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第1段
1 .<-NARRATOR:->Listen to part of a lecture in a marine biology class.
旁白：听下面一段海洋生物学课上的对话。
第2段
1 .<-FEMALE PROFESSOR:->OK, today we're going to continue our discussion of plant life in coastal salt marshes of North America.
教授：好的，今天我们继续前面关于北美地区海碱沼泽地带的植物的讨论。
2 .Salt marshes are among the least inviting environments for plants.
海碱沼泽是植物最难以生存的环境之一。
3 .The water is salty, there's 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.
那些地方的水盐分含量高，没有遮光物，并且起起落落的潮汐一直使沼泽处于被淹没的状态，所以，海碱地带的植物类型非常的单一。而在这些地方，你们可以发现一种叫做米草属的植物。
第3段
1 .In fact, the spartina genus is the dominant plant found in salt marshes.
事实上，米草属是在海碱地带发现的主要的植物。
2 .You can find one type of spartina, salt marsh cordgrass, growing in low marsh areas.
这个属中，生活在地势低的海碱地带的一般叫做海泽琴弦草。
3 .In higher marsh areas you're likely to find a spartina commonly called salt meadow hay.
生活在地势高的叫做海蒲草。
4 .So how is the spartina able to survive in an environment that would kill most plants?
这样的话，为什么米草属的植物的生活范围能够覆盖所有其他植物不能适应的地带呢？
第4段
1 .Well, it's because salt marsh grasses have found ways to adapt to the conditions there.
嗯，这是因为，这个属的植物通过各种方式适应了海碱地的环境。
2 .First of all, they're able to withstand highly saline conditions.
首先，它们能够承受高度的盐离子。
3 .One really interesting adaptation is the ability to reverse the process of osmosis.
这里涉及到一项非常有趣的适应机能，即逆渗透。
第5段
1 .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.
一般来说，渗透的原理是，当水穿过植物的细胞壁时，是含有盐分低的一方进入到含有盐分高的一方中去。
2 .So, imagine what would happen if a typical plant suddenly found itself in salt water.
所以，同学们可以假设一株一般的植物，突然被放置到盐水中，会发生什么呢？
3 .The water contained in the plant's cells- that's water with very little salt- would be drawn out toward the seawater-water with a lot of salt.
植物中含有的水分的盐含量非常低，所以这些水分就会被吸引到盐分高的海水中去。
4 .So you can see, the freshwater contained in the plant would be removed and the plant would quickly lose all its water and dehydrate.
所以，植物中所含的水分会被移除，我们看到的将会是植物的水分很快丢失，并且很快脱水。
第6段
1 .But, what about the spartinas?
但米草属的植物是怎样的呢？
2 .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.
它们允许一定量的盐进入它们的细胞，使得植物内部的水的含盐量比周围海水的含盐量略高。
3 .So instead of freshwater moving out of the plant's cells, salt from the seawater enters,-reverse osmosis- and this actually strengthens the cells.
这样的话，海水不仅不能抽走它的水分，反而还要进入到它的体内，这就是所谓的反渗透，这种能力增加了细胞的强度。
第7段
1 .Another adaptation to the salty environment is the ability to excrete excess salt back into the environment.
它们适应环境的另一项进化是排除超量盐分的能力。
2 .That's why you might see a spartina shimmering in the sunlight.
这个能力解释了为什么它在阳光下看起来总是闪闪发亮的。
3 .What's reflecting the light is not salt from seawater that has evaporated- although that's a good guess. But it's actually the salt that came from within the plant.
但是，反光的不是海水中蒸发水分而形成的盐结晶，虽然这个想法不错。实际上，反射光的，是植物内部的盐结晶。
4 .Pretty cool, huh?
很酷吧？
5 .You can really impress your friends and family with that little tidbit the next time you're in a salt marsh.
下一次到了海边的沼泽地带，你可以找一两株这样的植物，在你亲朋面前秀一下。
6 .But coping with salt is not the only challenge for plants in a salt marsh. Soil there is dense and very low in oxygen. So spartinas have air tubes.
但是，适应海碱地带过量的盐分并不足以保障他们的生存，因为那儿的泥土非常紧密，而且含氧量极低，所以，大米草还得长出氧气管。
7 .Air enters through tiny openings on the leaves.
空气可以通过叶片上的微小开口进入。
8 .The tubes provide a direct pipeline for the oxygen, carrying it down the leaves, through the stems and into the roots, where it's needed.
而这些管道专门为氧气提供了直接入口，直接从叶面把氧气输送到需要氧气的根部。
9 .If you pull up a spartina, you might even notice some reddish mud on some of the roots.
如果你拔起一株大米草，你甚至还能发现一些粘在根部的红色泥土。
10 .This is caused by oxygen reacting with iron sulfide in the soil and it produces iron oxide, or rust.
这些土壤的颜色是由氧气和土壤中的硫化铁发生反应形成的，这个反应生成氧化铁，俗名铁锈。
第8段
1 .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's yet another aspect of the harsh environment that they've had to adapt to: the force of the tides and occasional violent storms.
当然，尽管大米草适应了咸水的化学和物理方面的各种要求，使它们能够在盐水中茁壮成长，并为它们的根系提供氧气，但依然还存在其他它们需要适应的环境问题，即潮汐的撕扯和飓风的暴力。
2 .Wind and water are constantly crashing into these plants.
风和海水时时刻刻都在抓扯着它们。
第9段
1 .So as you might have guessed, they've developed a means of solidly anchoring themselves into the soil.
所以，正如同学们能够设想到的那样，米草有一种把自己固定在泥土中的本领。
2 .How? Well, they have tough sort of ... uh ...underground stems called rhizomes.
这是怎么做到的呢？它们长出一种叫做地茎的水下根系。
第10段
1 .Rhizomes from one plant grow through the muddy soil and interlock with those of other nearby plants.
一株草的地茎穿透、包围它覆盖的泥土，并且和其他植株的地茎铰链在一起。
2 .The plants form a kind of colony, a community that will survive or perish together, because alone, as single plants, they cannot survive.
形成一种稳固的领地，这样的话，这块领地上的植物就能够相互依托，共谋生存。它们单独在海中是无法存活的。
第11段
1 .Of course, the plants in these colonies also need tough, resilient stems above the soil, stems that can bend a lot but not break as water constantly crashes into them.
当然，这些领地上的植株还需要灵活性良好、能够随意弯折而不断开的分枝。
2 .So in addition to the interlocking underground rhizomes, they have yet another adaptation and it's, well,we're back to reverse osmosis again.
所以，除了相互铰链的地枝外，它们还有另一种进化… 嗯，我们还是回到反渗透吧！
3 .By adjusting the osmotic pressure so that its cells are always fully inflated the plant is able to withstand great pressure before snapping.
通过调节渗透压而保证细胞的饱和状态，大米草从而经受住了海底的巨大压强。
第12段
1 .So spartinas may look like simple marsh grass, but they're 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 would wilt and die within hours.
这似乎使我们觉得米草看上去就是简单的沼泽草类，但实际上，它们是化学物理学和结构工程学等的最佳范式，正是在这些方面独一无二的进化，使它们在别的植物无法忍受的环境中生存甚至兴旺。