作者：? ? 1. Amandine Erktan? 2.Melanie M. Pollierer? 3.Stefan Scheu? 翻譯者：小婧

小婧前言：簡單介紹一下，這三位作者都是全球頂尖的土壤科學(xué)家，他們將自己發(fā)表在權(quán)威土壤科學(xué)雜志上的研究成果，用最通俗易懂的方式描述出來，寫成面向青少年讀者的科普文章，非常值得一讀。

ABSTRACT（摘要）

“ 你是否曾注意到枯葉從不長時間積聚在森林里？對于這種服務(wù)我們可以感謝一支生活在土壤里的小小回收清潔團隊。死去的生物體是它們的食物來源，它們靠吃掉死去的生物體從而進行回收利用。了解土壤中“誰吃什么”或“誰吃誰”是理解這種循環(huán)機制本質(zhì)。但這其實很難知道的，因為很多生存在土壤的動物都是很微小，隱藏在土壤中的，這就導(dǎo)致它們無法告訴我們它們吃了什么。為了避開這些困難障礙，土壤學(xué)家已經(jīng)開發(fā)出一種特殊的方法。什么樣的方法呢？他們通過追蹤動物脂肪中的細(xì)菌、真菌、植物的特定標(biāo)記，今后便可以在確定它們吃的是什么。有些動物食用的食物來源種類繁多，有些動物食用的食物則是更具體化的，（也就相當(dāng)于單一性更強一些。）值得一提的是，許多生物體已經(jīng)開展出驚人的戰(zhàn)略——在土壤進食。畢竟在這樣一個如此黑暗的迷宮中尋找食物并沒有想象中的容易。

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，我們從來沒有在森林里看到過大堆的枯葉堆積在一起，躺在林地上的動物也十分罕見。這就不禁引發(fā)人們的思考，我們會因而產(chǎn)生疑問：“是誰打掃了森林的地面？”在城市里，清潔工會把所有的枯葉都清除掉，而在森林里，這項工作是由生活在土壤中的小小回收清潔團隊完成的。對于這些土壤中的小動物來說，死亡的生物是它們的食物來源，它們靠吃掉枯葉和死去的生物體從而對其進行回收利用。當(dāng)土壤里的小動物排除代謝廢物（其實就是排便）時，它們會釋放出可以促進植物生長的營養(yǎng)物質(zhì)。又或者，小的土壤動物被大的動物吃掉，這就可以促進大動物的生長。這個過程可以讓養(yǎng)分循環(huán)利用，是幫助植物生長的關(guān)鍵。對人類來說也是十分重要的，因為植物為我們提供里大量的商品如：蔬菜，谷物，水果等食物，還提供了建造家具和房屋所需的木材。了解土壤中誰消耗了什么（其實就是題目上說的誰吃了什么），對于理解這個珍貴的循環(huán)機制是非常重要的。

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?（土壤里有什么類型的植物—以及什么是土壤食物網(wǎng)？）

土壤里有什么食物呢？如果你在森林里挖土，你肯定不會挖掘到一盤肉醬意面！當(dāng)然，在這里我們不是來談這一類食物的！在土壤中，基本的食物來源是植物和其他生物體的死亡組織（任何大小的枯葉或土壤生物體）以及植物的根（(見下文圖片1 A項)），這些基本的食物主要是由細(xì)菌和真菌所消耗（就是被細(xì)菌和真菌吃掉），它們被稱為初級消費者。在此補充一下初級消費者的定義：（生物學(xué)意義上，根據(jù)不同的取食地位，直接依賴植物的枝、葉、果實、種子和凋落物為生的稱為初級消費者，也被稱為“一級消費者”）而真菌和細(xì)菌本身是較大生物如原生植物、線蟲、春筍和螨類的主要生物來源（大約0.1–2 mm; 見圖1).，這些較大的生物又被更大的捕食者如蜈蚣和蜘蛛（幾毫米的大?。┏缘簦ㄒ妶D片1? B項）。同時蚯蚓主要以真菌和細(xì)菌為食，但它們以一種更特殊但方式，將細(xì)菌和真菌連同土壤一起吃掉見圖片1? B項）。這就有點像你把盤子里的食物和盤子一起吃掉一樣！

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 圖1:- Organisms in a typical soil food web.（典型的土壤生物網(wǎng)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.? 一個食物網(wǎng)包含基本的食物來源，如植物的根部和死亡的生物體，以及初級和次級消費者和一些捕食者。箭頭表示誰吃誰和誰吃什么。注意：初級消費者是次級消費者的食物來源，而次級消費者本身也是捕食者的食物來源。

(B) Here you can see examples of soil primary and secondary consumers as well as predators.

