树会呼吸吗？
树仿佛一直都很默默无闻，仿佛能一直这么平凡下去，直至天荒地老。有时它们的枝叶会在微风中轻轻摇摆，到了秋天，它们也会顺其自然地掉叶子。但除了这些以外，我们对树木似乎还有很多无法理解的地方。
Researchers have found that, at night, many trees periodically move their branches up and down slightly. This suggests that perhaps the trees are pumping water upwards slowly, hinting that the trees have some semblance of a pulse.
研究人员发现，在夜间，许多树木都会周期性地上下摆动树枝，这说明树木可能正在向上慢慢抽水，而这说不定就是它们的心跳与脉搏。
"We’ve discovered that most trees have regular periodic changes in shape, synchronized across the whole plant and shorter than a day-night cycle, which imply periodic changes in water pressure," András Zlinszky of Aarhus University in the Netherlands told New Scientist.
荷兰奥胡斯大学的Andras Zlinszky告诉《新科学家》：“我们发现，大部分树木的形状都会在一定周期内呈规律性变化，并且此周期短于一昼夜，这意味着树体内的水压也会发生周期性的变化。”
For a 2017 study, Zlinszky and his colleague Anders Barfod used high-resolution terrestrial laser scanning, a technique often used in civil engineering to measure buildings. They surveyed 22 trees representing different species over a 12-hour period during a windless night to see if their canopies changed.
在2017年的一项研究中，Zlinszky和他的同事Anders Barford使用了高分辨率的地面激光扫描技术，这种技术常用于土木工程中测量建筑物。在一个无风的夜晚，他们对22棵不同种类的树木进行了研究，以观察它们是否发生了变化。
In several of the trees, branches moved by about a centimeter up or down. Some moved as much as 1.5 centimeters.
果不其然，他们发现有几棵树的树枝向上或向下移动了大约1厘米，而有些则移动了1.5厘米。
Looking for a heartbeat
寻找树的心跳
After studying the nocturnal tree activity, the researchers came up with a theory about what the movement means. They believe the motion is an indication that trees are pumping water up from their roots. It is, in essence, a type of "heartbeat."
在研究了树木的夜间活动后，研究人员就此现象提出了一个新的理论。他们认为，这一行为表示树木正在从树根中吸收水分;从本质上讲，这就是树的“心跳”。
Zlinszky and Barfod explain their theory in their newest study in the journal Plant Signaling and Behavior.
Zlinszky和Anders Barford在《植物信号和行为》杂志上发表的最新研究中解释了他们的理论。
"In classical plant physiology, most transport processes are explained as constant flows with negligible fluctuation in time, especially at the level of the entire plant, or on timescales shorter than a day," Zlinszky told New Scientist. "No fluctuations with periods shorter than 24 hours are assumed or explained by current models."
他告诉《新科学家》："在传统植物生理学中，我们认为大多数运输过程都是随着时间变化的、可忽略不计的波动，尤其是从植物的整体活动来看。目前已有的模型都没有解释这些周期小于24小时的活动的具体意义所在。"
But the researchers aren't sure how a tree successfully manages to pump water from its roots upwards to the rest of its body. They suggest maybe the trunk gently squeezes the water, pushing it upwards through the xylem, a system of tissue in the trunk whose main job is to transport water and nutrients from roots to shoots and leaves.
但是研究人员尚未确定，一棵树是如何成功地把水从它的根部向上泵到身体的其他部位的。他们认为，树干可能是轻轻地挤压水，通过木质部把水向上推进。木质部是一个植物体内的一种组织，其主要工作是把水和营养物质从根部输送到嫩枝和树叶中。
Circadian movements
昼夜节律?
In 2016, Zlinszky and his team released a study showing that birch trees "go to sleep"at night.
2016年，Zlinszky 和他的团队发布了一份研究报告，表明桦树会在晚上"睡觉"。
The researchers believe the dropping effect of birch branches before dawn is caused by a decrease in the tree's internal water pressure. With no photosynthesis at night to drive the conversion of sunlight into simple sugars, trees likely conserve energy by relaxing branches that would otherwise be angled towards the sun.
研究人员认为，桦树枝条在黎明前会垂落是由于树木内部水压下降造成的。 由于夜间没有光合作用将光能转化为简单的糖类，树木很可能通过“放松”树枝来储存能量，否则树枝就会向太阳倾斜。
These birch movements are circadian, following the day-night cycle. However, researchers don't believe the newly discovered movements are similar because they typically follow much shorter time periods.
桦树本身肯定也存在着昼夜节律，但研究人员们认为，新发现的这一现象与昼夜节律并不相同，因为其周期小于24小时。
