脚下那张看不见的网，比全人类加起来还重

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原文与参考译文

We might only think of fungi as the mold in our walls, the fleshy protrusions on rotting logs, or the button mushrooms for sale in the grocery store—but most fungal life takes place far out of human sight.

The "roots" of the fungus under the soil form the organism's mycelium. There, tiny filaments called hyphae form networks among plants and supply them with the essential nutrients they need to grow.

A new study, published today in Science, has attempted to quantify the extent of these hyphae networks. For the first time, scientists have created a global map showing where these types of fungi are most likely to be found.

Using machine-learning models and evidence from thousands of soil cores, scientists also found that a single type of fungus—called arbuscular mycorrhizal fungi—collectively weigh 300 megatons, four to six times the mass of every human on the planet. The tiny hyphal fingers of these networks reach far enough to stretch from Earth to the sun and back nearly a billion times.

"It really challenges the assumption of plants as stand-alone organisms and forces us to think about how organisms are involved in a myriad of interactions that we don't see," says Toby Kiers, a study author and evolutionary biologist at Vrije University in Amsterdam.

"Mycorrhizal symbiosis is a cooperation between plants and fungi that's quite ancient, about 450 million years old," says Justin Stewart, an evolutionary biologist with SPUN, who is also a study author. "You have plants that take carbon dioxide in through photosynthesis, and then they feed this to these bodies of mycelium in soil."

After a fungus receives carbon from a plant, it sends out "thin tubular threads. They're super, super small, a tenth or a twentieth of a human hair." "They go deep into soils and extract nutrients, such as nitrogen and phosphorus, and they trade it back to the plant."

It's such a good arrangement that more than 70 percent of plants partner with arbuscular mycorrhizal fungus—including crops such as wheat, corn, and rice. Fungi can provide up to 80 percent of the phosphorus these plants need, and up to 20 percent of the nitrogen.

In only the top 15 centimeters of soil, scientists estimate that every square centimeter of soil packs around 4.4 meters of hyphae, 50 times longer than the fine roots of the plants they parent with. Stretched end to end, that's 110 quadrillion kilometers, enough to stretch between Earth and the sun nearly a billion times.

The densest networks were in dry grasslands, such as the Tibetan steppe, and flooded grasslands like the Everglades in Florida and the Sudd wetland in South Sudan. Grassland areas alone made up 40 percent of the global hyphae biomass.

Where those grasses had been converted to croplands, the arbuscular mycorrhizal network was 47 percent less dense than naturally occurring grasslands.

The mass of fungal bodies in soil is more than just living matter. As hyphae die, the carbon they absorbed from plants stays underground. Kiers, Stewart, and their colleagues estimate that fungi help pack around four billion tons of carbon dioxide into soil. That's about 11 percent of the carbon dioxide humans pump into the atmosphere in a year.

"They are the circulatory system of the planet underground," she says. "We're starting to realize that we cannot diagnose, treat, or heal the ailments of Earth without looking at the mycorrhizal circulatory system."

核心词汇

长难句语法拆解

Using machine-learning models and evidence from thousands of soil cores, scientists also found that a single type of fungus—called arbuscular mycorrhizal fungi—collectively weigh 300 megatons, four to six times the mass of every human on the planet.

• Using machine-learning models and evidence from thousands of soil cores：现在分词短语，作状语，修饰主句动作，说明研究手段（使用机器学习模型 + 数千个土壤岩心证据）
• scientists：主语（S）
• also found：谓语（V），found 后接宾语从句
• that a single type of fungus collectively weigh 300 megatons：宾语从句（O），that 引导，a single type of fungus 是从句主语，weigh 是从句谓语
• —called arbuscular mycorrhizal fungi—：两个破折号夹住的插入语，对 a single type of fungus 进行补充说明（= which is called arbuscular mycorrhizal fungi）
• four to six times the mass of every human on the planet：同位语，补充说明 300 megatons 的量级含义（300 megatons 是全球人类总体重的 4-6 倍）

"They go deep into soils and extract nutrients, such as nitrogen and phosphorus, and they trade it back to the plant."

• They go deep into soils：主语（S）+ 谓语（V）+ 副词短语，描述菌丝深入土壤的动作
• and extract nutrients：并列谓语，与 go deep... 并列，省略主语 They
• such as nitrogen and phosphorus：插入的列举短语，举例说明 nutrients 的具体内容（氮和磷）；注意 such as 后的例子不能穷举，若穷举应用 namely
• and they trade it back to the plant：第二个并列分句，they 是主语，trade 是谓语，it 指代前文提到的 nutrients