新研究顯示微生物可以封存大量的碳

 原文網址：https://news.utk.edu/2021/04/26/new-study-shows-microbes-trap-massive-amounts-of-carbon/

強烈的板塊碰撞與劇烈的火山爆發正常來說並不會讓我們聯想到適合生命居住的條件。但是田納西大學諾克斯維爾分校的微生物學副教授Karen Lloyd參與的新研究，卻揭曉了在地球深處有一個巨大的微生物系統，它們運作所需的化學物質正是在這些板塊運動造成的劇變中產生。

圖片來源：田納西大學諾克斯維爾分校

海洋板塊和陸地板塊碰撞時，其中一方會被往下推到地函裡面，稱為隱沒作用；另外一方則會被往上推並且冒出許多火山。這是地球表面的化學物質進入地球內部的主要方式，而它們最終又會循環回地表。

「隱沒帶是個相當神奇的環境，它們產生的火山就像是條通道，讓碳可以在地球內部和表面之間往返移動。」國立哥斯大黎加大學的副教授Maarten de Moor表示。他是這篇研究的共同作者之一。

科學家一般認為這些過程牽涉到相當高的溫度和壓力，所以會在生命的管轄範圍之外。雖然幾乎可以肯定在地函和地殼混和產生岩漿的地方，此處的極端環境會讓生命無法生存，但是近幾十年來科學家也了解到微生物在地殼內部可以觸及的範圍比過去認為的還要深入許多。

這讓科學家在探討深處的板塊構造作用與生物的交互作用時，有機會發現前所未聞的作用類型。

之前一組跨領域的國際科學團隊在哥斯大黎加的天然溫泉中，採集從地下深處被帶到地球表面的微生物群集樣本。結果顯示在哥斯大黎加下方存在著一個龐大的微生物生態系，它們攝取的碳、硫、鐵等化學物質主要是在海洋板塊隱沒時產生。研究經費來自於深碳觀測計畫以及艾爾弗．史隆基金會。

團隊發現隱沒過程中產生的碳，有許多本該逸散到大氣裡面的卻被這座微生物生態系給封存了起來。這項作用造成估計運送到地函裡的碳有多少時，最多要下修22%。

「成果顯示這個幾乎不用來自太陽的能量就能運作的龐大生態系，可能會吸收大量的碳。這也代表生物或許可以影響碳進出地函的速率，使得科學家必須改變他們對於碳在地質時間尺度下是如何循環的想法，」研究共同作者，伍茲霍爾海洋研究所的助理科學家Peter Barry表示。

這些微生物稱為化學無機自營菌(chemolithoautotroph)。團隊發現它們可以封存大量碳質的原因來自於獨特的攝食方式，它們可以不用陽光就產生能量。

「化學無機自營菌是利用化學能來過活的微生物。它們就像樹木一樣，只不過它們運用的不是陽光而是化學物質，」這篇研究的共同通訊作者Lloyd表示。「這些微生物利用隱沒帶產生的化學物質來維生，以它們為基礎形成了一個大型生態系，其中含有各式各樣的初級和次級生產者。這就像是一片廣闊的森林，但卻位在地底深處。」

這項新研究代表我們想要了解從古至今碳是如何變化的時候，先前已經描述的地質和生物之間的關係，或許也能提供給我們實際的數字而帶來重大啟發。「我們已經知道生物可以透過許多方式來影響地球的適居程度，像是讓大氣中的氧氣濃度增加，」這篇研究的共同通訊作者，那不勒斯腓特烈二世大學的教授Donato Giovannelli表示。「而我們現在進行的工作則揭曉了生物和地球還能以另外一種驚奇的方式來共同演化。」

 

New study shows microbes trap massive amounts of carbon

Violent continental collisions and volcanic eruptions are not things normally associated with comfortable conditions for life. However, a new study, involving University of Tennessee, Knoxville, Associate Professor of Microbiology Karen Lloyd, unveils a large microbial ecosystem living deep within the earth that is fueled by chemicals produced during these tectonic cataclysms.

When oceanic and continental plates collide, one plate is pushed down, or subducted, into the mantle and the other plate is pushed up and studded with volcanoes. This is the main process by which chemical elements are moved between Earth’s surface and interior and eventually recycled back to the surface.

“Subduction zones are fascinating environments—they produce volcanic mountains and serve as portals for carbon moving between the interior and exterior of Earth,” said Maarten de Moor, associate professor at the National University of Costa Rica and coauthor of the study.

Normally this process is thought to occur outside the reach of life because of the extremely high pressures and temperatures involved. Although life almost certainly does not exist at the extreme conditions where Earth’s mantle mixes with the crust to form lava, in recent decades scientists have learned that microbes extend far deeper into Earth’s crust than previously thought.

This opens the possibility for discovering previously unknown types of biological interactions occurring with deep plate tectonic processes.

An interdisciplinary and international team of scientists has shown that a vast microbial ecosystem primarily eats the carbon, sulfur, and iron chemicals produced during the subduction of the oceanic plate beneath Costa Rica. The team obtained these results by sampling the deep subsurface microbial communities that are brought to the surface in natural hot springs, in work funded by the Deep Carbon Observatory and the Alfred P. Sloan Foundation.

The team found that this microbial ecosystem sequesters a large amount of carbon produced during subduction that would otherwise escape to the atmosphere. The process results in an estimated decrease of up to 22 percent in the amount of carbon being transported to the mantle.

“This work shows that carbon may be siphoned off to feed a large ecosystem that exists largely without input from the sun’s energy. This means that biology might affect carbon fluxes in and out of the earth’s mantle, which forces scientists to change how they think about the deep carbon cycle over geologic time scales,” said Peter Barry, assistant scientist at the Woods Hole Oceanographic Institution and a coauthor of the study.

The team found that these microbes—called chemolithoautotrophs—sequester so much carbon because of their unique diet, which allows them to make energy without sunlight.

“Chemolithoautotrophs are microbes that use chemical energy to build their bodies. So they’re like trees, but instead of using sunlight they use chemicals,” said Lloyd, a co-corresponding author of the study. “These microbes use chemicals from the subduction zone to form the base of an ecosystem that is large and filled with diverse primary and secondary producers. It’s like a vast forest, but underground.”

This new study suggests that the known qualitative relationship between geology and biology may have significant quantitative implications for our understanding of how carbon has changed through deep time. “We already know of many ways in which biology has influenced the habitability of our planet, leading to the rise in atmospheric oxygen, for example,” said Donato Giovannelli, a professor at the University of Naples Federico II and co-corresponding author of the study. “Now our ongoing work is revealing another exciting way in which life and our planet coevolved.”

原始論文：Katherine M. Fullerton, Matthew O. Schrenk, Mustafa Yücel, Elena Manini, Marco Basili, Timothy J. Rogers, Daniele Fattorini, Marta Di Carlo, Giuseppe d’Errico, Francesco Regoli, Mayuko Nakagawa, Costantino Vetriani, Francesco Smedile, Carlos Ramírez, Heather Miller, Shaunna M. Morrison, Joy Buongiorno, Gerdhard L. Jessen, Andrew D. Steen, María Martínez, J. Maarten de Moor, Peter H. Barry, Donato Giovannelli, Karen G. Lloyd. Effect of tectonic processes on biosphere–geosphere feedbacks across a convergent margin. Nature Geoscience, 2021; DOI: 10.1038/s41561-021-00725-0

引用自：University of Tennessee at Knoxville. "Microbes trap massive amounts of carbon."