Deep Roots

Deep nitrogen acquisition in warming permafrost soils: Contributions of belowground plant traits and fungal symbioses in the permafrost carbon feedback to climate

Plant acquisition of nitrogen (N) from thawing permafrost has the potential to play a critical role in the trajectory of future climate change. As permafrost soils thaw, organic matter that has been protected from decomposition for centuries to millennia is released as greenhouse gasses, resulting in one of the most likely destabilizing feedbacks between the biosphere and climate. Nitrogen released from deep, thawing soils may stimulate productivity and thus regulate the pace and magnitude of the permafrost carbon (C) feedback to climate. This regulatory role of N is predicated on the opportunistic capacity of arctic plants and their obligate mycobionts to forage as seasonally unfrozen ground deepens. The Deep Roots Project strives to develop a mechanistic understanding of belowground plant and fungal response to changing permafrost conditions as a first step towards understanding N regulation of the permafrost C feedback to climate. We are utilizing a suite of field experiments and observational studies coupled with model development and modeling experiments to investigate whether tundra plants can acquire deep permafrost N as soils thaw and whether this influences regional carbon balance.

Recent field campaigns:
To determine which plant species access N from thawing permafrost, we are implementing a multi-year 15NH4+ tracer study. Starting in the summer of 2015 we injected an isotopically labeled N tracer deep at the permafrost boundary and will quantify tracer recovery in plant biomass and identify active fungal communities associated with plant roots and frozen soils at depth increments. We will relate N uptake to rooting and mycobiont characteristics allowing us to determine N contribution to potential mediation of projected feedbacks between permafrost thaw and a warming atmosphere. This research is a collaborative effort between Northern Arizona University (Michelle Mack and Rebecca Hewitt), University of Alaska Fairbanks (Dave McGuire and Hélène Genet), and University of New Mexico (Lee Taylor).

Photo Credit: Keith Halloran

Photo Credit: Samantha Miller

Grants supporting this work:
National Science Foundation, ARCSS: The Roles of Deep Nitrogen, Plant Roots, and Mycorrhizal Fungi in the Permafrost Carbon Feedback to Warming Climate, 2015-2018, $1,610,000