The Taklamakan Desert（塔克拉玛干沙漠） in Norther China. 

(相关资料图)

A constantly shifting landscape of sand. Temperatures that swingfrom minus 20 to more than 40 degrees Centigrade. And most critically, almost entirely without rain.

Yet, here on the dunes, the Euphrates polar tree（胡杨）.

And it's not alone.

Some of these trees have lived here for a thousand years. They have exceptionallylong roots with which to collect water, and what is more, those roots are connected to neighboringtrees, so that if one strikeswater, others can share it.

strike此处： to discover a supply of oil, gas, or gold underground

In every desert across the planet, plants have found ways tonot only survive, but flourish.

Desert Worlds

This is the Gran Desiertoof Mexico and the United States.

These dunes may appear to be totally barren, in fact, they arefull of life. In the sand beneath my feet, there are seeds of many different kinds. In fact, you could say the dune itself is one great seed bank, and when it rains, it bursts with life.

But rain may come only once a decade, and even then, the long awaited storm may be very brief. So seeds must respond immediately.

This is sand verbena（沙地马鞭草）, it can grow from a seed to a sweetly scentedflowering plant in just a few weeks.

Primroses（沙丘月见草） and many other plants soon join the race to flower beforethe sand dries.

Desert blooms like this, however, are rare.

This is the first year for 20 years.

The combination of vibrantcolour and powerful scent attracts migrating pollinators such as these painted lady butterflies（小红蛱蝶） which fly into the middle of what were only recently barren dunes.

vibrant: Vibrant colour or light is bright and strong 

Everything is rushing to complete their lives before the moisture has gone.

Such spectacular blooms transform deserts all around the world.

From the Atacama in South America...

to the dusty plains of Southern Africa.

Rain in deserts, however, never last long, and all to soon, the flowers wither and die. But not before they've produced the next generation.

The seeds that will now wait in the sand for the next rains.

In the Sonoran desert（索诺拉沙漠） of North America, the huge saguaro cacti（巨人柱） have a different strategy. They store water in quantity and canlive to a great age, but in their early years, they are extremely vulnerable.

This little saguaro cactus is about 10 years old. When they're really small and growing out in the open, there's a real chancethey may shrivel up and die. But this one has been lucky. It's been growing in the shade of this mesquite tree（牧豆树）andit's got a very good chanceof surviving to maturity.

shrivel up: 干枯，枯萎

The young saguaro is protected by the mesquites branches. Theyhalvethe amount of scorching sunlight reaching the cactus（仙人掌） and so keep it cool. And the mesquites extremely long roots draw up water, bringing it within reach of the young saguaro. So the mesquite is known as a nurse plant, and a very effective one it is too.

In fact, this particular mesquite has already nurturedseven young saguaros over the past 30 years.

As a young cactus grows, it needs the protection of its nurse plant, not only from the heat, but from the other harzardsof desert life.

Temperatures can drop to minus 10 degrees overnight and, very occasionally, it even snows. If the waters stored inside the young cactus freeze, the cactus will die. 

But the nurse plant trapsa blanket of slightly warmer air around it, just enough to keep it alive.

Eventually, saguaros outgrowtheir nurses, but by that time, they are robust enough to face the elements by themselves.

No matter how old a desert plant is, water is always precious. Whether gathered from the melting snow, or a shower of rain.

So cacti have developed extraordinary adaptations that enable them to not only collect water, but toretainit. Instead of leaves which would lose precious moisture through evaporation, they have spines.

Each spine has a tiny padded-in space where the water is absorbed and then stored in the great swollentrunk. A large saguaro could hold 5,000 litres of water, and is able to do so because it has another special adaptation.

pad: to put pieces of soft material in something to make it soft, give it a different shape, or protect what it is side 

Theridgeson its surface are like thepleats on anaccordion（手风琴）, they allow the saguaro to change its shape. After the rain has fallen, the pleats expand and the saguaro fills up its water tank. In the dry times, it uses its water to grow, produce flowers, and eventually, seeds.

pleat: a narrow fold in a piece of cloth made by pressing or sewing two parts of the cloth together

Fully loaded with thousands of litres of water, the saguaro won't need to drink a single drop for another year. But such valuable stores of water attract thieves.

