1.Now, the classic explanation for why leaves change color is this.
对树叶为什么会变颜色的传统解释是:
2.In autumn, the leaves start preparing for the winter and stop synthesizing new chlorophyll.Since chlorophyll is sensitive to sunlight and to cold temperatures, both of which you get in autumn, the existing chlorophyll in the leaves breaks down.And since it’s not been replaced by the new chlorophyll, the green color of the leaves gradually fades away.As this happens, the other pigments present in the leaf become visible.According to the classic theory, this is true for the red pigment as well.It was there in the leaf all along but it was hidden by the green chlorophyll.
在秋天,树叶开始为冬天做准备,停止合成新的叶绿素。因为叶绿素对阳光和低温很敏感,而在秋天这两个因素都有,所以树叶中存在的叶绿素开始分解。由于没有新的叶绿素来代替它,树叶的绿色渐渐消退。这种现象发生时,树叶中的其他色彩开始显现。根据传统理论,这对红色也适用。它一直存在于树叶中,但是被绿色的叶绿素藏起来了。
3.OK, so that's the classic explanation and it's partially right.
好了,这是传统的解释,部分是对的。
4.Why do I say partially?
为什么我说部分?
5.Well, it's probably true for pigments like yellow or orange, but it doesn't seem to hold for the red pigment.
因为这对像黄色和橘色这样的色素可能是正确的,但是似乎不适用于红色色素。
6.Let's back up a bit.Just what produces this red color in leaves? It’s a red pigment called anthocyanin.
我们往回倒一点。什么产生了树叶中的红色呢?是一种叫做花青素的红色色素。
7.Here is where the classic explanation doesn't seem to apply to red.What’s interesting is that during the summer there was very little if any anthocyanin in the leaves,but in the weeks before a tree is about to drop its leaves, the production of anthocyanins increases significantly.In other words, unlike those other pigments, anthocyanins are not just unmasked by the breakdown of chlorophyll in autumn;they are actually created at this time.
这就是传统解释似乎不适用于红色的地方。有趣的是在夏天,树叶中几乎没有花青素,但是一棵树开始落叶前几个周,花青素开始大量增加。换句话说,和其他的色素不同,花青素不是因为叶绿素在秋天分解而开始显现,它们实际上是那个时候才产生的。
8.So that raises a question, why would a tree produce more anthocyanin just before dropping its leaves?Why does the tree spend so much of its resources doing this just before the leaves fall off?
那么这就提出了一个问题:一棵树在落叶之前为什么要制造出更多的花青素?为什么树要在所有的树叶掉落之前花那么多资源这么做?
9.On the surface, that doesn't make sense.It’d be like spending money to...I don’t know...to have your old car repainted when you know the car’s not going to last more than a couple of months.All this extra anthocyanin in the autumn seems like a waste.
从表面来看这一点都说不通。就像在你知道一辆老车无法继续使用超过几个月的情况下还花钱重新给它刷漆一样。所有这些秋天的额外的花青素似乎就是浪费。
10.But remember nature is very economical with its resources.So that means anthocyanin must be serving some function that’s important for the tree.
但是别忘了,大自然在它的资源方面是非常节约的。这就是说花青素一定有着对树木来说很重要的某种功能。