by phototrophic bacteria and eukaryotes (e.g., a moss) and predators (e.g., tardigrades) in habitats with biological soil crusts (gully and moraine). The gully and moraine also had significantly higher 16S and 18S ESV richness than the other two habitat types. We further found that many of the phototrophic bacteria and eukaryotes of the gully and moraine share high sequence identity with phototrophs from moist and wet areas elsewhere in the Dry Valleys and other cold desert ecosystems. These include a Moss (Bryum sp.), several algae (e.g., a Chlorococcum sp.) and cyanobacteria (e.g., Nostoc and Phormidium spp.). Overall, the results reported here broaden the diversity of habitat types that have been studied in the Dry Valleys of Antarctica and suggest future avenues of research to more definitively understand the biogeography and factors controlling microbial diversity in this unique ecosystem.

Highlights

In the cold, nutrient-poor, and hyper-arid McMurdo Dry Valleys (MDV) of Antarctica, water availability serves as a primary factor governing the persistence and distribution of life (Kennedy, 1993)
Our study addresses the following questions: How different are microbial communities among these habitats? Do the habitats with higher soil moisture support more diverse communities? Are phototrophs of the inland mixed zone (IMZ) found in lower elevations of the MDV or other cold deserts? By incorporating the full spectrum of life found in each habitat (Bacteria, Archaea, and eukaryotes) as well as identifying habitat-specific community compositions and individual organisms most associated with those habitats, we used a natural experiment to explore how the variation of terrain within a geomorphic zone governs soil moisture and influences microbial community structure in the IMZ of the MDV and identified potential connections with microbial communities of cryoconite holes on the glaciers below
We characterized microbial communities from mineral soils of four landscape features and found that all habitats supported significantly different microbial communities (16S, p = 0.001; 18S, p < 0.006), there was a notable separation between moist habitats with biological soil crusts and dry habitats with no crusts (Figure 3)

Summary

Introduction

Nutrient-poor, and hyper-arid McMurdo Dry Valleys (MDV) of Antarctica, water availability serves as a primary factor governing the persistence and distribution of life (Kennedy, 1993). Within the MDV, there are three geomorphic zones that are determined by interactions between climate conditions and landforms These zones are defined by summertime mean air temperature and relative humidity as well as prevailing winds and precipitation and include the coastal thaw zone (CTZ), the inland mixed zone (IMZ), and the stable upland zone (SUZ) (Fountain et al, 2014). These zones correspond with elevation above sea level and distance from the coast. On a broader scale soil moisture affects biological soil crust formation in other cold deserts (Costello et al, 2009; Solon et al, 2018), and even in hot deserts like the Negev Desert (Kidron and Benenson, 2014; Hagemann et al, 2017)

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Results

Conclusion