Now the spines funtion changes from collection to guarding. The spines of some species are a quarter of a metre long. Others are needle-likebarbs（倒刺） that grow in clusters and easily break off in the skin of any animal that touches them.

But perhaps the most vicious cacti belong to a group called the chollas（多刺仙人掌）.

This is called a teddy bear cholla, because the thick coating of spines on it, but don't be deceivedby the name, there is nothingcuddly about this paticular teddy bear. In fact, it's the most dangerous plant in the desert and I wouldn't dream of putting my hand anywhere near it without proper protection.

coating: a layer of a particular substance that covers a surface

cuddly: liking to cuddle, or making you want to cuddle

Brush against it, this could happen... Ouch. This can happen even with this glove on. One of them had just gone through, I can feel it. It's quite painful.

brush(v.): to touch (something) quickly and lightly or carelessly

Look losely at a spine and you can see very clearly why they're so dangerous. Each is like a splinterof glass, sharp enough to pierce flesh and they're covered with backward pointed barbs.

splinter: a small, sharp, broken piece of wood, glass, plastic, or similar material

So getting them out with a pair ofpliers（钳子） is quite hard. This is not pleasant at all and it won't come off without... Oh, look at that!

It's hard to imagine a more aggressive defence than this and it makes both the plant and its bud virtually invulnerable.

Most animals know to keepclear. Cholla buds grow like tiny barrels from the top of the adult plant and then drop off.

clear: not touching something, or away from something

If the young cholla put down roots here, it would compete with its parent for water.

Night falls...and this one is on the move.

A packrat（白喉林鼠）.

She knows how to deal with a cholla. She avoids the spines bygrippingit at the place where it broke off from its parent. And she works fast.

grip: to hold very tightly

There are packrat hunters here.

She uses the cholla to build a spiny wall around her nest. The flesh of the cholla supplies her with water and the severed spines further reinforce the defences.

This cholla bud might be next, but one accidental nudgeand it escapes.

The bud starts to put down roots, so the cholla, thanks to the packrats finds new territory and sets aboutclaiming it.

set about: 开始做某事

Few plants deal with the problems of desert living better than cacti. There are almost 2,000 different species of them, they're spread across the deserts of the American west from Arizona all the way to Mexico and beyond.

In south America, the ice covered peaks of the Andes（安第斯山脉） act as a rain barrier, beyond which lies the world's driest desert, the Atacama（阿塔卡马沙漠）.

In the desert world, water thieves can come in many forms to exploit even the smallest chinkin the plants defence.

chink: a small narrow crack or opening

One of the strangest travels within thegut（内脏，肠子） of a fruit-eating mockingbird（小嘲鸫）. These are the seeds, the Tristerix（桑寄生科）, a kind of mistletoe（仙钗寄生）.

Their goal is the water inside this hedgehog（刺猬）cactus.

Using the spines as anchors, the seeds start to germinate. Each produces a long probe with which to try and locate the cactus's skin. For most, that's a stretchtoo far and they perish. But for this one, the cactus's surface is within reach.

stretch: a continuous area of land or water

perish: to die, especially in an accident or by being killed, or to be destroyed

Itclamps on to it with a special sucker（吸盘） and then waits for darkness. At night, the cactus opens its pores in order to respire. Oxygens goes out, carbon dioxide goes in. And so does tristerix...

clamp: to fasten two things together, using a clamp

Once within, its tissues spread throughout the body of the cactus, sustained by the precious store of water that they find there.

Then, a year later, it breaks through the cactus's skin and bursts into flower.

Hummingbirds（蜂鸟） come to drink their nectarand pollinate them as they do so.

And then, to complete the cycle, Tristerix produces thousands of white, eye-catching seeds ready to be carried away by a bird to invade another cactus.

The Karoo desert（卡鲁沙漠） in Southern Africa and although it may look bare, its rockyground contains anunrivalled variety of plants that one way or another store water in their tissues.

