Why Do Leaves Change Color in the Fall?树叶为什么在秋天会变色？

秋天，道路两旁黄的、红的树叶将街道装点得秋意盎然。然而，树叶为什么会在秋天变黄或者变红，你知道其中的原因吗？

In early fall， the weather conditions start to change： Itgets cooler — with crisp， but not freezing， nights — andthe duration of daylight is reduced. 1）Collectively， there’sless sunlight for plants to 2）harvest using the chlorophyll intheir leaves， so 3）deciduous trees begin to pull back theirinvestment in keeping them alive.

While chlorophyll is the most common 4）pigment thatplants use to harvest light — green leaves look that waybecause chlorophyll absorbs red and blue light and reflectsgreen light — plants often have a variety of secondarypigments， too. As the chlorophyll in a tree’s leaves begins towane， these underlying pigments become visible. This is whatwe’re seeing when fall foliage peaks.

Red and purple hues stem from secondary pigmentscalled anthocyanins， while carotenoids and xanthophylls yieldoranges and yellows， respectively. Within a single group， suchas the maples， different species have evolved their own suiteof pigments. Red maples， for example， turn a brilliant scarlet inthe fall， while black maples become yellow.

1） collectively adv. 共同地

2） harvest v. 收获

3） deciduous adj. 落叶性的；脱落性的

4） pigment n. 色素；颜料

初秋时节，天气情况开始变化：天气变凉爽，夜晚温度下降，但尚未结冰，白昼缩短。（剩余233字）