Cloudy, wet autumns lead to drabber autumn leaves. If the summer has been dry, that helps too. In sunny conditions, photosynthesis can still occur in the autumn and this uses up the remaining chlorophyll (no longer being produced by the trees) and so the sugar concentration in the leaves further increases, and more anthocyanin is produced. In dry weather, the leaf sugars become concentrated and produce more anthocyanin. The ingredients for a perfect autumnĪccording to Kate Lewthwaite of the Woodland Trust – the manager of the Nature’s Calendar Project – the perfect ingredients for vibrant autumn colours are cold – but not freezing – nights, dry weather and bright sunny days. Crucially, the production of anthocyanin is boosted by sunlight, drought and temperatures staying above freezing. Concentrated in the leaf, sugars react with proteins in the cell sap to produce anthocyanin, a purply red pigment that causes apples to turn red and black grapes purple. Photograph: Armin Weigel/dpa/Corbis Photograph: Armin Weigel/ Armin Weigel/dpa/Corbis Why leaves turn redĪs a tree prepares to shed its leaves in winter, a layer of cells form across the base of the leaf stalk which restricts the movement of sugars back into the body of the tree. Low temperatures also destroy chlorophyll so cold nights quicken the yellowing of leaves.Ī girl throws many-colored autun leaves into the air in Straubing, Germany, 03 October 2013. As the green fades, the yellow carotene remains. This is a yellow pigment but it isn't visible until the production of chlorophyll slows in autumn. But the crucial chemical pigment behind leaves turning yellow is carotene – the main pigment in carrots, which is also found in leaf cells in the growing season. In winter, with less sunlight, chlorophyll is not produced. If a plant is kept away from sunlight, it yellows: a good example is grass covered by a tent. In summer, it is continuously created to keep the leaves green. Plants need sunlight and warmth to produce chlorophyll, which is also destroyed by bright sunlight. The sugars produced by photosynthesis are transported around the tree and stored in the leaves. This energy is captured by chlorophyll, the green pigment found in leaves and green parts of plants. Plants make food to grow via photosynthesis (which means “putting together with light”) converting carbon dioxide and water into sugars using the energy in sunlight.
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