Namib Desert dune/interdune transects exhibit habitat-specific edaphic bacterial communities.

Sandra Ronca,Don A Cowan,Brian E Jones,Mary Seely,Jean-Baptiste Ramond

doi:10.3389/fmicb.2015.00845

Abstract

The sand dunes and inter-dune zones of the hyper-arid central Namib Desert represent heterogeneous soil habitats. As little is known about their indigenous edaphic bacterial communities, we aimed to evaluate their diversity and factors of assembly and hypothesized that soil physicochemistry gradients would strongly shape dune/interdune communities. We sampled a total of 125 samples from 5 parallel dune/interdune transects and characterized 21 physico-chemical edaphic parameters coupled with 16S rRNA gene bacterial community fingerprinting using T-RFLP and 454 pyrosequencing. Multivariate analyses of T-RFLP data showed significantly different bacterial communities, related to physico-chemical gradients, in four distinct dune habitats: the dune top, slope, base and interdune zones. Pyrosequencing of 16S rRNA gene amplicon sets showed that each dune zone presented a unique phylogenetic profile, suggesting a high degree of environmental selection. The combined results strongly infer that habitat filtering is an important factor shaping Namib Desert dune bacterial communities, with habitat stability, soil texture and mineral and nutrient contents being the main environmental drivers of bacterial community structures.

Highlights

Despite extreme surface conditions, notably aridity, wide daily temperature fluctuations, high UV radiation and oligotrophy, edaphic microbial communities have been shown to flourish in desert soils (Makhalanyane et al, 2015)
Dune Soil Physico-chemistries Principal Component Analysis of 21 physico-chemical parameters from all 125 independent soil samples (Figure 2A) along the five dune-interdune transects (Figure 1) shows Top and Slope samples clearly separated along the PC2 axis (Figure 2A), explaining 10.7% of the sample variation
The bacterial community structures from cluster 1 were mainly driven by very fine sand (VFS), very coarse sand (VCS) and NH+4 -N, K, Fe, and P contents while those of cluster 2 by medium sand (MS) and Na contents. Communities from both clusters were further separated along the redundancy analysis (RDA) axis2 according to their dune biotope of origin, with granulometry parameters [fine sand (FS) and coarse sand (CS)] differentiating the structures of the Interdune and dune Base communities as well as the ones from the dune Top and Slope (Figure 7). These results demonstrate that environmental gradients in the four defined biotopes significantly impact the bacterial community structures of dune/interdune transects

Summary

Introduction

Notably (hyper-) aridity, wide daily temperature fluctuations, high UV radiation and oligotrophy, edaphic microbial communities have been shown to flourish in desert soils (Makhalanyane et al, 2015). The Namib Desert of south-western Africa is considered to be one of the oldest desert regions on Earth (Eckardt and Spiro, 1999). It is characterized by a wide range of different soil environments including gravel plains, sand dunes, inselbergs, escarpments, river beds, salt pans and playas (Seely, 2012; Eckardt et al, 2013a).

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Discussion

Conclusion