内容来源：https://www.quantamagazine.org/how-do-fungi-keep-the-planet-healthy-20261015/

内容总结：

地下“真菌网络”：科学家揭示地球隐藏的“循环系统”，每年固碳130亿吨

当我们脚下踩着泥土时，很少有人会想到，土壤之下隐藏着一张庞大而精密的“地下互联网”——菌根真菌网络。最新研究表明，这张网络不仅维系着地球上80%以上植物的生长，每年还从大气中吸收约130亿吨二氧化碳，相当于全球化石燃料排放量的三分之一。

存在了4.5亿年的古老 partnership

菌根真菌（mycorrhizal fungi）中的“myco”意为真菌，“rhizal”意为根。这类真菌与植物形成了极为亲密的共生关系，可追溯至约4.5亿年前。当时，真菌实际上充当了植物的根系，帮助水生植物逐步登陆。真菌擅长分解岩石、释放磷和氮等矿物质，而植物则通过光合作用将碳和脂类“喂给”真菌作为回报。这一关系至今仍是地球生态系统的基础。

荷兰阿姆斯特丹自由大学的进化生物学家托比·基尔斯（Toby Kiers）长期致力于让这个不可见的世界变得可见。她的实验室借助荧光量子点、成像机器人等工具，结合经济学和博弈论框架，研究真菌与植物之间的“交易”行为。

“双向河流”：同一管道内碳与养分同时反向流动

基尔斯描述，丛枝菌根真菌网络如同一套“开放式管道”，没有分隔细胞的分隔结构，有人甚至认为它们是地球上最大的细胞。令人惊叹的是，在这套管道中，碳向下流向真菌尖端，磷和氮则同时向上流向植物根部——就像一条同时向北和向南流动的河流。

研究人员利用荧光标记追踪碳的流动，发现真菌网络中存在类似“分子马达”的结构，能拖动脂类液滴在管道中移动。脂类与水不相溶，形成凝聚体，由马达蛋白沿着“微型铁轨”拉动，同时通过调节水通道蛋白产生压力差，驱动高速流体。两种机制结合，造就了网络内复杂而优美的流动模式。

经济学视角：植物和真菌都会“精打细算”

基尔斯团队通过精心设计的培养皿实验发现，植物能够区分“合作”与“不合作”的真菌菌株，把更多碳和脂类分配给提供更多磷的真菌；反过来，真菌也善于甄别，把更多磷提供给愿意付出更多碳的植物。这是一种“互惠剥削”——双方都在挑选最佳合作伙伴。

更令人惊讶的是，真菌会避免向处于阴影中的植物输送大量磷；会根据竞争者数量调整交易策略；甚至会将磷“囤积”在网络中，人为抬高价格，等待植物付出更多碳后再释放。在一项使用量子点的实验中，研究人员观察到真菌主动将磷从资源丰富的一侧运送到植物愿意“出更高价”的另一侧。

没有大脑，如何做出“决策”？

这些行为引发了一个深刻的问题：没有大脑和中枢神经系统的生物，如何做出策略性“决策”？

基尔斯表示，真菌通过在整个网络中处理信息来对环境作出反应，可能涉及电信号、流体动力学计算等机制。她谨慎地避免使用“意识”等词汇，更倾向于用“信息处理”来描述。“我们真正谈论的是编码在DNA中的策略，这些策略让生物体能够在世界中最大限度地利用资源。”

她的博士研究还发现，大豆能够“惩罚”不固氮的根瘤菌——通过切断氧气供应将其“窒息”。这说明，即使是植物，也能在单个根瘤层面感知氮的供应量并做出精准反应。

地下“亚马逊”：90%真菌热点缺乏保护

基尔斯于2021年创立了非营利组织SPUN（地下网络保护协会），目前在80多个国家拥有约600名合作者，资助了近140位“地下探索者”，在全球偏远生态系统中采集土壤、提取真菌DNA并测序。团队正在构建“地下地图集”，帮助决策者量化和保护隐藏的真菌群落。

2025年发表于《自然》的一项大型研究显示，90%的菌根真菌生物多样性热点位于保护区之外，仅10%受到保护。基尔斯警告，如果这些网络持续遭到破坏，将加剧全球变暖、加速生物多样性丧失，并扰乱地球的养分循环。

挑战传统认知：个体、性别与相互依存

真菌还挑战了人类对生命的基本认知。研究发现，丛枝菌根真菌的单个网络内可同时存在两套基因组，传统意义上的“个体”概念在这里变得模糊。这些真菌的繁殖方式也成谜——传统观点认为它们是无性繁殖，但越来越多证据暗示可能存在某种未知的“性别”机制。

基尔斯用“歌剧”来比喻自然界的互动：有时合作，有时冲突，但正是这种张力催生了创新和生物多样性。“冲突和张力不一定是坏事，它们能产生新的想法，让生态系统变得更加复杂。”

她认为，菌根真菌既是物理支架，将万物联结在一起，也是化学纽带，推动碳、磷、氮在系统中循环流动。“当我们问‘做你是什么感觉’时，我们是在以一种尊重的方式，让它们做自己，而我们退到一旁，开发工具去理解它们的内在生活。”

这张看不见的地下网络，或许正是地球生命最深刻的隐喻之一：相互依存，彼此博弈，在张力中维系着整个星球的健康。

中文翻译：

真菌如何守护地球健康？

引言

人们可能以为土壤不过是泥土，但它绝非毫无生机。在你脚下，一张庞大的菌根真菌网络正在辛勤运作，与植物根系交换矿物质。这一交换系统有助于肥沃土壤，每年还能封存130亿吨大气中的二氧化碳——大致相当于全球化石燃料排放量的三分之一。科学家们知道，这些真菌与地球上80%的植物物种结成伙伴关系，这种关系大约在4.5亿年前就已演化形成。但他们一直不明白的是，没有大脑或中枢神经系统的生物，如何能决定与谁交易、按什么条件交易。

托比·基尔斯是阿姆斯特丹自由大学的进化生物学家，她职业生涯的大部分时间都在努力让这个隐秘世界变得可见。她的实验室借助经济学和博弈论，运用从荧光量子点到成像机器人等各种工具，正在探究真菌与植物如何进行交易。这项工作引发了关于土壤、碳、甚至什么才算一个独立生物体的新问题。在本期节目中，基尔斯向联合主持人史蒂文·斯特罗加茨讲述这些没有大脑、去中心化的生物如何能有策略地行事——区分更好和更差的伙伴，并在网络中重新调配资源，将其输送到植物愿意“支付”更多的地方——以及她如何建立了一个全球研究者社区，来绘制这些地下网络的生物多样性地图并倡导保护它们。

可在Apple Podcasts、Spotify、TuneIn或你喜爱的播客应用上收听，也可以从Quanta网站流媒体播放。

文字记录

[音乐播放]

史蒂夫·斯特罗加茨：我是史蒂夫·斯特罗加茨。

詹娜·莱文：我是詹娜·莱文。

斯特罗加茨：这里是《为什么的乐趣》。

莱文：一档来自Quanta Magazine的播客，我们在这里探索当今数学和科学中一些最大的未解之谜。

斯特罗加茨：嘿，詹娜。我很想跟你聊一个大问题。

莱文：好啊。

斯特罗加茨：想象你在森林里或中央公园里散步。

莱文：那是我的森林！

斯特罗加茨：我知道，那你脚下是什么？你的鞋子踩到的是什么？

莱文：我觉得人们会非常惊讶，中央公园里竟然有真正的自然。所以你有草坪，你有树木。呃，有泥土。我们有鸟。

斯特罗加茨：我们把注意力放在泥土上。

莱文：泥土是我们今天的话题吗？

斯特罗加茨：泥土和我们的话题有关。我们想聊聊地下正在发生的事情，也就是所谓的菌根真菌。我了解到我应该念“fun-gee”。

莱文：不是“fun-guy”？

斯特罗加茨：不是“fun-guy”。

莱文：我说的是fun- fung- fun-guy。

斯特罗加茨：那我该怎么说？我可能会说——我不知道。Fun-ji？

莱文：所以现在我得说fun-gee？

斯特罗加茨：为了这期节目，你应该说fun-gee。

莱文：这像不像说Uranus那样？

斯特罗加茨：[笑]你就该那么说。

莱文：我确实是，对。

斯特罗加茨：好吧，我最近和一个人聊过，他改变了我对这些脚下真菌以及“木质万维网”的看法。不是万维网，是木质万维网。就是这些我们从未注意到的、位于地下的庞大真菌网络所构成的菌根网络，它们在连接根系、为树木和其他植物提供养分方面极其重要。全世界大约80%到90%的植物物种都在从这些真菌那里获得帮助。

它们还在帮助我们的大气和气候。它们肥沃土壤，帮助农民和生物多样性、农业。它们甚至可能通过释放孢子到雨林上空，促进云的形成。

莱文：哇。

斯特罗加茨：所以真菌可能不太受重视，但它们对世界的重要性不亚于动物和植物。

莱文：是啊，因为你总是听到细菌的作用，所以真菌能这样影响整个生态系统，真的很有意思。

斯特罗加茨：嗯，细菌与这些真菌关系非常密切。这也是我们将要从嘉宾那里听到的内容。

莱文：好的。

斯特罗加茨：她叫托比·基尔斯。她是阿姆斯特丹自由大学的进化生物学家，也是最近的麦克阿瑟奖得主。如果你准备好了，我们开始吧。

[音乐播放]

斯特罗加茨：托比，欢迎来到《为什么的乐趣》。

托比·基尔斯：非常感谢邀请我。

斯特罗加茨：嗯，这个领域对我来说完全陌生，我迫不及待想了解。你能先描述一下你的研究领域吗？就用非常宽泛的说法。

基尔斯：我研究一类叫做菌根真菌的生物。“菌根”这个词，“菌”指真菌，“根”指根系。所以这是一类与绝大多数植物形成非常密切关联的真菌。地球上超过80%的植物物种都形成这种伙伴关系，而且这是一种非常古老的伙伴关系。

它大约在4.5亿年前演化形成，实际上对于数亿年前身处潮湿水生环境中的植物开始殖民陆地，起到了根本性的作用。从那以后，它一直是构建我们今天赖以生存的生态系统中极其重要的关系。

我想很多人不知道，实际上真菌作为植物根系系统存在了数千万年之久。根系算是一种较新的进化创新，所以这是植物与真菌之间非常密切而古老的伙伴关系。

斯特罗加茨：所以你是说植物没有费心去长自己的根？它们在某种程度上利用真菌来替它们完成这件事？

基尔斯：正是如此。植物所做的是，把它们通过光合作用从大气中获取的碳输送出来，喂养这些松散的联合体——土壤中的这些真菌网络，作为回报，它们获得磷和氮等资源。你看，真菌非常擅长的一件事就是分解岩石，消化这些难以获取的矿物质。

所以它们把矿物质喂给植物，作为回报，植物提供碳。如今这种伙伴关系构成了我们地球生态系统的根基。

斯特罗加茨：哦，哇。我有一大堆问题。首先，说分解岩石真的很戏剧化。我从来没想过这件事。它们是怎么分解岩石的？

基尔斯：嗯，真菌会构建这些美丽而复杂的网络，真菌非常擅长在体外消化，并实际上与细菌等其他微生物合作来帮助分解岩石。所以有些人甚至说，它们非常擅长在体外“吃”岩石，让岩石溶解成可以被吸收的形式。

