The importance of deep roots in the carbon-climate feedback from thawing permafrost soils

Permafrost soils contain twice as much carbon (C) as the atmosphere, which they have protected for millennia.

As arctic temperatures soar and the rate of permafrost thaw accelerates, there is a growing concern about large C losses from permafrost soils into the atmosphere.

Even though around 80% of plant biomass in the arctic tundra is belowground, the crucial role of roots in carbon cycling remains unquantified. Roots can promote new C storage but also stimulate losses of old soil carbon.

Here, deep roots are likely to be disproportionally important, as they increasingly interact with newly-thawed, vulnerable soils. Yet, few studies include root measurements, particularly in deeper soils.

In this project we will quantify the role of deep roots in the carbon-climate feedback from thawing permafrost soils by using a long-term field experiment.

During the 4-year PhD project, we will assess changes in root growth and turnover with warming and permafrost thaw, selectively exclude roots at different depths and then measure changes in gas fluxes, root production and decomposition with depth, and release of millennia-old soil C depending on root presence.

The effects of species-specific root exudation on soil C cycling in active layer and permafrost soils will be established in a complementing microcosm experiment.

The results will define the importance of root dynamics in deep soils and strongly improve our ability to predict feedbacks from arctic tundra to climate change.