Microbial Nitrogen Cycling in Antarctic Soils

Abstract

The Antarctic continent is widely considered to be one of the most hostile biological habitats on Earth. Despite extreme environmental conditions, the ice-free areas of the continent, which constitute some 0.44% of the total continental land area, harbour substantial and diverse communities of macro-organisms and especially microorganisms, particularly in the more “hospitable” maritime regions. In the more extreme non-maritime regions, exemplified by the McMurdo Dry Valleys of South Victoria Land, nutrient cycling and ecosystem servicing processes in soils are largely driven by microbial communities. Nitrogen turnover is a cornerstone of ecosystem servicing. In Antarctic continental soils, specifically those lacking macrophytes, cold-active free-living diazotrophic microorganisms, particularly Cyanobacteria, are keystone taxa. The diazotrophs are complemented by heterotrophic bacterial and archaeal taxa which show the genetic capacity to perform elements of the entire N cycle, including nitrification processes such as the anammox reaction. Here, we review the current literature on nitrogen cycling genes, taxa, processes and rates from studies of Antarctic soils. In particular, we highlight the current gaps in our knowledge of the scale and contribution of these processes in south polar soils as critical data to underpin viable predictions of how such processes may alter under the impacts of future climate change.

In-depth characterization of denitrifier communities across different soil ecosystems in the tundra

“…The 796 MAGs obtained in the present study by a manual binning and curation effort represent one of the largest genomic catalogues of microorganisms from tundra soils to date. Earlier genecentric investigations have demonstrated the potential for complete denitrification in tundra soils [22,79], however, these approaches fail to reveal the wider genomic context of the genes.…”

“…Investigations of denitrifier diversity in the tundra have been largely limited to gene-centric surveys using microarrays, amplicon sequencing, qPCR, and read-based metagenomics, which provide limited information on the taxonomic identity and genomic composition of community members. These studies have shown that denitrifier communities in the tundra are dominated by members of the phyla Proteobacteria, Actinobacteria, and Bacteroidetes, and that the potential for complete denitrification is usually present at the community level [25][26][27][28][29]. However, it is not known whether the complete denitrification potential occurs within discrete microbial populations or is widespread throughout populations of truncated denitrifiers lacking one or more denitrification genes.…”

First Insights into the Microbiology of Three Antarctic Briny Systems of the Northern Victoria Land

“…Most of the studies related to the N-cycling functional markers in Antarctica have focused on the core genes involved in N-fixation, nitrification, and denitrification processes [47]. Nitrate is, here, predicted to be reduced through two dissimilatory membranebound respiratory (Nar) nitrate reductases, which generate a transmembrane proton motive force allowing ATP synthesis.…”

Effects of Sugarcane and Soybean Intercropping on the Nitrogen-Fixing Bacterial Community in the Rhizosphere

“…Recent studies have shown that nitrogen fixation by rhizobia is not limited to legumes ( Pold et al, 2018 ; Noh et al, 2019 ), but is found in other non-leguminous higher plants, including sugarcane ( Zhao et al, 2020 ). In addition, the relative abundance of Burkholderiales was high ( Figure 4B ), and Burkholderiales have been shown to play an important role in nitrogen input to newly colonized soils ( Ortiz et al, 2020 ). In the cluster modules of the co-occurrence network of the two intercropping patterns, the number of ASVs was greater and Alphaproteobacteria, Betaproteobacteria, and Verrucomicrobia were more abundant in the ZZ9 than in the ZZ1 intercropping system ( Figure 5B ).…”