作者： 1. Amandine Erktan 2.Melanie M. Pollierer 3.Stefan Scheu 翻译者：小婧
小婧前言：简单介绍一下，这三位作者都是全球顶尖的土壤科学家，他们将自己发表在权威土壤科学杂志上的研究成果，用最通俗易懂的方式描述出来，写成面向青少年读者的科普文章，非常值得一读。
ABSTRACT（摘要）
“ 你是否曾注意到枯叶从不长时间积聚在森林里？对于这种服务我们可以感谢一支生活在土壤里的小小回收清洁团队。死去的生物体是它们的食物来源，它们靠吃掉死去的生物体从而进行回收利用。了解土壤中“谁吃什么”或“谁吃谁”是理解这种循环机制本质。但这其实很难知道的，因为很多生存在土壤的动物都是很微小，隐藏在土壤中的，这就导致它们无法告诉我们它们吃了什么。为了避开这些困难障碍，土壤学家已经开发出一种特殊的方法。什么样的方法呢？他们通过追踪动物脂肪中的细菌、真菌、植物的特定标记，今后便可以在确定它们吃的是什么。有些动物食用的食物来源种类繁多，有些动物食用的食物则是更具体化的，（也就相当于单一性更强一些。）值得一提的是，许多生物体已经开展出惊人的战略——在土壤进食。毕竟在这样一个如此黑暗的迷宫中寻找食物并没有想象中的容易。
Did you ever notice that dead leaves never accumulate in forests? For that service, we can thank a cleaning team of tiny recyclers living in the soil. Dead organisms are their food source, and they recycle them by just eating them. Knowing who eats what or whom in soils is essential to understand this recycling machinery. But that is hard to know, because many soil animals are tiny, hidden in the soil, and unable to tell us what they ate! To bypass these difficulties, soil ecologists have developed a special method. They track specific markers of bacteria, fungi, and plants in the fat of animals and hence can identify what they fed on. Some animals consume a large variety of food sources, others are more specific. Remarkably, many organisms have developed amazing strategies to feed in soil, because finding food in such a dark maze is not that easy!”
你是否有曾注意到，我们从来没有在森林里看到过大堆的枯叶堆积在一起，躺在林地上的动物也十分罕见。这就不禁引发人们的思考，我们会因而产生疑问：“是谁打扫了森林的地面？”在城市里，清洁工会把所有的枯叶都清除掉，而在森林里，这项工作是由生活在土壤中的小小回收清洁团队完成的。对于这些土壤中的小动物来说，死亡的生物是它们的食物来源，它们靠吃掉枯叶和死去的生物体从而对其进行回收利用。当土壤里的小动物排除代谢废物（其实就是排便）时，它们会释放出可以促进植物生长的营养物质。又或者，小的土壤动物被大的动物吃掉，这就可以促进大动物的生长。这个过程可以让养分循环利用，是帮助植物生长的关键。对人类来说也是十分重要的，因为植物为我们提供里大量的商品如：蔬菜，谷物，水果等食物，还提供了建造家具和房屋所需的木材。了解土壤中谁消耗了什么（其实就是题目上说的谁吃了什么），对于理解这个珍贵的循环机制是非常重要的。
Have you ever noticed that we never see huge piles of dead leaves accumulating in the forest? It is also very rare to encounter a dead animal lying on the forest floor. That should encourage us to ask the question, “who is cleaning the forest floor?” In cities, city workers remove all the dead leaves. In the forest, the work is done by a team of tiny recyclers living in the soil. For these small soil animals, dead organisms are a food source and they recycle leaves and other dead things by just eating them. When the soil animals defecate (meaning poop) they release nutrients that can be used by plants to grow. Or, small soil animals are eaten by larger animals, and that allows the bigger animals to grow. This process allows the recycling of nutrients and is essential to help plants grow. It is also very important for humans, as plants provide us with plenty of goods, such as foods like vegetables, cereals, and fruits, and also wood to build furniture and houses. Understanding who consumes what in soil is essential to understand this precious recycling machinery.