They belong to many different families（科）, but as a group, they're known as succulents（多肉植物）.

Some are small and low and barely distinguishablefrom their surroundings. These look like little pebbles. They resemble them so closely that animals which might be only too glad to steal their water just pass them by.

When rain does fall, they absorb it and quickly expand, but even this doesn't spoil their disguise, they just look like larger pebbles. Nor are they green.

The cells on their top surface are transparent and allow sunlight to pass through. Deep within and out of sight, are the green cells where photosynthesis occurs. The process produces this light to make food for the plant.

When the time comes toreproduce, however, the stone plant abandons its disguise. And now, it blooms.

The flowers open and close every 24 hours. So, for a few dangerous days, the plant advertisesits pollinators before returning to life as a pebble.

Some dessert plants have developed a very different way of attracting pollinators. This is a stapelia（毛犀角）, it produces what is perhaps the deserts strangest disguise. It uses water stored in its stems to grow buds the size of tennis balls. 

The flower, once opened, is called a desert starfish.

Instead of releasing millions of loose pollen grains as most flowers do, the desert starfish produces them packed in five tiny sacks. But if its strategy is successful, just one of them wil produce hundreds of seeds and this depends on deception.

The flower appears to have hair, wrinkly skin, and it produces astenchlike thecarcassof a dead animal. And when a carrion fly（丽蝇） investigates, the flower dumpsa tiny sack of pollento its probiscis（口器）.

stench: a strong, unpleasant smell

It's not easy to feed with such encumbered mouth parts, but try as it might, the fly can't get rid of it. And it's still there when the fly leaves to try and feed from another bogus carcass.

encumber: to weigh someone or something down, or to make it difficult for someone to do something

bogus: false, not real, or not legal

This time, however, when its clamped up（收紧的）probiscis slots into the flower, the pollen sack is released. 

slot: to put something into a slot or fit together using slots

With pollination complete, the fly is no longer needed...

and just as well.

just as well 无妨

Some deserts can be so dry that plants must find techniques of surviving for long periods without any water whatsoever.

whatsoever: used after a negative phrase to add emphasis to the idea that is being expressed

One of them is to grow extremely slowly and few plants grow more slowly than this one, the creosote bush（三齿团香木）. It isinactivefor most of its life and only wakes up and grows for a brief period if and whenthere is a fall of rain.

I've seen evidence of this grow slowly strategy for myself. 40 years ago, I came here to California's Mojave desert（莫哈韦沙漠） to visit one particular plant.

"An individual cresote bush tends to spread not by setting seeds and producing a new genetration, but by sending out new stems around its base. This plant started growing between 10 and 12 thousand years ago."

That was in 1982.

Since then, careful measurement has shown that it has increased in size by less than one inch.

Its ability to endure is truly extraordinary. So efficient is cresote at collecting what little rain falls here that few other plants can compete with it. As a result, over the last 12,000 years, it has come to completely dominate this landscape.

The Chihuahuan desert（奇瓦瓦沙漠） in North Mexico.

Here, one paticular plant plays the waiting game so well that it spends much of its life looking dead and certainly not worth eating, and it can survive like this for a decade.

This is the resurrection plant（鳞叶卷柏（还魂草））.

It's a kind of moss（卷柏属）. It barely has roots and it certainly can't store much water, but it can travel.

After a particularly long drought, it breaks away from its roots and becomes a tumbleweed（风滚草）.

Moving across the desert, it can travel a mile in a week. With luck, it may find water.

Just a shower of rain can bring it back to life. As itfrondssoak up the water, they unfurl. In its protected centre, it still has green cells which absorb both the water and sunlight and rapidly produce the food it needs to resume its growth.

frond: a long, thin leaf of a plant

unfurl: If a flag, sail, or banner unfurls, it becomes open from a rolled position, and if you unfurl a flag, etc... you make it fo this.

It will grow for just as long as there is moisture, but when that disappears, it closes up once more and resumes its travels.

