Early Autumn Senescence in Red Maple (Acer rubrum L.) Is Associated with High Leaf Anthocyanin Content.

Rachel Anderson,Peter Ryser

doi:10.3390/plants4030505

Abstract

Several theories exist about the role of anthocyanins in senescing leaves. To elucidate factors contributing to variation in autumn leaf anthocyanin contents among individual trees, we analysed anthocyanins and other leaf traits in 27 individuals of red maple (Acer rubrum L.) over two growing seasons in the context of timing of leaf senescence. Red maple usually turns bright red in the autumn, but there is considerable variation among the trees. Leaf autumn anthocyanin contents were consistent between the two years of investigation. Autumn anthocyanin content strongly correlated with degree of chlorophyll degradation mid to late September, early senescing leaves having the highest concentrations of anthocyanins. It also correlated positively with leaf summer chlorophyll content and dry matter content, and negatively with specific leaf area. Time of leaf senescence and anthocyanin contents correlated with soil pH and with canopy openness. We conclude that the importance of anthocyanins in protection of leaf processes during senescence depends on the time of senescence. Rather than prolonging the growing season by enabling a delayed senescence, autumn anthocyanins in red maple in Ontario are important when senescence happens early, possibly due to the higher irradiance and greater danger of oxidative damage early in the season.

Highlights

Development of the bright colours of many deciduous trees and shrubs during autumn senescence is arguably the most spectacular and attractive form of plant senescence
While the yellows and oranges are a result of unmasking the carotenoids during chlorophyll degradation, and the browns oxidation products of phenolics associated with cell death, the reds are mostly caused by de novo synthesis of anthocyanins [1]
Our data show a strong link between time of senescence and maximal anthocyanin accumulation in senescing leaves among the studied red maple trees, with early senescing leaves having higher anthocyanin concentrations than late senescing ones

Summary

Introduction

Development of the bright colours of many deciduous trees and shrubs during autumn senescence is arguably the most spectacular and attractive form of plant senescence. Theories about the role of anthocyanins range from an extravagancy without a vital function [1], excretions to detoxify the plant [4], a warning signal to deter herbivores [5,6] to an important factor for protecting leaves against excessive light [7]. Leaves with anthocyanin tolerate more light than green leaves before photosystem II is inhibited [11] and anthocyanin-deficient mutants of deciduous shrubs are more damaged by photo-oxidative stress than wild types with anthocyanin [12]. The elaborate xanthophyll system dissipates excess energy, but anthocyanins would provide a biochemically more parsimonious alternative to this in a senescing leaf [14]

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