01
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WHAT KIND OF FOOD IS IN SOIL … AND WHAT IS A SOIL FOOD WEB?（土壤里有什么类型的植物—以及什么是土壤食物网？）
土壤里有什么食物呢？如果你在森林里挖土，你肯定不会挖掘到一盘肉酱意面！当然，在这里我们不是来谈这一类食物的！在土壤中，基本的食物来源是植物和其他生物体的死亡组织（任何大小的枯叶或土壤生物体）以及植物的根（(见下文图片1 A项)），这些基本的食物主要是由细菌和真菌所消耗（就是被细菌和真菌吃掉），它们被称为初级消费者。在此补充一下初级消费者的定义：（生物学意义上，根据不同的取食地位，直接依赖植物的枝、叶、果实、种子和凋落物为生的称为初级消费者，也被称为“一级消费者”）而真菌和细菌本身是较大生物如原生植物、线虫、春笋和螨类的主要生物来源（大约0.1–2 mm; 见图1).，这些较大的生物又被更大的捕食者如蜈蚣和蜘蛛（几毫米的大小）吃掉（见图片1 B项）。同时蚯蚓主要以真菌和细菌为食，但它们以一种更特殊但方式，将细菌和真菌连同土壤一起吃掉见图片1 B项）。这就有点像你把盘子里的食物和盘子一起吃掉一样！
What kind of food is in the soil? If you dig in soil in the forest, you would not find a plate with spaghetti Bolognese! We are not talking about this kind of food, of course! In soil, the basic food sources are dead tissues from plants and other organisms (dead leaves or dead soil organisms of any size), and plant roots (Figure 1A). These basic food sources are mainly consumed by bacteria and fungi, which are called primary consumers. Fungi and bacteria themselves are the main food source for larger organisms, such as protists, nematodes, springtails, and mites (about 0.1–2 mm; Figure 1).These organisms again are eaten by larger predators (a few millimeters in size), such as centipedes and spiders (Figure 1B). Earthworms also mainly eat bacteria and fungi, but in a special way, they eat them together with soil (Figure 1B). This is a bit like if you ate the food on your plate together with the plate!
Figure 1 图1:- Organisms in a typical soil food web.（典型的土壤生物网中的生物）
(A) A food web contains basic food sources, like plant roots and dead organisms, as well as primary and secondary consumers and a selection of predators. Arrows indicate who consumes what or whom. Note that primary consumers are a food source for secondary consumers, which themselves are a food source for predators. 一个食物网包含基本的食物来源，如植物的根部和死亡的生物体，以及初级和次级消费者和一些捕食者。箭头表示谁吃谁和谁吃什么。注意：初级消费者是次级消费者的食物来源，而次级消费者本身也是捕食者的食物来源。
(B) Here you can see examples of soil primary and secondary consumers as well as predators.
在这里你可以看到土壤中的初级和次级消费者以及一些捕食者的相关例子。
尽管一些土壤动物，如弹尾虫、线虫主要以吃细菌和真菌等微小的生物为食，但它们也可以以植物组织，尤其是根部或根部所释放的营养液为食。总而言之，土壤中有许多食物来源，多到从植物组织到动物组织，从死亡生物到活体动物，且大多数土壤生物体都会食用其中的几种食物。所有的关于“谁吃了谁”以及“谁吃了什么”的环节，称为“土壤食物网”（soil food web）。（见图片1 A项）
Although some soil animals, such as springtails or nematodes, mainly eat tiny living creatures like bacteria and fungi, they can also eat plant tissue, notably the roots or the nutritious liquid roots release. Altogether, there are many food sources in soil, ranging from plant to animal tissues and from dead to living organisms, and most soil organisms consume several of these food sources. All the links of who consumes what or whom is called a soil food web. (Figure 1A).
02
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HOW DO WE STUDY SOIL FOOD WEBS?
