甲烷预算中的一些线条物品，如管道泄漏和牛屁，得到了很好的理解。“澳大利亚南部大学的生物地德大学生物地球化学博览会卢克·杰弗里斯说，”湿地和内陆水域有很多差距和不确定因素，特别是在湿地和内陆水域。从全球碳项目到一个2020年，湿地发射了地球每年甲烷释放的约20％至31％ - 超过了化石燃料生产的量。在潮湿或淹水的土壤中沐浴的树木吸收甲烷，然后通过树皮泄漏。微生物咯咯地甲烷，减少了约三分之一的树木的潜在排放。
甲烷预算中的一些线条物品，如管道泄漏和牛屁，得到了很好的理解。但其他人是Hazier。 “澳大利亚南部大学的生物地德大学生物地球化学博览会卢克·杰弗里斯说，”湿地和内陆水域有很多差距和不确定因素，特别是在湿地和内陆水域。从全球碳项目到一个2020年，湿地发射了地球每年甲烷释放的约20％至31％ - 超过了化石燃料生产的量。
但在过去的十年中，研究人员们在一个违反温室气体排放来源的违反直觉来源：树木。淡水湿地树，特别是。在潮湿或淹水的土壤中沐浴的树木吸收甲烷，然后通过树皮泄漏。在2017年的研究中，生态学家Sunitha Pangala，那么在英国的公开大学，发现亚马逊的树木对其他湿地森林的树木负责200倍，占该地区总排放的44％至65％ 。
这是否对地球是糟糕的树木？当然不是。树木吸在大气中的二氧化碳。在一项研究中发表于4月9日的自然通信，Jeffrey和他的团队报告了树木也可以是甲烷水槽，避难地将其转换为较少损坏的CO 2。 sub>他的团队发现了一种名为Paperbarks的树木的甲蛋白或吃甲烷的微生物，这些树木在东部澳大利亚沼泽中生长。微生物咯咯地甲烷，减少了约三分之一的树木的潜在排放。该发现为树木因素变成了专家表示对气候预测至关重要的难以捉摸的甲烷预算。
“当我看到这篇论文时，我刚才说，”圣洁的狗屎，这真的很有趣，“印第安纳大学奥尼尔公共和环境学院的教授杰弗里怀特说，”杰弗里白人说。没有参与该研究的白色已经研究了甲烷循环30多年，并说它优雅地解决了研究人员 - 但尚未能够钉住的亨希 - 甲蛋白活动发生在树皮中。他称之为“深刻很重要”。
杰弗里想要更多的清晰度。几年前，他的注意力转向了纸张。 “这是一棵树的树皮，”杰弗里说。这些层湿润，黑暗，已知含有甲烷。 （Jeffrey有时是指它作为“赛道”。）“我们只是认为它可能是甲蛋白的理想点，”他继续。所以他出发了证明煤气吃的微生物在那里隐藏着。杰弗里设计了一系列会迎合他们的胃口的实验。首先，他将树皮从三个湿地的景点切成树木，并密封含有甲烷的玻璃瓶内的那些条带。然后，他等了。一周多，他测量了瓶子中的甲烷水平。在一些样品中，其中一半以上消失了。在控制瓶中，含有灭菌的树皮或根本没有什么，甲烷水平仍然是纸扁平的。
然后Jeffrey将称为二氟甲烷的气体注入室中。二氟甲烷是对甲蛋白萎缩的偷偷摸摸 - 它暂时抑制他们的食欲。 “它实际上阻止他们消耗甲烷，”杰弗里说。在让气体漫射到一个小时后，杰弗里弗朗普，并重新审视排放。因为微生物停止进食，所以甲烷水平跳跃。平均而言，团队计算，微生物已经去除了36％的甲烷，否则将被渗入大气中。
杰弗里说，大多数甲烷实际上源于湿土。微生物在污垢和释放甲烷中消化有机物。有些人从土壤或水中铺设，但有些人通过像吸管一样通过树根流淌，或者浸泡在树皮中，然后通过木材扩散出来。 （不同的微生物也可以在树内制作自己的甲烷，但杰弗里已经发表了证据表明，在树皮中甲烷的同位素签名在土壤中。）由于树木居住的微生物，它较少地释放到大气中甲烷，因为它们将其转化为较小的有害CO 2 sub>。 “这种土壤中的甲烷可能会从湿地上来上来。如果他们穿过树木，他们必须通过这种细菌的这种手套，“杰弗里说。 “所以这个新的发现 - 我现在看起来像几乎像甲烷过滤器。”
“这对我来说真的很令人兴奋，因为这是一个很长一段时间感兴趣的问题，”弗吉尼亚州霍林斯大学的微生物生态学家Mary Jane Carmichael说，弗吉尼亚州没有参与这项研究。 Carmichael在2017年的研究中报道，死树也发出甲烷。 （同样，在以前的一项研究中，Jeffrey表明死树却排出了八次生活中的甲烷。）“我从来没有真正惊讶的是微生物能力，”Carmichael说。 “我们可能会看到这是一个非常普遍的现象。”
了解如何从环境中加入和减去甲烷将有助于科学家调整一种地球宽的碳结石。虽然卫星数据有助于从上面跟踪排放，但凡尔赛大学的环境科学家Marielle Sanunois表示，而凡人·普朗斯大学的环境科学家Marielle Saunois表示，每个来源和水槽的细节都是必不可少的。但这项研究不会立即改变气候模型。 “这个过程很重要，但非常本地人，”她说。难以向全球甚至区域角度扩大吠声微生物效应。虽然这项工作有助于预测湿地排放如何随着气候变化，全球模型尚未包括这些反馈效果。 “理想情况下，”她说，“它应该。”
地球的气候行为具有反馈环：例如，温度，水分和CO 2 sub>影响树种如何分布，这影响了影响气候的甲烷排放，依此类推。了解这些微生物存在 - 和未来的研究可以通过使甲烷模型更加强大，改善气候预测。
Jeffrey下次计划审查树木过滤温室气体的变化与季节。自从他发表的研究以来，人们已经为如何利用森林甲虫治疗气候行动而推出了各种各样的想法。科学家们可以用微生物接种其他树种，建立甲烷 - 鹅卵石吗？我们可以在锯末文化它们，并在森林地板上喷洒它们吗？我们可以喂他们给奶牛吗？ “我不知道，说实话，”杰弗里说。 “而我的个人偏好是不要对大自然进行修补。”
Many of today’s geoscientists are carbon voyeurs. Knowing that human disregard for the carbon cycle has screwed the climate, they have kept a close eye on carbon's hottest variants—carbon dioxide (CO 2) and methane. Both gasses trap heat on the planet through the greenhouse effect, and over a span of 100 years methane is 28 times more potent than CO2. Rigorously accounting for greenhouse gas flow is step one of building models that predict the future climate.
