Threads of underground fungal networks are long enough to reach beyond the Solar System
Threads of underground fungal networks are long enough to reach beyond the Solar System
地下真菌网络之长，足以延伸至太阳系之外
Hidden underground around the world lie 110 quadrillion kilometers of arbuscular mycorrhizal fungal networks—webs of ultra-thin threads that, if connected in a single line, would stretch almost a billion times the distance between the Earth and the sun, according to new research published in Science on Thursday. 根据周四发表在《科学》杂志上的一项新研究，全球地下隐藏着 11 亿亿公里的丛枝菌根真菌网络。这些由超细丝线构成的网络如果连接成一条直线，其长度将达到地球与太阳之间距离的近 10 亿倍。
These fungal communities form intimate relationships with the roots of plants, which they provide with nutrients like phosphorus and nitrogen in exchange for carbon, 1 billion tons of which the networks sequester underground annually, previous research has found. If the fungal network wasn’t storing it, that carbon would be warming the atmosphere. But those networks have never been mapped globally until now. 先前的研究发现，这些真菌群落与植物根系形成了密切的共生关系，它们为植物提供磷和氮等营养物质，以换取碳。这些网络每年在地下封存 10 亿吨碳。如果不是这些真菌网络在储存碳，这些碳本会进入大气层导致气候变暖。然而，直到现在，这些网络还从未被进行过全球范围的测绘。
The new study led by Society for the Protection of Underground Networks, or SPUN, an organization founded to map mycorrhizal fungi networks, used a combination of literature review, soil samples from around the globe, machine learning and laboratory testing to estimate the distribution and mass of these systems and map where they are densest. 这项新研究由“地下网络保护协会”（SPUN）领导，该组织旨在绘制菌根真菌网络地图。研究团队结合了文献综述、全球土壤样本、机器学习和实验室测试，估算了这些系统的分布和质量，并绘制了它们密度最高的区域。
“This is the moment where we went from knowing that this system exists to really knowing where it is, how dense it is and where it’s been,” said Toby Kiers, executive director and co-founder of SPUN and a co-author of the study. “这是我们从‘知道该系统存在’到‘真正了解它在哪里、密度如何以及它分布范围’的关键时刻，”SPUN 执行董事、联合创始人兼该研究的合著者托比·基尔斯（Toby Kiers）表示。
For decades, researchers have known arbuscular mycorrhizal fungi form intimate symbiotic relationships with roughly 80 percent of the globe’s plant species and are found nearly everywhere plants are. But the extent of those networks and where they are densest, such as grasslands, and where they are being lost, like in agricultural areas, hasn’t been well understood until now. 几十年来，研究人员一直知道丛枝菌根真菌与全球约 80% 的植物物种形成了密切的共生关系，且几乎在有植物的地方都能发现它们。但直到现在，人们对于这些网络的覆盖范围、密度最高区域（如草原）以及它们正在消失的区域（如农业区）仍缺乏深入了解。
“[The study] helps us come to grips with how important these below ground organisms can be to everything that we see above ground,” said James Bever, a professor of ecology and evolutionary biology at the University of Kansas who studies the interactions between plants and microbes like fungi in soils but was not involved in the new study. “（这项研究）帮助我们理解这些地下生物对于我们地面上所见的一切有多么重要，”堪萨斯大学生态学与进化生物学教授詹姆斯·贝弗（James Bever）说。他研究土壤中植物与真菌等微生物之间的相互作用，但并未参与这项新研究。
Justin Stewart, an evolutionary ecologist at SPUN and lead author of the study, said previous studies the team had done on biodiversity of fungi were similar to asking someone to describe the forest outside their home. “They could say ‘well there are three tree species in it.’ That’s great. That tells me about the biodiversity,” he said. “But you don’t actually know how big the forest is, how far apart the trees are. You don’t have information on its structure.” SPUN 的进化生态学家、该研究的主要作者贾斯汀·斯图尔特（Justin Stewart）表示，团队此前对真菌生物多样性的研究，就像是让人描述家门外的森林。“他们可能会说‘里面有三种树’。这很好，这告诉了我生物多样性的情况，”他说，“但你实际上并不知道森林有多大，树木之间的距离有多远。你没有关于其结构的信息。”
Mycorrhizal fungal networks are made up of hyphae, each smaller than a strand of human hair. These living pipes transport the nutrients and carbon between the plants and fungi. Because they are so long and thin, Stewart said, they can reach deeper into soils than roots, getting nutrients deep underground that plants can’t reach, while simultaneously storing carbon where it can stay put for a long time under the right conditions. 菌根真菌网络由菌丝组成，每一根菌丝都比人类的头发丝还要细。这些“生命管道”在植物和真菌之间输送营养物质和碳。斯图尔特说，由于它们又长又细，它们能比根系更深入土壤，获取植物无法触及的深层地下养分，同时在适宜条件下将碳长期封存在地下。
