Structure of soil bacterial communities in relation to environmental variables in a semi-arid region of Mongolia

Patterns in soil bacterial communities, and the factors that determine them, have been little explored in arid and semi-arid environments. It is unclear to what extent the diversity and community composition of arid-land soil bacterial communities follow vegetation habitats, or conversely other relatively independent soil variables. It is also unclear whether the factors (e.g. pH) that contribute to variation in bacterial communities in some moister environments also operate on a local scale in semi-arid environments. To identify the main factors in shaping bacterial community structure in semi-arid environments, we sampled a mosaic of habitats under different vegetation, landscape and edaphic conditions in central Mongolia, including steppe, forest-steppe, and abandoned wheat field. Soil DNA was extracted and pyrosequenced for 16S rRNA gene identification. NMDS results showed that bacterial community structures are slightly different from one habitat to another. However, the similarity between communities both within and between habitats is determined more strongly by soil texture than by vegetation type and drainage conditions. Moreover, the relative abundances of certain phyla are correlated with specific soil properties such as salinity and soil texture, in ways that have not previously been found in semi-arid environments. Actinobacteria, for example, show a negative correlation with salinity and Bacteroidetes display a positive relationship with percentage silt and clay. It also appears that the most important environmental variables (soil texture and salinity) affecting the bacterial community within this semi-arid environment are different from those found in moister environments, with no detectable effect of pH.

► Bacterial community composition was determined more strongly by soil texture than vegetation form.
► Bacteroidetes showed a positive relationship with percentage silt and clay.
► Actinobacteria displayed a negative correlation with salinity.
► 16 soil bacterial lineages at the phylum or subphylum level were newly found in Mongolian steppe region.