Is thawing permafrost as a result of global warming a possible significant source of degradable carbon for microbiota residing in situ and in Arctic rivers?


Arctic Research Initiative
2007 Funded Project


Northern high-latitude ecosystems contain about 44% of the world’s soil carbon, most of which is stored in permanently frozen soil (permafrost). Global warming through the 21st century is expected to induce permafrost thaw, which will increase microbial organic matter decomposition and release large amounts of the greenhouse gasses methane (CH4) and carbon dioxide (CO2) into the atmosphere.In addition, Arctic rivers are a globally important source of terrestrial organic carbon to the ocean and further permafrost melting as a result of global warming will impact surface runoff, directly affecting groundwater storage and river discharge.It has been estimated that the sediment flux of the largest Arctic rivers will increase up to 125% by 2100.Up to now, it remains largely unknown to what extent the ancient organic matter (OM) stored in newly thawing permafrost can be consumed by microbes residing in the permafrost or by microbes residing in Arctic rivers which become exposed to newly discharged permafrost OM. This information is essential to calculate how much CH4 or CO2 is likely to be released from Arctic soils to the atmosphere as a result of global warming. In addition, we know little about which microorganisms are capable of degrading permafrost OM.

A sensitive approach to study this is to measure activities of extracellular enzymes (ectoenzymes) which are released by micro organisms to initially cleave organic matter into smaller molecules. These smaller molecules can then easily be consumed by a wide variety of microbes such as fermenting bacteria which produce the greenhouse gas CO2 whereas part of this CO2 will be further microbially converted into the even stronger greenhouse gas methane. We propose to undertake a field trip to the Toolik Lake Arctic Long Term Ecological Research (LTER) field station in northern Alaska in order to collect permafrost cores from the most common Arctic landscape types (tussock tundra and wet sedge tundra) near the KuparukRiver. From different depths in the core we will thaw currently frozen permafrost and measure the activities of ectoenzymes involved in the degradation of a wide range of organic compounds mediated by (1) microbes residing in permafrost and (2) microbiota residing in the Arctic river when they become exposed to the complex organic matter stored in newly thawed permafrost. The resulting ectoenzyme activity rates will provide new insights in the actual availability of bacterial carbon substrates in permafrost and how much and how fast easily consumable degradation products would become available for microbes responsible for the production of greenhouse gasses. Furthermore, the active permafrost microbiota as well as the riverine microbiota which have the potential to degrade the complex biopolymers stored in permafrost will be identified based on the analysis of their expressed genes using advanced molecular ecological techniques.