英語聽力文摘 南極地衣

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南極地衣是地球上最古老的植物之一，是一類原始型的低等植物，它能適應南極洲那種沙漠般的干燥和極度寒冷的環(huán)境，所以它是分布最廣、種類最多的南極土著植物。它主要分布于南極大陸的綠洲和時有冰雪覆蓋的巖石表面，甚至在離南極點僅有幾個緯度的巖石上，也有它的蹤跡。

南極洲的350余種地衣，形態(tài)各異，大的有10～15厘米高，小的僅有幾毫米。地衣的生長速度十分緩慢，即使個體最大、生長速度較快的種類，每100年才生長1毫米。據(jù)說一株10厘米高的地衣，其壽命約1萬年。地衣靠孢子繁殖后代。

地衣生長所需的水分是冰雪融化時得到的。地衣所需要的營養(yǎng)是由巖石的化學風化物提供的，也許是由于風把鳥糞從遠處帶來，像風吹塵埃一樣，吹到地衣生長地。最近的研究表明，有幾種地衣，其假根可以分泌地衣酸，溶解巖石，一方面固定自己，另一方面從中得到營養(yǎng)。

Antarctica. Picture desolate 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, 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 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 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 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.

譯文

提到南極洲，眼前浮現(xiàn)的是一片荒涼的冰域，毫無生命氣息，凜冽刺骨的風拍打著這塊土地。

盡管南極洲98%的土地都被厚厚的冰覆蓋著，但巖石表面仍然有一些次生裸地。這些所謂的“干旱河谷”是地球上十分荒涼的地方。那里的氣溫遠遠低于結(jié)冰點，同時由于強大的颶風吸收了雪和其他的水分，這又是一個干旱的荒漠。

假如說您是南極洲干谷里的一種微生物，是否能想到在哪里能躲過這干燥刺骨的風?

對于隱藏巖內(nèi)生物來講，答案就是-巖石里。這些南極的隱藏巖內(nèi)生物是一種地衣，其名字可以翻譯為“隱藏在巖石里的”。在南極洲這樣一個又冷又干燥的土地上，它們?nèi)匀恍枰欢康臏嘏退忠跃S持生命。那在巖石里生活怎樣幫助他們保持溫暖和濕度?

南極地衣生活在多孔透氣性好的砂巖里，它們鐘情于朝北的巖石，因為這些巖石一整天能吸收陽光，加熱維持熱量。

即使空氣十分寒冷，這些裸曬的巖石仍然能有足夠的熱量去融化那些在饑渴的風里逃過一劫的小雪塊。融化的水快速滲透到多孔的巖石里，隨著巖石溫度的升降，水不斷的結(jié)冰再融化，周而復始，因此能夠保持好些周。

不可避免地，遇到及其艱難的日子，地衣在一天里也會凍結(jié)-融化好幾個回合，但它們能過獲得足以存活的水分和熱量，無論怎樣，這就是生活的全部。