播音/撰稿 艾瑞克˙巴若（Erika Beras）
翻译 郭丰茹
校对 丁可含
It’s easy to see that some plants change from day to night—flowers open and close, and even turn to face the sun. In 1880 Darwin noted that the leaves and seedlings of various plants appeared to engage in nighttime changes that he called sleep. But there’s now evidence that some entire trees may have their own version of sleep, which lets them recharge for the following day. That’s according to a study in the journal Frontiers in Plant Science. [Eetu Puttonen et al., Quantification of Overnight Movement of Birch (Betula pendula) Branches and Foliage with Short Interval Terrestrial Laser Scanning]
一些植被从白天到晚上会有所变化，这样的现象很常见——花儿早晨开放，傍晚闭拢，甚至可以旋转花茎面向太阳。早在1880年达尔文（Darwin）提出多种植被的叶子和幼苗会在午夜闭拢，他把这样的现象叫做睡眠。但是现在已经有证据表明，有的树木会有它们特有的睡眠模式，让它们为第二天补足精神。这项研究发表在《植物科学》的研究前沿板块（journal Frontiers in Plant Science）。[Eetu Puttonen et al., Quantification of Overnight Movement of Birch (Betula pendula) Branches and Foliage with Short Interval Terrestrial Laser Scanning]
Researchers used lasers to scan birch trees in both Finland and Austria. They found that the branches drooped by as much as four inches at night compared with daytime.
研究者在芬兰和奥地利用镭射激光扫描白桦林。他们发现，在晚上桦树的枝桠比白天低4英寸。
And exposure to the elements was not responsible—the trees were surveyed from sunset to sunrise over enough time to rule out the changes being caused by wind or other external environmental factors.
揭示这种现象产生的因素的说法有点牵强——从日落到日出，有充足的时间排除风或者其他外部因素对桦树的影响。
The researchers have a couple of ideas about what’s causing the branches to slouch. One is that the fluid pressure inside the tree decreases—something like dehydration.
研究者对枝桠低垂的原因有许多猜想。其中一个是，桦树枝干内的液体压力减弱，这有点类似于脱水。
The other proposal is that the trees are actually engaged in a botanical version of sleep. During the daylight hours the leaves perk upwards to get more sun, but with no chance to catch rays at night, they relax. And even before the sun rose, some branches were found to be returning to their daytime position—as the researchers say, perhaps governed by their internal circadian clock in preparation for a new day of light gathering.
另一种见解是：其实桦树会进入植物学上的睡眠模式。白天日光充足，桦树拼命伸展叶子吸取阳光，但在晚上叶子没有机会接触阳光，就会休息。甚至日出之前，发现有些枝桠会回到白天的位置——就像研究员说的那样，或许在它们自身生物钟的调节下，为新的一天阳光的汲取做好准备。
But unlike us, there’s no evidence that trees sleep in on the weekend.
和我们不同，还没有证据表明桦树会在周末睡懒觉。
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