A test of the photoprotection hypothesis for the evolution of autumn colours: Chlorophyll resorption, not anthocyanin production, is correlated with nitrogen translocation.

Abstract

A prominent hypothesis for the adaptive value of anthocyanin production in the autumn leaves of trees and shrubs is that anthocyanins protect leaves from photooxidative stress at low temperatures, allowing a better resorption of nutrients-in particular, nitrogen-before leaf fall. While there is evidence that anthocyanins enable photoprotection, it is not clear whether this translates to improved nitrogen translocation and how this can explain inter-specific variation in autumn colours. A recent comparative analysis showed no correlation between temperature and anthocyanin production across species but did not analyse nitrogen content and nitrogen resorption efficiency. Here, we provide this comparison by analysing the nitrogen content of mature and senescent leaves and their autumn colours in 55 species of trees. We find no correlation between the presence of anthocyanins and the efficiency of nitrogen resorption. We find, instead, that nitrogen resorption is more efficient in species with yellow autumn colours, pointing to chlorophyll resorption, rather than anthocyanin synthesis, as the main determinant of nitrogen translocation efficiency. Hence, our results do not corroborate the photoprotection hypothesis for the evolution of autumn colours.