Here, in the canyonlands of Utah, lives a plant that has developeda finely balanced relationshipwith the animals with which it shares this dramtic desert.

Rain does occasionally fall here and turns dust into mud, but that doesn't last long.

A brief window of opportunity opens.

Seeds that have been buried for years may now be exposed to light andcome to life.

This is coyote tobacco（郊狼烟草）. In just a few weeks, it grows a metre tall and produces dozens of flowers. 

The night air becomes heavywith their fragrance.

Soon, they attract hawkmoths（天蛾） which sip their nectar and in doing so, pollinate them, but the moths also lay their eggs on them.

Soon, the caterpillars have hatched and are munching the leaves.

munch: to eat something, especially noisily

Theirnibbles expose the plants sap to the drying air, but the tobacco plant has a defence.

nibble(v.): to eat something by taking a lot of small bites

nibble(n.): to bite something gently and repeatedly

The leaves under attack produce nicotine. This chemicalssedatesthe caterpillars and slows them down. And what is more, it makes themgive off a particular scent, one that summons others tocome to the plants aid.

sedate: to cause a person or animal to be very calm or go to sleep by giving them a drug

Big eyed bugs（大眼长蝽）, miniature assassins only 2mm long, and whiptail lizards（鞭尾蜥）. Big or small, they make a meal ofthe caterpillars.

It's certainly effective, 

but there's more to this strategy than meets the eye.

When the leaf of a tobacco plant is attacked by a caterpillar, all the rest of the leaves prepare to defend themselves. But how does this leaf know that that leaf there is under attack?

Well, scientists here in the United States have specially genetically modifiedthese tobacco plants, so that under special lighting conditions, this microscope can show us exactly what is going on.

I'm going to attack one of the leaves of this plant with thesetweezers（镊子） which to the plant will seem as if it's being nibbled by a caterpillar.

Signals are being transmitted along the veins that link the leaf to the rest of the plant. It's rather like a very simple nervous system. From that initial injury, the whole of that little plant is aware that something has happened.

This signal warns each leaf of the danger, so that it is ready to produce nicotine the moment it is attacked. With this defence at the ready, the tobacco plant can continue to grow until eventually it produces seeds.

It's particularly important in deserts for seeds to be distributedas widely as possible, so that some wil have a chance of reaching moisture.

distribute（此处）：to spread or scatter something over an area

And deserts have an excellent agentto help them do that.

agent（此处）: a person or a thing that produces a particular effect or change

The wind.

Many seeds have adaptationsto help them exploit it. They have shells to protect the seeds within from abrasion or 'wings' to help them catch the air. As the temperature rises throughout the day, desert winds increase in strength.

abrasion: the process of rubbing away the surface of something

Here, in Arizona, the land is regularly swept by what is known as a haboob. It's a giant sandstorm, but also in affect, a seed storm. 

Countless millions of them are swept up into the air. Some seeds can travel thousands of miles on the wind, so that plants may eventually reach even the most isolateddesert.

Some have landed on an island in the middle of the world's largest salt flat（盐滩） in Bolivia（玻利维亚）.

In the Galapagos（加拉帕戈斯群岛）, theysprout on fields of recently erupted lava.

They've even reached one of the most inhospitableof all sites, the tiny island of San Pedro Martir（圣佩德罗玛蒂尔岛）, a scorched lonely rock off the coast of Mexico.

inhospitable（此处）: an inhospitable area is not suitable for humans to live in

This is the home of the giant cardon（武伦柱）, the species of hugecactus that can weigh up to 12 tonnes. They're able to thrive here, because of an extraordinarypartnership with brown and blue-footed boobies（褐鲣鸟和蓝脚鲣鸟）.

The cardons here can become so broad that they provide cooling shade fornesting birds. As the boobies chicks get older, theyrepay the cardons with theirdroppings.

Guano（海鸟粪）, the digested remains of vast shoalsof fish. Thi s guano is of such strength and quantity that most plants would be poisoned by it.

shoal: a large number of fish swimming as a group

These cardons however, have evolved the ability to tolerate the toxins in the guano and digest the nutrients.

