［问题］听力TPO-09-L2 冻土为什么在summer长灌木？

nicolezhangUID: 3597455

没听懂里面那个主要说为什么夏天会增加灌木而不是冬天和春天。
lecture给的原因是
因为冬天没那么冷，微生物就不死，然后冬天有很多养分。
所以，这就是夏天张灌木的原因，这说的我怎么看不懂。。。。




1. Well, it may be biological processes that occur in the soil in the winter, that cause increased shrub growth in the summer, and here's how: there are "microbes", microscopic organisms that live in the soil.
2 .These microbes enable the soil to have more nitrogen, which plants need to live and they remain quite active during the winter.
3 .There're two reasons for this: first, they live in the active layer, which, remember, contains water that doesn't penetrate the permafrost; second, most of the precipitation in the Arctic is in the form of snow.
4 .And the snow, which blankets the ground in the winter, actually has an insulating effect on the soil beneath it.
5 .And it allows the temperature of the soil to remain warm enough for microbes to remain active.
6 .So there's been increase in nutrient production in the winter.
7 .And that's what's responsible for the growth of shrubs in the summer and their spread to new areas of the tundra.
8 .Areas with more new nutrients are the areas with the largest increase in shrubs.