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Identification of riverine and indigenous permafrost microbiota (eukarya, archaea, bacteria) involved in the (an)aerobic degradation of ancient organic matter stored in thawing permafrost

Arctic Research Initiative
2009 Funded Project

Abstract

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.  To date, 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 that 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. 

With previous ARI funding we analyzed the initial microbial enzymatic cleavage of particulate OM stored in up to 1 meter of permafrost underlaying moist acidic tundra located near the Kuparuk River at the Toolik Field Station in northern Alaska.  Our results suggest that large amounts of phosphate could be liberated through soil microbial activities in thawing permafrost and this would cause eutrophication of lakes and rivers via ground water discharge.  Similar high activities were found for an enzyme which cleaves complex organic carbon compounds into glucose.  This process would fuel heterotrophic bacteria to produce carbon dioxide which, in turn, could be converted to the 25x stronger greenhouse gas methane by methanogenic archaea.  In the absence of oxygen, such as would prevail in water-logged thawed permafrost, these microbial activities were lower but still significant.  In addition, our results imply that microbes in the Kuparuk River water and surface sediment can also use ancient permafrost OM as a source of carbon and phosphorus for growth.  Furthermore, we noticed a significant increase in gene expression indicative of the presence of metabolically active bacteria, archaea and eukaryotes in thawed permafrost that was incubated with and without oxygen at 4 °C for up to 28 days as well as in time series where riverine microbes were exposed to sterile organic matter from permafrost.  

For this ARI round we request additional funding to conduct experiments that will prove that the enzymes involved in permafrost organic matter degradation were present inside intact living cells and that we did not just measure activities from ancient preserved extracellular enzymes which were reactivated upon thawing of the pristine permafrost.  In addition, we request additional ARI funding for an extensive phylogenetic analysis of clone libraries in order to reveal the identity of the metabolically active populations involved in permafrost OM degradation and to prove that these species were indigenous to the soils as opposed to contaminants.

Last updated: September 14, 2010