O'Grady, Christopher James (2019) The structure and function of microbial communities at the soil-atmosphere interface. PhD thesis, University of Warwick.

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Abstract

The soil surface exhibits distinct physical and biotic characteristics in comparison to bulk soil due to the specific environmental conditions it is exposed to. The uppermost layer of soil can form a microbiotic layer, known as the Biological Soil Crust (BSC), that is composed of bryophytes, autotrophic algae, cyanobacteria, fungi and bacteria. In arid regions, BSCs are known to perform substantial roles in nutrient cycling, water infiltration and protection from soil erosion. However, our understanding of BSCs in temperate agricultural soils is currently limited and their functional importance in these ecosystems remains unknown. Here, using DNA amplicon sequencing it was revealed that temperate agricultural BSCs and bulk soils had substantial differences in microbial community composition, diversity and co-occurrence network topology, and were driven by different community assembly processes. Compositional differences between BSCs and bulk soils were mainly attributed to significant enrichments of Cyanobacteria, Bacteroidetes, Agaricomycetes, Dothideomycetes, Rhizaria, and Dinophyceae in the soil crust. Furthermore, BSC communities displayed significant temporal variation, marked by significant reductions in diversity and shifts in community composition. Substantial enrichments of moss sequences, which are keystone taxa for soil crust development in arid regions, were detected after just 7-8 months of development. X-ray CT image analysis revealed that a structural seal forms at the soil surface, that had substantially lower porosity, higher soil pore connectivity and more complex soil pore descriptors relative to lower depths. Additionally, soil pore differences across depths became exacerbated as BSCs developed over time. Shotgun metagenomic analysis of mature BSCs and bulk soils revealed that soil crust communities had a higher genetic potential for a number of key processes, including nitrogen fixation, nitrification, oxygenic photosynthesis, phosphonate degradation and breakdown of complex carbohydrates. This highlights that communities at the soil surface may have substantially different contributions to biogeochemical cycling than soils from lower depths. Together, results presented here all indicate that BSCs in a temperate agroecosystem form a distinct soil compartment that has a substantially different physical soil structure, biological composition and functional capacity relative to lower depth soil.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QH Natural history > QH301 Biology Q Science > QR Microbiology S Agriculture > S Agriculture (General)
Library of Congress Subject Headings (LCSH):	Soil microbiology, Crust vegetation, Biogeochemical cycles, Soils -- Composition
Official Date:	September 2019
Dates:	Date Event September 2019 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Bending, G. D. (Gary D.) ; Schäfer, Hendrik ; Van der Gast, Christopher J.
Sponsors:	Biotechnology and Biological Sciences Research Council (Great Britain)
Format of File:	pdf
Extent:	xvi, 278 leaves : illustrations (some colour)
Language:	eng

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