Some line items in the methane budget, such as pipeline leaks and cow farts, are well understood. But others are hazier. “There's lots of gaps and uncertainties, particularly in wetlands, and inland waters,” says Luke Jeffrey, a biogeochemistry postdoc at Southern Cross University in Australia. By one 2020 tally from the Global Carbon Project, wetlands emit about 20 to 31 percent of Earth’s annual methane release—more than the amount from fossil fuel production.
But in the past decade, researchers have zeroed in on a perhaps counterintuitive source of greenhouse gas emissions: trees. Freshwater wetland trees, in particular. Trees bathing in wet or flooded soil absorb methane and then leak it through their bark. In a 2017 study, ecologist Sunitha Pangala, then at the Open University in the United Kingdom, found that trees in the Amazon were responsible for 200 times more methane than trees in other wetland forests, accounting for 44 to 65 percent of the region’s total emissions.
Does this mean trees are bad for the planet? Of course not. Trees suck carbon dioxide out of the atmosphere. And in a study published April 9 in Nature Communications, Jeffrey and his team report how trees can also be methane sinks, sheltering microbes that convert it to the less damaging CO2. His team discovered methanotrophs, or methane-eating microbes, in a species of trees called paperbarks, which grow in eastern Australian swamps. The microbes gobble up methane, reducing the trees’ potential emissions by about a third. The finding brings more clarity to how trees factor into the elusive methane budget that experts say is vital for climate predictions.
“This is an important contribution and one that’s timely,” says Patrick Megonigal, a biogeochemist with the Smithsonian Environmental Research Center who is not affiliated with the study. Megonigal has researched the release of methane from trees for over a decade, and is an expert in the flows of greenhouse gases throughout wetland and upland forests.
“When I saw this paper, I just said, ‘Holy shit, this is really interesting,’” says Jeffrey White, a professor emeritus at the O’Neill School of Public and Environmental Affairs at Indiana University. White, who was not involved in the study, has studied methane cycling for over 30 years, and says it elegantly addressed a hunch that researchers have had—but haven’t been able to nail down—that methanotroph activity occurs in tree bark. He calls the work “profoundly important.”
Methanotrophs are everywhere and have been for as long as atmospheric oxygen has existed on Earth, so White is confident this isn’t an isolated case: He’s noticed similar behavior in Minnesota birch trees.
Wetlands contribute more methane to the atmosphere than any other natural source. But without methanotrophs, they’d release an estimated 50 to 90 percent more. These microbes turn methane into carbon dioxide similar to the way combustion does. The process is, almost literally, a slow burn. But it prevents a majority of wetland methane from reaching the sky, making soil a source and a sink. Far less is known about the methane feasts taking place inside trees.
