Throughout the summer, trees provide rich nutrition for leaves, making them absorb sunlight better. However, with the arrival of autumn, trees began to concentrate nutrition on the trunk and roots. The cork layer of the cell is formed at the slender petiole, leaving a "scar" and slowly suffocating. As a result, the leaves stopped producing chlorophyll and the green gradually faded. Those leaves with more lutein and carotene will appear yellow at this time.
After the nutrient supply of leaves is cut off, the remaining sugar can produce a pigment to brighten the leaves. Every year is different, depending on the temperature and sunshine.
In particular, in late autumn, the leaves of maple, cotinus coggygria and torch will turn red one after another. The reason is that the cells of their leaves contain not only chlorophyll, carotene and lutein, but also anthocyanin, which is a rare substance in other tree species. Under the climatic conditions of low temperature, low humidity and low light, the contents of chlorophyll, carotene and lutein gradually decreased, while anthocyanins increased. Anthocyanins turn leaves red under the action of acidic cell sap of maple leaves and other tree species.