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                                                                                              沙漠荒凉的真正原因
                                                                                                         高 峰
       ①沙漠是地球上最荒凉的区域之一。为什么沙漠如此荒凉?按照我们一贯的理解是,沙漠地区缺乏生命所需的水,所以鲜有生命能在那些地区生存。最近,美国康奈尔大学的研究人员却发现,不少沙漠地区并非干得不能生长植物,而是肥力不够,因为沙漠土壤中缺乏植物赖以生存的氮。而且,令人担忧的是,随着气候不断变暖,沙漠地区土壤中含量可怜的氮还会不断挥发,以气体的形式大量流失,从而导致生长在沙漠里的植物越来越少。
       ②研究人员在美国莫哈韦沙漠地区选了几处试验点,通过精密测量仪器了解土壤中的氮是如何随着气温升降而变化的。研究发现,不管有没有阳光照耀沙漠,当土壤温度达到40℃至50℃的高温时,土壤中的氮会以气体形式从土壤中迅速释放出来。而在沙漠中,地表温度达到40℃以上是轻而易举的事情。研究人员还发现,地表温度越高,沙漠土壤中释放氮的速度越快。因此,随着全球气候变暖的加剧,沙漠的气温和地表温度也将越来越高,土壤中的氮也将越来越少,沙漠会变得越来越荒凉和贫瘠。
       ③研究人员还表示,除了沙漠地区,在世界任何高温干旱的地方都可能出现类似的情况。近年来让农林科研人员头疼的现象也由此找到了原因,他们在干旱地区种植实验田地,虽然保障了充分的水和肥料,但是土地的出产还是不尽如人意。
       ④干旱地区的氮不但从土壤中偷偷溜走,而且很难再回到土壤之中。在气候温和地区,氮在土壤和大气中的循环是平衡的,当地土壤中的一部分氮虽然也会通过分解或植物收割流向大气;但是在雷雨天,空气中的氮气会在雷电的作用下变成氮肥回到土壤中。然而,干旱地区很少会有雷雨天气,也就很少会有氮再返回到土地中。正是因为干旱地区氮的流失是不可逆转的,我们花再大的代价,比如不计成本地往其中施放氮肥,也不可能让沙漠变成绿洲。除非,我们可以让沙漠地区的气温及地表温度降下来。
       ⑤今天如果我们不能有效遏制气候变暖的发展趋势,代表着沙漠未来希望的零星绿色将越来越少,直至完全绝迹,沙漠的扩张也将变得气势汹汹而且肆无忌惮。那样令人绝望的未来,并非是我们所希望看到的!

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    Camels are large animals living in dry areas. There are two species of camels; the Arabian camel with a single hump(驼背) from the dry desert areas of West Asia, and the Bactrian camel with two humps from Central and East Asia. Camels are over 7 feet tall and weigh over 1,600 pounds. They will live up to 40 to 50 years. Most camels are domesticated(驯化) and fed by people. Camels are plant-eaters.

    Camels are very strong animals with wide, padded feet. They have thick leathery pads on their knees and chest. Camels have nostrils(鼻孔)that can open and close, protecting them from the desert environment. Bushy eyebrows and two rows of long eyelashes protect their eyes from sand. Their mouth is extremely tough, allowing camels to eat thorny(带刺的)desert plants. Their widened feet help them move without sinking into the sand. Their thick coats reflect sunlight, and also protect them from the intense heat from desert sand. Their long legs help by keeping them further from the hot ground.

    Camels can go without food and water for 3 to 4 days. They do not store water in their humps as is commonly believed.The humps are actually a container of fat. Camels are incredibly well-adapted to their environment. When conditions heat up, camels can increase their own body temperature, which prevents sweating and therefore water loss. They may not sweat at all during the day.

    Camels are sometimes called“ships of the desert”because people ride them around the hot, dry deserts of the world.However, the number of camels is becoming smaller for various reasons.