然后真菌吸收这些养分，通过庞大的网络运输，喂给植物根系。作为回报——显然它们不是免费做这些的——植物喂养它们糖和脂质（如脂肪）组成的食物。这就像是植物提供给真菌的最绝妙的糖和脂肪饮食。这种伙伴关系非常普遍。我可以说，它几乎遍布所有陆地生态系统。正因为这种伙伴关系，也因为植物不断将碳输送到这些网络中，我们实际上称之为地球的循环系统之一。

斯特罗加茨：哦，不错。所以“网络”这个词现在大家都在用。我们听说互联网。我们知道人体内有自己的循环系统，血管网络。但当你谈论菌根真菌网络时，我该想象什么？

基尔斯：正是。这很清楚。我真正想让人们理解的一件事是，植物不是真菌，真菌也不是植物，它们是非常不同的生命界。所以当你有一根植物根系，把它从地里拔出来，那是一幅美丽的画面，但你不太能看到从根系上垂下来的这些丝线。它们比我头上的头发还细，只有几微米宽。

我们真正重点研究的那类叫做丛枝菌根真菌，我们可以聊聊这个名字的由来。但这些特定的网络就像一个开放管道系统。它们真的就像一根管子。在某种意义上，人们认为它们是地球上最大的细胞，因为它们没有把网络分隔成独立区室的隔膜。

所以我们在实验室做的很多工作，就是让这些网络在某种透明土壤上生长，几乎就像一种能让你看到网络并用显微镜追踪这些网络、理解它们如何在空间中导航的方式。我们与阿姆斯特丹生物物理研究所AMOLF的生物物理学家一起开发了这些成像机器人，使我们能够追踪这些网络中的各个节点。所以在任何一次实验中，我们要追踪大约50万个这样的节点，这些真菌做出的决定——是向左还是向右，或者在融合时架桥。

它们实际上构成了一条美丽的供应链，因为你所想象的——我希望你真的闭上眼睛想象一下——是植物将碳注入根系，而这些碳，我们现在可以用荧光标记标记它，所以我们实际上可以观察它通过这个开放管道系统一路向下到达尖端，真菌在那里利用碳继续构建网络。当它们构建网络时，它们在收集磷、氮和水，并将它们沿相反方向运回根系。这个共生关系最迷人的地方之一是，这是一个开放管道系统，却有流向同时朝两个方向移动。

就像一条河同时向北和向南流。所以当你说想象它时，这实际上是我见过的最美丽的事物之一。生物物理学家第一次看到它时说：“这不可能是真的。它们是怎么做到的？”

斯特罗加茨：这太神奇了。这跑题了，但我还是想说——我高中时，一位科学老师给我展示了一个伽利略在17世纪描述过的实验，伽利略说他拿一小壶水和另一壶酒，然后他可以把这两个储液器连接起来，酒在下面，水在上面。有一根细长的垂直管子连接它们。伽利略说酒会通过管子上升，水会通过管子向下流，它们会穿过彼此而不混合，互换位置。我实际上做了这个实验。

基尔斯：成功了吗？

斯特罗加茨：成功了。它们在管子里没有混合。我的老师拍了照片。我13岁时，它发表在一本科学史杂志上。重点是，一位科学史家说伽利略在造假，他编造了这个实验，因为我们都知道当两种东西通过同一根管子时，它们会混合。

你跟我讲的是一个关于两种不同流通过整个管网的故事。

基尔斯：正是，正是。

斯特罗加茨：我这样想是对的吗？

基尔斯：你大致方向是对的，这是我们实验室目前一个很大的开放问题，所以我们一直在思考它。我想我睡前在想，醒来也在想。但你必须记住，植物给真菌的食物富含脂肪，而脂肪不太容易与水混合。

所以有所谓的凝聚体，就是网络内部这些大的脂质滴。我们认为正在发生的是，网络内部有这些美丽的分子马达，它们实际上把脂质、脂肪拖到网络的尖端，这样真菌就能用它来生长。我们认为就是这样，当你把这些脂质拉在……分子马达，你可以把它想象成一条小铁轨，上面有一节车厢，人们前后推拉来前进。分子马达就长这样。

斯特罗加茨：嗯哼。

基尔斯：你可以在实验室里看到这个。看脂质在这些轨道上移动真是太美了。但这不是唯一发生的事情——脂质在分子马达中拉动流体，实际上产生了压力。所以如果你朝一个方向拉，而另一端堵住了，压力就会迫使液体朝另一个方向流。

所以我们认为，真菌实际上在打开和关闭这些美丽的Aquaporin，这些小孔帮助调节多少水进出，这有助于驱动网络内部的压力。所以这是活跃的分子马达拉动，加上细胞内部压力产生的非常快速的流动的组合。结果就是内部出现这些非常复杂的模式。因为我们可以标记碳，它就像美丽的荧光，看起来几乎像熔岩灯在非常细的液体中、非常细的管子中移动，一路到尖端再回来。令人着迷。

斯特罗加茨：[笑]我相信任何听这个节目的人都能听出你对自己的课题有多兴奋，听起来既激动人心又富有感染力。但我想，如果有人还没听懂，我们能不能把故事往回拉一点？为什么普通公民应该关心这些他们可能根本不知道存在的地下网络？

基尔斯：嗯，这些网络真的能支持我们应对当今人类面临的一些最大挑战。我的意思是，它们在调节气候方面极其重要。这是一个非常新的领域。我们在2023年发表的一些研究发现，这些菌根网络每年处理大约130亿吨二氧化碳。

这大概相当于化石燃料排放量的三分之一。换个说法，植物从大气中吸收所有这些碳，然后每年将其中约130亿吨分配给这些网络。所以它们真的帮助调节我们的气候。一旦碳进入土壤深处，网络会把它带到深层，在那里它可以留存，不会大量释放。

当然，真菌是活的，所以它们会呼吸，会失去一些碳，但它们也会产生这些非常粘稠的、美丽的化合物，这些化合物很难分解，所以有助于将碳留在地下。你可以把它们想象成一种脚手架，把土壤固定在一起。如果没有它们，土壤就会侵蚀消失。

所以，它们不仅在调节气候方面很重要，还帮助我们种植粮食。正如我所说，植物确实依赖这些网络来吸收磷、氮和水。植物高达80%的磷首先通过真菌网络。这意味着，甚至我们自己DNA的骨架——磷骨架——也首先通过了真菌网络。就像我们是由经过真菌的磷构成的。

斯特罗加茨：哦，这真好。

基尔斯：太美了。它们还真的调节水的可用性。新研究表明它们非常擅长分解污染物和重金属。所以我们担心的是，人们没有关注这些网络，如果我们继续破坏它们，就有可能加剧全球变暖、加速生物多样性丧失，并真正扰乱地球的养分循环。

斯特罗加茨：嗯。好，非常有说服力的回答。你确实论证了我们应该关心它们，即使我们可能不知道或看不到它们。

基尔斯：我认为最重要的一点是，人们往往认为土壤是死的或惰性的。这很可能是因为土壤生命在很大程度上是不可见的。所以我们做的很多工作就是试图让那些不可见的生命变得可见，让人们真正开始看到并连接地下世界，某种程度上翻转他们的视角，把地下生态系统看作生命开始的地方。

斯特罗加茨：我们来聊聊这个。我想很多听众已经理解这一点了，但我必须承认，我相对较晚才开始意识到泥土不只是泥土，泥土以各种方式活着，通过思考这一点，我们可以理解，比如为什么农民要轮作作物之类的。我的意思是，这不完全是我们这里讨论的内容，但请帮我们理解，当有人说土壤是活的，这意味着什么。

基尔斯：当我们想到土壤时，大多数人没听过的最令人惊讶的统计数字之一是，地球上59%的物种生活在地下。所以即使我们只是认真对待保护生物多样性，这也必须包括地下生命。

我认为问题之一就是试着让人们好奇，对吧？试着去理解，让他们踩在地球上时开始思考脚下正在发生的所有相互作用。我的意思是，没有健康的土壤，生态系统就会崩溃，土地就会退化。空气、水和气候之间有一种美丽的平衡，真的不能被破坏，我认为农民在很多方面真的很擅长了解这种平衡，并试图生成土壤、再生土壤，而不是仅仅把它当作不断被索取的东西。

斯特罗加茨：嗯哼。好，让我们稍微聚焦在你已经提到的一些事情上。你之前用了“共生”这个词，植物向真菌提供碳流，真菌交换氮和磷回去。这听起来像是市场和交易的语言。听起来像经济学，这也是你为人所知的一点——帮助我们通过这种市场视角来看待事物。

所以跟我们讲讲吧。我的意思是，这就像一个合作市场，有分工——你做我不能做的事，我做你不能做的事，我们都开心？还是这种系统中存在某种张力？

基尔斯：这些都是很好的问题，也是我几十年来一直在问自己的问题。用经济学视角来看，确实能帮助我们理解这些交易动态。交易之所以成立，是因为生物都需要稍微不同的资源，而获取这些资源带来好处。所以特定行为要演化出来，就必须增加某种好处。

研究这些交易模式的好处在于，它让生物能够获得它们自己无法获取的非常不同的材料。但存在张力，你用了这个词，我觉得这里的张力相当有趣，因为当我们拿植物和它们的真菌为例时，植物进行光合作用和提供碳是昂贵的，真菌出去收集这些资源也是昂贵的。

所以我们把它作为一种地下经济来研究，试图理解在什么条件下某些交易行为会演化出来？什么使真菌收集资源并把它们给某种植物，反之亦然？什么使植物给一个真菌网络比另一个更多的碳？我们在实验室设置这类实验，这些非常操控性的实验，然后观察双方怎么做。

斯特罗加茨：抱歉，我在笑，因为你用“操控性”这个词有一种迷人的双关意味。给我们举个操控策略的例子，或者你发现的什么东西。也许，我知道你有很多，但给我一些你的经典案例。

基尔斯：我觉得最基本的一个，我们只是想看看植物是否能区分非常合作和不太合作的真菌菌株。我们做的实验通常在培养皿中进行。所以是非常实验室化的，我们首先承认自然界中发生的事情显然非常不同，受到许多其他生物的影响。

但这种实验室设置确实让我们能非常精确地控制条件。所以我们会做实验，比如想象一个培养皿，一个圆分成三个区室，其中一个有根系。然后我们可以在根区室的任一侧加入不同的真菌，我们可以在一个区室比另一个加入更多资源，然后实际追踪多少碳流向那些不同的真菌区室。

那些真菌区室，有时我们叫它真菌竞技场，因为那里是所有行动发生的地方。我们做了这个实验，发现植物确实能区分有效和不太有效的菌株，并持续给那些回报更多磷的真菌更多的碳、更多的脂肪和糖。

这几乎不算太令人惊讶，但然后我们做了反向实验，我们有两个根系由单一真菌网络连接，根系给出更少或更多的碳。我们再次发现真菌非常擅长区分，它们给更多碳的植物更多磷。所以你所拥有的是某种意义上的互惠剥削，双方都非常擅长区分并选择正确的伙伴。

斯特罗加茨：嗯。所以当你描述一个实验，你某种程度上做了手脚，让竞技场的一侧能提供更多好东西，然后真菌 reciprocate，偏向那一侧并回报更多。这听起来和人类的行为方式非常相似。