As a result, the cacti now grow in a denseforest over a million strong.

But such relationshipsare very finely balanced and can only too easilytip into catastrophe as is now happening in Northern Zimbabwe（津巴布韦）.

tip: to (cause to) move so that one side is higher than another side

For six months of the year, the savannah here is kept lushand green by daily rains.

lush: A lush area has a lot of green, healthy plants, grass, and trees

But when therainy seasonis over, it becomes as dry as any desert. So, to survive here, trees must be able to tolerate both conditions.

And these giants are adapted to do just that, they arebaobabs.

This one might be over a thousand years old. 

It survives herein partthanks to its ability to store thousands of litres of water within the spongy wood of its trunk, but its batteredsurface is evidence of a very finely balanced relationship. 

battered: hurt by being repeatedly hit

These huge trees are a focus for animals of all kinds. And they are particularly important for elephants. In wet season, they eat the baobabs fruit anddispersethe seeds in their dung. Now, as the dry season begins, they migrate to distant watering holes（水源）.

disperse: to spread across or move away over a large area, or to make something do this

The baobabs have damp inner wood and the elephants use it to quench their thirst on the journey.

quench（此处）: to drink liquid so that you stop being thirsty

This relationship can only work, because baobabs have aremarkable ability to heal themselves. Between each damaging attack, they expand their spongy wood and grow new skin. And they've done this time and time again over centuries.

Today, however, it is harder for the baobabs to recover as dry seasons become longer and drier due to climate change. Not only that, but the elephants are forced to take ever more wood from the trees in order to survive.

In some parts of Africa, many of the largest and oldest baobabs have fallen in the last decade. The loss of a vital species like the baobab strikes a blowat all life in the desert.

In thesehostilelands, few living organisms can survive without help from others.

You can find an extraordinaryillustrationof this in Arizona's saguaro country.

illustration: an example that explains or proves something

If you wander off the beaten trackhere, you may be lucky enough to find one of these. It might look like an old boot, but in fact it is part of a saguaro cactus. Almost every saguaro has one right up there.

A beaten path or track is one that people walk along regularly so that the ground has become hard and the path is clear. keep to the beaten track: 循规蹈矩 off the beaten track: 不落俗套

It has been produced indirectly by woodpeckers（吉拉啄木鸟）, which regularly dig homes for themselves in the bloatedtrunks of these saguaros.

bloated: swollen and rounded because of containing too much air, liquid, or food

In the next six months, the cactus heals the wound and so creates a safe, cool, and watertightnest hole. Its tough lining will persist for years, even after the cactus itself has died and rotted away.

watertight: having no openings to allow water to get in

A single saguaro may hold several of these extraordinary homes, so over its lifetime, it may provide accommodation for some 3,000 chicksof several different species. Butin the long term, the saguaro benefits as their lodgersrepay the cactus by pollinating its flowers and dispersingits seeds.

lodger: someone who pays for a place to sleep, and usually for meals, in someone else's house

It's relationships like these that enable life to flourishin some of the world's harshest landscapes. Over millions of years, plants have becomesuperbly adapted to hostile desert conditions, but it's a very finely balanced existence and one that makes them uniquely vulnerable.

However, our growingunderstanding of the complex ways by which desert animals and plants rely on one another is now helping us to understand how best we can protect them.

90 years ago, a photograph was taken from this very spot that shows a population of saguaro cactus that was very different from what it is today.

In the last 50 years, the population of saguaros here has greatly diminished, not because of a direct assaulton the cactus, but because many of the shade-giving nurse trees were harvested forfirewood, leaving the young saguaro to die in the sun.

Now the relationship is understood and the nurse trees are protected, there are already signs that the saguaros are recovering.

Wherever there is a desert, plants have evolved tomeet its challenge, but everywhere, they need our help. As we understand more about them and their intimate and complex relationships, we will be better able to protect them and all life in these beautiful but increasingly fragile worlds.

附： droppings和dung的区别

droppings: solid waste produced by animals and birds

dung: solid waste from animals, especially cattle and horses

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