Jeffrey wanted more clarity. A few years ago, his attention turned to the paperbarks. “It's such a unique tree with amazing layers of bark,” Jeffrey says. These layers are moist, dark, and known to contain methane. (Jeffrey sometimes refers to it as “treethane.”) “We just thought it could be an ideal spot for methanotrophs,” he continues. So he set out to prove that the gas-eating microbes were hiding there. Jeffrey designed a series of experiments that would cater to their appetites. First, he sliced bark from trees in three wetland sites and sealed those strips inside glass bottles containing methane. Then, he waited. Over a week, he measured as the methane levels in the bottles dropped. In some samples, more than half of it vanished. In control bottles that contained either sterilized bark or nothing at all, methane levels remained paper-flat.
Jeffrey’s team also knew that methanotrophs have picky palates. Methane’s one carbon atom can exist as either of two stable isotopes: the classic carbon-12 or the heavier carbon-13 that lugs around an extra neutron. Carbon-13’s bonds are harder to break, so methanotrophs would rather snack on the lighter isotope. Jeffrey’s team found that the relative levels of carbon-13-methane in the bottles increased with time. Something in the bark was alive and selectively eating, like a kid leaving the yellow Starbursts in the bag after picking out the pinks.
Encouraged by these traces of activity, they sent bark across town to the microbiologists at Monash University, who ran a microbial analysis of all of the species that were living in the bark. The verdict: Paperbark samples contained a bustling unique population of bacteria not found in the surrounding soil or swamp, most of which fall into the methane-hungry genus Methylomonas.
But all of those results arose in a lab, and Jeffrey’s team needed to see how real, live trees behave, specifically how fast they leak methane. They waded through a wetland forest in New South Wales, gently attached sealed chambers and spectrometers to the sides of paperbarks, and measured how much the trees emitted per second.
Then Jeffrey injected a gas called difluoromethane into the chamber. Difluoromethane is a sneaky treat for methanotrophs—it temporarily inhibits their appetite. “It actually stops them consuming methane,” Jeffrey says. After letting the gas diffuse in for an hour, Jeffrey flushed it and reexamined the emissions. Because the microbes stopped eating, methane levels jumped. On average, the team calculated, microbes had been removing 36 percent of the methane that would otherwise seep into the atmosphere.
Most of that methane actually originates in the wet soil, Jeffrey says. Microbes digest organic matter in the dirt and release methane. Some burbles out of the soil or water, but some flows up through tree roots like they’re straws, or soaks into the bark then diffuses out through the wood. (Different microbes can also make their own methane within the tree, but Jeffrey has published evidence that isotope signatures of the methane in bark matches that in the soil.) Thanks to the tree-dwelling microbes, less of it gets released into the atmosphere as methane, because they transform it into less harmful CO2. “This methane in soil is possibly going to come up anyway from a wetland. If they're coming up through trees, they have to get through this gauntlet of bacteria,” says Jeffrey. “So this new discovery—I'm kind of looking at trees now as almost like methane filters.”
“It's really exciting for me, because this has been a question that I've been interested in for a long time,” says Mary Jane Carmichael, a microbial ecologist at Hollins University in Virginia not involved in the study. Carmichael reported in a 2017 study that dead trees emit methane, too. (Similarly, in a previous study, Jeffrey showed that dead trees emitted eight times the methane of living ones.) “I'm never really surprised by what microorganisms are capable of,” Carmichael says. “We probably will see that it's a pretty widespread phenomenon.”
Understanding how trees add and subtract methane from the environment will help scientists adjust a sort of planet-wide carbon calculus. While satellite data helps track emissions from above, finer details for each source and sink are essential to really make predictions, says Marielle Saunois, an environmental scientist with the University of Versailles Saint Quentin who coordinates the Global Methane Budget. But this study won’t change climate models right away. “The processes are important, but very local,” she says. It’s hard to scale up bark microbe effects to a global or even regional perspective. And while this work helps predict how wetland emissions change with climate, global models don’t yet include these feedback effects. “Ideally,” she says, “it should.”
“Vegetation and plant based pathways in methane emissions are actually a really under-studied component of the global methane budget,” agrees Carmichael.
Earth’s climate behavior is rife with feedback loops: For example, temperature, moisture, and CO2 affect how tree species are distributed, which affects methane emissions, which affects climate, and so on. Knowing that these microbes exist—and future studies that can pinpoint where else they exist—will improve climate predictions by making methane models more robust.
“This is good news,” says Megonigal. In wetland forests that are rich in methane, the microbes buffer emissions. In drier upland forests that produce less methane, he says, “they might actually be removing methane from the atmosphere on our behalf.”
Jeffrey next plans to examine how the trees’ filtering of the greenhouse gas changes with the seasons. Since he published the study, people have pitched him a variety of ideas for how to harness forest methanotrophs for climate action. Could scientists inoculate other tree species with the microbes to establish methane-gobbling forests? Could we culture them in sawdust and spray them on forest floors? Could we feed them to cows? “I have no idea, to be honest,” Jeffrey says. “And my personal preference is not to tinker with nature too much.”