基尔斯：正是。非常相似。这就是数亿年来演化出来的东西——区分好伙伴和坏伙伴的能力。再次，我不觉得这有那么令人惊讶，但我认为这就是使用经济学这个想法的切入点——如果你有这种区分能力，这些伙伴关系能变得多复杂？你能有多个伙伴吗？植物同时区分多个不同菌株的能力有多强？如果不只是两个，你能增加数量吗？反之亦然？然后真正试图理解这些交换中的模式。

多年来我们记录的一些最有趣的策略是，比如，真菌会避免向阴凉处生长的植物输送大量磷。所以如果我们操控甚至整株植物，把植物遮阴，真菌能分辨出来并提供更少的磷。它会根据有多少真菌竞争者存在而进行不同的交易，这真的很有意思。真菌可以通过在网络中囤积磷来人为抬高价格，然后推高磷的价格，基本上等到植物能够提供更多碳作为回报。我们有一个了不起的实验，我们使用了所谓的量子点，这些是明亮的荧光纳米颗粒，你可以把它们附着在磷上，真正看到真菌如何在非常复杂的网络中移动磷。

我们设置了一个实验，我不讲所有细节，但基本上我们记录到的是，真菌在网络中非常丰富的一侧吸收磷，并主动把它一路运到网络的另一侧，那里植物愿意支付更多。所以主动移动资源以获得更高的价格。

斯特罗加茨：真的难以置信。想到一棵可怜的植物碰巧被遮阴了，所以它无法获得它想要的阳光量。它不高兴被遮阴，对吧？这东西因为自己的悲惨处境而难以提供碳，结果还被真菌惩罚了。我听得对吗？

基尔斯：是的，所以我们得小心“惩罚”这个词。

斯特罗加茨：我不该那么说，对吧？

基尔斯：不，完全不是。你可以继续说。但我觉得应该说区分，因为那是一种选择，所以不像是它在主动惩罚它。

斯特罗加茨：不，你说得对。

基尔斯：因为自然界中确实有主动惩罚，而那实际上对生物本身是有代价的。但这一切都在自然界中发生。只是复杂得多，所以我们在实验室里把它大大简化，这样我们才能真正看到这些模式浮现出来。

但是的，我认为它教给我们的是，这些生物对它们的环境极其敏感，它们演化出了各种策略来最大化这种资源交换。甚至有些植物完全不进行光合作用。这太不可思议了。

有些兰花种类不产生光合作用的躯体。它们仍然在地上开花，但它们实际上接入菌根网络，偷取碳。所以就像反过来。它们在欺骗真菌，把碳抽出来，这样就不必浪费时间进行光合作用。

所以自然界中有很多这样的策略，我认为我们的工作就是理解并有耐心去记录它们。

[音乐播放]

莱文：哇。当然你会想拟人化，但有趣的是这在某种程度上可以无意识地完成。我的意思是，没有人会真的认为真菌在有意识地做决定。但显然有某种朝那个方向发展的东西。有张力，然后有回应。我的意思是，这相当了不起。

斯特罗加茨：确实。比如，哄抬价格。

莱文：哄抬价格，太疯狂了。

斯特罗加茨：你知道，你不需要有头脑或心怀恶意才能意识到……不是意识到。太难谈论这个了。

莱文：是不可能的，对。

斯特罗加茨：以符合我们所谓的哄抬价格的方式行事。在这个案例中，在这种特定的相互作用中，从进化上看显然被选择为那样行事。

莱文：我的意思是，似乎有一种暗示，这种经济学的说话方式，就市场行为而言，是一种隐喻，但也许它不仅仅是隐喻。我的意思是，我们确实有这些复杂的网络，人类网络，它们正是以这种方式运作的。市场本身没有头脑。确实个体参与者有，但你知道，也许这里不仅仅是某种隐喻。

斯特罗加茨：嗯，我们可能高估了我们意识的重要性。你知道，因为我们碰巧有意识，我们就认为一切都跟它有关。但实际上，竞争与合作发生在整个生命世界中，在每个尺度上，你知道吗？

莱文：嗯哼。

斯特罗加茨：所以显然不真的跟意识有关。

莱文：嗯，这也很有意思，因为我很欣赏她的克制，没有过度拟人化，对吧？但与此同时，我们知道有些复杂网络确实会涌现出思维和意识，大概它们只是基于同类机制、同类基本机制的复杂网络。所以，在某个阶段，复杂网络发生了转变。我不知道。

斯特罗加茨：是啊，所以也许你知道，从我们想认为是完全无意识的，到如你所说，有某种地方，如果它是神经元的复杂网络，它就变得有意识了，这是一个连续统吗？

莱文：这是个大问题。

斯特罗加茨：嗯，这就是我们要探索的那类问题：这种类似市场的行动如何在没有任何中枢神经系统的情况下真正发生？我们将在休息后听到这方面的内容。

[音乐播放]

斯特罗加茨：欢迎回到《为什么的乐趣》。我们一直在与进化生物学家托比·基尔斯了解菌根网络。

所以帮我们理解，对于那些没有大脑、没有语言的实体，策略或区分意味着什么。没有大脑你怎么谈判？

基尔斯：是的。自然界中有很多生物没有中枢神经系统也能谈判，它们被研究得太少了。我们真的呼吁总是把研究去中心化决策的其他领域的人拉过来开始研究真菌，因为太多关注都集中在有大脑的生物上，好像那是做决定的唯一方式。但实际上，真菌非常擅长处理信息。它们在整个网络中处理信息，我们很多工作就是试图确切理解它们怎么做。是电信号吗？是内部的流动充当计算器吗？我们有很多正在测试的假说。它们确实处理信息，所以你是否想用“智能”这个词是一个大辩论，我觉得可以 comfortably 说它们是智能生物，取决于你如何定义智能。

但我倾向于使用的词是信息处理，对吧？因为这样就很清楚，它们能够对环境敏感，适应并在其生命过程中做出决定，对吧？甚至不是在进化时间尺度上，而是在那些时刻调整行为来真正优化交易。所以当然，在人类和微生物之间画平行线总是有很大的风险，特别是因为语言被不同人以不同方式解读。“决定”和“不”这样的词可能给人一种印象，即一个非认知生物表现出了意图。但我们真正谈论的是实际上内置在生物DNA中的策略，这些策略允许生物在一个世界中生活和行动，我会说，允许它们充分利用那个世界，这是研究没有大脑的生物的一个非常有趣的方式。

斯特罗加茨：我注意到你刚才用了“微生物”这个词，我觉得我们可能一直有点忽视——也许在你的思路中真菌是微生物。我这里更多想到的是我知道你有时研究和摆弄的细菌。

基尔斯：是的，正是。我的意思是，这实际上是真菌学内部的一个大辩论——这些真菌网络，它们是微生物吗？在某些情况下它们可以长到厘米到米长，对吧？所以那……但它们肉眼不可见。所以它们是微生物吗？这真的取决于你的定义。

如果我们一般性地谈论菌根真菌，有一类叫做外生菌根真菌，意思是根外面的。它们长在根外面，形成蘑菇。我们喜欢吃 的很多蘑菇都是由菌根真菌形成的。那你会认为那些是微生物吗？这是个大问题。

所以我们试着更明确地说“细菌”和“真菌”，而不是用“微生物”这个词。但我认为很多人用“微生物”来描述细菌和真菌两者。

斯特罗加茨：我记得读过一个涉及细菌和大豆的实验，某种大豆。也许你已经描述过了，但我想知道——还是我们没聊到？就是细菌最终被窒息的那个。

基尔斯：是的，这是我的博士工作，聚焦于大豆——豆科植物——如何区分并实际上惩罚不能提供氮的固氮细菌。在这里我们用“惩罚”这个词。我可以给你一些关于我们用大豆和细菌设置的操控性实验的背景。我们真的想理解植物如何防止这些细菌占用太多资源。同样，当你有一个非常密切的共生关系时，总有可能微生物本身变成寄生者，开始从内部消耗资源。退一步说，豆科植物是自然界中一个了不起的植物科，它们形成根瘤，里面充满了根瘤菌，也就是固氮细菌。

这些细菌了不起。它们从空气中获取氮，打破那个非常强的三键，把它转化成植物可以利用的氮形式。所以它们实际上是在用空气制造肥料。它们能做的绝对令人难以置信，但这非常昂贵。

它们打破空气中的氮键并喂给大豆植物需要大量能量。所以当然，它们不是免费做的，它们得到大量碳作为回报。数百万年来，它们演化出了一种美丽的结构，叫做根瘤，长在大豆根系上，保护这些非常重要的细菌。它也保护它们免受氧气的影响。所以，如果我说得太书呆子了，请告诉我。

斯特罗加茨：不，我喜欢。继续。嘿，我们这里都是书呆子。继续。[笑]

基尔斯：好。所以能打破那个键的唯一问题是，那种酶对氧气非常敏感，如果暴露在氧气中，它就不工作了。所以大豆演化出的是一个非常复杂的结构，细菌本身需要氧气才能生存。它们是细菌，所以它们在呼吸，但它们必须防止那种酶暴露在氧气中。长话短说，大豆根瘤就像进化的伟大壮举，你应该总是花时间去看看它。但我们想理解如果根瘤内的根瘤菌——这些细菌——不能为植物提供肥料会怎样。

如果它们停止固氮会怎样？我们做了这个非常——我至今认为很聪明，那是2000年代初，但对我来说仍然非常聪明——我们强迫细菌作弊，把它们放在氩气环境中培养。所以突然间，可怜的细菌拼命想制造氮，但你无法从氩气中制造氮，氩气只是惰性气体，所以它不会伤害根瘤。然后我们非常耐心地观察植物对这种作弊的回应是什么。就像你说的，这正是发生的事情——大豆实际上窒息了那些不能提供氮的细菌。它能在单个根瘤的水平上感知到多少氮被提供了，然后切断氧气。从那以后，人们发现了许多其他机制，植物如何真正控制细菌不让它们在根瘤中过度生长。

斯特罗加茨：我自己的领域是数学，尤其是应用于现实世界的数学，比如生物学、物理学和社会科学。所以当我听你说的时候，听起来就像是研究博弈论的人喜欢思考的进化动力学部分的一个案例研究。

基尔斯：我们确实参加很多博弈论会议。我们与牛津的理论家合作，研究许多可以用博弈论回答的不同问题。合作效果很好，因为我们可以在实验室直接测试其中一些想法。所以在某些情况下，我们发现了一些东西，然后试图用博弈论来解释它；在其他情况下，博弈论已经存在，我们用操控性实验来测试它是否成立。

斯特罗加茨：你提到了一些你在实验中使用的工具。我想多听一点，既然我们在这里当书呆子。你提到了荧光……你说过量子点。

基尔斯：量子点。我们使用量子点，这又是一种让养分以明亮纯净的颜色发光的方法。量子点的好处是不同的波长对应不同的颜色。所以如果你想拿磷，把它变成三种不同的颜色，你可以做到。

所以你可以在三个不同时间点加入它，然后看多少磷被移入植物，取决于它是什么时间、什么颜色。所以这是追踪交易的好技术。另一种技术是熔岩灯式的技术。那可能是最美丽的，用荧光标签标记网络内部的脂质，然后追踪它穿越许多不同节点。

