Narrator: Listen to part of the lecture in an environmental science class.

旁白：听一个环境科学的讲座

Professor: Many organisms have developed the ability to survive in harsh environmental conditions: extreme heat or cold, or very dry conditions.

教授：许多生物已经发展了在恶劣环境中生存的能力：酷热、严寒，或者非常干燥的环境。

Like plants in the desert.

比如沙漠中的植物。

Your textbook doesn't have much about the specifics on desert plants, but I think that desert plants are great examples of specialized adaptations to extreme environmental conditions.

你们的教科书中没有很多关于沙漠植物的具体细节，但我认为沙漠植物是能适应极端环境的很好的例子。

So, with desert plants, there are basically three different adaptive strategies.

因此，对于沙漠植物，基本上有三种不同的适应策略。

And I should point out that these strategies are not specific to any particular species.

我应该指出，这些策略并不局限于任何特定的物种。

Many different species have developed each of the adaptations.

许多不同的物种已经发展了其中特有的适应策略。

So, first of all, there are succulent plants.

因此，首先是肉质植物。

There are many different species of succulent plants, but they all can absorb and store a lot of water.

有许多种肉质植物，但他们都可以吸收和储存大量的水。

Obviously, opportunities to get water in the desert are few and far-between.

显然，在沙漠中获得水的机会很少。

Generally rains are light and short.

一般情况下，雨量很少且很短缺。

So the rain doesn't seep too far down into the soil.

所以雨水就不会渗透到土壤深处

And there's a limited window of time for any plant to get the water before it evaporates.

在水分蒸发之前，任何植物获取水分的时间都是有限的。

But succulent plants have a spread-out and shallow root system that can quickly pull in water from the top inches of soil, though the soil has to be saturated since succulents aren't good at absorbing water from soil that's only a little moist.

但是，肉质植物的根系分布广泛且较浅，可以迅速从土壤顶部几英寸处吸收水分， 尽管土壤必须保持湿润，因为肉质植物不擅长从只有一点湿润的土壤中吸收水分。

Succulent plants also are well suited to retaining water, important in an environment where rainy days are rare.

肉质植物也非常适合保存水分， 这在雨天稀少的环境中非常重要。

Succulent plants can store water in their leaves, in their stems, or in their roots.

肉质植物可以将水储存在他们的叶子、茎干和根中。

And to keep that moisture from evaporating in the hot, desert Sun, most succulent plants have a waxy outer layer that makes them almost waterproof when their stomates are closed.

为了防止水分在炎热、干燥的环境中蒸发，大部分肉质植物有一层蜡质外层，使他们在气孔封闭时几乎是防水的。

They also preserve water by minimizing their surface area.

他们也通过最小化表面积来储水。

The more of the plant that's out in the Sun, the more potential there is to lose stored-up water.

植物暴露在阳光下的时间越长，就越有可能丢失其储存的水。

And that means that most succulent plants have few, if any, leaves.

这就意味着大部分肉质植物的叶子都很少。

Now, besides succulent plants, there're also drought-tolerant plants.

现在，除了肉质植物，还有耐旱植物。

Drought-tolerant plants are like bears in a way.

耐旱植物就像熊一样。

You know how bears mostly sleep through the winter.

你们知道熊在冬天大多都是在睡觉。

They can survive without eating because their metabolism slows down.

他们可以不进食生存因为他们的新陈代谢减慢了。

Well, drought-tolerant plants also go into a dormant state when resources, in their case, water, run short.

耐旱植物也会进入休眠状态，当他们的主要资源，也就是水短缺的时候。

A drought-tolerant plant can actually dry out without dying.

耐旱植物实际上在干枯时也不会死掉。

I said before that most desert rains are light and brief, but occasionally there is a heavy one.

我之前说过，沙漠中的雨大都小且少，但是偶尔也会有大雨。

Drought-tolerant plants revive after one of these significant rainfalls.

耐旱植物在一场大雨之后可以重新活过来。

And they are able to absorb a good bit of the rainfall due to their deep roots.

并且由于它们很深的根系，能够吸收大量的雨水

Actually the root system for drought-tolerant plants is more extensive than the root systems of many plants that live in wetter climates.

实际上，耐旱植物的根系比生长在较为湿润的气候中的植物根系更广泛。

Drought-tolerant plants can even absorb water from relatively dry soil because of their deep roots in contrast to succulent plants.

耐旱植物因其深根甚至可以从相对干燥的土壤中吸收水分，这一点和多肉植物不同。

The third adaptive strategy is to avoid the drought conditions altogether.

第三种适应策略是避免所有干旱条件。

Yes! There are plants that do this: Annual plants!

是的！有这样的植物：一年生植物！

An annual plant will mature and produce seeds in a single season that will become the next generation of annual plants.

一年生植物会在的一个季节中成熟，结出种子，种子之后成为下一代的一年生植物。

In desert conditions, annual plants grow in the fall or spring to avoid the heat of summer and the cold of winter.

在沙漠条件下，一年生植物生长在秋天或者春天，以避开夏天的炎热和冬天的寒冷。

Of course, these plants could face a serious problem if a particular fall or spring happened to be very dry.

当然，这些植物可能会遇上一个严重的问题当某个秋天或者春天恰好非常干旱。

They would have difficulty growing and could die before producing seeds.

他们生长会很困难，可能会在结出种子之前死亡。

But they have a mechanism to prevent one year of low rainfall from wiping them out.

但他们有一个机制，以防止在降雨量少的年份灭绝。

Not all seeds an annual plant puts out will grow the following year.

并不是所有一年生植物的种子都在下一年长出来。

Some seeds remain dormant in the ground for several years.

一些种子在地里休眠好几年。

It's a type of insurance that protects the annual plants from a season of poor growing conditions, of unfavorable weather.

这在生长环境恶劣、天气不适宜的季节对一年生植物是一种保障。