Aeolian transported and deposited microbial communities differ along an elevation gradient in the Southern Sierra CZO
As the climate changes, California's Central Valley is beginning to experience prolonged droughts that have been predicted for the Southwestern United States by climate models. Drought can increase the exposed bare soil in this region, and therefore the aeolian movement of soil from an exposed region to another location. Soil microorganisms may be able to survive such transport, and may be viable when they enter another soil system, whether it is nearby or distant. These non-indigenous microorganisms may become invasive if they alter the phylogenetic or functional diversity of the existing soil microbial community in the new location.
In order to investigate the movement and deposition of soil- and otherwise-derived microorganisms along an elevational gradient, sterile dust collectors were deployed at 3 locations in the Sierra Nevada mountains. These locations are study sites of the Southern Sierra Critical Zone Observatory (SSCZO). Four dust collectors were installed in these locations in April 2014, were deployed for three months, and then sampled in July 2014 for microorganisms, nutrients and isotopic content. Here, we present the microbial communities collected from the dust collectors at these elevations. The dust was washed out of the collectors using sterile water, filtered in the laboratory, and the filter was used to perform DNA extraction using the MoBio PowerWater kit. These extracts were amplified for the V3-V4 regions of the 16S ribosomal RNA gene, to capture the full diversity of bacteria and archaea in these samples, and then sequenced using the Illumina MiSeq platform.
The lowest elevation site (SJER) had the greatest richness of Operational Taxonomic Units (OTUs), at 97% similarity cutoff, and OTU richness decreased with increasing elevation. Using a PCoA analysis of the UniFrac metric, the community composition of dust samples from all three sites were distinct (Pseudo-F = 2.5, P<0.055). Across all samples, Proteobacteria were dominant on average, and made up more than half of the OTUs in samples from the middle elevation site, and most samples from the highest elevation site. Fermicutes were dominant in most samples from the lowest elevation site. Cyanobacteria and Actinobacteria were also prevalent in many samples. In conclusion, we find that the microbial communities entering the ecosystems at these three elevations are distinct, but overlapping. This suggests a different composition of sources for the dust depositing at these different elevations, and may inform our understanding of aeolian dust as a vector for microbial dispersal.