我觉得有趣的是，我们有能力观察碳来到我们所谓的决策点，那里有一个岔路口，它可以向左或向右，我们可以观察成百上千个这样的决策点，再次尝试用数学来理解碳如何以非常高效和有效的方式在网络中移动。我们捕捉到的最美丽的实时视频之一是一个碳的团块来到一个交汇点，它一路向左移动。然后它到了下一个决策点的一半左右，又退回到决策点，然后几乎完美地分成两半，同时向左和向右。

再次，这只是一个观察。但看到这些精妙之处真的很美。几乎就像窥视这些生物的内在生活。我的意思是，首先它们是透明的，这一点多美啊，我们甚至可以让光穿过它们看到它们在做什么。这在很多方面真的是一种邀请，邀请我们在它们自己的层面上、以它们自己的方式理解它们。有时我把它描述为像灵长类动物学家。涉及很多观察，因为你只是在实时观察这些行为。不像细菌，你知道它们会繁殖，你得等着看会发生什么，当你在培养皿上在显微镜下有一个正在生长的网络时，你可以实时与它互动。你可以非常靠近培养皿，它们对外部环境如此精妙地敏感，以至于你的呼吸就能改变流动的方向。

斯特罗加茨：嗯，当你谈到你的一些实验室实验时，我感觉你可能在某个时候被同事批评过，说你在实验室提供了理想化条件，让你能看到某些模式。

基尔斯：当然，当然。

斯特罗加茨：啊，你已经领会我问题的要点了。

基尔斯：哦，是的。不，但我把它当作一种邀请，因为这些系统，我第一个承认它们被大大简化了。前几天，我们有一个培养皿被污染了，上面长满了细菌，我们看整个网络，有这些像……它们看起来像快乐的小糖豆，就这样移动。他们称之为真菌高速公路。细菌利用网络的弯月面以令人难以置信的速度移动，日本有关于细菌如何利用网络的美丽研究。

当它们这样做时，它们在提供磷，它们与真菌网络以如此密切的方式互动，以至于它们几乎可以自己操控真菌网络向不同方向移动，通过产生激素和化合物，对吧？

所以这是一个非常嵌套的共生关系，如果你愿意这么说的话，是许多相互作用的地下生物。而我们只是在研究冰山一角，用只有宿主植物和真菌的实验。你知道，有时我们会有多个伙伴，不同种类的根系，不同种类的真菌，但它们都在非常简化的系统中。

斯特罗加茨：所以，就科学过程和问题解决而言，如果我听得对，你是在说你完全清楚你在做刻意简化的工作，试图梳理出某些相互作用，但不是在假装自然界就是那样。

基尔斯：是的，正是，几乎相反，因为我实际上也做了相当多的野外工作，我们还没聊到。我的意思是，我大约一半时间在实验室，一半时间在野外收集土壤，以理解全球尺度的真菌群落和动态。

我实际上对学术界非常沮丧，因为感觉我们发表的关于菌根网络重要性的工作并没有真正被决策者吸收。在发表和世界实际运作、决策如何做出之间有一个巨大的鸿沟。这些菌根网络的重要性就是没有超越文献。

所以我想做的是创办一个组织，一个非营利组织，能够引起人们对所有这些令人难以置信的同行评审研究的关注——老实说，这些研究已经发表了几十年，显示了菌根网络的重要性，但就是没有被关注。

所以在2021年，我创办了一个叫SPUN的组织，代表地下网络保护协会。它有一个非常大胆的使命，就是绘制地球上这些菌根网络的生物多样性地图，并开始倡导保护它们。

我们真的想改变真菌在气候变化战略、保护议程和恢复工作中被使用的方式。所以我们创办了这个组织，现在资助着全球近140名地下探索者，他们在研究地球上一些最缺乏研究的偏远生态系统中的真菌群落，并实际努力使这些不可见的网络变得可见。

斯特罗加茨：太棒了。这是一个很好的过渡。我实际上希望我们去那里。我以一种奇怪的方式通过问你那个挑衅性问题到达了那里。所以我想听更多关于这个的。你在寻找什么，发现了什么？

基尔斯：让我想想。我最近参加的探险是去不丹，去喜马拉雅山麓的高海拔生态系统。绝对令人难以置信的生态系统，多样性非常高，而且我们认为地球上一些最密集的丛枝菌根网络就在这个地区。

在所有情况下，我们所做的是与当地合作者合作，他们对生态系统有非常具体的问题，然后出去使用网格系统采集土壤样本，实际上把取芯器打入地下，取出芯样，把土壤带回实验室，提取真菌DNA，开始对这些群落进行测序。

斯特罗加茨：所以你在测序。你只是想要一个那里多样性的分类？还是问题是什么？

基尔斯：嗯，我觉得十年前，创建地球地下活真菌网络的蓝图似乎是不可能的，对吧？我觉得从历史上看，我们了解地球上森林的模式。我们了解海洋模式。我的意思是，我们的工具真的局限于地球表面发生的事情。

但现在我们有了这些惊人的新兴技术——遥感、机器学习、真菌测序和机器人技术——我们实际上可以开始理解地下正在发生什么。通过这样做，我们正在了解如何利用真菌来恢复退化土地、提高农业可持续性、减少碳。

有太多了。甚至试着去那些有污染的地方，了解那里有什么真菌群落，它们基因组中的什么使它们能够分解污染物？用这些数据集我们可以问太多问题了。

斯特罗加茨：听你说的时候，我感觉就像人们开始探索海洋时想知道那里有什么。你知道，这是一个非常简单的类型的问题。我们甚至不知道那里有什么。感觉这就是驱动其中一些工作的东西，有一个巨大的未探索的未知领域，恰好在地下。

基尔斯：不仅驱动着它，而且真菌是最有魅力、最有意思的合作生物。所以全世界真菌学家有这种真正的热情，他们一直资金不足，在很多方面被边缘化，因为直到1970年代、我觉得是60年代末，真菌才被承认为自己的界。我的意思是，之前它们只是被归入植物。所以这真的是在照亮生物多样性中的弱者。

所以我们现在做的是与所有这些数据集和全世界所有这些科学家合作。我想现在大约有600名SPUN合作者，在80多个国家，我们正在一起创建所谓的“地下地图集”。这是一个数字工具，让决策者能够真正开始量化、追踪和保护隐藏的地下真菌群落。我们在问，地下的亚马逊在哪里？在亚马逊吗？这些生物多样性热点在哪里，它们是否受到保护？

所以我觉得是在去年，2025年，我们在《自然》杂志上发表了一篇重要论文，显示90%的菌根生物多样性热点在保护区之外。所以目前只有10%的热点在保护区内。所以我们试图把这些地图送到决策者手中，说：“听着，这是长期被忽视的关键生物多样性”，它也是一个解决方案库，应对世界面临的非常重要的问题，比如我们如何恢复退化土地？

你需要这些真菌网络来启动那些土壤系统，但如果所有那些当地栖息地、那些如此关键的真菌避难所，那些菌株，所有那些生物多样性都失去了呢？你怎么开始恢复一个地下生态系统？

斯特罗加茨：让我追问几个你说的非常引人注目的事情，真的很多。用“有魅力”这个词是其中之一。我觉得你已经为真菌的一些有魅力特征做了论证，但我想知道你还有没有没机会提到的？

基尔斯：嗯，我们使用美丽的技术，比如共聚焦显微镜来观察这些生物。如果你放大真正看这些生物的孢子，它们包含数百个细胞核，像气球里面闪亮的小星星，它们是你见过的最不可思议的结构。想想这些孢子正在空气中旅行，实际上在改变我们的天气模式，对吧？我的意思是，我们越来越开始理解空气中的孢子、真菌孢子，是雨林上空产生云的重要输入。

这有什么没有魅力的呢？它们在微观层面上如此美丽，然后在大气中漂浮形成云。我的意思是，没有什么比得上它。

斯特罗加茨：太好了。当我们接近对话尾声时，我想把镜头拉得更远，跟你聊聊一些关于生命、相互依赖、智能、进化等大问题。我感觉你的工作挑战了很多关于个体与网络、合作与竞争、生物体与生态系统的通常二元对立。真菌是否迫使我们重新思考什么是生命系统？

基尔斯：我认为真菌真的挑战了我们对生命世界所知的很多。它们挑战我们对性的理解。它们挑战我们对定义什么是个体的理解。它们挑战我们对如此小的东西如何在全球层面产生如此巨大影响的理解，即使它是如此小的微生物，几乎不可见。我认为这就是与它们合作如此有趣的原因——每天与菌根真菌合作时，你都在被挑战。它们让你永远不知道某个实验会发生什么。它们让你一直猜测。我们有时叫它们天后，以最善意的方式，因为它们让我们不断回来，因为它们开启了这种好奇心驱动的科学的理念。

你知道，我们在实验室问这个问题：“做你是什么感觉？”我们在问真菌，“做你是什么感觉？”我认为这是一个非常尊重的问题，因为它允许它们做它们自己，让我们在旁边开发工具来真正尝试理解它们的内心生活。所以，当我们谈论经济学和使用不同术语时，只是以不同方式提问，花时间理解这些生物如何如此不同地生活在世界中。

斯特罗加茨：嗯哼。好。我不能让你走而不多听听……你怎么说的？它们在迫使我们重新定义我们所说的性之类的？

基尔斯：是的，它们在挑战我们对性的理解。菌根真菌，特别是这些丛枝菌根真菌，是一个很好的例子。我们阿姆斯特丹小组有Vasilis Kokkoris领导的工作，他在很多方面是一位了不起的遗传学家，研究菌根真菌。他研究发现单个网络内同时有两个基因组。所以想象我们人体，但不是有一个基因组，而是在同一个我们认为是独立个体的东西内有两个基因组。这完全说不通，所以他开始理解，这两个基因组之间有合作吗？谁能在网络的哪些部分定殖？一个个体到底是一个网络，还是一个基因组，漂浮在这根管子里的微小细胞核？真的很难理解。

然后我们甚至不知道，这些基因组，它们会重组吗？很多年来，传统观点认为这些是无性生物，但我们看到暗示也许有不同种类的性在发生。

所以关于这些真菌如何繁殖有很多开放问题。我们知道它们产生孢子。我们知道这些孢子进入空气。我们知道孢子萌发并形成你会认为是新个体的东西。但因为一个孢子内有数百个细胞核，而且它们不全都一样，用我们传统的遗传学理解就说不通。

斯特罗加茨：嗯。它们似乎是真正以相互依赖方式生活的典范，甚至跨越界。我的意思是，我们可以向它们学习。我不知道。你对此有什么想法？自然界更合作吗？它们是否展示了即使是自我优先时合作可以是什么样子的范式？

基尔斯：对于菌根真菌，我们视它们既是把一切固定在一起的物理脚手架，这真正强调了相互依赖的理念，对吧？很多生物建立在这个生命脚手架之上。但也有这种美丽的化学相互依赖，对吧？它们在系统中移动碳，真菌在收集磷和氮，有这种美丽的依赖和资源流动。几乎就像这么多生物层层叠加的嵌套互动。即使在网络本身内部，也可能有曾经是自由生活细菌的细胞器。

