Microbial Mats of the McMurdo Dry Valleys, Antarctica: Oases of Biological Activity in a Very Cold Desert

Jill A Sohm,Douglas G Capone,Thomas D Niederberger,Alexander E Parker,Troy Gunderson,Joëlle Tirindelli,Edward J Carpenter,Stephen Craig Cary

doi:10.3389/fmicb.2020.537960

Abstract

Cyanobacterial mats in the Antarctic Dry Valleys are photosynthetic microbial ecosystems living at the extreme of conditions on Earth with respect to temperature, light, water and nutrient availability. They are metabolically active for about 8 weeks during the austral summer when temperatures briefly rise above freezing and glacial and lake melt waters are available. There is much to learn about the biogeochemical impact of mats in these environments and the microbial communities associated with them. Our data demonstrate that these mats attain surprisingly high rates of carbon (CO2) and dinitrogen (N2) fixation when liquid water is available, in some cases comparable to rates in warmer temperate or tropical environments. C and N2 fixation in Dry Valley mats in turn substantially elevate dissolved organic C and inorganic N pools and thereby promote enhanced microbial secondary production. Moreover, the microbial community fingerprint of these mats is unique compared with the more ubiquitous dry soils that do not contain mats. Components of the heterotrophic microbiota may also contribute substantially to N inputs through N2 fixation.

Highlights

The McMurdo Dry Valleys of Antarctica are thought to be the coldest, driest environments on Earth and the largest ice-free region on the continent (McKnight et al, 1999)
In our study, conducted in January and December 2009, N2 and CO2 fixation activity, bacterial activity, and nutrient concentrations in lakes/ponds and pore waters were investigated in association with cyanobacterial mats located in, and at sites adjacent to, the Miers Valley, one of the smaller (11 km long) and southerly of the McMurdo Dry Valleys (Figure 1)
Dinitrogen and CO2 fixation rates were highly variable in the Miers Valley and adjacent areas and ranged from 0 to 10.9 nmol N cm−3 h−1 and 0 to 7.05 mmol C cm−3 h−1, respectively (Table 1 and Figure 3); the N2 fixation rates are of the same order of Overlying water μM

Summary

Introduction

The McMurdo Dry Valleys of Antarctica are thought to be the coldest, driest environments on Earth and the largest ice-free region on the continent (McKnight et al, 1999). Stretching over about 6500 km, the Dry Valleys experience minimal precipitation, strong katabatic winds, and temperatures below −60◦C during the austral winter (Fountain et al, 1999; Cary et al, 2010) These extreme conditions are the reason that the Dry Valleys were once considered to be unfavorable for life, with much of the dry soils thought to be sterile (Horowitz et al, 1972); the Dry Valleys host a microbial community consisting of phylogenetically diverse bacteria, microalgae and fungi (McKnight et al, 1999; Wood et al, 2008; Cary et al, 2010; Dreesens et al, 2014). The presence and source of organic matter in the Dry Valleys is a defining feature of the system with regards to life

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