為什么秋天樹葉會變色?

為什么秋天樹葉會變色?

Albert Camus once said, "Autumn is a second spring when every leaf is a flower." It's easy to agree with such a sentiment if you've ever taken a scenic autumn drive in New England or the Rockies, but what's the science behind those breathtaking fall colors?

加繆說過:“秋天是第二個春天，每一片葉子都是一朵花。”如果你曾經(jīng)在新英格蘭或落基山脈進(jìn)行過秋景駕車旅行，你很容易就會同意這種觀點，但這些令人驚嘆的秋色背后的科學(xué)依據(jù)是什么呢?

A brilliant canopy of fall foliage in Bukk, Hungary. (Photo: Fesus Robert/Shutterstock)

There are several reasons why leaves change color in the fall, but the most significant contributing factors are shorter daylight hours and longer nighttime hours, and how those factors affects the chemical process inside each leaf.

葉子在秋天變色有幾個原因，但最重要的原因是白天時間變短，夜晚時間變長，以及這些因素如何影響每片葉子內(nèi)部的化學(xué)過程。

It all comes down to biological pigments (also known as "biochromes"), which are molecular substances that manifest in living things as specific colors by absorbing or reflecting wavelengths of lights.

這一切都?xì)w結(jié)于生物色素(也被稱為“生物色素”)，這是一種分子物質(zhì)，通過吸收或反射光線的波長在生物中表現(xiàn)為特定的顏色。

You might already know a little something about chlorophyll — it's the green pigment produced by plants during the photosynthesis process. Some of the other pigments found in plants are carotenoids, which are responsible for oranges, and anthocyanins, which yield red and purple leaves. While chlorophyll and carotenoids are present throughout the growing season, most anthocyanins are produced exclusively in late summer and early autumn.

你可能已經(jīng)對葉綠素有所了解了——它是植物在光合作用過程中產(chǎn)生的綠色色素。在植物中發(fā)現(xiàn)的其他一些色素是類胡蘿卜素和花青素，類胡蘿卜素是橙子的主要成分，花青素產(chǎn)生紅色和紫色的葉子。雖然葉綠素和類胡蘿卜素存在于整個生長季節(jié)，但大多數(shù)花青素只在夏末秋初產(chǎn)生。

As the days become shorter and the nights become longer, the amount of light required for photosynthesis wanes and chlorophyll production gradually comes to a halt. Without any new chlorophyll being produced, the leaves' characteristic green color begins to break down and vanish. This mechanism essentially "unmasks" the colors of the carotenoids and anthocyanins that were lurking beneath.

隨著白天變短，夜晚變長，光合作用所需的光量減少，葉綠素的產(chǎn)生逐漸停止。沒有任何新的葉綠素產(chǎn)生，樹葉特有的綠色開始分解和消失。這一機(jī)制從本質(zhì)上“揭示”了隱藏在下面的類胡蘿卜素和花青素的顏色。

The gorgeous red leaves of a Japanese maple tree in autumn. (Photo: TOMO/Shutterstock)

While the waning hours of sunlight are the most significant contributing factor to affect changing foliage colors, temperature and humidity can also play a role in the intensity of these seasonal displays. For example, warm, sunny days coupled with cool, mild nights are a particularly potent recipe for brilliance.

雖然日照時間的減少是影響樹葉顏色變化的最重要因素，但溫度和濕度也會影響這些季節(jié)性展示的強度。例如，溫暖、陽光明媚的白天加上涼爽、溫和的夜晚是創(chuàng)造輝煌的一個特別有效的方法。

As the National Forest Service explains: "During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions — lots of sugar and lots of light — spur production of the brilliant anthocyanin pigments, which tint reds, purples and crimson."

正如美國國家林業(yè)局所解釋的那樣:“在這些日子里，葉子里會產(chǎn)生大量的糖分，但涼爽的夜晚和進(jìn)入葉子的靜脈的逐漸關(guān)閉阻止了這些糖分的流出。”這些條件——大量的糖和大量的光——刺激了燦爛的花青素色素的產(chǎn)生，使紅色、紫色和深紅色變得鮮艷。”

The elevation and type of tree species are two other factors that affect the timing of fall foliage. Trees in higher mountain elevations are likely to change colors more quickly than their valley counterparts within the same latitude.

海拔和樹種類型是影響落葉時間的另外兩個因素。高海拔地區(qū)的樹木比同一緯度地區(qū)的山谷樹木更容易變色。

If you'd like to keep tabs on how the year's leaf-peeping season is shaping up, be sure to check out the Fall Foliage Prediction Map, which is a great resource and tool for timing your autumn road trips to coincide with peak foliage colors.

如果你想了解這一年的賞葉季節(jié)是如何形成的，一定要看看秋季賞葉預(yù)測圖，這是一個很好的資源和工具，可以為你的秋季公路旅行安排好時間，使之與賞葉高峰的顏色一致。

Autumn foliage at Daigoji Temple in Kyoto, Japan. (Photo: cowardlion/Shutterstock)