所以，我认为我们看得越多，看到的相互依赖和嵌套就越多。当然，这并不意味着没有张力，对吧？总是有张力。生物之间

英文来源：

How Do Fungi Keep the Planet Healthy?
Introduction
People may think of soil as just dirt, but it is anything but inert. Beneath your feet, a vast network of mycorrhizal fungi is hard at work, trading minerals with plant roots. This trading system helps enrich the soil, and it sequesters 13 billion tons of atmospheric carbon dioxide each year — roughly equivalent to one-third of the world’s fossil-fuel emissions. Scientists know that these fungi form partnerships with 80% of all plant species on Earth, a relationship that evolved some 450 million years ago. What they have not understood is how organisms with no brain or central nervous system can decide whom to trade with, and on what terms.
Toby Kiers, an evolutionary biologist at Vrije Universiteit Amsterdam, has spent much of her career making this hidden world visible. Drawing on economics and game theory, and using tools that range from fluorescent quantum dots to imaging robots, her lab is probing how fungi and plants conduct their trade. The work raises new questions about soil, carbon, and even what counts as an individual organism. In this episode, Kiers tells co-host Steven Strogatz how these brainless, decentralized organisms can behave strategically — discriminating between better and worse partners and shifting resources across the network to wherever a plant will “pay” more for it — and how she has built a worldwide community of researchers to map the biodiversity of these underground networks and advocate for their protection.
Listen on Apple Podcasts, Spotify, TuneIn or your favorite podcasting app, or you can stream it from Quanta.
Transcript
[Music plays]
STEVE STROGATZ: I’m Steve Strogatz.
JANNA LEVIN: And I’m Janna Levin.
STROGATZ: And this is The Joy of Why.
LEVIN: A podcast from Quanta Magazine where we explore some of the biggest unanswered questions in math and science today.
STROGATZ: Hey there, Janna. I would love to talk to you about a big question.
LEVIN: Okay.
STROGATZ: Imagine you’re walking around in the forest or in Central Park.
LEVIN: That’s my forest!
STROGATZ: I know, so what’s under your feet? What are your shoes hitting?
LEVIN: I think people would be very surprised that there’s real nature in Central Park. So you got the grass, you got the trees. Uh, there’s dirt. We have birds.
STROGATZ: Let’s focus on the dirt.
LEVIN: Is dirt our topic today?
STROGATZ: Dirt is related to our topic. We wanna talk about what’s happening underground in the form of what are called mycorrhizal fungi. I learned that I’m supposed to say fun-gee.
LEVIN: Not fun-guy?
STROGATZ: Not fun-guy.
LEVIN: I say fun- fung- fun-guy.
STROGATZ: Well, what would I say? I would probably s- I don’t know. Fun-ji?
LEVIN: So now I have to say fun-gee?
STROGATZ: You’re supposed to say fun-gee for the purpose of this episode.
LEVIN: Is that like saying Uranus?
STROGATZ: [Laughs] You should be saying that.
LEVIN: I do yeah.
STROGATZ: Well, so I spoke to someone recently that changed my perspective about these fungi under our feet and the wood wide web. Not the worldwide web, the wood wide web. It’s the mycorrhizal network of these vast networks of fungi that we never notice that are underground, and they’re incredibly important in connecting the roots and supplying nutrients to trees and other plants. Something like 80% to 90% of all the plant species all over the world are getting help from these fungi.
They’re also helping our atmosphere and our climate. They enrich the soil to help farmers and biodiversity, agriculture. They may even contribute to cloud formation through the release of their spores over rainforests.
LEVIN: Wow.
STROGATZ: So they may not get much respect, the fungi, but they’re right up there with the animals and plants in mattering to the world.
LEVIN: Yeah, ’cause you always hear about the role of bacteria, and so it’s really interesting how fungi could affect the whole ecosystem like that.
STROGATZ: Well, the bacteria are very intimately associated with these fungi. and That’s something that we’re going to hear from our guest about.
LEVIN: Alright.
STROGATZ: Toby Kiers is her name. She is an evolutionary biologist at the Vrije University in Amsterdam, and a recent MacArthur Fellow. So if you’re ready, here we go.
[Music plays]
STROGATZ: Welcome to The Joy of Why, Toby.
TOBY KIERS: Thanks so much about having me.
STROGATZ: Well, this is an area that is not familiar to me at all, and I’m dying to hear about it. Can you describe what your subject area is first, just in very broad terms?
KIERS: I study the class of organisms called mycorrhizal fungi, and the word mycorrhizal means myco, which means fungus, and rhizal, which means root. So these are a class of fungi that form a very intimate association with the vast majority of plants. So over 80% of all plant species on Earth form these partnerships, and it’s a very old partnership.
It evolved some 450 million years ago, and was actually really fundamental for plants that were in a wet, aquatic environment to start colonizing land hundreds of millions of years ago. And since then, it’s been an incredibly important relationship in building ecosystems that we live and survive on today.
And I don’t think many people know, but actually the fungus served as a plant root system for even tens of millions of years. Roots are kind of a new evolutionary innovation, so it’s a very intimate and old partnership between plants and fungi.
STROGATZ: So you’re saying the plants didn’t go to the bother of making their own roots? They were somehow using the fungi to do that for them?
KIERS: Exactly. So, what the plants were doing was they were sending carbon that they were photosynthesizing and taking out of the atmosphere and feeding it to these loose associations, these fungal networks that were in the soil, and in return they were getting resources like phosphorus and nitrogen. See, the thing that fungi are very good at is breaking up rocks and digesting these hard-to-access minerals.
And so they were feeding it to the plants, and in return the plants were giving carbon. And now this partnership really underlies our ecosystems on Earth.
STROGATZ: Oh, wow. I have all kinds of questions. First of all, very dramatic to say breaking up rocks. I don’t, just haven’t thought about it. What are they doing to break up rocks?
KIERS: Well, the fungi make these beautiful complex networks, and fungi are very good at digesting outside of their bodies and actually partnering with other microbes like bacteria that can help break down rocks. So, some people even say they’re very good at eating rocks on the outside of their bodies and having it dissolve into a form that can then be taken up.
And so the fungi then take up these nutrients and move them through these vast networks and feed them to plant roots. And in return —obviously they don’t do this for free — the plants are feeding them a diet of sugar and lipids like fats. It’s like the most brilliant diet of sugar and fats that is provided by the plants to the fungi. And this partnership is very common. It’s almost ubiquitous, I would say, across terrestrial ecosystems. And because of this partnership and because plants are constantly feeding carbon down to these networks, we actually call it one of Earth’s circulatory systems.
STROGATZ: Oh, nice. So, network is a word that everybody is using these days. We hear about the internet. We know we have our own circulatory system in our body, networks of blood vessels. But so when you talk about a mycorrhizal fungal network, what should I picture?
KIERS: Exactly. And it’s very clear. One thing I really want people to understand is that plants are not fungi , and fungi are not plants, and they’re very different kingdoms of life. So when you have a plant root and you were to pull it up from the ground, that’s a beautiful image, you would not quite be able to see these threads that are hanging from the root. They’re thinner than the hairs on my head, just a few microns across.
And the type that we really concentrate on are called arbuscular mycorrhizal fungi, and we can get into where that name comes from. But these particular networks are like an open-pipe system. They’re literally like a tube. And in some senses, people think they’re the largest cells on Earth because they don’t have the septa that break it up into individual compartments.
And so a lot of what we do in the lab is growing these networks across sort of a transparent soil almost, like a way that you can see the networks and use microscopy to follow these networks and understand how they navigate space. We have developed together with biophysicists at the Biophysics Institute called AMOLF here in Amsterdam, these imaging robots that allow us to track individual nodes across these networks. So in any given experiment, we’re tracking about half a million of these nodes, these fungal decisions whether to go left or right or make a bridge when they fuse together.
And they actually make a beautiful supply chain because what you’re imagining —and I want you to really close your eyes and picture this — is that the plant is pouring carbon down into this root system, and the carbon, which now we can label with a fluorescent label, so we can actually watch it travel through this open-pipe system all the way down to the tips where the fungi use the carbon to keep building their network. Now, as they’re building that network, they’re collecting the phosphorus and the nitrogen in the water that they’re moving in an opposite direction back to the root system. Now, one of the most fascinating things about this symbiosis is that this is an open-pipe system, yet it has flows moving in two directions at the same time.
So it’s like a river going north and south at the same time. So when you say picture it, it’s actually one of the most beautiful things I’ve ever seen. And the biophysicists when they saw it for the first time, they said, “ This just can’t be true. How do they do it?”
STROGATZ: This is amazing. This is off topic, but I’m just gonna throw it out there but when I was a kid in high school, I had a science teacher who showed me how to do an experiment that Galileo had described in the 1600s, where Galileo said he took a little jug of water and another jug of wine, and then he could connect these two reservoirs, the wine on the bottom and the water on the top. And there’s this thin vertical tube connecting them. Galileo said that the wine will rise through the tube and the water will flow down through the tube, and they will pass through without mixing and they will trade places. And I actually did this experiment.
KIERS: Did it work?
STROGATZ: And it worked. They didn’t mix in the tube. My teacher took a photograph of it. It was published in a history of science magazine when I was 13 years old. The, the point being that a historian of science said Galileo was fudging and he had made up this experiment because we all know that when two things pass through the same tube, they would mix.
You’re telling me a story about two different flows through a whole network of tubes.
KIERS: Exactly, exactly.
STROGATZ: Am I on the right track thinking like this?
KIERS: You are kind of on the right track, and it’s something that is a big open question in our lab right now, so it’s something we’re constantly thinking about. I think I go to bed thinking about it and wake up thinking about it. But what you have to remember is that the diet that the plants give the fungi is full of fat, and fat doesn’t mix very well with water.
And so there are these things called condensates, which are these big lipid droplets inside the network. And what we think is happening is that there’s these beautiful molecular motors that are inside the network that actually drag the lipids, the fats, to the tip of the network so the fungus can use it to grow. And we think that’s what’s happening, is that when you pull these lipids on these… So a molecular motor, you can think of it as, a little railroad track that has, one of those cars on it that people move up and down and up and down to move forward. That’s what a, a molecular motor looks like.
STROGATZ: Uh-huh.
KIERS: And you can see this in the lab. It’s so beautiful to watch the lipids move inside on these tracks. But it’s not the only thing that’s happening, is that these, um, by the lipids in the molecular motors pulling the fluid, it actually creates a pressure. And so if you’re pulling one way and you’re- have a, an end that’s plugged up, it forces the liquid to go the other way because of pressure.
And so the fungus actually, we think, is opening and closing these beautiful aquaporins, these little pores that help regulate how much water is going in and out, and that’s helping drive pressure inside, in the network. And so it’s a combination of the active molecular motors pulling, but then these very fast flows that are created by the pressure inside the cell. And as a result, you get these very complex patterns inside. And because we can label the carbon, it’s this sort of beautiful fluorescent, almost looks like a lava lamp moving through a very thin liquid, a very thin tube, all the way up to the tip and back. And it’s mesmerizing.
STROGATZ: [Laughs] Well, I’m sure anyone listening to this can hear how excited you are by your own subject, and this is thrilling and infectious to listen to. But I wonder though if anyone is not getting it, can we just pan back in our story? Why should the average citizen care about these underground networks that they probably didn’t even know existed?
KIERS: Well, these networks, they really can support us in tackling some of the biggest challenges facing humanity today. I mean, they are incredibly important in regulating our climate. And that’s a really new field. So some work that we published in 2023 found that these mycorrhizal networks are processing about 13 billion tons of CO2 every year.
So that’s like roughly a third of emissions from fossil fuels. So to say that another way, plants are taking up all of this carbon from our atmosphere and then allocating about thirteen billion tons of that to networks every year. So they really help regulate our climate. And once that carbon is down in the soil, the networks bring it down deep where it can stay and not be released so much.
