Divergent responses of permafrost peatlands to recent climate change

Thomas Sim,Mariusz Gałka,Graeme Swindles,Claire Cooper,Marco Aquino-López,Donal Mullan,Angela Gallego-Sala,Andy Baird,Werner Borken,Dan Charman,Paul Morris,Thomas Roland

doi:10.5194/egusphere-egu21-3220

Abstract

&lt;p&gt;Permafrost peatlands are found in high-latitude regions and store globally-important amounts of soil organic carbon. These regions are warming at over twice the global average rate, causing permafrost thaw and exposing previously inert carbon to decomposition and emission to the atmosphere as greenhouse gases. However, it is unclear how peatland hydrological behaviour, vegetation structure and carbon balance, and the linkages between them, will respond to permafrost thaw in a warming climate. Here we show that permafrost peatlands follow divergent ecohydrological trajectories in response to recent climate change within the same rapidly warming region (northern Sweden). Whether a site becomes wetter or drier depends on local factors and the autogenic response of individual peatlands. We find that bryophyte-dominated vegetation demonstrates resistance, and in some cases resilience, to climatic and hydrological shifts. Drying at four sites is clearly associated with reduced carbon sequestration, while no clear relationship at wetting sites is observed. We highlight the complex dynamics of permafrost peatlands and warn against an overly-simple approach when considering their ecohydrological trajectories and role as C sinks under a warming climate. &amp;#160;&amp;#160;&lt;/p&gt;

Highlights

Permafrost peatlands have developed in cold regions during the Holocene and store a disproportionate amount of organic carbon (C) for their extent, estimated to total ∼277 Gt C (Tarnocai et al 2009)— making up around a fifth of all permafrost soil C (Hugelius et al 2014)
Deeper thaw increases the amount of soil organic matter vulnerable to decomposition, while rising temperatures simultaneously increase the rate of microbial decomposition; both contribute to increased greenhouse gas (GHG) emissions and a positive feedback with climate (Jeong et al 2018)
Implications for ecohydrological and carbon dynamics in global permafrost peatlands Here we show a divergent response of permafrost peatland ecohydrological regimes to climate change over the last century and highlight the importance of internal autogenic and site-specific factors in these ecosystems

Summary

Introduction

Permafrost peatlands have developed in cold regions during the Holocene and store a disproportionate amount of organic carbon (C) for their extent, estimated to total ∼277 Gt C (Tarnocai et al 2009)— making up around a fifth of all permafrost soil C (Hugelius et al 2014) These ecosystems experience a short growing season where a seasonal active layer thaws (French 2017), and C accumulates when the addition of plant litter exceeds losses from decomposition (Yu et al 2011). Climate-driven drying may expose peat to increased aerobic decomposition, leading to increases in carbon dioxide (CO2) emissions (Ise et al 2008), while thaw-induced wetting has been associated with elevated methane (CH4) emissions (Christensen et al 2004) These C losses may be partially offset or even reversed by improved plant productivity during longer growing seasons (Gallego-Sala et al 2018, Taylor et al 2019, Heffernan et al 2020)

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