Effect of biological soil crusts on soil elemental concentrations: implications for biogeochemistry and as traceable biosignatures of ancient life on land

Abstract

Biological soil crusts (BSCs) are topsoil biosedimentary structures built by photosynthetic microbes commonly found today on arid soils. They play a role in soil stabilization and the fertility of arid lands, and are considered modern analogues of ancient terrestrial microbial communities. We determined the concentrations of four biogenic and 21 other elements, mostly metals, in surface soils that hosted BSCs, in the soils underneath those crusts, and in proximate but non-crusted surface soils. The samples were from six sites in the Colorado Plateau highlands and the Sonoran Desert lowlands. In spite of the variability in climate and geologic setting, we found statistically significant overall trends of enrichment in biogenic elements and depletion in non-biogenic elements when BSCs were compared with non-crusted soils. The differences between crusted and non-crusted soils were statistically significant at approximately 95% confidence for C, N (enrichments) and for Ca, Cr, Mn, Cu, Zn, As, and Zr (depletions). These trends are best explained by the activity of microbes. As expected, no differences in the concentrations of C, N, P, and S were detected between the soils underneath the crusts and the non-crusted soils, but the former showed depletion of non-biogenic elements, indicating that the leaching effect of crust microbes extends downward in the soil. These patterns speak to the need for a sustained input of allochthonous material, possibly dust, to maintain BSC fertility. These elemental patterns can be considered a biosignature that may be preserved in the rock record and might help identify ancient microbial communities on land.

Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in theca.3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia

“…Microbially induced sedimentary structures are created by microbial mats colonizing most aquatic environments, including shelves, tidal flats, lagoons, riverine shores, lakes, dune fields, and sabkhas (e.g., Gerdes and Krumbein, 1987; volume by Hagadorn et al, 1999;Eriksson et al, 2000;Prave, 2002; volume by Schieber et al, 2007;Beraldi-Campesi et al, 2009;volume by Noffke, 2009;Noffke, 2010; volume by Noffke and Chafetz, 2012). In contrast to stromatolites, MISS arise exclusively from the response of microbiota to physical sediment dynamics.…”

Aerobic Degradation of Petroleum Components by Microbial Consortia

“…The appearance of cyanobacterial akinetes (for N 2 fixation) in the Paleoproterozoic [184] attests to this early adaptation. The limiting nutrients such as P, can be supplied for organisms on land by dust deposition [185,186], which may be an alternative process for replenishment of nutrient loss by runoff and leaching in such environments [168,187]; S can also be acquired from minerals, aerosols, and as gaseous sources, likely present in the early atmosphere [188]. Thus, the nutritional requirements for oxygenic, photoautotrophic, primary producers seem not to have been a limiting factor for the colonization of the land.…”

Microbial Nursery Production of High-Quality Biological Soil Crust Biomass for Restoration of Degraded Dryland Soils

“…Biocrusts are complex, topsoil microbial assemblages that develop on the primary production of soil cyanobacteria, microalgae (sometimes in algal symbioses), or mosses and that support a large diversity of heterotrophic bacteria (9), archaea (10), and fungi (11). Considered to be a "mantle of fertility" in arid lands (12), biocrusts provide essential goods and services; they stabilize soils and thus reduce rates of wind erosion and dust particle production (13), can influence soil temperature (14,15), contribute significantly to soil C and N inputs into the ecosystem (16), increase the lixiviation of micronutrients (17), control soil hydrological dynamics (18), and are thought to provide good conditions for plant germination and establishment (19).…”