Why do leaves change color?

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Leaves change color during autumn due to a combination of factors, including changes in pigments, the length of daylight, and temperature. Throughout spring and summer, leaves are green because of the presence of chlorophyll, a pigment that plays a crucial role in photosynthesis. As autumn approaches, trees prepare for winter by stopping the production of chlorophyll, causing the green color to fade. This reveals other pigments present in the leaves, such as carotenoids (yellow and orange) and anthocyanins (red and purple) 1. The process of chlorophyll loss is influenced by weather conditions. A succession of warm, sunny days and cool, crisp nights promotes the most spectacular color displays. During these days, lots of sugars are produced in the leaf, but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions, with abundant sugar and light, spur the production of anthocyanin pigments, which tint reds, purples, and crimson1. Carotenoids, responsible for yellow and gold colors, are always present in leaves, so these colors remain fairly constant from year to year1. Soil moisture also affects autumn colors. The countless combinations of temperature, moisture, and other environmental factors ensure that no two autumns are exactly alike. A late spring or a severe summer drought can delay the onset of fall color, while a warm period during fall can lower the intensity of autumn colors1.
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