A Taxon-Wise Insight Into Rock Weathering and Nitrogen Fixation Functional Profiles of Proglacial Systems

Abstract

The Arctic environment is particularly affected by global warming, and a clear trend of the ice retreat is observed worldwide. In proglacial systems, the newly exposed terrain represents different environmental and nutrient conditions compared to later soil stages. Therefore, proglacial systems show several environmental gradients along the soil succession where microorganisms are active protagonists of the soil and carbon pool formation through nitrogen fixation and rock weathering. We studied the microbial succession of three Arctic proglacial systems located in Svalbard (Midtre Lovénbreen), Sweden (Storglaciären), and Greenland (foreland close to Kangerlussuaq). We analyzed 65 whole shotgun metagenomic soil samples for a total of more than 400 Gb of sequencing data. Microbial succession showed common trends typical of proglacial systems with increasing diversity observed along the forefield chronosequence. Microbial trends were explained by the distance from the ice edge in the Midtre Lovénbreen and Storglaciären forefields and by total nitrogen (TN) and total organic carbon (TOC) in the Greenland proglacial system. Furthermore, we focused specifically on genes associated with nitrogen fixation and biotic rock weathering processes, such as nitrogenase genes, obcA genes, and genes involved in cyanide and siderophore synthesis and transport. Whereas we confirmed the presence of these genes in known nitrogen-fixing and/or rock weathering organisms (e.g., Nostoc, Burkholderia), in this study, we also detected organisms that, even if often found in soil and proglacial systems, have never been related to nitrogen-fixing or rock weathering processes before (e.g., Fimbriiglobus, Streptomyces). The different genera showed different gene trends within and among the studied systems, indicating a community constituted by a plurality of organisms involved in nitrogen fixation and biotic rock weathering, and where the latter were driven by different organisms at different soil succession stages.

Microbial dynamics in soils of the Damma glacier forefield show succession in the functional genetic potential

“…Another way for the ecosystem to obtain reactive N is N 2 fixation. Nitrogenase genes were found in all SSDs but at low abundance, which is in line with reports from Arctic glacier forefields (Nash et al, 2018;Varliero et al, 2021). Interestingly, N-cycling genes related to N 2 fixation were less abundant in the barren soils and highest in biological soils crust, which supports our fourth hypothesis.…”

“…The involvement of Bradyrhizobium and Variovorax in oxalate and siderophore biosynthesis has also been reported in Arctic proglacial systems (Varliero et al, 2021). Microorganisms can grow on rock surfaces or within rocks, where plants are unable to develop, in particular through microbial chemosynthesis supported by mineral weathering (de los Rios et al, 2003;Frey et al, 2010;Garrido-Benavent et al, 2020;Varliero et al, 2021;Wierzchos et al, 2018). In these environments, microorganisms together with lichens pave the way for subsequent plant colonization, as inorganic nutrients are released that can eventually be used by plants (Wild et al, 2022).…”

“…We also identified weathering genes (e.g., obcA genes that are involved in the first step of oxalate biosynthesis, genes involved in cyanide synthesis and genes involved in siderophore synthesis and transport) and their taxonomic affiliation following procedure in Varliero et al (2021).…”

“…Weathering-active alphaproteobacterial taxa have also been isolated from the granitic surfaces of rock sediments of recently deglaciated barren soils in the Damma glacier forefield (Frey et al, 2010;Lapanje et al, 2012). The involvement of Bradyrhizobium and Variovorax in oxalate and siderophore biosynthesis has also been reported in Arctic proglacial systems (Varliero et al, 2021). Microorganisms can grow on rock surfaces or within rocks, where plants are unable to develop, in particular through microbial chemosynthesis supported by mineral weathering (de los Rios et al, 2003;Frey et al, 2010;Garrido-Benavent et al, 2020;Varliero et al, 2021;Wierzchos et al, 2018).…”

Shotgun Metagenomics of Deep Forest Soil Layers Show Evidence of Altered Microbial Genetic Potential for Biogeochemical Cycling

“…In addition, specific environmental enzymes involved in S and Fe metabolisms could be relevant ( Jiang et al, 2019 ; Li et al, 2020 ). Genes related to such weathering processes could be those involved in oxalate biosynthesis, in cyanide synthesis, and in siderophore synthesis and transport ( Varliero et al, 2021 ).…”