So, of course, the fungi are living, so they respire, so they lose some of that carbon, but they also create these very sticky, beautiful compounds that are very hard to break down, and so that helps keep carbon underground. You can think of them as like a scaffolding that sort of holds the soil together. If they weren’t there, the soil would just erode and disappear.
So, not only are they important in regulating our climate, but they also help with our ability to grow food. So, as I was saying, the plants really depend on these networks for their phosphorus uptake, for their nitrogen, for their water. Up to 80% of a plant’s phosphorus first passes through a fungal network. So, what that means is even the DNA, backbone, the phosphorus backbone of our own DNA first passed through a fungal network. Like we are made up of phosphorus that passed through fungi.
STROGATZ: Oh, that’s nice.
KIERS: It’s so beautiful. And they also, they really regulate water availability. New work has shown that they’re very good at breaking down pollutants and heavy metals. And so what we worry about is that people are not paying attention to these networks, and if we keep destroying them there’s chances for more increased global warming, accelerating biodiversity loss, and really disrupting the Earth’s nutrient cycles.
STROGATZ: Mmmm. Okay, very convincing answer. You’ve really made the case that we should care about them even though we may not be aware or able to see them.
KIERS: I think that’s the most important part is that people tend to assume that soils are sort of dead or inert. This is likely because, like, soil life has been largely invisible. And so a lot of what we do is trying to make that invisible life visible, and so that people actually start to see and connect with the underground, kind of flip their perspective and think about underground ecosystems as places where life begins.
STROGATZ: Let’s talk about that a little bit. I think that many of our listeners will already get this point, but I have to admit, it was relatively late in my life that I started to appreciate that dirt is not just dirt, that dirt is alive in all kinds of ways, and that by thinking about that, we can understand, like, why does a farmer rotate their crops or something like that. I mean, this isn’t exactly what we’re talking about here, but just help us understand what it means when someone says the soil is a living thing.
KIERS: So when we think about soils, one of the most surprising statistics that most people haven’t heard is that 59% of all species on Earth live underground. And so if even if we’re serious about just protecting biodiversity, this has to include life underground.
One of the problems I think, is just trying to make people curious, right? Trying to understand, so that they step on the Earth and they start thinking about all of the interactions that are happening right under their feet. I mean, without healthy soils, ecosystems collapse, lands degrade. There’s this beautiful balance of air and water and climate that really can’t be disrupted, and I think farmers are really good at knowing about that balance in many ways and trying to generate the soil, regenerate the soil, rather than just having it be something that’s constantly being extracted from.
STROGATZ: Mmm-hmmm. Okay, so let’s zoom in a little bit on some of the things that you already mentioned. I mean, you used the word symbiosis earlier, that the plants are providing carbon flows down to the fungi, the fungi are trading nitrogen and phosphorus back up. It all sounds like this is the language of markets and trading. It sounds like economics, and that’s one of the things that you’re known for is helping us see things through this market perspective.
So tell us about that. I mean, is it just like a cooperative market where there’s a division of labor — you do something I can’t do, so I do something you can’t do, and we’re both happy? Or is there any tension in this sort of system?
KIERS: These are all brilliant questions and ones that I’ve been asking myself for many decades now. And this idea of using an economic lens, it can really help us understand these trade dynamics. Now trade works because organisms, they all need slightly different resources, and access to those resources, they bring benefits. So for particular behaviors to evolve, it has to increase a benefit.
What is nice about studying these trade patterns is that it allows organisms access to very different materials that they couldn’t get themselves. But there’s a tension, and you used that word, and I think the tension here is quite interesting because when we take an example like plants and their fungi, it’s expensive for plants to photosynthesize and to feed that carbon, and it’s expensive for the fungi to go out and collect these resources.
And so we study it as sort of an underground economy and trying to understand under what conditions do certain trade behaviors evolve? What makes fungi collect resources and give them to a certain plant and vice versa? What makes a plant give more carbon to one fungal network than the other? And we set up these kinds of experiments in the lab, these very manipulative experiments, and then we watch to see what both partners do.
STROGATZ: I’m sorry, I’m chuckling because the word “manipulative” you use in such a charmingly double entendre sense there. Give us an example of a manipulative strategy or something that you figured out. Maybe, I know you have lots of them, but give me some of your greatest hits.
KIERS: I think one of the most basic ones, we just wanted to see if plants could discriminate between very cooperative and less cooperative fungal strains. And so, the experiments that we do often take place in a Petri plate. So they’re very lab-based, and we are the first to admit that what’s happening out in nature is obviously very different and influenced by so many other organisms.
But this lab setup really allows us to have very precise control over conditions. And so we would do experiments, for example, imagine a plate, a circle that’s broken into three compartments, and one of those compartments has a root system. Then we can add different fungi to either side of the root compartment, and we can add more resources, let’s say, on one compartment than the other, and then actually track how much carbon goes to those different fungal compartments.
Those fungal compartments, sometimes we call it fungal arenas because that’s where all the action happens. And we did this, and we found that plants indeed were able to discriminate between effective and less effective strains, and consistently gave more carbon, more fats and sugars to the fungi that were giving more phosphorus in return.
Now, that almost wasn’t that surprising, but then we did the reverse experiment where we had two root systems that were connected by a single fungal network, and the root systems gave less carbon or more carbon. And we found again that the fungi were very good at discriminating, and they were giving more phosphorus to the plants that gave more carbon. And so what you have there is this sort of reciprocal exploitation in a sense, where both partners are very good at discriminating and choosing the correct partner.
STROGATZ: Huh. So when you describe an experiment where you sort of stack the deck by making it possible for one side of the arena to provide more of the goodies, and then the fungi reciprocate by favoring that one and providing more in return. That sounds very familiar to the way that people operate.
KIERS: Exactly. It’s very familiar. And that’s sort of what has evolved over these hundreds of millions of years, is just that ability to discriminate between a good partner and a bad partner. And again, I don’t think that’s so surprising, but I think this is where this idea of using economics came in, was that if you have this discrimination, how complicated can these partnerships get? Can you have multiple partners? And, how good are plants at discriminating against multiple different strains simultaneously? If it’s not just two, can you up the number and vice versa? And then really trying to understand the patterns inside these exchanges.
Some of the most interesting strategies that we have documented over the years is, you know, for example, a fungus will avoid sending lots of phosphorus to plants growing in the shade. So if we manipulate even in whole plants and cover plants in the shade, the fungus can tell and provide less phosphorus. It will trade differently depending on how many fungal competitors are present, which is really interesting. Fungi can artificially inflate the price by hoarding the phosphorus in their network and then driving the price of it, waiting basically until the plant is able to provide more carbon in return. We had this incredible experiment where we used something called quantum dots, which are these, like, bright fluorescent nanoparticles that you can attach to phosphorus to really see, okay, how do the fungi move their phosphorus around these very complex networks?
And we set up an experiment that, I won’t go into all of the details, but basically what we documented was that the fungus was taking up phosphorus on a very rich side of the network and moving it actively all the way to the other side of the network where the plant was willing to pay more. So actively moving resources to get a higher price.
STROGATZ: It’s really unbelievable. The idea that like a poor plant that happens to be shaded, so it’s not able to get the amount of sunlight it would like. It’s not happy about being shaded, right? This thing is having trouble providing the carbon because of its sad condition, and it ends up getting punished to boot by the fungi. Did I hear that right?
KIERS: Yeah, so we have to be careful about the word “punished” right.
STROGATZ: I shouldn’t talk like that, right?
KIERS: No, not at all. You can go ahead. But I think discriminate because that’s a choice, so it’s not like it’s actively punishing it.
STROGATZ: No, you’re right.
KIERS: Because there is active punishment in nature as well, and that actually comes at a cost to the organism. But this is all happening in nature. It’s just a lot more complex, and so we make it very simplified in the laboratory so we can really see these patterns emerge.
But yes, I think what it teaches us is just that these organisms are incredibly sensitive to their environment, and they have evolved all kinds of strategies to maximize this resource exchange. There’s even plants that don’t photosynthesize at all. This is incredible.
There’s types of orchids that make no photosynthetic body. They still bloom above ground and make a flower, but they actually tap into the mycorrhizal network, and they steal the carbon. So it’s like a reverse. So they’re cheating the fungi and pulling the carbon out so that they don’t have to waste time photosynthesizing.
So, there’s so many strategies like this in nature, and I think it’s our job to kind of understand and have the patience to document them.
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LEVIN: Wow. So you want to anthropomorphize here, of course, but it is fascinating that this can be done mindlessly, to some extent. I mean, nobody really is going to have a good argument that fungi are consciously making decisions. But there’s clearly something on the way towards that. There’s a tension, and then there’s response. I mean, it’s, it’s quite remarkable.
STROGATZ: It is. For instance, the price gouging.
LEVIN: The price gouging, that’s crazy.
STROGATZ: You know, you don’t need a mind or be sinister or anything to realize… Not realize. It’s so, so hard to talk about this.
LEVIN: It’s impossible, yeah.
STROGATZ: To behave in a way that is consistent with what we would call price gouging. It’s evolutionarily apparently selected in this case, in this particular interaction, to act like that.
LEVIN: I mean, it seems that there’s a suggestion that this economic way of speaking, in terms of marketplace behaviors, is a metaphor, but maybe it’s not just a metaphor. I mean, we do have these complex networks, human networks, and they play out in precisely this way. The marketplace itself doesn’t have a mind. It’s true the individual players do, but, you know, maybe there’s more than just a kind of metaphor here.
STROGATZ: Well, we may overestimate the importance of our consciousness. You know, because we happen to have that, we think it’s all about that. But in fact, competition and cooperation occur all throughout the world of life at every scale, you know?
LEVIN: Mm-hmm.
STROGATZ: So it’s not really about consciousness apparently.
LEVIN: Well, it’s so interesting too because I appreciate her discipline in not falling into too much anthropomorphizing, right? But at the same time, we do know of complex networks where thinking does emerge and consciousness does emerge, and presumably they’re just complex networks that are based on the same kinds of mechanics, you know, the same kinds of elementary mechanics. So, at some stage, complex networks make the transition. I don’t know.
STROGATZ: Yeah, and so maybe you know, is it a continuum from what we wanna think of as totally unconscious to, as you say, there is some kind of place where if it’s a complex network of neurons, it becomes conscious.
LEVIN: It’s the big question.
STROGATZ: Well, that’s the kind of thing we’re gonna explore: How does this marketplace-like action really take place without any sort of central nervous system? And we’ll be hearing about that right after the break.
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STROGATZ: Welcome back to The Joy of Why. We’ve been learning about mycorrhizal networks with evolutionary biologist Toby Kiers.
So help us understand how to think about what strategies or discrimination mean in entities that don’t have brains, that don’t have language. How can you negotiate without a brain?
