But, the correct answer is: less daylight.

匱乏的雨水但是正確的答案是

Temperature can affect the intensity of leaf color, which I will explain in a minute, but less daylight actually causes color change.

比較少的日照溫度能夠影響 葉子變色的程度

Most leaves contain chlorophyll, a green pigment that starts the process of photosynthesis.

待會我就會解釋但是較短的日照才是葉子變色的原因 大多數葉子都含有葉綠素

Chlorophyll helps convert sunlight, carbon dioxide and water into sugars that travel to the branches and the roots, feeding the tree.

它是一種綠色的色素

Chlorophyll breaks down and is replenished all summer long.

能夠使得光合作用開始進行

As daylight hours shorten, however, veins that bring water and nutrients to the leaf gradually close off.

葉綠素幫忙植物把陽光、二氧化碳、還有水轉換成在枝幹以及根中被傳輸的醣類

The old chlorophyll disappears, and no new chlorophyll forms.

讓樹因而得到養分在整個夏天，葉綠素不斷分解

The green color fades.

然後又被補足

Yellow and orange pigments, which were there all along, become visible.

但當日照時數開始縮短的時候

But what about the red colors?

為葉子帶來水分跟營養的葉脈

They actually form during the fall.

會逐漸關閉

As veins close, sugars get trapped in the leaf.

就這樣，舊的葉綠素消失之後

They react with other chemicals to form the red pigments.

不會有新的葉綠素補足綠色也因而褪去

You'll remember I said intensity is connected to temperature.

另一方面，一開始就存在的

If days are bright, and nights are cold, more sugars get trapped, and the reds intensify.

黃色和橘色色素就這樣變得明顯 那紅色又從何而來?

Eventually, the drier autumn weather triggers a hormone telling the tree to drop its leaves.

它們其實是在秋天形成的

Otherwise, the leaves would use up water that the tree needs to keep its roots alive during the winter.

當葉脈關閉之後，醣類會被困在葉子中

Okay, what about evergreens?

在與化學物質作用之後

The needles have a waxy coating, and less surface area, which reduces water loss.

就會形成紅色色素如果你還記得，我說過溫度會影響變色程度

They also contain a chemical like anti-freeze, so the roots and the leaves can survive the winter.

這是因為如果白天很晴朗，而夜晚很冷的話會有更多的醣類被困住

Now that you know the science behind colorful autumn leaves, let's identify some of them:

秋葉的紅色因而加深最後，秋天乾燥的天氣

Oaks turn red and brown.

會促使一種激素的產生，它會告訴樹該掉葉子了

Hickories turn bronze;

不然的話，葉子會用掉太多的水分

Aspen and poplar turn gold and yellow;

這樣在冬天的時候，根部就沒有足夠的水分維生

Sugar maples turn orange;

好吧，那長青樹呢？

Black maples turn yellow;

它們的針狀葉有蠟質覆蓋

And red maples turn -- what else?-- brilliant red.

還有比較少的表面積

For Scientific American's Instant Egghead,

因此能減少水分的散失

I'm Mark Fischetti.

它們也有一種像防凍劑的化學物質