Why Leaves Change Color
秋季彩葉紛飛(Chinese)

The Splendor of Autumn
Every autumn we revel in the beauty of the fall colors. The mixture of red, purple, orange and yellow is the result of chemical processes that take place in the tree as the seasons change from summer to winter.

During the spring and summer the leaves have served as factories where most of the foods necessary for the tree's growth are manufactured. This food-making process takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green color. This extraordinary chemical absorbs from sunlight the energy that is used in transforming carbon dioxide and water to carbohydrates, such as sugars and starch.

Along with the green pigment are yellow to orange pigments, carotenes and xanthophyll pigments which, for example, give the orange color to a carrot. Most of the year these colors are masked by great amounts of green coloring.

Chlorophyll Breaks Down
But in the fall, because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process. The chlorophyll breaks down, the green color disappears, and the yellow to orange colors become visible and give the leaves part of their fall splendor.

At the same time other chemical changes may occur, which form additional colors through the development of red anthocyanin pigments. Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange. The autumn foliage of some trees show only yellow colors. Others, like many oaks, display mostly browns. All these colors are due to the mixing of varying amounts of the chlorophyll residue and other pigments in the leaf during the fall season.

秋季彩葉紛飛(Colorful Fall Leaves)
最近自然歷史步行導覽活動
最近綠色文化生態旅遊活動

一般植物的綠葉除了葉綠素以外，還同時含有花青素、胡蘿蔔素、葉黃素等其他色素，到秋冬之際，葉柄基部產生厚壁組織「離層」，切斷葉片與枝幹間水分與養分的交流。秋冬白天強烈的陽光促使葉綠素分解，入夜後 氣溫驟然降低，阻礙葉綠素的合成，於是綠色便逐漸褪去，殘存於葉片中的其他色素便顯現出來。

若殘存的色素是胡蘿蔔素與葉黃素時，葉片便呈黃色；若黃色素中含有單寧物質，則葉片呈金黃色；而紅葉則 是葉片驟然遇到低溫，大量堆積的醣類將葉黃素還原成花青素，再加上類胡蘿蔔素分解後所產生的紅色色素，於是一場綠葉換紅葉的表演，就陸續的在山野間上演了。