在這里你可以看到土壤中的初級和次級消費者以及一些捕食者的相關(guān)例子。

盡管一些土壤動物，如彈尾蟲、線蟲主要以吃細(xì)菌和真菌等微小的生物為食，但它們也可以以植物組織，尤其是根部或根部所釋放的營養(yǎng)液為食?？偠灾?，土壤中有許多食物來源，多到從植物組織到動物組織，從死亡生物到活體動物，且大多數(shù)土壤生物體都會食用其中的幾種食物。所有的關(guān)于“誰吃了誰”以及“誰吃了什么”的環(huán)節(jié)，稱為“土壤食物網(wǎng)”（soil food web）。（見圖片1 A項）

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?

（我們應(yīng)該如何學(xué)習(xí)土壤食物網(wǎng)？）

盡管在過去的幾十年中進行了大量的研究，但研究人員仍然對土壤中的動物“誰吃了誰”以及“誰吃了什么”知之甚少。他們之所以還不知道，是因為土壤中的動物都是隱藏在土壤中且體型十分微小，它們無法告訴我們它們吃了什么！所以，研究人員要想知道誰在土壤中吃了什么，必須充當(dāng)偵探。他們想出了一種新奇的方法：他們研究土壤動物的脂肪（見圖2）。當(dāng)你在吃東西的時候，食物作為能量的來源，（為你的身體提供能量），你就可以生長和活躍的運動。然而，你不可能一下子把所有的能量都消耗掉，所以你的身體必須把這些能量儲存起來，以便以后食用。那能量又是如何儲存的呢？當(dāng)我們吃的東西超過了我們當(dāng)時的所需量時，脂肪作為儲存能量的組織，會在體內(nèi)堆積。這些在體內(nèi)堆積的脂肪會在人體需要的時候“燃燒”以功能。對于人類和動物而言，身體更容易吸收和儲存食物中已有的脂肪，而不是制造新的脂肪?，F(xiàn)在，訣竅是：并不是所有的脂肪都是一樣的！細(xì)菌、真菌、植物都有不同類型的脂肪，研究人員可以在食用這些食物（就是前文說的“食物來源于（已標(biāo)注）……）的動物身上追蹤這些所謂的脂肪酸標(biāo)記。所以，至始至終我們可以識別動物體內(nèi)的脂肪是都來源于細(xì)菌、真菌、或植物，從而知道這些動物們吃了什么。

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.圖2--通過觀察脂肪酸標(biāo)記物從而確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. 土壤動物如細(xì)菌、真菌或枯葉等，根據(jù)它們所吃的食物來源不同，它們體內(nèi)的脂肪種類也不同。

(B)The fats can be extracted (removed) from these animals in the form of fatty acids.這些脂肪可以以脂肪酸的形式從這些動物身上提?。ㄈコ?/p>

(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 這些脂肪酸可以用一種叫做氣相色譜儀的設(shè)備進行分析。通過氣相色譜儀的數(shù)據(jù)，研究人員可以確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食物專家）

通過研究土壤植物的脂肪，研究人員發(fā)現(xiàn)，許多彈尾蟲喜歡以真菌為食，但也可以吃細(xì)菌或植物。正因為它們可以吃不同類型的食物，所以它們被認(rèn)為是“食物的通才（food generalists ”，這意味著如果你請它們吃飯，想讓它們得以滿足并不困難。有些生物體是“食物專家”，它們往往只吃一種食物。例如：有些線蟲喜歡吃細(xì)菌，而有些線蟲則喜歡吃真菌。甚至有些捕食性的線蟲會去吃其他線蟲。每一類的線蟲都有著不一樣的嘴形，這些嘴形就是為了專門吃某一種食物。

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?

（為什么在土壤中的覓食顯得如此特別？）

土壤里是黑暗的。你有曾試過在烏漆麻黑的環(huán)境中吃完飯嗎？在黑暗的環(huán)境中要找到食物并不是一件容易的事。土壤動物也面臨著同樣的問題。它們的眼睛在土壤中不起作用，所以許多土壤動物甚至都沒有了眼睛。與此相反的是：大多數(shù)的土壤動物會有一個完美無瑕的“鼻子”。例如：線蟲，彈尾蟲和蚯蚓嗅覺都很靈敏（它們靠嗅覺來尋找食物），它們能探測到食物的位置并向著食物的方向移動。線蟲“聞到”50cm以外的細(xì)菌后可在兩周內(nèi)到達(dá)它們的身邊。這對于線蟲而言是相當(dāng)長的一段距離，因為這些小蟲子通常只有幾百微米長（1微米=0.001毫米；作為比較，人類頭發(fā)的寬度是100微米），這就好比人類可以在70km外的地方就能聞到食物的味道！

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!

