樹會呼吸嗎？

Trees don't seem to do all that much. Occasionally their branches might sway in the breeze and many of them drop leaves on a regular basis. But it seems there's a lot more going on with trees that we thought.

樹仿佛一直都很默默無聞，仿佛能一直這么平凡下去，直至天荒地老。有時它們的枝葉會在微風中輕輕搖擺，到了秋天，它們也會順其自然地掉葉子。但除了這些以外，我們對樹木似乎還有很多無法理解的地方。

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.

研究人員發(fā)現(xiàn)，在夜間，許多樹木都會周期性地上下擺動樹枝，這說明樹木可能正在向上慢慢抽水，而這說不定就是它們的心跳與脈搏。

"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.

荷蘭奧胡斯大學的Andras Zlinszky告訴《新科學家》：“我們發(fā)現(xiàn)，大部分樹木的形狀都會在一定周期內(nèi)呈規(guī)律性變化，并且此周期短于一晝夜，這意味著樹體內(nèi)的水壓也會發(fā)生周期性的變化。”

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年的一項研究中，Zlinszky和他的同事Anders Barford使用了高分辨率的地面激光掃描技術(shù)，這種技術(shù)常用于土木工程中測量建筑物。在一個無風的夜晚，他們對22棵不同種類的樹木進行了研究，以觀察它們是否發(fā)生了變化。

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，他們發(fā)現(xiàn)有幾棵樹的樹枝向上或向下移動了大約1厘米，而有些則移動了1.5厘米。

Looking for a heartbeat

尋找樹的心跳

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."

在研究了樹木的夜間活動后，研究人員就此現(xiàn)象提出了一個新的理論。他們認為，這一行為表示樹木正在從樹根中吸收水分;從本質(zhì)上講，這就是樹的“心跳”。

Zlinszky and Barfod explain their theory in their newest study in the journal Plant Signaling and Behavior.

Zlinszky和Anders Barford在《植物信號和行為》雜志上發(fā)表的最新研究中解釋了他們的理論。

"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."

他告訴《新科學家》："在傳統(tǒng)植物生理學中，我們認為大多數(shù)運輸過程都是隨著時間變化的、可忽略不計的波動，尤其是從植物的整體活動來看。目前已有的模型都沒有解釋這些周期小于24小時的活動的具體意義所在。"

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.

但是研究人員尚未確定，一棵樹是如何成功地把水從它的根部向上泵到身體的其他部位的。他們認為，樹干可能是輕輕地擠壓水，通過木質(zhì)部把水向上推進。木質(zhì)部是一個植物體內(nèi)的一種組織，其主要工作是把水和營養(yǎng)物質(zhì)從根部輸送到嫩枝和樹葉中。

Circadian movements

晝夜節(jié)律?

In 2016, Zlinszky and his team released a study showing that birch trees "go to sleep"at night.

2016年，Zlinszky 和他的團隊發(fā)布了一份研究報告，表明樺樹會在晚上"睡覺"。

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.

研究人員認為，樺樹枝條在黎明前會垂落是由于樹木內(nèi)部水壓下降造成的。 由于夜間沒有光合作用將光能轉(zhuǎn)化為簡單的糖類，樹木很可能通過“放松”樹枝來儲存能量，否則樹枝就會向太陽傾斜。

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.

樺樹本身肯定也存在著晝夜節(jié)律，但研究人員們認為，新發(fā)現(xiàn)的這一現(xiàn)象與晝夜節(jié)律并不相同，因為其周期小于24小時。