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树是怎么在冬天存活下来的?

How do Trees Survive Winter?

化石记录告诉我们,约2.5亿年前,地球上没有一棵树
Fossil records tell us that about 250 million years ago, there wasn’t a tree on Earth designed
为了在低于结冰值的温度中生存。在热带地区,一切都是为了生活而创造。
to survive in temperatures below freezing. They were all built for life in the tropics,
那里温暖,水是流体,叶子全年不落
where it’s always warm, water is always liquid, and leaves are safe year-round without fear
不用担心冰冻
of frost.
如果你把一棵热带树(无论古老或现代)移植到冬天的西伯利亚
If you took a tropical tree (whether ancient or modern) and transported it to Siberia or
或者巴塔哥尼亚它的水会冻结成刀状冰晶体 刺死
Patagonia in winter, its water would freeze into sharp-edged ice crystals, fatally puncturing
它叶子中的所有活细胞 同样的事情也发生在
the living cells in all of its leaves. The same thing that happens to lettuce and spinach
生菜和菠菜冻结时
when it freezes.
寒冷的天气也意味着树中的垂直系统中的水结冰了
Cold weather also means that water in the tree’s plumbing system freezes, and dangerous
冰中从空气来的危险的气泡仓促地溶解在液体水中
bubbles form in the ice from air that was previously dissolved in the liquid water.
冰本身不会引起太大的伤害,但当它融化,泡沫依然存在,这是
The ice itself doesn’t cause much harm, but when it thaws, the bubbles remain, which is
一个严重的问题,因为整个管道系统依赖于水分子内部的吸引力
a problem because the whole plumbing system relies on the inter-molecular attraction of
互相牵拉向上以对抗重力 气泡破坏了
water molecules pulling each other upward against gravity. Air bubbles break the chain
分子链条 从本质上切断了水流
of molecules, essentially shutting off the flow of water.
所以为了在寒冬中生存 树需要避免两件事:他们管道中的气泡
So to survive in cold weather, trees need to avoid two things: bubbles in their pipes
和冰结晶对活细胞的直接伤害
and direct damage to living cells due to ice crystals.
他们甚至在离开热带前就解决了第一个问题 因为气泡
They solved the first problem before ever leaving hot climates, because air bubbles
在干旱时也是个问题当植物努力从土中获得水分时
are also a problem during drought. When plants work harder to get water from the soil, their
他们的导水管道不时从周围组织吸进小气泡
water-conducting pipes can accidentally suck in tiny pockets of air from the surrounding
为了抵抗这个 热带干旱地区的树木进化出更窄的管道
tissue. To combat this, trees in the dry tropics developed skinnier pipes, which, thanks to
多亏了反物理直觉的气泡 使其比热带湿润地区的大容量管道拥有更少的气泡阻隔
the counterintuitive physics of bubbles, develop fewer bubble blockages than the high-capacity
所以适应干旱的祖辈树
pipes of their wet-tropical cousins. So the plumbing of ancestral drought-adapted trees
误打误撞地也提前适应了寒冷 在它们开始
was accidentally pre-adapted to the cold as well, well before they began to spread beyond
传播出热带之前
the tropics.
一到达寒冷地区 树木进化出了两种沿用至今的抵御冰冻的技术:
Upon arriving in cold places, trees then evolved two techniques they still use to avoid frozen
一种是向叶活细胞中填充浓缩糖液
leaves: one is to fill living leaf cells with concentrated sugary sap, a biological version
一种生物版本的防冻液 一些树——大多是常绿松柏类像松树或云杉——用
of anti-freeze. Some trees — mostly evergreen conifers like pines or spruce — use solely
这种技术保护他们的针叶——像用防冻液终年保护叶子不被冰冻
this technique and keep their needle-like leaves unfrozen year-round with a super strong
但是其他种类 像枫树 桦树和落叶松叶子里没有那么浓的糖分
anti-freeze. But other species, like maples and birches and larches, combine a less extreme
通过用在冬季落叶的做法
level of sugar in their leaves with the practice of going leafless during the winter to avoid
以防止叶冻伤
foliar frostbite.
这些技术是应付寒冷的独特改编——好吧 他们曾经
These techniques are uniquely cold-beating adaptations – well, they were, until descendants
直到后代落叶树回到热带干旱地区 在那里它们的这种策略帮助它们
of leaf-dropping trees made it back to the dry tropics, where their strategy helps them
应对发生在季风气候中的延长干旱季节
deal with the extended seasonal droughts that occur in monsoonal climates.
据我们所知 含糖树液仍是在寒冷地区唯一有用的适应方式
As far as we know, sugary sap remains the only adaptation that’s only useful in cold
这就是为什么你要想挖出可以帮助你过冬的甜甜的防冻液
places, which is why you have to come to the north if you want to tap into the sweet, sweet,
就要到北方来 ——我们叫它枫糖浆,而且它很美味
anti-freeze that might just help you survive the winter – we call it maple syrup,and it’s delicious.

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https://www.youtube.com/watch?v=d260CmZoxj8

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