土壤里不僅漆黑一片，而且是一個迷宮，土壤生物不能在其中自由活動。土壤就像是一塊有著大大小小的孔的海綿。細(xì)菌等較小的生物體一般為1-2微米，可以“躲”在小孔中。例如：我們知道如果細(xì)菌位于小于2-3微米的孔中（見圖1）原生生物是無法抵達(dá)細(xì)菌獵物的。線蟲也是同樣的情況，線蟲不能吃位于小于30微米洞孔中的細(xì)菌（見圖3 A項）。土壤中的洞孔越小，細(xì)菌就越能藏在其中以防止被捕食者發(fā)現(xiàn)并吃掉。但是，盡管存在這些問題，捕食者還是發(fā)展出了捕食策略。例如：變形蟲是具有柔軟身體的原生生物。它的身體可以接受任何形狀的洞口（見圖3B）（就是不管洞口多大，它都可以毫無阻礙地鉆進去。）可以將一條又細(xì)又長的 "手臂"伸進小洞里捕捉隱藏的細(xì)菌。春尾蟲則有一個不同的戰(zhàn)略，它們根本不怎么挑剔它們所吃的食物—它們是食物的“通才”。它們可以吃細(xì)菌和真菌，也可以吃枯葉和線蟲（見圖3C）。這則取決于它們爬行過的土壤中有什么可獲取的東西，（它們可以吃這吃那，毫不挑剔）這種靈活性有助于它們每天都有東西吃。蚯蚓則受土壤中獲取食物的艱難條件影響較小。這些動物直接攝取土壤，使得它們能夠在土壤迷宮中輕松地尋找獲取食物。此外，它們還可以消化細(xì)菌和真菌，以及 隨土壤攝入的植物死物。當(dāng)蚯蚓排便時，那些未被消化的遺留物一般情況下會形成小碗狀的土壤。

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.

動物已經(jīng)進化出克服在黑暗土壤中覓食的困難的方法

(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. 在土壤中的小洞孔為土壤中的小型生物體（線蟲、原生生物和細(xì)菌）提供了一個可躲避被其他動物吃掉的地方。

(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. 為了接近獵物，變形蟲(原生動物的一種)可以伸出一條長20微米、薄1微米的“手臂”來捕捉隱藏在小土洞中的細(xì)菌。

(C)Springtails are flexible in the food sources they consume, allowing them to have something to eat each day.? 春尾魚的食物來源很靈活（不單一），這使得它們每天都有東西吃。

(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蚯蚓在攝取食物的同時也攝取土壤，并消化攝取土壤中的細(xì)菌和真菌。這也為它們在土壤迷宮中創(chuàng)造了一條道路，使它們更容易穿越土壤迷宮。記?。?微米比1毫米小1000倍！

05

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A NEW LOOK INTO FEEDING IN A DARK MAZE（對在黑暗的迷宮中覓食的新看法）

在土壤中覓食就像在黑暗的迷宮里尋找食物。為了理解我們腳下的土壤下黑暗的環(huán)境中是“誰吃誰”，土壤生態(tài)學(xué)家必須充當(dāng)真正的偵探，無論是在森林里還是在實驗室里，都須使用各種復(fù)雜的技術(shù)?，F(xiàn)在你知道在土壤中進食的滋味，你就再也不會用同樣的眼光看待土壤動物了。

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!

來自翻譯者的碎碎念：

? ? 本文中英文加起來足足有6000多字，算是我到目前為止翻譯的最長的一篇文章，真可謂嘔心瀝血。這篇文章是幾位土壤科學(xué)家寫的科普文章，面向?qū)ο笫巧倌陜和Ｎ恼率强茖W(xué)貓頭鷹群里的一個網(wǎng)友推給我的，他跟我說：“我一個成年人讀了之后，都覺得受益匪淺。我想，如果能有人把這樣美好的又有意義的英文文字翻譯成中文，讓廣大中國青少年兒童收益，那真是太有意義了。”當(dāng)我認(rèn)認(rèn)真真讀完這篇文章時，我也不得不承認(rèn)我在此獲取了不少新知識，開闊了自己的視野。

其實現(xiàn)在翻譯或解讀科研、科普、科學(xué)資訊類文章的很多了，那種專門面向少年兒童的真正的科普做的人其實是較少的，而我們青少年兒童正是需要培養(yǎng)科學(xué)實踐與創(chuàng)新的能力，而我如果愿意邁出翻譯的這一步，我或許可以填補這個空缺。在此感謝網(wǎng)友Chattachete給我的建議和指導(dǎo)，感激不盡～

? ? 還有就是這篇文章算是初稿吧，如果精益求精的話文字圖片應(yīng)該改一改的，起碼把英文的改成中文的，但這工程量未免大了些，就拿翻譯文章+拍版而言就花了將近9個小時，而且我還有很多學(xué)業(yè)上的任務(wù)未完成，文?？赡苓€有什么錯漏的地方，等下星期修改后再重新發(fā)一次吧，各位就將就著看吧～

原文出處：https://kids.frontiersin.org/article/10.3389/frym.2020.544803#figure-1

本文章翻譯版權(quán)歸翻譯者小婧所有，轉(zhuǎn)載請完整保留作者及翻譯者的信息