英語聽力文摘 冬小麥
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. How do these plants pull it off?
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 forty-eight 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.
由那首著名的歌得知，美國(guó)因它廣闊的天空，紫色的山巒，還有琥珀色的谷浪而美麗。如果你打算取材于這些歌詞作曲，那你也許想要夏末載滿果實(shí)的樹和晴朗藍(lán)天下翻滾的麥浪的圖像吧。
但是有谷浪的地方，那樣的形象也許稍令人誤解吧。雖然美國(guó)和加拿大或多或少有些小麥?zhǔn)窃诖禾觳シN，夏天收割，但大部分是晚秋播種，第二年春天收割的。
冬小麥設(shè)法在結(jié)冰的溫度下生存，還要埋于厚厚的大雪下。這些作物是怎樣成功生存的呢?
在仲秋或晚秋播種后，冬小麥種子經(jīng)歷了被稱為冷馴化的過程。它們?cè)跉鉁亟档?8華氏溫度后開始沖破土壤生長(zhǎng)。當(dāng)小麥葉吸收陽(yáng)光后，種子產(chǎn)出大量的碳并儲(chǔ)存在植物冠中，這是根和芽在地底下交匯的地方。
同時(shí)，吸收的光和低溫結(jié)合促使某種基因的產(chǎn)生，以幫助作物忍耐低溫。
盡管科學(xué)家們并未完全準(zhǔn)確弄明白這個(gè)過程是怎樣進(jìn)行的，但是生產(chǎn)碳和忍受低溫對(duì)作物的生長(zhǎng)很必要，這一點(diǎn)是顯而易見的。
春天雪融化，氣溫也升高了，這時(shí)冬小麥已經(jīng)存儲(chǔ)了大量供穩(wěn)定生長(zhǎng)的能量了。到仲春的時(shí)候，許多北美小麥地因有大片待收割的小麥浪而美麗無比。
