为什么树叶在秋天变红?

现在，我们进入了秋天，你可能都注意到了树上美丽的红色和橙色的叶子，而且，大量的树叶堆积在地上。但究竟是什么导致了这种情况的发生呢?我们采访了剑桥大学植物园主任贝弗利·格洛弗教授，他找到了这个问题的根源。

贝弗莉:我们坐在花园里，看着一些树在变颜色，有很多漂亮的橙色和红色。树叶正在改变颜色，因为在每年的这个时候，落叶树会从叶子中提取营养物质因为它们会把叶子掉下来，这样它们就不会浪费尤其是蛋白质，氮。树叶对树木来说很难得到，它们不想浪费任何叶子。树木和其他植物的叶子通常是绿色的，因为它们含有一种叫做叶绿素的色素，它可以进行光合作用。它从阳光中为植物提供能量。所以，当它们分解绿色叶绿素时，就会发现黄色和橙色的类胡萝卜素，它们一直都在那里。但它们不容易损坏，所以寿命更长。我们在一些树上看到的红色是由树木产生的新色素产生的。这些色素叫做花青素。我们真的不知道树为什么会变红。 Some people think it's to protect the leaves from UV damage. Other people think it's actually a signal to insects to say that these leaves aren't good to eat anymore, and so, don't waste your energy and time coming here. So, the leaves fall off deciduous trees because they can't really do anything useful over the winter. There's not going to be enough light or warmth to photosynthesise. Actually, having a lot of leaves can be quite dangerous if it's very windy. It adds to the surface area of the tree and makes it more vulnerable to losing branches or even being blown over entirely in strong winds. So, this whole process starts off because day length starts to decrease. That sends signals around the plant to start this process of breaking down the chlorophyll and getting the leaves ready to shed. So, people often ask if climate change is likely to affect this process. It won't affect the onset because that's regulated by day length and of course, the reason trees use day lengths to decide when it's winter is that it's the most reliable cue. It doesn't matter what the weather is doing. If the days are getting shorter then winter is coming. So climate change won't affect that, but the degree to which it's warm will affect how quickly the process occurs and how long those lovely colours are around for, and how quickly the leaves are shed.