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树过冬的三种极端方式 – 译学馆
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树过冬的三种极端方式

3 Extreme Ways Trees Survive the Winter

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[音乐]
Living through a cold winter is not easy — for any of us living things.
对于任何一种生物来说 过冬不是件容易的事
Our cells just don’t do well in the freezing cold.
因为我们的细胞在寒冷中不能很好地生存
Animals that live in cold climates have all kinds of adaptations
而生活在寒冷中的动物有各种方法
to keep themselves alive when it’s freezing.
使它们在寒冷中生存下来
Bears hibernate; seals have plenty of blubber;
例如熊可以冬眠;海豹有大量的鲸脂;
humans seek shelter and wear clothing and shoes.
人类可以通过寻找庇护所和穿衣服鞋子来御寒
But plants in cold climates also need ways to get themselves through the winter.
但生长于寒冷气候的植物也需要通过各种方法过冬
And they don’t really have the option of blubber — or shoes, for that matter.
而且它们没有像鲸脂和鞋子之类的东西
Many plants just die every winter and regrow in the spring.
许多植物每年冬天死亡 春天重新生长
But trees are too big to regrow every year.
但是树太大了 并不能每年重新生长
So, to get themselves to spring, they have other, stranger adaptations.
所以为了能看到春天 它们有其他奇怪的方法
Including, in some cases, turning themselves into glass.
例如在某些情况下 它们会把自己变成玻璃态
The problem begins when the temperature falls
当树细胞中的水温降到冰点以下
below the freezing point of the water in a tree’s cells
这种情况就会发生
which normally happens at 0 degrees Celsius.
一般发生在零摄氏度
Water expands when it freezes, and if that’s allowed to happen inside a cell,
水结冰膨胀 而如果发生在细胞内
ice crystals can pierce through the cell’s membranes.
冰晶就会穿透细胞膜
Which is not great!
这可就不妙了!
In fact, it kills the cell.
事实上 这等于杀死细胞
Luckily for trees
而树很幸运
ice only forms inside their cells when the temperature drops
因为只有气温骤降到冰点以下时
below freezing very suddenly.
细胞内液体才会结冰
When it falls more gradually — which is what usually happens as winter approaches
而当气温像正常冬天一样逐渐下降时
ice tends to form in the spaces between the cells,
细胞之间的空隙会结冰
in a process called extracellular freezing.
这个过程叫做细胞外冻结
As the temperature slowly falls
随着气温逐渐降低
ice forms on the outside of the tree’s cell walls
在细胞内温度达到结冰之前
before the inside of the cell gets cold enough to freeze.
细胞壁外层就已经结冰了
Then, once there’s some ice between the cells,
一旦细胞之间结冰
the water inside the cells does something weird.
细胞内的水分会做一件奇怪的事情
It flows outward toward the ice.
水分会从内向外流至冰层
That movement is because of a property known as chemical potential.
这种运动是因为一种名为化学势的性质
As a general rule
一般来说
substances move from areas with higher chemical potential
就是物质会从化学势高的地方
to areas with lower chemical potential.
向化学势低的地方运动
And because of the way its molecules are arranged
而且由于分子排列的方式
ice has a lower chemical potential than the liquid inside the cell.
冰的化学势比细胞内水的化学势低
So the water inside the cell moves toward the ice outside the cell and freezes there,
所以细胞内的水流向细胞外后结冰
instead of freezing inside the cell and destroying it.
而不在细胞内结冰之后破坏细胞
Great!
太棒了!
Problem solved!
问题解决了!
Except, there’s more to surviving in the winter
但是为了能在冬天生存
than just keeping your cells from rupturing.
仅仅防止细胞破裂还不够
I mean, pretty much all plants undergo extracellular freezing
我的意思是 无论耐寒与否
whether they’re cold-tolerant or not.
几乎所有的植物都要经历细胞外冻结
But not all of them survive the process.
但并不是所有的植物都存活下来
See, the water moving out of the cells causes another problem: dehydration.
比如说 水流向细胞外会导致另外一个问题:脱水
Dehydration is bad for all kinds of reasons, but for trees,
出于各种原因 脱水并没有益处 但对于树来说
the main danger is that as a cell shrinks from water loss
主要危害是随着细胞失水皱缩
its cell membranes can move close enough together to react.
细胞膜靠得更近足以发生反应
That can tear the membranes apart and is generally just not a good idea.
从而撕裂细胞膜 这样并不好
So, trees that are good at surviving cold temperatures have a whole bunch of different strategies
所以 冬天存活的树有各种各样的措施
to avoid this dehydration problem.
来避免脱水问题
One of the most common techniques they use is called supercooling.
其中最常见的一个技巧叫做过度冷却
That’s what happens when water falls below the temperature where it would normally freeze
这是指当水温降到通常会导致结冰的温度以下时
but stays liquid.
却依然保持液态
There are a few reasons a liquid might not freeze at its normal temperature, but for
有一些理由用于解释为何液体没在通常温度下结冰
trees’ cells, the thickness of the liquid inside them
但对于树细胞来说 细胞内液体浓度
also known as viscosity, is one of the main ones.
也就是粘度 是重要原因之一
This liquid gets thicker during extracellular freezing, as water is drawn from the cell
细胞外冻结时 细胞内液体浓度变高 因为水流出细胞
and leaves behind a thicker concentration of dissolved substances.
