The Bacterial Microbiome Associated With Arid Biocrusts and the Biogeochemical Influence of Biocrusts Upon the Underlying Soil

Abstract

Biocrusts are aggregated crusts that exist on the soil surface of arid environments. They are complex microbial communities comprised of cyanobacteria, lichens, mosses, algae and fungi. Recently, biocrusts have gained significant attention due to their ubiquitous distribution and likely important ecological roles, including soil stabilization, soil moisture retention, carbon (C) and nitrogen (N) fixation, as well as microbial engineers for semi-arid ecosystem restoration. Here, we collected three co-occurring types of biocrust (Cyanobacterial crust, Crustose lichen, and Foliose lichen) and their underlying soil from arid zones within Western Australia. Bacterial microbiome composition was determined through 16S rRNA gene amplicon sequencing to assess the extent of microbiome selection within the crusts versus underlying soil and biogeochemical measures performed to determine whether the crusts had significant impact upon the underlying soil for nutrient input. We determined that the bacterial communities of native biocrusts are distinct from those in their underlying soil, where dominant bacterial taxa differed according to crust morphologies. δ15N revealed that N-fixation appeared most evident in Foliose lichen crust (1.73 ± 1.04‰). Consequently, depending upon the crust type, biocrusts contained higher concentrations of organic C (2 to 50 times), total N (4 to 16 times) and available ammonium (2 to 4 times), though this enrichment did not extend to the soils underneath them. These findings demonstrate that biocrust communities are seemingly islands of biological activity in an arid landscape, uniquely different from their surrounding and underlying soil.

A world of possibilities: six restoration strategies to support the United Nation's Decade on Ecosystem Restoration

“…The impact of degraded soil microbiomes on human health are now being explored and tested (Wall et al ), and new scientific discoveries illustrate the encouraging possibility of restoring soil biodiversity so as to ameliorate soil health, ecosystem health, and human health, in rural and in urban areas (Liddicoat et al ; Robinson et al ; Liddicoat et al ). This strategy may be especially relevant in the vast areas of arid, semiarid, and desertified lands worldwide that have already been significantly or completely degraded, and are often strongly reliant upon microbial communities for maintaining productivity through the provisioning of key ecological functions such as nutrient cycling (Soussi et al ; Neilson et al ; Moreira‐Grez et al ). Significantly increase on‐site training and capacity building opportunities at ecological restoration and restorative action sites for early career professionals, community leaders, practitioners, administrators, and academics. The numbers of competent restoration scientists, managers, restoration entrepreneurs, and practitioners is insufficient to meet global ecological challenges.…”

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

“…and Nostoc spp. In places such as the Colorado Plateau, the Mojave desert, the north part of the Chihuahuan Desert (Sevilleta LTER) in the USA, Alicante in Spain, Western Australia [49], temperate areas in Mexico [33], and the Brazilian savannah (Cerrado) [52], where the mean annual temperature during the growth season falls between the 17 and 23 • C range, this microbial replacement will likely happen faster than at those locations exhibiting mean average temperatures below 17 • C, that are not projected to reach sensitive temperature ranges for decades to centuries, or locations with average temperatures above 24 • C, which already exhibit a dominance of Scytonema spp. (Figure 4).…”

“…We performed a literature search, and either downloaded from public databases or directly requested raw sequence data from authors from multiple environmental biocrust surveys conducted at different locations around the world. We collected data from different arid and semiarid regions in USA [6,34,[46][47][48], Mexico [33] and Australia [49], from arid, semiarid and alpine regions in Europe [32,50], from the arid Gurbantunggut desert in China [51], and from the Brazilian savannah (Cerrado) [52]. A complete list of the biocrust surveys with locations, environmental variables, and other relevant information can be found in Table S4.…”

Divergence among biological soil crust communities developing under different environmental conditions

“…Given that cyanobacteria and cyanolichens contribute substantially to N fixation, N requirements and possible N growth limitations have not been considered to explain their occurrence in the landscape (Bowker et al, 2016). Instead, it has been shown that they preferentially occupy microenvironments rich in available P, K, organic C and micronutrients (Bowker et al, 2006;Ochoa-Hueso et al, 2011;Moreira-Grez et al, 2019). However, it is not unreasonable to consider possible N limitation, since the fate of the N fixed by…”

“…BSCs is unknown and has limited influence on the underlying soil (Castillo-Monroy et al, 2010;Moreira-Grez et al, 2019). Indeed, some previous experiments adding N-rich fertilizers to BSC cyanobacteria and BSC cyanolichen cultures have shown a positive response on biomass and cover in comparison to cultures grown with no addition of a N source (Maestre et al, 2006;Antoninka et al, 2016;Roncero-Ramos et al, 2019).…”