Possible nitrogen fertilization of the early Earth Ocean by microbial continental ecosystems

Abstract

While significant efforts have been invested in reconstructing the early evolution of the Earth’s atmosphere–ocean–biosphere biogeochemical nitrogen cycle, the potential role of an early continental contribution by a terrestrial, microbial phototrophic biosphere has been largely overlooked. By transposing to the Archean nitrogen fluxes of modern topsoil communities known as biological soil crusts (terrestrial analogs of microbial mats), whose ancestors might have existed as far back as 3.2 Ga ago, we show that they could have impacted the evolution of the nitrogen cycle early on. We calculate that the net output of inorganic nitrogen reaching the Precambrian hydrogeological system could have been of the same order of magnitude as that of modern continents for a range of inhabited area as small as a few percent of that of present day continents. This contradicts the assumption that before the Great Oxidation Event, marine and continental biogeochemical nitrogen cycles were disconnected.

Biological Soil Crusts as Modern Analogs for the Archean Continental Biosphere: Insights from Carbon and Nitrogen Isotopes

“…This assumption is consistent with studies suggesting that continental colonization by microbial communities may have triggered oxidative weathering on continental surfaces prior to the Great Oxidation Event (e.g., Lalonde and Konhauser, 2015;Havig et al, 2019). Early life on land would have also enhanced the delivery of nutrients to the oceans such as fixed nitrogen (Thomazo et al, 2018) and would have increased the productivity of Paleoarchean shelfs and coastal margin environments (Lyons et al, 2014). Cyanobacterial land-based modern ecosystems may therefore hold keys in understanding how Earth's early terrestrial biogeochemical cycles were established and how they were linked to biogeochemical cycling in the marine environment.…”

“…However, later findings showed that sulfur vapor and hydrocarbon smog in the primitive ozone-free atmosphere may have strongly attenuated UV radiation (Kasting et al, 1989), and that the Archean landmasses could have been provided sufficient refugia to early photosynthesizers even under high UV fluxes (Garcia-Pichel, 1998). From a theoretical perspective, a continental * microbial phototrophic biosphere could have therefore existed early, before the Great Oxidation Event (Beraldi-Campesi et al, 2009;Lalonde and Konhauser, 2015), and have colonized emergent land surfaces (Thomazo et al, 2018).…”

“…fluvial with periods of terrestrial subaerial exposure and desiccation) and that their coupled carbon isotope compositions of organic matter and bulk nitrogen isotope compositions are statistically different from strictly marine examples preserved elsewhere in the Moodies Group (e.g, Homann et al, 2015). In addition, Thomazo et al (2018) carried out a meta-analysis of the biogeochemical cycling of nitrogen by the modern terrestrial phototrophic biosphere and highlighted that this ecosystem would have been capable of importing nitrogen gas from the early atmosphere and exporting ammonium and nitrate to the Archean ocean, presumably through fluvial networks. The present contribution fills the gap between these two recent studies by addressing the N and C isotopic signals of modern cyanoBSCs in order to compare their biosignatures with the emerging geochemical continental record of Archean continental life.…”

Niche Partitioning with Temperature among Heterocystous Cyanobacteria (Scytonema spp., Nostoc spp., and Tolypothrix spp.) from Biological Soil Crusts

“…Biological fixation thus remains a necessity for continued growth. Fixed atmospheric C and N [20,22,23], along with other elements [24] can then be exported to underlying soils, improving landscape soil fertility. Because drylands cover nearly 45% of the total Earth continental area [25], and aridity is predicted to increase due to global warming [26][27][28], this N export activity of biocrusts matters not only locally, but also globally.…”

Nursing biocrusts: isolation, cultivation, and fitness test of indigenous cyanobacteria

“…This microbial mantle provides ecosystem services such as protection from wind (Belnap & Gillette ; Zhang et al ) and water erosion (Gaskin & Gardner ). Biocrusts also contribute to soil fertility by fixing atmospheric carbon (Elbert et al ; Sancho et al ) and nitrogen (Barger et al ), by exporting significant proportions of both C and N, but also other elements to the soils they cover (Thiet et al ; Johnson et al ; Beraldi‐Campesi et al ; Thomazo et al ), and by trapping dust particles (Reynolds et al ). Unfortunately, biocrusts are very susceptible to trampling associated with human activities (Belnap & Eldridge ; Zaady et al ).…”