The phenomenon of red and yellow autumn leaves: Hypotheses, agreements and disagreements

• Published in: Journal of evolutionary biology Vol. 35; no. 10; pp. 1245 - 1282
• Main Author: Lev‐Yadun, Simcha
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.10.2022; John Wiley and Sons Inc
• Subjects: Amino acids; Amino Acids - metabolism; Anthocyanins; Anthocyanins - metabolism; aphids; aposematism; Autumn; carotenoids; Chlorophyll; Chlorophyll - metabolism; color; Coloration; co‐evolutionary hypothesis; Ecologists; Ecology; Environmental degradation; evolutionary biology; Herbivory; Hypotheses; leaf abscission; Leaf fall; Leaves; photoprotection; Photosynthesis; Physiology; Pigments; Plant Leaves - metabolism; radiation resistance; Red pigments; Review; Reviews; Scientists; Seasons; Woody plants; co-evolutionary hypothesis; anthocyanins; carotenoids; herbivory; photoprotection; aposematism; aphids
• ISSN: 1010-061X; 1420-9101; 1420-9101
• DOI: 10.1111/jeb.14069

Yellow and red autumn leaves are typical of many temperate/boreal woody plants. Since the 19th century, it has been either considered the non‐functional outcome of chlorophyll degradation that unmasks the pre‐existing yellow and red pigments or that the de novo synthesis of red anthocyanins in autumn leaves indicated that it should have a physiological function, although it was commonly ignored. Defending free amino acids and various other resources released especially following the breakdown of the photosynthetic system, and mobilizing them for storage in other organs before leaf fall, is the cornerstone of both the physiological and anti‐herbivory hypotheses about the functions of yellow and red autumn leaf colouration. The complicated phenomenon of conspicuous autumn leaf colouration has received significant attention since the year 2000, especially because ecologists started paying attention to its anti‐herbivory potential. The obvious imperfection of the hypotheses put forth in several papers stimulated many other scientists. Hot debates among physiologists, among ecologists, and between physiologists and ecologists have been common since the year 2000, first because the various functions of yellow and red autumn leaf colouration are non‐exclusive, and second because many scientists were trained to focus on a single subject. Here, I will review the debates, especially between the photoprotective and the anti‐herbivory hypotheses, and describe both the progress in their understanding and the required progress. Yellow and red autumn leaves typical to temperate/boreal trees defend important resources released following the photosynthetic system breakdown, and mobilized for storage to be used in the next spring. This coloration, especially red, defends from excess light and oxidative stress and against herbivores. I describe the hypotheses, findings and disagreements about the functions and evolution of yellow/red autumn leaves.