Sediment Drying Triggers Complex Microbe–Environment Feedbacks

The Science

Seeking to better understand how microbes influence ecosystem function, scientists have proposed conceptual frameworks linking environmental microbiomes with their environment and emergent function. However, these proposed frameworks largely remain untested. Recently, a multi-institutional team modified a current conceptual framework for hyporheic zones that exist within riverbed sediments. They tested the framework with controlled laboratory experiments of wetting-drying transitions using sediment from the hyporheic zone of the Columbia River’s Hanford Reach. Results strongly supported all framework components and provided the most comprehensive evaluation of such a framework to date.

The Impact

These results provide a conceptual model to understand how historical drought impacts how microbes and their environment influence an ecosystem’s response to rewetting. This model is transferable across all environmental systems, providing a new opportunity to link divergent systems together under a common theory. This unification is key to incorporating additional mechanistic detail into ecosystem models.

Summary

Hyporheic zone ecosystems are areas where groundwater and surface water mix, and they are also hotspots for microbiome activity involving nutrient cycling. Physical moisture variation also modifies chemical reactions in this environment. The resulting biological and chemical dynamics can impact ecosystem function. A multi-institutional team of scientists developed and tested a conceptual framework to describe microbe–environment–ecosystem interactions in hyporheic zone ecosystems, and they evaluated their framework using controlled laboratory experiments. The team exposed hyporheic zone sediment from the Columbia River to wetting–drying transitions. Then they performed molecular analyses to determine key framework characteristics and conditions. Some of these experiments used instruments at the Environmental Molecular Sciences Laboratory, EMSL, a U.S. DOE Office of Science user facility located at Pacific Northwest National Laboratory. Results suggest that sediment drying initiates previously unrecognized internal feedbacks in the microbial community. These responses drive biological and chemical dynamics, and those dynamics influence microbial responses to re-wetting that depend on drying history. These results demonstrate that the impacts of disturbance can be thought of as an external forcing that triggers internal dynamics contingent on the environmental history of the system.

Principal Investigator

James Stegen
Pacific Northwest National Laboratory
[email protected]

Program Manager

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

Funding

This work was supported as part of an Early Career Award to James Stegen by the Office of Biological and Environmental Research (BER) within the U.S. Department of Energy’s (DOE) Office of Science. It was also supported by the PREMIS Initiative at Pacific Northwest National Laboratory (PNNL), with funding from the Laboratory Directed Research and Development Program.

References