地球陆地表面的植被覆盖是降水状况的最基本的反映。降水越少,植被越稀疏,其生产力也越低。在最干旱的地区(降水量<300mm/a),尽管偶尔也会发现薄薄的一层藻类和地衣,地表上只有很少一部分有维管束植被,其余大部分是裸露的。根系分布区的水分在一年中只有很短一段时间仅够植株进行蒸腾作用。这就是为什么光合作用和生物量生产极为有限的原因。影响植被覆盖的第二个最重要的因素 Vegetation coverage on Earth’s land surface is the most fundamental reflection of precipitation. The less precipitation, the more sparse vegetation and the lower productivity. In the driest areas (precipitation <300 mm / a), only a small part of algae and lichens are found on occasion, with only a small part of the surface covered with vascular vegetation, most of which are bare. Roots of the distribution of water in a year only a short period of time only transpiration of plants. This is why the photosynthesis and biomass production are extremely limited. The second most important factor affecting vegetation cover