“You’re getting a win-win,” Stewart said. “The plants are growing better, and carbon’s being drawn down. That all depends on having dense fungal networks and soils that are active and alive.” “这是一个双赢的局面，”斯图尔特说，“植物生长得更好，碳也被封存起来。这一切都取决于拥有密集的真菌网络以及活跃的土壤。”
Quantifying these fungal networks started with a review of existing studies on mycorrhizal fungi. Those studies contained 16,000 core samples taken from ecosystems around the world to understand the length of the fungal threads in a volume of soil. Each sample was geolocated, and from there the team was able to use machine learning to create predictive maps of fungal networks globally, and identify where the model is performing well and where uncertainties show more data is needed. 量化这些真菌网络始于对现有菌根真菌研究的综述。这些研究包含了从全球生态系统中采集的 16,000 个核心样本，旨在了解单位体积土壤中真菌丝的长度。每个样本都进行了地理定位，团队随后利用机器学习创建了全球真菌网络的预测地图，并确定了模型表现良好的区域，以及因不确定性而需要更多数据的区域。
Working with AMOLF, a research institute in Amsterdam, they developed a technique using a robot with a camera that recorded fungal networks growing over time in a lab, to get better estimates of their widths. From there, the team was able to calculate the network’s mass, which amounted to about five times the weight of all humans on Earth. 通过与阿姆斯特丹的研究机构 AMOLF 合作，他们开发了一种利用带有摄像头的机器人技术，记录了实验室中真菌网络随时间的生长情况，从而更准确地估算了它们的宽度。在此基础上，团队计算出了该网络的总质量，约为地球上全人类总重量的五倍。
The study only covers living arbuscular mycorrhizal fungal networks, Stewart said, and doesn’t include dead fungal networks, which also help to store carbon and add to the total biomass and influence of the networks on ecosystems. Research into dead fungal networks is still being explored. 斯图尔特指出，这项研究仅涵盖了活的丛枝菌根真菌网络，并未包括死亡的真菌网络。事实上，死亡的真菌网络也有助于储存碳，并增加了总生物量以及对生态系统的影响。目前，关于死亡真菌网络的研究仍在探索中。
The study also found where these networks are most threatened. Fungal network densities across croplands are about half of what they are in wild ecosystems. Meanwhile, wild grassland ecosystems hold about 40 percent of the world’s arbuscular mycorrhizal biomass. Yet those grasslands are among Earth’s least protected ecosystems, and they are converted into farmland at four times the rate of forests, posing a potential threat to these networks and the benefits they bring to plant life and carbon storage. 研究还发现了这些网络受威胁最严重的地区。农田中的真菌网络密度仅为野生生态系统中的一半左右。与此同时，野生草原生态系统拥有全球约 40% 的丛枝菌根生物量。然而，这些草原是地球上保护程度最低的生态系统之一，它们被转化为农田的速度是森林的四倍，这对这些网络及其为植物生命和碳储存带来的益处构成了潜在威胁。
Previous research from SPUN has found 90 percent of fungal communities across the globe are unprotected, and many ecosystems, like the deserts of the American Southwest, are understudied. What exactly is driving mycorrhizal fungi losses, and the consequences of that decline, need to be explored next, the researchers said, which is why the SPUN team will be at this year’s United Nations Climate Change Conference—COP31—to present to policymakers about the importance of the networks and the role they could play in protecting ecosystems and sequestering carbon. SPUN 此前的研究发现，全球 90% 的真菌群落处于无保护状态，而许多生态系统（如美国西南部沙漠）的研究尚不充分。研究人员表示，接下来需要探索导致菌根真菌减少的确切原因及其后果。这也是为什么 SPUN 团队将参加今年的联合国气候变化大会（COP31），向政策制定者展示这些网络的重要性，以及它们在保护生态系统和封存碳方面可能发挥的作用。
Understanding mycorrhizal fungi more deeply at the ground level is key, said Corentin Bisot, an AMOLF biophysicist and co-author of the study. “We’re still far from completely understanding how, if you have a grassland next door, and you want to [increase] microbes and fungi there,” Bisot said. “We don’t have the toolbox for you to do it.” AMOLF 的生物物理学家、该研究的合著者科伦丁·比索特（Corentin Bisot）表示，在地面层面更深入地了解菌根真菌是关键。“我们距离完全理解如何操作还很远，比如如果你隔壁有一片草原，你想增加那里的微生物和真菌，”比索特说，“我们目前还没有为你提供实现这一目标的工具箱。”
This study, Stewart said, is just the first map. And like the first maps the Spaniards drew of California—which presented the state as an island, he said, there will be new discoveries about the density of fungi. 斯图尔特说，这项研究仅仅是第一张地图。就像西班牙人绘制的第一张加利福尼亚地图（当时将该州描绘成一座岛屿）一样，未来关于真菌密度的研究还会有新的发现。