KIERS: Yeah. There are so many organisms in nature that negotiate without a central nervous system, and they’re so understudied. And so we have a real plea in trying to always pull people from other fields that sort of study decentralized decision-making to start studying fungi, because there’s so much focus on organisms with brains, and that’s the only way to make decisions. But actually, fungi are very good at processing information. They process information all across their networks, and a lot of our work is trying to understand exactly how they do that. Is it electrical signaling? Is it the flows inside that act as a calculator? There’s lots of ways that we’re — hypotheses that we’re testing. They definitely process information, and so whether you wanna use the word intelligence is a big debate, one that I do feel comfortable saying that they are intelligent creatures, depending on how you define intelligence.
But the words that I tend to use are information processing, right? Because that makes it really clear that they’re able to be sensitive to their environment and adapt and make decisions over the life of their organism, right? So not even over evolutionary time, but adapt behaviors to really optimize trade in those moments. And so, of course, there’s always these big hazards in drawing parallels between human, humans and microbes, especially because the language is interpreted in so many different ways by different people. words like “decision” and “no”, they can give the impression that a non-cognitive organism shows intent. But what we’re really talking about is strategies that are actually built into the DNA of the organism, and that those strategies allow the organism to live in a world and behave in a world that, I would say, allows them to make the most of that world, and that’s a really interesting way of studying organisms that don’t have a brain.
STROGATZ: I notice you used the word “microbe” just now, and I feel like we’ve maybe been giving short shrift to, maybe in your way of thinking the fungi are microbes. I’m thinking here more in terms of the bacteria that I know you’ve sometimes studied and played with.
KIERS: Yeah, exactly. I mean, it’s, it’s actually a big debate within mycology in general is like, are these fungal networks, are they microbes? In some cases they can be centimeters to meters long, right? So that’s … but they’re invisible to the naked eye. And so are they a microbe? It really depends on your definition.
If we talk about mycorrhizal fungi in general, there is a type, a class called ectomycorrhizal fungi, meaning outside the root. They grow outside the root, and they form mushrooms. Many of the mushrooms that we love to eat are formed by mycorrhizal fungi. And, would you consider those a microbe is a big question.
So we, we try to be more clear and say “bacteria” and “fungi” rather than using the word “microbe.” But I think many people use the word “microbe” to describe both bacteria and, and fungi.
STROGATZ: There was one experiment that I remember reading about involving bacteria and soy, a certain type of soybean. Maybe you’ve already described it, but I wonder if … or have we not talked about it? The one where the bacteria ended up getting suffocated.
KIERS: Yeah, this is my PhD work, focused on the ways in which soybeans, so legumes, are able to discriminate and actually punish. Here we use the word punish, their nitrogen-fixing bacteria if they fail to provide nitrogen. So I can give you some context about these manipulative experiments that we set up with soybeans and bacteria. We really wanted to understand how plants prevent these bacteria from taking too much resources. Again, when you’ve got a very intimate symbiosis, there’s always a chance that the microbe itself can turn into a parasite and just start to consume resources from inside. And just to take a step back, legumes are this incredible family of plants in nature that form nodules that are full of something called rhizobia, which are nitrogen-fixing bacteria.
And these bacteria are incredible. They take nitrogen from the air, and they break that really strong triple bond, and they put it into a form of nitrogen that the plant can use. So they’re actually making fertilizer out of the air. It’s absolutely incredible what they can do, but it’s really expensive.
It takes a lot of energy for them to break that nitrogen bond from the air and feed it to soybean plants. So of course, they don’t do it for free, and they get lots of carbon in return. Now, over millions of years, they have evolved a beautiful structure called a nodule on the root system of soybeans that keeps these very important bacteria safe. And it also keeps them safe from, from oxygen. So again, maybe please tell me if I’m getting too nerdy.
STROGATZ: No, I like it. Keep going. Hey, we’re nerds here. Go. [Laughs]
KIERS: Okay. So the only problem with being able to break that bond is that enzyme is very sensitive to oxygen, and if it gets exposed to oxygen, it doesn’t work. And so, what the soybean has evolved is a very complex structure where the bacteria themselves need oxygen to survive. They’re bacteria, so they’re respiring, but they have to keep that enzyme from being exposed to oxygen. So long story short, a soybean nodule is like a great feat of evolution, and you should always take the time to look at it. But we wanted to understand what would happen if the rhizobia, these bacteria inside the nodule, failed to provide this fertilizer to their plant.
What if they just stopped fixing nitrogen? And so we did this very, I still think it clever, it was in the early 2000s, but to me it’s still incredibly clever, where we forced the bacteria to cheat by growing them in an argon atmosphere. So all of a sudden, the poor bacteria were trying so hard to make nitrogen, but you can’t make nitrogen out of argon, and argon’s just an inert gas, so it didn’t hurt the nodules. And then we watched very patiently to see what was the response of the plant to this cheat. And like you said, that’s exactly what happened, was that the soybean actually suffocated the bacteria that failed to provide nitrogen. It could sense at the level of an individual nodule, how much nitrogen was being provided, and it cut off oxygen. And since then, there have been many other mechanisms that have been discovered, by which how the plants really keep a check on that bacteria from overgrowing the nodule.
STROGATZ: My own world is math, especially, math applied to the real world, to things like biology and physics and social science. And so as I listen to you, it just sounds like such a case study in the part of evolutionary dynamics that people who study game theory like to think about.
KIERS: We do go to a lot of game theory conferences. We work with theoreticians at Oxford on many kinds of different questions that you can answer with game theory. And the collaboration works out quite well because then we can test some of these ideas very directly in the lab. So in some cases, we’re discovering something and then trying to use game theory to explain it, and in other cases, there’s game theory that’s existing, and we use manipulative experiments to test if it’s true.
STROGATZ: You mentioned something about some of the tools that you use in your experiments. I’d like to just hear a little more about that, since we’re being nerdy here. You mentioned something about fluorescent… you talked about quantum dots.
KIERS: Quantum dots. We use quantum dots, and again, yeah, this is just a way to make nutrients fluoresce in bright, pure colors. And the beauty about quantum dots is there’s different colors depending on different wavelengths. So if you want to take phosphorus and make it three different colors, you can.
So you can add it at three different time points and then see how much of that phosphorus was moved into the plant, depending on what time and what color it was. So that’s a really nice technique to actually track trade. Another technique is the lava lamp sort of technique. That’s probably the most beautiful, using a fluorescent tag to label the lipids inside the network and then tracking it across many different nodes.
I think that’s what’s interesting, is that we have an ability to watch the carbon come up to what we call a decision point, where there’s a fork in the road, and it can either go left or it can go right, and we can watch hundreds and thousands of these decision points and try to, again, use math to understand how the carbon is being moved across the network in a very efficient and effective way. One of the most beautiful videos that we captured live was that there was this sort of blob of carbon coming up to a junction, and it moved all the way to the left. And then it was about halfway up into the next decision point, and it backed down to the decision point and then split almost perfectly in half and went both to the left and the right.
And again, this is just one observation. but it was really beautiful to see the intricacies. It’s almost like looking into the inner lives of these organisms. I mean, how beautiful that they’re transparent, first of all, that we can even shine light through them and see what they’re doing. It’s really an invitation in many ways to understand them on their own level, on their own way. Sometimes I describe it as being like a primatologist. There’s so much observation involved because you’re just watching these behaviors in real time. And unlike bacteria, which you know multiply and you have to wait to see what happens, when you have a network growing on one of these Petri plates under the microscope, you can interact with it in real time. You can get down very close to the Petri plate, and they’re so exquisitely sensitive to the outside environment that just your breath changes the direction of the flows.
STROGATZ: Well, when you spoke about some of your lab experiments, I got the feeling that you might have been criticized by colleagues at some point for providing idealized conditions in the lab that allowed you to see certain patterns.
KIERS: Of course, of course.
STROGATZ: Ah, you’re already getting the thrust of my question.
KIERS: Oh, yes. No, but I take it as an invitation, because these systems, I’m the first to admit they’re incredibly simplified. The other day, we had a plate that was contaminated in the sense that there was bacteria growing all over it, and we looked across the network and there were these like… they looked like little happy jelly beans, just like moving along. They call that the fungal highway. Bacteria use the meniscus of the network to move incredibly fast, and there’s just beautiful work coming out of Japan on how bacteria use the network.
And while they do that, they are giving phosphorus, and they’re interacting in such an intimate way with the fungal network that they can almost manipulate the fungal network in and of themselves to move different directions by producing, like hormones and compounds, right?
So it’s just a very nested symbiosis, if you will, of so many interacting organisms underground. And we are just studying the tip of the iceberg by doing these experiments with just the host plant and just the fungi. You know, sometimes we’ll have multiple partners, different kinds of root systems, different kinds of fungi, but they’re in very simplified systems.
STROGATZ: So, just as far as the process of science and problem-solving, that if I’m hearing you right, you’re saying you know full well that you’re doing deliberately simplified work to try to tease out certain interactions, but not pretending that that’s the way it is in nature.
KIERS: Yeah, exactly, and almost the opposite, because I’m actually doing quite a lot of work in the field as well, which we haven’t talked about. I mean, so I spend about half my time in the lab and about half my time out in the field collecting soils to understand fungal communities and dynamics at the global scale.
I actually got very frustrated with academia because it felt like the work that we were publishing on the importance of mycorrhizal networks wasn’t really being absorbed by decision-makers. That there’s a big leap, this chasm, between publication and how the world actually works and how decisions are made. The importance of these mycorrhizal networks, it just wasn’t getting past the literature.
And so what I wanted to do was start an organization, a nonprofit, that was able to draw attention to all of this incredible peer-reviewed research that had been being published, honestly, for decades showing the importance of mycorrhizal networks, but that just wasn’t being paid attention to.
So in 2021, I founded an organization called SPUN, which stands for the Society for the Protection of Underground Networks. And it had an audition, a very, very audacious mission, and that was to map the biodiversity of these mycorrhizal networks across Earth and start advocating for their protection.
And so, we really wanted to transform how fungi were being used in climate change strategies and conservation agendas and really in restoration efforts. And so we started this organization that’s now funding close to 140 Underground Explorers all over the world, are studying the fungal communities in some of the most understudied remote ecosystems on Earth and actually working to make these invisible networks visible.
STROGATZ: Fantastic. That’s a beautiful segueway. I was actually hoping we would go there. I got there in a weird way by asking you this provocative question. So I wanna hear a lot more about this. What are you looking for and what are you finding?
KIERS: Let’s see. The most recent expedition I went on was to Bhutan, uh, to these high-altitude ecosystems at the, in the Himalayan foothills. Absolutely incredible ecosystems with really high diversity, and also some of what we think are the most dense arbuscular mycorrhizal networks on Earth is in this area.
And in all cases, what we do is we work with local collaborators who have very specific questions about the ecosystems, and actually go out and use a grid system to take soil samples, and actually pound a core into the earth and extract that core and bring the soil back to a lab, extract the fungal DNA, and start sequencing these communities.
STROGATZ: So you’re sequencing them. Do you just wanna have a taxonomy of the kind of diversity out there? Or what is the question?
KIERS: Yeah, well, I think like a decade ago creating a blueprint of Earth’s living underground fungal networks would’ve seemed impossible, right? I think like historically, we understand the patterns of forests across the Earth. We understand ocean patterns. I mean, really our tools have been confined to what’s happening at the Earth’s surface.
