Our climate is changing rapidly, leading to thawing of the permafrost in northern latitudes. Microbes play important roles in northern soils contributing to carbon storage and release. Understanding the underlying mechanisms that govern whether a permafrost-affected ecosystem will store or release carbon over the long term is critical to our planet’s future as the climate warms.

When permafrost thaws, microbial communities undergo major structural shifts. Some of these shifts are goverend by the physics, chemistry, and biology of the ecosystem. Other shifts depend on stochastic ecological processes (such as demographics, ecological drift, and dispersal). This makes predicting the outcomes of that thaw on global carbon cycles challenging. I am involved in several projects that aim to understand the effect of this thaw on microbial communities and to develop models to better predict the outcomes for microbial communities and landscape-level carbon cycles in northern ecoystems.

Stable States in an Unstable Landscape: Microbial Resilience at Stordalen Mire

Stordalen Mire, Abisko Sweden (68° 21’ N, 19° 20’ E) is a discontinuous permafrost peatland in Swedish Lapland. The site is a model ecosystem and has been studied in one form or another for over a century.

Stordalen Mire, Sweden. An area of rapidly thawing permafrost. (Photo: Scott Salenska)

As permafrost thaws, habitats, biochemsitry, and microbial communities change, leading to increasing release of methane and carbon dioxide. The Mire is experiencing rapid thaw - fens have doubled over the last 50 years and researchers frequenly observe habitat conversion. Yet, over the last ten years, microbial communities within each habitat have remained remarkably stable, despite warming ground temperatures and active layer deepening. This project uses hand-currated microbial metabolic ‘omics data, community assembly modeling, and network analyses to understand the underpinnings of this microbial resilience to change.

The typical progression of permafrost thaw in Stordalen Mire, Sweden. Upland Palsas thaw into sphagnum-dominated bogs (disconnected from the water table), and further thaw into fens (connected to the water table). (Figure: Hannah Holland-Moritz)

Towards a systems perspective of arctic priming

Following permafrost thaw, plant productivity, microbial communities, and soil minerals interact in complex ways. The outcomes of these interactions determine whether more carbon is released to the atmosphere or stored belowground. One way that carbon is released rather than stored in thawing arctic soils is priming. Priming occurs when plants introduce new organic material to a soil, stimulating decomposition of previously stored soil carbon. Priming is an emergent property of the complex tripartite interaction of plants, microbes, and minerals yet it is rarely studied through all three lenses at once.

During priming, plants secrete sugars and organic acids into the soil. Microbes decompose the carbon and respire it, but in the process, previously stored soil organic matter (SOM) can be decomposed, leading to a net loss of carbon from the soil. (Figure: Hannah Holland-Moritz)

We are exploring how microbial carbon-processing traits are linked to growth rates in microbial communities associated with priming during permafrost thaw.