（我们应该如何学习土壤食物网？）
尽管在过去的几十年中进行了大量的研究，但研究人员仍然对土壤中的动物“谁吃了谁”以及“谁吃了什么”知之甚少。他们之所以还不知道，是因为土壤中的动物都是隐藏在土壤中且体型十分微小，它们无法告诉我们它们吃了什么！所以，研究人员要想知道谁在土壤中吃了什么，必须充当侦探。他们想出了一种新奇的方法：他们研究土壤动物的脂肪（见图2）。当你在吃东西的时候，食物作为能量的来源，（为你的身体提供能量），你就可以生长和活跃的运动。然而，你不可能一下子把所有的能量都消耗掉，所以你的身体必须把这些能量储存起来，以便以后食用。那能量又是如何储存的呢？当我们吃的东西超过了我们当时的所需量时，脂肪作为储存能量的组织，会在体内堆积。这些在体内堆积的脂肪会在人体需要的时候“燃烧”以功能。对于人类和动物而言，身体更容易吸收和储存食物中已有的脂肪，而不是制造新的脂肪。现在，诀窍是：并不是所有的脂肪都是一样的！细菌、真菌、植物都有不同类型的脂肪，研究人员可以在食用这些食物（就是前文说的“食物来源于（已标注）……）的动物身上追踪这些所谓的脂肪酸标记。所以，至始至终我们可以识别动物体内的脂肪是都来源于细菌、真菌、或植物，从而知道这些动物们吃了什么。
Despite all the research that has happened in the last decades, researchers still know little about who consumes what or whom in soil. This lack of knowledge is because soil animals are tiny, hidden in the soil, and cannot tell us what they ate! To know who consumes what in the soil, researchers must act as detectives.They developed a curious method: they study the fat of soil animals (Figure 2). When you eat something, the food serves as a source of energy, so you can grow and be active.However, you cannot use all the energy at once, so your body must store it for later use. How is energy stored? When we eat more than we need at that moment, the body builds up fat as an energy-storage tissue. The fat will later be “burned” for energy when we need it.For both humans and animals, it is even easier for the body to take up and store the fat that is already in the food, instead of making new fat. Now, the trick is that not all fat is the same! Bacteria, fungi, and plants have different types of fat,and researchers can track these so-called fatty acid markers in the animals that consumed these food sources. So, in the end, we can identify if the fat stored in an animal has come from bacteria, fungi, or plants—and thus know what they ate.
Figure 2 - Determining what soil organisms eat by looking at fatty acid markers.图2--通过观察脂肪酸标记物从而确定土壤中的生物吃什么。
(A)Soil animals have different types of fats in their bodies, depending on the food sources they eat, such as bacteria, fungi, or dead leaves. 土壤动物如细菌、真菌或枯叶等，根据它们所吃的食物来源不同，它们体内的脂肪种类也不同。
(B)The fats can be extracted (removed) from these animals in the form of fatty acids.这些脂肪可以以脂肪酸的形式从这些动物身上提取（去除）
(C)Those fatty acids can then be analyzed using a piece of equipment called a gas chromatograph. The data from the gas chromatograph allows researchers to identify which foods the soil organisms ate 这些脂肪酸可以用一种叫做气相色谱仪的设备进行分析。通过气相色谱仪的数据，研究人员可以确定土壤中的生物吃了哪些食物。
03
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FOOD GENERALISTS VS. FOOD SPECIALISTS
（食物的“通才”VS食物专家）
通过研究土壤植物的脂肪，研究人员发现，许多弹尾虫喜欢以真菌为食，但也可以吃细菌或植物。正因为它们可以吃不同类型的食物，所以它们被认为是“食物的通才（food generalists ”，这意味着如果你请它们吃饭，想让它们得以满足并不困难。有些生物体是“食物专家”，它们往往只吃一种食物。例如：有些线虫喜欢吃细菌，而有些线虫则喜欢吃真菌。甚至有些捕食性的线虫会去吃其他线虫。每一类的线虫都有着不一样的嘴形，这些嘴形就是为了专门吃某一种食物。
By studying the fat of soil animals, researchers discovered that many springtails preferably feed on fungi, but can also eat bacteria or plants. Because they can eat different food sources, they are consideredfood generalists. This means that they are not difficult to satisfy if you invite them for dinner! Some other organisms arefood specialistsand tend to eat only one thing. For example, some nematodes prefer eating bacteria, while others prefer fungi. There are even predatory nematodes that eat other nematodes! Each class of nematode has a different mouth shape, specific for eating a certain type of food.
04
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WHY IS IT SO SPECIAL TO FEED IN THE SOIL?