But now we’ve got these amazing emerging techniques in remote sensing, in machine learning, in fungal sequencing, and in robotics that we can actually start to understand what’s happening underground. And by doing that, we’re learning how fungi can be leveraged to restore degraded lands, to increase agricultural sustainability, to draw down carbon.
There’s so many. Even trying to go to these places where there’s pollution and understand what fungal communities are there, and what is it about their… what is it in their genomes that allow them to break down pollutants? So many questions that we can ask with these data sets.
STROGATZ: I’m getting the feeling listening to you that sort of like when people began to explore the oceans wondering what’s there. You know, it’s just a very simple kind of question. We don’t even know what’s out there. It feels like that’s what’s animating some of this, that there’s a vast unexplored terra incognita that happens to be subterranean.
KIERS: Not only is that animating it, but fungi are the most charismatic and fun-to-work-with organisms. So there’s this real passion of mycologists all over the world that have been so underfunded and so marginalized in many ways because it wasn’t even until sort of the 1970s, late ‘60s I think, that fungi were recognized as their own kingdom. I mean, before they were just placed in with plants. And so it’s really shining a light on the underdog of biological diversity.
And so what we’re doing now is working with all these data sets and all of these scientists all over the world. I think now there’s about 600 SPUN associates in, like, over 80 countries, and we’re working together to create something called the Underground Atlas. And that’s this digital tool that allows decision-makers to actually start quantifying and tracking and protecting hidden underground fungal communities. We’re asking, where’s the Amazon of the underground? Is it in the Amazon? Like, where are these hotspots of biodiversity, and are they being protected?
So I think it was in last year, in 2025, we had a big paper in Nature that showed that 90% of mycorrhizal biodiversity hotspots are outside protected areas. So only 10% of hotspots are actually inside protected areas currently. And so, we’re trying to get these maps to decision-makers and say like, “Listen, this is key biodiversity that’s been ignored for so long,” and it’s also a library of solutions to really important questions facing the world in terms of, like, how are we gonna restore degraded lands?
Like you need these fungal networks to jumpstart those soil systems, but what if all of those local habitats, the fungal refugia that are so key, and those strains, those, the, all that biodiversity is lost? How are you going to start to restore an underground ecosystem?
STROGATZ: Let me follow up on a few very striking things you said, so many really. The use of the word “charismatic” is one of them. I think you’ve made the case for some of the charismatic features of fungi, but I wonder if you have more that you didn’t have a chance to mention yet?
KIERS: Well, we use beautiful techniques, for example, confocal microscopy to look into these organisms. If you were to zoom in and actually look at the spores of these organisms, they contain hundreds of nuclei that shine like little bright stars inside a balloon, and they’re the most incredible structures that you’ve ever seen. And to think that these spores are traveling through the air and actually changing our weather patterns, right? I mean, more and more we’re starting to understand how spores, fungal spores in the air, are an important input to generate clouds over rainforests.
What is not charismatic about that? They’re so beautiful on a small microscopic level, and then up in the atmosphere they’re floating around forming clouds. I mean, there’s just nothing quite like it.
STROGATZ: Great. As we come towards the end of our conversation, I’d like to sort of pan back even further now to talk to you about some big questions about life, interdependence, intelligence, evolution, things like that. I get the feeling that your work challenges a lot of the usual binaries about individuals versus networks or cooperation versus competition or organism versus ecosystem. Do fungi force us to rethink what a living system is?
KIERS: I think fungi really challenge so much of what we think we know about the living world. They challenge our understanding of sex. They challenge our understanding of defining what is an individual. They challenge our understanding of how something so small can have such magnitudes of effects at the global level, even though it’s such a small microbe, it’s almost invisible. And I think that’s what makes it so interesting to work with is that every day when you’re working with mycorrhizal fungi, you’re challenged. They make it so you never know what’s going to happen in a given experiment. They keep you guessing. We call them divas sometimes, in the nicest way possible, because they keep us coming back, because they open up this idea of curiosity-driven science.
You know how, we ask this question in the lab, “What is it like to be you?” We’re asking the fungi, “What is it like to be you?” And I think it’s a very respectful question because it allows them to be them and for us to be on the sidelines to develop tools to actually try to understand their inner lives. So, when we talk about things like economics and using different terminologies, it’s just asking questions in a different way and taking the time to understand how these organisms live so differently in the world.
STROGATZ: Uh-huh. Okay. Well, I can’t leave you without hearing more about… How did you put it? They’re forcing us to redefine what we mean by sex or something like that?
KIERS: Yeah, they’re challenging our understanding of sex. So mycorrhizal fungi, these arbuscular mycorrhizal fungi in particular, are a great example. There’s work coming out of our group here in Amsterdam led by Vasilis Kokkoris, who’s an incredible geneticist in many ways studying mycorrhizal fungi. And he studies that there are two genomes simultaneously inside a single network. So it’s, imagine our human body, but instead of having one genome, it has two genomes inside the same, what we would think of as an individual. It just doesn’t make any sense, and so he’s starting to understand, is there a cooperation between these two genomes? Who gets to colonize what parts of the network? Is an individual even a network, or is an individual just a genome, tiny little nuclei floating inside this tube? It just, it’s really hard to understand.
And then we don’t even know, do these genomes, do they recombine? For, for many years, the conventional idea is that these are asexual organisms, yet we see hints that maybe there’s a different kind of sex going on.
So lots of open questions about how these fungi just reproduce. We know they make spores. We know these spores go into the air. We know that the spores germinate and make what you would think is a new individual. But because there’s hundreds of nuclei inside a spore, and they’re not all the same, it just doesn’t make much sense using our conventional understanding of genetics.
STROGATZ: Hmm. They seem to be real champions of living in an interdependent way, even across kingdoms. I mean, we could do well to learn from them. I don’t know. Do you have thoughts about this? Is nature more cooperative? Are they a paradigm of what cooperation can look like even when you’re looking out for number one?
KIERS: With mycorrhizal fungi, we see them as both like a physical scaffold that holds everything together, and that really drives home this idea of interdependence, right? So many organisms are built upon this scaffold of life. But there’s also this beautiful chemical interdependence, right? They’re moving carbon through the system, and fungi are collecting phosphorus and nitrogen, and there’s this beautiful sort of dependence and movement of resources. And it’s almost like this nested interaction of just so many organisms layered on. Even in the networks themselves, there can be organelles that used to be free-living bacteria inside the networks themselves.
So, I think the more we look, the more interdependence and nestedness we see. Now, that doesn’t mean there’s no tension, right? There’s always a tension. It’s a beautiful tension between organisms because they have different needs. They have different resources that they need to access, to reproduce, and that creates a beautiful opera of interactions that’s not always beneficial, not always cooperative, but instead it creates a beautiful tension, very much like an opera, where sometimes the characters are getting along, and sometimes they’re not.
STROGATZ: I really like your analogy there because it is operatic in that, this traditional framing, or at least very commonplace about selfishness, puts such a negative tone on the thing, whereas when you speak of it as opera or drama, it’s like each character has desires. It needs certain things. It wants what it wants, and that’s not exactly selfish. It’s just, it’s the nature of being alive. We all have our needs.
KIERS: Exactly. And I just don’t think that we should be scared of studying that tension in a curious way because that tension leads to innovation, right? When there’s some kind of conflict between organisms, that leads to the generation of new ideas. And that’s always really interesting is that it’s not s- everybody thinks that conflict in and of itself or that tension is a bad thing, but actually can generate biological diversity and allow organisms to create ecosystems that are much more complex than they would be otherwise.
STROGATZ: That’s beautiful. Well, you really give the impression of someone having fun being a scientist.
KIERS: Yes, lots of fun and very little sleep ’cause there’s a lot to do. There’s a lot to do.
STROGATZ: All right. Well, thank you very much, Toby. This has been great fun for us too. We’re really happy to have you on The Joy of Why.
KIERS: It was so fun. Thanks so much for having me.
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LEVIN: It’s so interesting to imagine organisms interacting competitively, operatically. I love that image. But also beyond co-dependence, I mean, there are bacterial organelles that have been synthesized into fungi. That seems like the boundary between separate organisms has also diffused, and that’s pretty remarkable. There also seems to be this kind of, like, evolutionary idea that pressure creates evolution. It drives evolution, right?
STROGATZ: Yeah, that’s right. We do use that phrase, right? Selective pressure. We tend to think, oh, stress is a bad thing. We need to reduce stress in our lives or conflict, and I think it’s an interesting instructive point that Toby makes that, yes, of course, you don’t wanna overdo it with stress and tension and all that, but a certain amount of tension or stress or competition can lead to complexity, she mentions, innovation. It does appear to be very deeply woven into the nature of life.
LEVIN: Yeah, I feel like there’s also a metaphor for life there somehow. You know, how to take lessons from nature and how to evolve.
STROGATZ: Anyway, we don’t have much choice. That does seem to be the way things are.
LEVIN: So these fungi are really so interconnected and so interdependent that, do they talk about that boundary of organisms where they have really begun to merge to some extent?
STROGATZ: Yeah, it’s very tricky to think about what’s an organism, what’s a system, an ecosystem, a population, a colony. It’s an issue we’ve gotten into with some of our other guests in The Joy of Why.
It’s really maybe a case where our human-imposed distinctions may not line up very well with the way nature operates. We’re putting categories on things that are just more subtle than that.
LEVIN: I wonder if people are also thinking about ways to induce these networks to help clean up some of the climate crisis that we’re facing. If these are so influential and they have such an important role in terms of, if you like, the economics of the ecosystem or the economics of the biosphere, is there a way that we can guide a fungi to help clean up this mess?
STROGATZ: Hmm. You know, I don’t know that they need any encouragement from us. They just need protection to not have their ecosystems devastated. And, she did mention that a vast amount of these mycorrhizal networks are not the places being protected.
LEVIN: Wow, right.
STROGATZ: So, this is what she and her colleagues are trying to bring attention to. Because we don’t see them, we don’t notice or think about them but they may be just as important.
LEVIN: Yeah. Maybe nature will show us the way.
STROGATZ: Yeah. As always, it’s been a pleasure.
LEVIN: Thank you, Steve.
STROGATZ: See you next time.
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LEVIN: If you’re enjoying The Joy of Why and you’re not already subscribed, hit the subscribe or follow button wherever you’re listening. You can also leave a review for the show. It helps people find this podcast. Find articles, newsletters, videos and more at quantamagazine.org.
STROGATZ: The Joy of Why is a podcast from Quanta Magazine, an editorially independent publication supported by the Simons Foundation. Funding decisions by the Simons Foundation have no influence on the selection of topics, guests or other editorial decisions in this podcast or in Quanta Magazine.
The Joy of Why is produced by PRX Productions; the production team is Caitlin Faulds, Jade Abdul-Malik, Genevieve Sponsler, and Merritt Jacob. The Executive Producer of PRX Productions is Jocelyn Gonzales. Edwin Ochoa is our project manager.
From Quanta Magazine, Simon Frantz and Samir Patel provided editorial guidance, with support from Samuel Velasco, Kit Sudol, Simone Barr, and Michael Kanyongolo. Samir Patel is Quanta’s Editor-in-Chief.
The episode art is by Chanelle Nibbelink and our logo is by Jaki King and Kristina Armitage. Special thanks to Garth Avery at the Cornell Broadcast Studio.
I’m your host, Steve Strogatz. If you have any questions or comments, please email us at [email protected]. Thanks for listening.
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