Why do only some leaves turn red in the fall? Scientists can't agree on an answer
Summary
Scientists are unsure why only some trees' leaves turn red in the fall. While there are theories, including that red pigments act as a sunscreen, there is no single agreed-upon explanation.Key Facts
- Some trees' leaves turn red in autumn, but scientists do not know exactly why.
- All trees lose green chlorophyll as leaves die, revealing yellow colors that were already present.
- Red pigments are newly made just before the leaves fall.
- One theory suggests red pigments protect leaves from too much light as chlorophyll fades, called the photoprotection hypothesis.
- More red trees are found in the northeastern United States than in Europe, which has less sunlight.
- Trees working with nitrogen-fixing bacteria, which supply plenty of nitrogen, often do not turn red.
- There is no consensus among scientists about the reason for red leaf colors.
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