（为什么在土壤中的觅食显得如此特别？）
土壤里是黑暗的。你有曾试过在乌漆麻黑的环境中吃完饭吗？在黑暗的环境中要找到食物并不是一件容易的事。土壤动物也面临着同样的问题。它们的眼睛在土壤中不起作用，所以许多土壤动物甚至都没有了眼睛。与此相反的是：大多数的土壤动物会有一个完美无瑕的“鼻子”。例如：线虫，弹尾虫和蚯蚓嗅觉都很灵敏（它们靠嗅觉来寻找食物），它们能探测到食物的位置并向着食物的方向移动。线虫“闻到”50cm以外的细菌后可在两周内到达它们的身边。这对于线虫而言是相当长的一段距离，因为这些小虫子通常只有几百微米长（1微米=0.001毫米；作为比较，人类头发的宽度是100微米），这就好比人类可以在70km外的地方就能闻到食物的味道！
Soil is dark. Have you ever tried to eat your dinner in the dark? It is not that easy to find where the food is. Soil animals have the same problem. Eyes do not work in the soil, so many soil animals do not even have them. By contrast, most soil animals have very fine “noses.” For example, nematodes, springtails, and earthworms are very efficient at smelling their food. They can detect the location of food and move toward it. Nematodes can “smell” bacteria up to 50 cm away and reach them in 2 weeks . This is a considerable distance for a nematode, as these little worms are usually only a few hundred microns long (1 micron= 0.001 mm; for comparison, the width of a human hair is 100 microns). This would be like humans being able to smell food from about 70 km away!
土壤里不仅漆黑一片，而且是一个迷宫，土壤生物不能在其中自由活动。土壤就像是一块有着大大小小的孔的海绵。细菌等较小的生物体一般为1-2微米，可以“躲”在小孔中。例如：我们知道如果细菌位于小于2-3微米的孔中（见图1）原生生物是无法抵达细菌猎物的。线虫也是同样的情况，线虫不能吃位于小于30微米洞孔中的细菌（见图3 A项）。土壤中的洞孔越小，细菌就越能藏在其中以防止被捕食者发现并吃掉。但是，尽管存在这些问题，捕食者还是发展出了捕食策略。例如：变形虫是具有柔软身体的原生生物。它的身体可以接受任何形状的洞口（见图3B）（就是不管洞口多大，它都可以毫无阻碍地钻进去。）可以将一条又细又长的 "手臂"伸进小洞里捕捉隐藏的细菌。春尾虫则有一个不同的战略，它们根本不怎么挑剔它们所吃的食物—它们是食物的“通才”。它们可以吃细菌和真菌，也可以吃枯叶和线虫（见图3C）。这则取决于它们爬行过的土壤中有什么可获取的东西，（它们可以吃这吃那，毫不挑剔）这种灵活性有助于它们每天都有东西吃。蚯蚓则受土壤中获取食物的艰难条件影响较小。这些动物直接摄取土壤，使得它们能够在土壤迷宫中轻松地寻找获取食物。此外，它们还可以消化细菌和真菌，以及 随土壤摄入的植物死物。当蚯蚓排便时，那些未被消化的遗留物一般情况下会形成小碗状的土壤。
Soil is not only dark, it is also a maze, through which soil organisms cannot freely move. Soil is like a sponge with larger holes and smaller holes. The smaller organisms, such as the bacteria, typically measure 1–2 microns and can “hide” in small holes. For example, we know that protists (Figure 1) cannot reach bacterial prey if the bacteria are located in holes smaller than 2–3 microns (Figure 3A). The same applies to nematodes, which cannot eat bacteria located in holes with openings smaller than 30 microns (Figure 3A). The smaller the holes in soil, the more the bacteria can hide in them and avoid being caught and eaten by predators.But predators have developed strategies to feed despite these problems. For example, amoebae (the plural of “amoeba”) are protists with soft bodies that can adopt any shape (Figure 3B). Amoebae can extend a very thin and long “arm” into small soil holes to catch hidden bacteria [5]. Springtails have a different strategy: they are simply not very picky about the food sources they consume—they are food generalists.They can eat bacteria and fungi, but also dead leaves and nematodes(Figure 3C). Depending on what is available in the small holes of the soil they are crawling through, they eat one food source or another. This flexibility helps them to have something to eat every day. Earthworms are less affected by the difficulties of accessing food in the soil.These animals directly ingest soil, enabling them to search for and access food easily in the soil maze (Figure 3D).Moreover, they can digest bacteria and fungi, as well as dead plant material that is ingested with the soil. When earthworms poop, the undigested leftovers typically form small bowls of soil.
