The Nightlife Of Plants
Most plants grow buds, flower, or lie dormant at specific times of year.
What Triggers These Seasonal Changes?
Temperature and rainfall often play a role, but the most important factor to many plants is the length of the day. At least, that’s what biologists thought until the 1940s, when the whole concept of day length sensitivity in plants was turned upside down.
Experiments showed that plants that seem to flower in response to day length actually respond to night length. In other words, what prompts irises to bloom in summer in North America isn’t longer sunny days, but shorter nights.
Here’s how biologists figured out how important nightlife can be to plants. They started with the cockle burr plant, which flowers when days are short. Midway through the day, the biologists exposed the plants to a brief period of complete darkness. What effect did this have on flowering? Absolutely none.
Next, for several nights, in the middle of the night, they exposed the plants to a brief period of light. To the biologists’ surprise, this brief interruption of the darkness inhibited flowering. Clearly it was the long period of darkness and not the short period of light that caused flowering.
Although plants are sensitive to the nighttime part of the light-and-dark cycle, biologists and gardeners often still refer to plants as day length sensitive.
For example, poinsettias are called “short-day” plants because they flower in winter. A stickler for accuracy might call poinsettias “long-night” plants, because what prompts their flowering isn’t the short days of winter, but the long nights.
譯文：
植物的夜生活
大多數植物在每年的特定時間發芽，開花，或者冬眠。
是什麼引起植物這些季節性的變化呢？
溫度和降雨通常會有所影響，但是對許多植物來說，最重要的因素是晝長。至少在20世紀40年代之前，生物學家們是這樣認爲的，之後植物對晝長敏感的理論被徹底推翻。
實驗顯示，那些看起來受日長影響而開花的植物實際上是受夜長影響。換句話說，促使北美地區的鳶尾花在夏季盛開的`不是更長的白天，而是更短的夜晚。
下面讓我們來揭祕生物學家是怎樣確定夜生活對植物的重要性的。他們由蒼耳開始研究，這種植物在晝長較短時開花。生物學家讓植物在白天一個短暫的時期內陷入完全的黑暗。這對植物開花有什麼影響嗎？答案是：完全沒有影響。
接下來，他們連續幾晚讓植物在半夜接受短時間的光照。令生物學家吃驚的是，這對黑暗的短暫中斷抑制了植物開花。很明顯是由於長時間的黑暗，而不是短時間的光照導致的開花。
儘管植物對日夜交替中的夜間部分敏感，但是生物學家和園丁們還是通常傾向於認爲植物是對晝長敏感的。
舉個例子，一品紅因爲在冬天開花被叫做“短日照”植物。一個堅持細節的人爲了精確可能稱一品紅爲“長夜”植物，因爲促使它們開花的不是冬天的短暫白晝，而是冬天的漫漫長夜。
