Name: 大自然的奧妙！仙人掌是如何在沙漠中生存的？(Nature's fortress: How cacti keep water in and predators out - Lucas C. Majure)
Uploaded: 2022-02-06T21:01:20.000Z
Duration: 4 min 20 s

If you were a jackrabbit hopping through the desert, you'd be glad to stumble — well, maybe not stumble — across a cactus; the succulent flesh of these plants is a water source for many desert animals.

如果你是一隻跳躍穿過沙漠的野兔，你會很慶幸碰到，或許不是真的「碰」到，一棵仙人掌。這些多汁的多肉植物是許多沙漠動物的水分來源。

Native to the Americas and known for their spines and succulent stems, cacti of all shapes and sizes have evolved to not just survive, but thrive, in some of the harshest desert climates on Earth.

仙人掌原產於美洲大陸，因上面的針刺和多汁的莖而聞名。在地球上一些最惡劣的沙漠氣候中，各種形狀及大小的仙人掌不但進化成能夠生存，還能茁壯成長。

A cactus' spines are one key to its survival, but not for the reason you might think.

仙人掌的刺是它的生存關鍵之一，但箇中原因可能和你想得不太一樣。

它的刺是一種高度演化過後的葉子。

A normal leaf's large surface area would be ill-suited to the desert, transpiring massive amounts of water under the baking sun.

一片大表面積的普通樹葉不適用於沙漠之中，因為大量的水分會在烈日下蒸發出去。

The dramatically reduced surface area of the spines limits water loss.

仙人掌刺明顯地減少表面積，以限制水分的流失。

They also shade the cactus and reflect the sun's rays, reducing the plant's core temperature during the heat of the day.

它們同時為仙人掌製造陰影並反射太陽光，藉此在炎熱的白天裡降低仙人掌的果核溫度。

Then, at night, when air temperatures plummet, the spines act as an insulating layer, keeping the cactus from cooling down too much.

然後在夜裡氣溫驟降時，刺能作為保溫層來防止仙人掌過度冷卻。

These functions are just as important, if not more, than defending against predators.

這些功能和預防天敵比起來一樣，或是更加重要。

From Cuba to Mexico, and as far south as Brazil and Peru, Melon cacti grow on limestone soils in seasonally dry tropical forests, where they're constantly exposed to the beating sun.

從古巴到墨西哥，再往南至巴西和秘魯，在有著季節性乾旱的熱帶森林裡，甜瓜仙人掌長在石灰岩中，並不斷被暴露在烈日下。

They rely on another adaptation common to cacti: a thick skin, which is coated in a waxy substance called a cuticle that limits water loss.

它們依賴和其它仙人掌一樣普遍的適應特性：上面覆蓋著一種叫做角質層的蠟，可以限制水分流失。

Meanwhile, the stomata, tiny holes that allow the exchange of gases that enable photosynthesis, remain firmly closed until night when they open.

與此同時，讓氣體交換促成光合作用的的氣孔，則會在夜晚開啟前維持緊閉。

The lower temperatures at night mean the cactus loses less water from the stem when the stomata open.

夜裡氣溫降低，意味著氣孔打開時，仙人掌透過莖流失的水分會減少。

The bulk of the plant acts as a large barrel of water, storing it for times of need.

仙人掌的主體就像一個大水桶一樣，可以把水存起來作為應急。

But to survive the desert, a cactus can't just limit water loss. It has to be prepared to take full advantage of the rare situations where water is readily available.

但要在沙漠中生存，仙人掌不能只是限制水分流失，它在罕見的水分充足情況下還必須做好準備，才能充分利用水分。

In North America's Sonoran Desert, the towering Saguaro cactus can grow up to 20 meters tall and live for up to 200 years.

在北美洲的索諾拉沙漠，高大的巨人柱仙人掌能長到 20 公尺高，最多能活到 200 歲。

Woody tissue, like the kind found in tree trunks, gives the Saguaro its height, but the Saguaro survives with way less water than most trees.

木質似的組織就像樹幹一樣，讓巨人柱仙人掌變高大。但它們依靠比大多樹木還要少上許多的水生存著。

Most of its roots are only a few inches deep.

大部分巨人柱仙人掌的根只有幾英寸深而已。

Just below the soil's surface, they spread out laterally for meters and hold the plant in place.

在土壤層下，從側面看這些根延伸好幾公尺，並將巨人柱仙人掌固定住。

Even its single deepest root, the taproot, extends less than one meter into the ground.

就連它最深的根，也就是主根，往地面下延伸的長度也不會超過一公尺。

After a rain, the lateral roots respond in real time, rapidly growing and spreading.

在下雨過後，它的側根會即時作出反應，快速地生長並延伸出去。

They produce ephemeral rain roots that quickly take up the available water.

這些側根會長出能快速吸收水分的短暫雨根。

The water is then pulled up into the plant body and stored in cells that contain mucilage, a gluey substance that clings to water molecules and stops them from evaporating if the plant's tissue is ever damaged and exposed.

水分會被快速吸入植物體內，並存放在含有黏液的細胞裡。那是一種像膠水的物質，它會吸附在水分子上，並防止它們在植物組織被破壞和暴露的情況下蒸發。

As the soil dries after the rain, the small rain roots also start to dry and wither away, and the cactus awaits the next time it can take advantage of a shower.

土壤在下完雨變得乾燥之後，細小的雨根會開始變乾和枯萎，而仙人掌也得等待下一次利用降雨的機會。

Taken together, these features make cacti well-equipped to survive their environments, from the driest desert to... a tropical rainforest?

總結來看，這些特性讓仙人掌們變得適合在最乾燥的沙漠到熱帶雨林的環境中都能生存？

The mistletoe cactus can live on the branches of trees in the rainforest.

榭寄生仙人掌能夠生存在雨林中的樹幹上。

Though there's lots of water around, not much of it reaches the cactus here, and there's nowhere for its roots to go.

儘管周圍有很多水分，卻很少被這些仙人掌吸收，而且它們的根也沒辦法延伸。

So even here, the cactus survives using adaptations that, long ago, helped its ancestors survive the desert.

所以在這裡，這些仙人掌就能利用它們祖先在沙漠中生存的特性，在雨林中生存。

Other plant adaptations more closely resemble booby traps.

其他植物適應環境的案例比較像是陷阱裝置。

From bed bug harpoons to flyswatters, check out some of the amazing ways plants defend themselves with this video.

從床蝨魚叉到捕蠅草都有，觀看這部影片來看看植物都用了哪些方法來保護自己。

字幕列表影片播放

大自然的奧妙！仙人掌是如何在沙漠中生存的？(Nature's fortress: How cacti keep water in and predators out - Lucas C. Majure)

constantly

massive

thrive

native