英语听力 学英语,练听力,上听力课堂! 注册 登录
> 在线听力 > 英语高级听力 > 科学一刻 >  第13篇

科学一刻 冬小麦

所属教程:科学一刻

浏览:

2016年03月26日

手机版
扫描二维码方便学习和分享
https://online2.tingclass.net/lesson/shi0529/0009/9695/2016_04_02_winter_wheat.mp3
https://image.tingclass.net/statics/js/2012
  Harvest Time

  According to the famous song, America is beautiful for its spacious skies, purple mountains, and amber waves of grain. If you were to make a music video based on these lyrics you’d probably want mid- to late-summer images of fruit-laden trees and fields of rippling 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.
winter wheat

  Cold Acclimation

  After being planted in the mid- to late-fall, winter wheat seedlings undergo a process called cold acclimation. They begin to grow and poke through the soil as the temperature drops to around 48 degrees Fahrenheit. 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 genes that help the plant tolerate freezing temperatures. Although scientists do not fully understand precisely how this process works, it is clear that carbon production and freezing tolerance 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.

用户搜索

疯狂英语 英语语法 新概念英语 走遍美国 四级听力 英语音标 英语入门 发音 美语 四级 新东方 七年级 赖世雄 zero是什么意思六安市徽盐湖公馆(光明路)英语学习交流群

网站推荐

英语翻译英语应急口语8000句听歌学英语英语学习方法

  • 频道推荐
  • |
  • 全站推荐
  • 推荐下载
  • 网站推荐
Baidu
map