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Narrator:Listen to part of a lecture in a marine biology class.
獨白:聽下面一段海洋生物學課上的對話。
Professor:Ok, today we are going to continue our discussion of plant life in coastal salt marshes of North America.
教授:好的，今天我們繼續前面關于北美地區海堿沼澤地帶的植物的討論。
Salt marshes are among the least inviting environments for plants.
海堿沼澤是植物最難以生存的環境之一。
The water is salty, there is little shade and the ocean tide comes in and out, constantly flooding the marsh, so the variety of plants found in salt marshes is limited, but there is a plant genus that thrives there, the Spartina.
那些地方的水鹽分含量高，沒有遮光物，并且起起落落的潮汐一直使沼澤處于被淹沒的狀態，所以，海堿地帶的植物類型非常的單一。而在這些地方，你們可以發現一種叫做米草屬的植物。
In fact, the Spartina genus is the dominant plant found in salt marshes. You can find one type of the Spartina, Saltmarsh Cordgrass, growing in low marsh areas. In higher marsh areas, you are likely to find a Spartina commonly called Salt-meadow Hay.
這個屬中，生活在地勢低的海堿地帶的一般叫做海澤琴弦草，生活在地勢高的叫做海蒲草。
So how is the Spartina able to survive in an environment that would kill most plants?
這樣的話，為什么米草屬的植物的生活范圍能夠覆蓋所有其他植物不能適應的地帶呢？
Well, it is because salt marsh grasses have found ways to adapt to the conditions there.
嗯，這是因為，這個屬的植物通過各種方式適應了海堿地的環境。
First of all, they are able to withstand highly saline conditions.
首先，它們能夠承受高度的鹽離子。
One really interesting adaptation is the ability to reverse the process of osmosis.
這里涉及到一項非常有趣的適應機能，即逆滲透。
Typically, the process of osmosis works... Well, when water moves through the wall of a plant cell, it will move from the side containing water with the lowest amount of salt into the side containing the highest amount of salt.
一般來說，滲透的原理是,嗯，當水穿過植物的細胞壁時，一般來說，是含有鹽分低的一方進入到含有鹽分高的一方中去。
So imagine what would happen if a typical plant suddenly found itself in salt water, the water contained in the plant cells, that is water with very little salt would be drawn out toward the seawater, water with a lot of salt.
所以，同學們可以假設一株一般的植物，突然被放置到鹽水中，會發生什么呢？植物中含有的水分的鹽含量非常低，所以這些水分就會被吸引到鹽分高的海水中去。
So you can see the fresh water contained in the plant will be removed and the plant will quickly lose all its water and dehydrate.
所以，我們看到的將會是植物的水分很快丟失，并且很快脫水。
But what about the Spartinas, well, they allow a certain amount of salt to enter their cells, bringing the salt content of the water within the plant, to a slightly higher concentration than that of the surrounding seawater.
但米草屬的植物是怎樣的呢？它們會允許一部分海水進入它們的細胞，從而把鹽分帶入到植物中，形成一個比周圍海水含鹽度更高的鹽溶液。
So instead of fresh water moving out of the plant cells, salt from the seawater enters, reverse osmosis, and this actually strengthens the cells.
這樣的話，海水不僅不能抽走它的水分，反而還要進入到它的體內，這就是所謂的反滲透。這種能力增加了細胞的強度。
Another adaptation to the salty environment is the ability to excrete excess salt back to the environment.
它們適應環境的另一項進化是排除超量鹽分的能力。
That's why you might see a Spartina shimmering in the sunlight.
這個能力解釋了為什么它在陽光下看起來總是閃閃發亮的。
What's reflecting the light is not salt from seawater that has evaporated, although that's a good guess.
但是，反光的不是海水中蒸發水分而形成的鹽結晶，雖然這個想法不錯。
But it is actually the salt that came from within the plant. Pretty cool, eh?
實際上，反射光的，是植物內部的鹽結晶。很酷吧？
You can really impress your friends and family with that little? The next time you are in a salt marsh.
下一次到了海邊的沼澤地帶，你可以找一兩株這樣的植物，在你親朋面前秀一下。
But coping with salt is not the only challenge for plants in the salt marsh.,soil there is dense and very low in oxygen,
但是，適應海堿地帶過量的鹽分并不足以保障他們的生存，因為那兒的泥土非常緊密，而且含氧量極低，
so Spartinas have air tubes, air enters through tiny openings on the leaves, the tubes provide direct pipe line for oxygen, carrying it down the leaves through the stems and into the roots, where it is needed.
所以，大米草還得長出氧氣管，空氣可以從這些管道的微笑開口透入；而這些管道中專門為氧氣提供了直接入口，直接從葉面把氧氣輸送到需要氧氣的根部。
If you pull up a Spartina, you might even notice some reddish mud on some of the roots, this is caused by oxygen reacting with iron sulfide in the soil, and it produces iron oxide or rust.
如果你拔起一株米草屬，你甚至還能發現一些粘在根部的紅色泥土，這些土壤的顏色是由氧氣和土壤中的硫化鐵發生反應形成的，這個反應生成氧化鐵，俗名鐵銹。
Now, although the Spartinas have adapted several chemical and physical mechanisms that allow them to thrive in salt water and to feed oxygen to their roots. There is yet another aspect of the harsh environment that they have to adapt to, the force of tides and occasional violent storms.
當然，盡管大米草適應了咸水的化學和物理方面的各種要求，依然還存在其他它們需要適應的環境問題，即潮汐的撕扯和颶風的暴力。
Wind and water are constantly crashing into these plants.
風和海水時時刻刻都在抓扯著它們，
So as you might have guessed, they have developed a means of solidly anchoring themselves into the soil. How?
所以，正如同學們能夠設想到的那樣，大米草有一種把自己固定在泥土中的本領。這是怎么做到的呢？
They have tough sort of underground stems called rhizome, rhizomes from one plant grow through the muddy soil and interlock with those of other nearby plants, the plants form a kind of colony, a community that will thrive and perish together.
它們長出一種叫做地莖的水下根系，一株草的地莖穿透、包圍它覆蓋的泥土，并且和其他植株的地莖鉸鏈在一起，形成一種穩固的領地，這樣的話，這塊領地上的植物就能夠相互依托，共謀生存。
Because alone as single plants, they cannot survive.
它們單獨在海中是無法存活的。
Of course the plants in these colonies also need tough resilient stems above the soil, stems that can bent a lot but not break as water constantly crashes into them.
當然，這些領地上的植株還需要靈活性良好、能夠隨意彎折而不斷開的分枝。
So in addition to the interlocking underground rhizomes, they have yet another adaptation, and it is ... well,
所以，除了相互鉸鏈的地枝外，它們還有另一種進化…
we are back to reverse osmosis again, by adjusting the osmotic pressure so that the cells are always fully inflated, the plant is able to withstand great pressure before snapping, so Spartinas may look like simple marsh grass,
嗯，我們還是回到反滲透吧！通過調節滲透壓而保證細胞的飽和狀態，大米草從而經受住了海底的巨大壓強。這似乎使我們覺得大米草看上去就是簡單的沼澤草類，
but they are really a wonder of chemistry, physics and structural engineering that allows them to survive and even thrive in an environment in which most other plants will wilt and die within hours.
但實際上，它們是化學，物理學和結構工程學等的最佳范式，正是在這些方面獨一無二的進化，使得它們能夠在別的植物無法忍受的環境中生存，甚至興旺。
