June 13, 2019

Hillslope and Floodplain Position Exert Strong Controls on Microbial Community Structure and Function

Microbial communities across a hillslope-riparian transect are shaped by proximity to stream, groundwater, and weathered bedrock.

Spatial abundance of genes central to metabolic pathways. Samples from the floodplain (blue clade) are distinct from samples of the hillslope (black clade), particularly with respect to carbon fixation and selenate reduction. Furthermore, weathered shale samples at PLM6 are distinct from other hillslope samples.

[Reprinted under a Creative Commons Attribution 4.0 International License (CC BY 4.0) from Lavy, A., et al. "Microbial Communities Across a Hillslope-Riparian Transect Shaped by Proximity to the Stream, Groundwater Table, and Weathered Bedrock." Ecology and Evolution 9 (12), 6869–900 (2019). DOI:10.1002/ece3.5254.]

The Science

Within mountainous watersheds, microbial communities affect water chemistry and element fluxes as water from precipitation events discharges through soils and underlying weathered rock. However, there is limited information regarding the structure and function of these communities. Within the East River, Colorado, watershed, a team of researchers conducted a depth-resolved, hillslope-to-riparian zone transect study to identify factors that control how microorganisms and their functionality are distributed. The researchers found that microbial community structure and metabolic potential are strongly affected by distance from the river and proximity to groundwater and underlying weathered shale.

The Impact

Riparian zone and deep soil microbial communities are functionally differentiated from shallow hillslope communities based on their metabolic capacity. Researchers anticipate that the drivers of community composition and metabolic potential identified along this representative hillslope-to-floodplain transect will predict patterns across similar transects within mountainous systems.

Summary

Metagenomic and geochemical analyses indicate that distance from the East River and proximity to groundwater and underlying weathered shale strongly impact microbial community structure and metabolic potential. Riparian zone microbial communities are compositionally distinct from the phylum to species level from all hillslope communities. Bacteria from phyla lacking isolated representatives consistently increase in abundance with increasing depth, but only in the riparian zone saturated sediments did the researchers find Candidate Phyla Radiation bacteria. Riparian zone microbial communities are functionally differentiated from hillslope communities based on their capacities for carbon and nitrogen fixation and sulfate reduction. Selenium reduction is prominent at depth in weathered shale and saturated riparian zone sediments and could impact water quality.

Principal Investigator

Jillian F. Banfield
University of California–Berkeley
[email protected]

Program Manager

Paul Bayer
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the U.S. Department of Energy’s Office of Biological and Environmental Research (BER) within the Office of Science. Work was conducted as part of the Watershed Function Scientific Focus Area funded by BER under award number DE-AC02-05CH11231.

References

Lavy, A., et al. "Microbial Communities Across a Hillslope-Riparian Transect Shaped by Proximity to the Stream, Groundwater Table, and Weathered Bedrock." Ecology and Evolution 9 (12), 6869–900 (2019). https://doi.org/10.1002/ece3.5254.