使细胞内留下浓度更高的溶液
The thicker the liquid, the harder it is for ice crystals to begin forming,
液体浓度越高 则冰晶越难形成
and the more it can be supercooled.
且越容易过度冷却
As temperatures fall, trees that use supercooling also start producing more of certain molecules,
随着温度下降 过度冷却的树开始产生一些分子
like sugars, that make the liquid inside them even thicker.
例如糖 它可以使液体浓度更高
You might be familiar with this liquid.
你可能认识这种液体
We call it sap.
我们称之为植物的汁液
With supercooling,
在过度冷却中
trees can avoid getting too dehydrated by extracellular freezing
树可以通过细胞外冻结避免过多失水
and hold more liquid inside their cells without it freezing into ice.
并且在细胞内保存更多液体却不会结冰
The combination of extracellular freezing and supercooling can keep trees alive through
细胞外冻结和过度冷却的组合
temperatures as low as -40 degrees Celsius.
可以让树存活于零下四十度的环境中
But around -40 or -50 degrees, supercooling backfires.
但在零下四五十的环境中 过度冷却会使之适得其反
At a certain point, it doesn’t matter what you do to try to keep ice crystals from forming
到了某一个温度点后 用何种方式试图阻止其结冰已无关紧要
— all of the liquid will just spontaneously freeze.
因为所有的液体都会自然结冰
And if a tree’s cells still have a bunch of liquid inside them
并且如果一棵树的细胞内仍有大量液体
a sudden freeze is very much a death sentence.
则温度骤降就给这棵树判了死刑
Luckily, for the vast majority of the world’s surface, this limit isn’t important.
幸运的是 对于地球表面大部分生物而言 这种极限温度并不重要
Protection down to -40 degrees is more than enough.
零下四十度的保护已经绰绰有余
But that’s not true everywhere.
但并不是所有情况都是这样
In some places — like in the Arctic — normal winter temperatures fall as low as -60 degrees Celsius.
在一些地区 例如北极 正常的冬季温度可低至零下六十度
And there are still trees that live there!
但仍有许多树存活!
In fact, there are plenty of trees, like the black locust, white pine, and northern white cedar,
事实上 这里有很多种树 像刺槐 美国五针松 还有北部白雪松
that can survive being submerged in liquid nitrogen — a temperature of -196 degrees Celsius.
它们能在零下196度的液氮中生存
And some trees, like the Japanese white birch,
其他的树 例如日本白桦树
can survive exposure to liquid helium, which is -269 degrees Celsius.
能在-269度的液氦中存活
Not that they’d ever encounter that in the wild.
并不是说它们在野外遇到这种情况
But, you know.
但是你知道的
Sometimes, you’ve got a tree and a bunch of helium,
有时候 当你得到了一棵树和一瓶液氦
and one thing leads to another… Anyway.
你就会想做一些其他事情…
These trees don’t survive those temperatures through supercooling.
这些树并不能在这种温度下通过过度冷却存活
Instead, the insides of their cells turn into glass,
而是通过一种名为玻璃化的过程
in a process known as vitrification.
使细胞内部变为玻璃态
Researchers describe it as a kind of suspended animation
研究人员把它描述为一种假死状态
where molecules don’t really move.
也就是分子不能运动
Normally, ice spreads as crystals of ice come in contact with other molecules.
通常来说 冰晶通过连接其他分子之后形成冰
But if the molecules aren’t moving, they’re not reacting with each other, either.
但如果分子不能运动 它们也就不能相互反应
We don’t yet know the exact mechanism that leads to this vitrification,
我们至今也不知道导致玻璃化的确切化学机制
but researchers think it’s helped along by high concentrations of sugars in the tree’s cells,
但研究人员认为细胞内高浓度的糖以及脱水蛋白
along with proteins called dehydrins.
有助于这一过程
These proteins seem to bind themselves to the cell’s membranes
这些蛋白质看起来像是结合在细胞膜上
keeping them apart from each other.
这使得这些蛋白质之间彼此分开
Meanwhile, other parts of the proteins might tangle with the sugars in the cell,
同时 这些蛋白质的其他部分可能与细胞中的糖结合
helping arrange them into a glassy state.
帮助它们形成玻璃态
Once the tree’s cells turn into glass, it doesn’t really matter how cold it gets.
一旦树细胞变成玻璃态 无论外界环境多冷都不重要了
They’re essentially preserved in a way that keeps the cells from being damaged,
细胞已经处于一种被保护且不被伤害的状态了
so whenever it does warm up again, they can pretty much get back to normal.
所以无论温度何时升高 细胞总能恢复正常
Which I kind of wish I could do during winters here in Montana,
这就像我想在蒙大纳的冬天做的事情
but as far as I know, humans still can’t turn themselves into glass.
但至少我知道 人类并不能把自己变成玻璃态
So, a coat and boots it is, I guess.
所以 我猜我只能穿大衣和靴子了
But even if you’re out there shivering through winter like me,
但即使你在冬天的屋外冻的瑟瑟发抖
you’ve got to admire trees
你也必须尊敬这些树
and their ingenious tricks for making it through the cold.
和它们过冬的巧妙技巧
Thanks for watching this episode of SciShow!
感谢收看本期科学秀!
And if you want to find out about even more reasons why trees are amazing,
如果想了解更多树的神奇之处
you might like this video about
你可以看这个视频:
how trees use underground networks to communicate with each other.
树怎样通过地下网来相互联系
You can watch that one right after this.
你可以看完这个视频后再看另一个
♪♪♪
[音乐]

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