永凍土融化時其中的微生物群會助長氣候變遷
一項由昆士蘭大學領導的研究可以讓我們更加準確地預測未來100年內，由於永凍土融化而釋放出來的溫室氣體對全球暖化速率造成的影響。
泥炭土丘正在融化並崩解，逐漸轉變成沼澤。(來源：Moira Hough)
這項關於微生物的研究包含了永凍土中碳的分解情況，結果顯示微生物群集和生物地球化學的改變，與溫室氣體排放量上升有關。
研究由澳洲生態經濟學中心的研究人員領導(隸屬於昆士蘭大學化學和分子生物學系)，包括Ben Woodcroft博士、博士生Caitlin
Singleton和Gene Tyson教授，以及其他國際上的合作人員。
Woodcroft博士表示：「許多本來在常年結凍的永凍土中封存的碳，隨著全球溫度上升變成可以被微生物分解。」
「由於我們對永凍土中的微生物群落和它們代謝碳的方式所知有限，因此迄今我們仍難以精確預測出永凍土融化後會產生多少溫室氣體至大氣中。」
研究人員從瑞典北部仍然完好的永凍土、融化中和已經融化的永凍土採集超過200具樣品，再利用Tyson教授開發的基因定序技術來研究它們。
DNA定序的復原結果中，超過1500種微生物基因組對科學界來說是全新的發現，而它們也構成了相當複雜的生物化學網路。
這項研究同時運用昆士蘭大學的超級電腦來運行新的總體基因體學軟體，結果指出其中某些微生物是和製造溫室氣體有關的全新譜系。
Singleton表示全世界蘊藏在土壤中的碳(約1.58兆噸)有將近百分之50是儲存在永凍土中。
她說：「政府間氣候變化專門委員會的報告預估到了2100年，位於地表附近的永凍土將有30%到99%會消失不見。」
「全世界排放至大氣的甲烷中，北半球永凍土層中的濕地貢獻了很大一部份。特別是崩解的永凍土可以創造出完美的缺氧環境，提供給製造甲烷的微生物(甲烷菌，methanogen)以及協助它們進行代謝的其他微生物繁榮生長的空間。」
「甲烷的重要之處是其為強力的溫室氣體――它把太陽輻射保留在大氣中的能力是二氧化碳的25倍。」
她說永凍土融化時也會排放出更多甲烷，這會形成一種正向回饋――甲烷會讓氣溫升高，然後又造成更多永凍土融化。
此研究發表在期刊《自然》(Nature, DOI:
10.1038/s41586-018-0338-1)，共同作者包括了俄亥俄州立大學、羅徹斯特理工學院、佛羅里達州立大學、西北太平洋國家實驗室、新罕布夏大學、斯德哥爾摩大學、亞里桑納大學等機構的研究人員。
Thawing permafrost microbiomes fuel climate change
A University
of Queensland-led international study could lead to more accurate predictions
of the rate of global warming from greenhouse gas emissions produced by
thawing permafrost in the next 100 years.
The study of
the microorganisms involved in permafrost carbon degradation links changing
microbial communities and biogeochemistry to the rise of greenhouse gas
emissions.
It was led by
Australian Centre for Ecogenomics researchers in the UQ School of Chemistry and
Molecular Biosciences Dr Ben Woodcroft, PhD student Caitlin
Singleton, Professor Gene Tyson and
international colleagues.
“As global
temperatures rise, large amounts of carbon sequestered in perennially frozen
permafrost are becoming available for microbial degradation,” Dr Woodcroft
said.
“Until now, accurate
prediction of greenhouse gas emissions produced from thawing permafrost has
been limited by our understanding of permafrost microbial communities and their
carbon metabolisms.”
Using sequencing techniques
pioneered by Professor Tyson, over 200 samples from intact, thawing and thawed
permafrost sites in northern Sweden were examined.
DNA sequences of more than
1500 microbial genomes all new to science and involved in complex biochemical
networks were recovered.
The research, which
included new metagenomics software run on UQ supercomputers, also implicated a
number of these entirely new lineages in the production of greenhouse gases.
Ms Singleton said
permafrost stores around 50 per cent of the total global soil carbon (or 1580
billion tonnes).
“The Intergovernmental
Panel on Climate Change report estimated that between 30 and 99 per cent of
near-surface permafrost could disappear by 2100,” she said.
“Northern permafrost
wetlands contribute a significant portion of global methane emissions,
particularly as collapsing permafrost can create the perfect anaerobic
conditions for methane-producing microorganisms (methanogens), and their
metabolic partners, to thrive.
“This is important as
methane is a potent greenhouse gas - 25 times more efficient at trapping the
sun’s radiation in our atmosphere than carbon dioxide.”
She said that as permafrost
thaws, methane emissions increase, causing a positive feedback loop where
increased atmospheric warming caused more thawing.
The study is published in Nature (DOI: 10.1038/s41586-018-0338-1)
and co-authored by researchers at The Ohio State University, Rochester
Institute of Technology, Florida State University, Pacific Northwest National
Laboratory, University of New Hampshire, Stockholm University, and the
University of Arizona.
原始論文：Ben J.
Woodcroft, Caitlin M. Singleton, Joel A. Boyd, Paul N. Evans, Joanne B.
Emerson, Ahmed A. F. Zayed, Robert D. Hoelzle, Timothy O. Lamberton, Carmody K.
McCalley, Suzanne B. Hodgkins, Rachel M. Wilson, Samuel O. Purvine, Carrie D.
Nicora, Changsheng Li, Steve Frolking, Jeffrey P. Chanton, Patrick M. Crill,
Scott R. Saleska, Virginia I. Rich, Gene W. Tyson. Genome-centric view
of carbon processing in thawing permafrost. Nature, 2018;
DOI: 10.1038/s41586-018-0338-1
引用自：University of Queensland. "Thawing
permafrost microbiomes fuel climate change."
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