Figure 3 - Animals have developed ways to deal with the difficulty of feeding in the dark soil.
动物已经进化出克服在黑暗土壤中觅食的困难的方法
(A)Small holes in the soil provide a place for tiny soil organisms (nematodes, protists, and bacteria) to hide from the animals that eat them. 在土壤中的小洞孔为土壤中的小型生物体（线虫、原生生物和细菌）提供了一个可躲避被其他动物吃掉的地方。
(B)To reach its prey, an amoeba (a type of protist) can extend an arm 20 microns long and 1 micron thin to catch bacteria hidden in small soil holes. 为了接近猎物，变形虫(原生动物的一种)可以伸出一条长20微米、薄1微米的“手臂”来捕捉隐藏在小土洞中的细菌。
(C)Springtails are flexible in the food sources they consume, allowing them to have something to eat each day. 春尾鱼的食物来源很灵活（不单一），这使得它们每天都有东西吃。
(D)Earthworms ingest soil along with their food and digest the bacteria and fungi contained in the ingested soil. This also creates a path through the soil maze, making it easier for them to travel through it. Remember 1 micron is 1,000 times smaller than 1 mm蚯蚓在摄取食物的同时也摄取土壤，并消化摄取土壤中的细菌和真菌。这也为它们在土壤迷宫中创造了一条道路，使它们更容易穿越土壤迷宫。记住：1微米比1毫米小1000倍！
05
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A NEW LOOK INTO FEEDING IN A DARK MAZE（对在黑暗的迷宫中觅食的新看法）
在土壤中觅食就像在黑暗的迷宫里寻找食物。为了理解我们脚下的土壤下黑暗的环境中是“谁吃谁”，土壤生态学家必须充当真正的侦探，无论是在森林里还是在实验室里，都须使用各种复杂的技术。现在你知道在土壤中进食的滋味，你就再也不会用同样的眼光看待土壤动物了。
Feeding in soil is like finding food in a dark maze. To understand who eats whom in the soil darkness below our feet, soil ecologists have to act as real detectives and using all sorts of complicated techniques, either in the forest or in the laboratory. Now that you know what it is like to feed in soil, you will never look at soil animals in the same way!
来自翻译者的碎碎念：
本文中英文加起来足足有6000多字，算是我到目前为止翻译的最长的一篇文章，真可谓呕心沥血。这篇文章是几位土壤科学家写的科普文章，面向对象是少年儿童。文章是科学猫头鹰群里的一个网友推给我的，他跟我说：“我一个成年人读了之后，都觉得受益匪浅。我想，如果能有人把这样美好的又有意义的英文文字翻译成中文，让广大中国青少年儿童收益，那真是太有意义了。”当我认认真真读完这篇文章时，我也不得不承认我在此获取了不少新知识，开阔了自己的视野。
其实现在翻译或解读科研、科普、科学资讯类文章的很多了，那种专门面向少年儿童的真正的科普做的人其实是较少的，而我们青少年儿童正是需要培养科学实践与创新的能力，而我如果愿意迈出翻译的这一步，我或许可以填补这个空缺。在此感谢网友Chattachete给我的建议和指导，感激不尽～
还有就是这篇文章算是初稿吧，如果精益求精的话文字图片应该改一改的，起码把英文的改成中文的，但这工程量未免大了些，就拿翻译文章+拍版而言就花了将近9个小时，而且我还有很多学业上的任务未完成，文。可能还有什么错漏的地方，等下星期修改后再重新发一次吧，各位就将就着看吧～
原文出处：https://kids.frontiersin.org/article/10.3389/frym.2020.544803#figure-1
本文章翻译版权归翻译者小婧所有，转载请完整保留作者及翻译者的信息
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