十万个为什么·科学启蒙30篇（1）
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Why Do Leaves Change Color in Autumn?
为什么树叶在秋天会变色？
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In autumn, days get shorter and temperatures drop slowly.秋天，白昼变短，气温缓慢下降。
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Trees sense these changes and begin to prepare for winter rest.树木感知到这些变化，开始为冬季休眠做准备。
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Chlorophyll, the green pigment in leaves, breaks down as sunlight fades.随着光照减弱，叶片中的绿色色素叶绿素逐渐分解。
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When green fades, yellow and orange pigments called carotenoids become visible.绿色褪去后，类胡萝卜素呈现的黄色和橙色便显露出来。
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Some trees also make red pigments called anthocyanins when sugars get trapped in leaves.有些树木在糖分滞留在叶片中时，还会生成红色色素花青素。
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Soil moisture and weather conditions affect how bright the colors appear.土壤湿度和天气状况会影响秋叶色彩的鲜艳程度。
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This color change helps trees conserve energy before shedding leaves.这种变色有助于树木在落叶前节约能量。
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Not all trees change color—evergreens keep their needles year-round.并非所有树木都会变色——常绿树全年保持针叶。
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Deciduous trees lose leaves to avoid water loss in cold, dry air.落叶树通过落叶来避免在寒冷干燥空气中失水。
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Scientists study leaf chemistry to understand climate change effects on forests.科学家通过研究叶片化学成分，了解气候变化对森林的影响。