英语听力文摘 English Digest 320、南极地衣-英语课

时间：2019-02-24 作者：英语课 分类：英语听力文摘 English Digest

英语课

　　南极地衣

南极地衣是地球上最古老的植物之一，是一类原始型的低等植物，它能适应南极洲那种沙漠般的干燥和极度寒冷的环境，所以它是分布最广、种类最多的南极土著植物。它主要分布于南极大陆的绿洲和时有冰雪覆盖的岩石表面，甚至在离南极点仅有几个纬度的岩石上，也有它的踪迹。

南极洲的350余种地衣，形态各异，大的有10～15厘米高，小的仅有几毫米。地衣的生长速度十分缓慢，即使个体最大、生长速度较快的种类，每100年才生长1毫米。据说一株10厘米高的地衣，其寿命约1万年。地衣靠孢子繁殖后代。

地衣生长所需的水分是冰雪融化时得到的。地衣所需要的营养是由岩石的化学风化物提供的，也许是由于风把鸟粪从远处带来，像风吹尘埃一样，吹到地衣生长地。最近的研究表明，有几种地衣，其假根可以分泌地衣酸，溶解岩石，一方面固定自己，另一方面从中得到营养。

Antarctica. Picture desolate 1 plains of ice, lifeless, bitten by a fierce, bitter wind.

Although ninety-eight percent of Antarctica is covered by thick ice, there are bare patches where the rocky surface shows through. These so-called “dry valleys” are some of the most inhospitable places on Earth. Air temperature is well below freezing, and it’s dry as a desert because arid 2, hurricane-force winds suck the snow and other moisture away.

If you were a microorganism in one of Antarctica’s dry valleys, where would you hide to escape the biting, arid wind?

For a cryptoendolith, the answer is inside a rock. These Antarctic cryptoendoliths are a type of lichen 3 whose very name translates as “hiding inside rocks.” Even in this cold, dry land, these lichen need a certain amount of warmth and moisture to survive. How does living inside a rock help them keep warm and wet?

These lichen live a fraction of an inch inside pieces of porous 4 sandstone. They prefer north-facing stones, which absorb sunlight and heat up during the day.

　　Even if the air stays bitterly cold, these sunbaked rocks can warm enough to melt whatever tiny patches of snow have escaped the thirsty wind. The water is quickly absorbed by the porous rock, and it can stay inside for weeks–freezing and re-melting as the rock warms and chills.

Of course the lichen freeze and thaw 5 too, as much as several times an hour during a particularly rough day. But they get just enough heat, and just enough moisture, to stay alive. Which is what survival is all about anyway.

译文

提到南极洲，眼前浮现的是一片荒凉的冰域，毫无生命气息，凛冽刺骨的风拍打着这块土地。

尽管南极洲98%的土地都被厚厚的冰覆盖着，但岩石表面仍然有一些次生裸地。这些所谓的“干旱河谷”是地球上十分荒凉的地方。那里的气温远远低于结冰点，同时由于强大的飓风吸收了雪和其他的水分，这又是一个干旱的荒漠。

假如说您是南极洲干谷里的一种微生物，是否能想到在哪里能躲过这干燥刺骨的风？

对于隐藏岩内生物来讲，答案就是-岩石里。这些南极的隐藏岩内生物是一种地衣，其名字可以翻译为“隐藏在岩石里的”。在南极洲这样一个又冷又干燥的土地上，它们仍然需要一定量的温暖和水分以维持生命。那在岩石里生活怎样帮助他们保持温暖和湿度？

南极地衣生活在多孔透气性好的砂岩里，它们钟情于朝北的岩石，因为这些岩石一整天能吸收阳光，加热维持热量。

即使空气十分寒冷，这些裸晒的岩石仍然能有足够的热量去融化那些在饥渴的风里逃过一劫的小雪块。融化的水快速渗透到多孔的岩石里，随着岩石温度的升降，水不断的结冰再融化，周而复始，因此能够保持好些周。

不可避免地，遇到及其艰难的日子，地衣在一天里也会冻结-融化好几个回合，但它们能过获得足以存活的水分和热量，无论怎样，这就是生活的全部。