未登录,请登录后再发表信息
最新评论 (0)
播放视频

一棵树能长多高?

How tall can a tree grow? - Valentin Hammoudi

Trees are poems that the earth writes upon the sky–Kahlil Gibran
树木是大地写给天空的诗——纪伯伦
Reaching heights of over 100 meters,
由于高度达百余米
Californian sequoias tower over Earth’s other estimated 60,000 tree species.
加州红衫比地球上其他约六万个树种都高
Growing in the misty Sierra Nevada mountains,
生长于雾蒙蒙的内华达山脉
their massive trunks support the tallest known trees in the world.
它们粗大结实的树干能支撑起世界最高的树
But even these behemoths seem to have their limits.
但是即使是这样的“巨兽”也有生长极限
No sequoia on record has been able to grow taller than 130 meters –
有记录以来 没有哪一棵红衫有超过130米
and many researchers say these trees won’t beat that cap
且许多研究者表示加州红衫不能突破这个极限
even if they live for thousands of years to come.
即使它们再长个千万年也不行
So what exactly is stopping these trees from growing taller, forever?
所以 究竟是什么 永远地 在限制它们长高
It all comes down to sap.
这一切都归结于树汁
In order for trees to grow,
为了树木的生长
they need to bring sugars obtained from photosynthesis
树汁需要把从光合作用中获得的糖分和
and nutrients brought in through the root system to wherever growth is happening.
从根系吸收的营养带到任何正在生长的地方
And just like blood circulates in the human body,
就像人体的血液循环
trees are designed to circulate two kinds of sap throughout their bodies –
树木需要在全身循环两种液体
carrying all the substances a tree’s cells need to live.
它们能携带树木细胞生存所需的所有物质
The first is phloem sap.
第一种是韧皮部树汁
Containing the sugars generated in leaves during photosynthesis,
它含有光合作用过程中叶片产生的糖
phloem sap is thick, like honey,
韧皮树汁很粘稠 类似于蜂蜜
and flows down the plant’s phloem tissue to distribute sugar throughout the tree.
汁液沿着植物韧皮部组织向下流动 将糖分配到整颗树木
By the end of its journey,
在旅程的终点
the phloem sap has thinned into a watery substance,
韧皮汁液已经稀释成水状物质
pooling at the base of the tree.
聚集在树的底部
Right beside the phloem is the tree’s other tissue type: the xylem.
韧皮部之下是树的另一种组织:木质部
This tissue is packed with nutrients and ions like calcium, potassium, and iron,
这种组织富含树木从根系吸收的
which the tree has absorbed through its roots.
营养物质和离子 如钙 钾和铁
Here at the tree’s base,
这里是树的底部
there are more of these particles in one tissue than the other,
木质部的小分子比韧皮部的多
so the water from the phloem sap is absorbed into the xylem
所以水会从韧皮部流向木质部
to correct the balance.
以纠正平衡
This process, called osmotic movement,
这个过程叫做渗透运动
creates nutrient-rich xylem sap,
富含营养的木质部汁液产生之后
which will then travel up the trunk to spread those nutrients through the tree.
汁液沿着树干向上把这些营养物质分配到整颗树
But this journey faces a formidable obstacle: gravity.
但这个过程面临一个强大的阻碍:重力
To accomplish this herculean task, the xylem relies on three forces:
为了完成这项艰巨的任务 木质部依靠了三种力量:
transpiration, capillary action, and root pressure.
蒸腾作用 毛细作用和根压
As part of photosynthesis, leaves open and close pores called stomata.
作为光合作用的一部分 叶片会打开和关闭气孔
These openings allow oxygen and carbon dioxide in and out of the leaf,
这些气孔允许氧气和二氧化碳进出叶片
but they also create an opening through which water evaporates.
同时水分也会在这里蒸发掉
This evaporation, called transpiration,
这种蒸发称为蒸腾作用
creates negative pressure in the xylem, pulling watery xylem sap up the tree.
蒸腾作用在木质部产生负压 将木质部汁液向上拉
This pull is aided by a fundamental property of water called capillary action.
这种牵引借助于水的一种基本性质–毛细作用
In narrow tubes,
在狭窄的管道中
the attraction between water molecules
水分子之间的吸引力
and the adhesive forces between the water and its environment can beat out gravity.
以及水与环境之间的粘附力可以战胜重力
This capillary motion is in full effect in xylem filaments
这种毛细管运动在比人的发丝还细的
thinner than human hair.
木质部细丝中是完全有效的
And where these two forces pull the sap,
而在这两种力牵引树汁的情况下
the osmotic movement at the tree’s base creates root pressure,
树基的渗透运动产生根压
pushing fresh xylem sap up the trunk.
把新鲜的木质部汁液推向树干
Together these forces launch sap to dizzying heights,
这几种力一起将树汁推向令人眩晕的高度
distributing nutrients and growing new leaves to photosynthesize
分配营养物质 促进叶片在距离树根很远的地方
far above the tree’s roots.
进行光合作用
But despite these sophisticated systems,
尽管有这些复杂的系统
every centimeter is a fight against gravity.
但每一厘米的攀登都是一场艰巨的重力对抗战
As trees grow taller and taller,
树越长越高
the supply of these vital fluids begins to dwindle.
维持生存所需的液体的供应却越来越少
At a certain height,
到了一定高度
trees can no longer afford the lost water that evaporates during photosynthesis.
树木再也不能提供光合作用过程蒸发所需的水分
And without the photosynthesis needed to support additional growth,
而额外增长所需的光合作用一旦停止
the tree instead turns its resources towards existing branches.
树就会把资源转向现有的枝干
This model, known as the “hydraulic limitation hypothesis,”
这个被称为“水力极限假说”的模型
is currently our best explanation for why trees have limited heights,
是目前我们对树木生长极限最好的解释
even in perfect growing conditions.
包括那些拥有完美生长条件的树木
And using this model alongside growth rates
结合植物的生长速率
and known needs for nutrients and photosynthesis,
并了解光合作用所需的营养再套用这个模型
researchers have been able to propose height limits for specific species.
研究人员已经能够测算出特定植物的极限高度
So far these limits have held up –
到目前为止这些 这个假说仍然经受得住考验
even the world’s tallest tree still falls about fifteen meters below the cap.
即使是世界上最高的树 也比其极限高度矮15米左右
Researchers are still investigating the possible explanations for this limit,
研究人员仍在探索树木生长极限的其他可能的解释
and there may not be one universal reason why trees stop growing.
树木停滞生长可能没有一个普遍认可的原因
But until we learn more,
但就目前我们所知的
the height of trees is yet another way that gravity,
树木的高度是重力塑造
literally, shapes life on Earth.
地球生命的另一种方式

发表评论

译制信息
视频概述

研究人员提出“水力限制假说”来解释为什么树木有其生长极限

听录译者

收集自网络

翻译译者

w星野

审核员

审核员SRY

视频来源

https://www.youtube.com/watch?v=vvtPJKWUb2g

相关推荐