【英语时差8，16】冬麦
时间：2015-10-29 06:02:28
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（单词翻译）
According to the famous song, American is beautiful for its spacious1 skies, purple mountains, and amber2 waves of grain. If you were to make a music video based on these lyrics3 you'd probably want mid4 to late summer images of fruit-laden trees and fields of rippling5 wheat under sunny blue skies. But where the amber waves of grain are concerned, the image might be slightly misleading. While at least some wheat in the United States and Canada is planted in the spring and harvested in the summer, much is planted in the late fall and harvested in the spring. Winter wheat manages to survive freezing temperatures and being buried under piles of snow.
How do these plants pull it off?
After being planted in the mid to late fall, winter wheat
seedlings6 undergo a process called cold
acclimation7. They begin to grow and
poke8 through the soil as the temperature drops to around forty-eight degrees
Fahrenheit9. As the plant's leaves absorb light the seedlings produce large amounts of carbon and store it in the crown, the part of the plant where root and shoot meet underground.
At the same time, the absorption of light combined with low temperatures triggers the expression of certain
genes10 that help the plant tolerate freezing temperatures. Although scientists do not
fully11 understand
precisely12 how this process works, it is clear that carbon production and freezing
tolerance13 are necessary for the plant's survival.
When the snow melts and temperatures rise in the spring, the plant has plenty of stored energy for steady growth. By mid spring many North American wheat fields are beautiful with waves of grain ready for harvest.
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