The Compositionally Distinct Cyanobacterial Biocrusts From Brazilian Savanna and Their Environmental Drivers of Community Diversity.

Náthali Maria Machado-De-Lima,Ferran Garcia-Pichel,Vanessa Moreira Câmara Fernandes,Janaina Rigonato,Sergio Velasco Ayuso,Luis Henrique Zanini Branco,Daniel Roush

doi:10.3389/fmicb.2019.02798

Abstract

The last decade was marked by efforts to define and identify the main cyanobacterial players in biological crusts around the world. However, not much is known about biocrusts in Brazil’s tropical savanna (cerrado), despite the existence of environments favorable to their development and ecological relevance. We examined the community composition of cyanobacteria in biocrusts from six sites distributed in the Southeast of the country using high throughput sequencing of 16S rRNA and phylogenetic placement in the wider context of biocrusts from deserts. Sequences ascribable to 22 genera of cyanobacteria were identified. Although a significant proportion of sequences did not match those of known cyanobacteria, several clades of Leptolyngbya and Porphyrosiphon were found to be the most abundant. We identified significant differences in dominance and overall composition among the cerrado sites, much larger than within-site variability. The composition of cerrado cyanobacterial communities was distinct from those known in biocrusts from North American deserts. Among several environmental drivers considered, the opposing trend of annual precipitation and mean annual temperature best explained the variability in community composition within Brazilian biocrusts. Their compositional uniqueness speaks of the need for dedicated efforts to study the ecophysiology of tropical savanna biocrust and their roles in ecosystem function for management and preservation.

Highlights

Biological soil crusts (BSCs or biocrusts) are microbial assemblages present at the top soil of several terrestrial ecosystems, especially in drylands
Arid land biocrusts are usually first colonized by Microcoleus species, which stabilize the soil and start fixing carbon (GarciaPichel and Wojciechowski, 2009), enriching the soil and allowing heterocytous nitrogen-fixing cyanobacteria, usually Scytonema sp. and Tolypothrix sp. to colonize
The samples that did not reach the plateau were still included in the subsequent analyses because they were similar in community composition with other samples from the same localities that did

Summary

Introduction

Biological soil crusts (BSCs or biocrusts) are microbial assemblages present at the top soil of several terrestrial ecosystems, especially in drylands. Cyanobacteria contribute to important soil functions within biocrusts, providing stability and protection against erosive forces (Belnap, 2003, 2005) and are responsible for carbon and nitrogen fixation, enriching soils with macronutrients (Johnson et al, 2007) and micronutrients (Beraldi-Campesi et al, 2009). These contributions of cyanobacteria to the ecosystem highlight the importance of understanding their composition and function worldwide. Whenever compositional studies have been carried out in biocrust from other climates, apparently differentiated communities were encountered (Pushkareva et al, 2015; Muñoz-Martín et al, 2019)

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Conclusion