Seasonal changes in photosynthetic pigments and antioxidants in beech (Fagus sylvatica) in a Mediterranean climate: implications for tree decline diagnosis

Abstract

Seasonal changes in all major and minor photosynthetic pigments and antioxidants were studied in sun and shade in beech (Fagus sylvatica L.) leaves and buds under Mediterranean conditions. Both sun and shade leaves differed progressively in their biochemical and morphological characteristics during the course of leaf ageing. Sun leaves were 3-fold thicker, pigment content was highly reduced and the leaves were protected by a much more powerful antioxidative system. Pigment content decreased progressively during summer in sun leaves and remained stable in shade leaves. From July to September, there was no chlorophyll (Chl) biosynthesis, so photodegradation of Chl was not compensated by production of new Chl. This reduction in Chl occurred in parallel with an increment in tocopherols. Natural leaf senescence occurred first in sun leaves. During this process, Chl was completely degraded, xanthophylls were esterified with fatty acids, and violaxanthin was converted into zeaxanthin, while carotenes remained stable. One of the main indicators of tree decline and air pollution is accelerated leaf ageing, and this process is characterised in beech leaves by tocopherol and pigment destruction, so we have used these criteria to verify whether these parameters can be used as early indicators of tree decline. All pigments and antioxidants (including α -tocopherol) decreased with beech decline, except xanthophyll cycle pigments. As reduction of these compounds is concomitant with a similar level of Chl degradation, Chl determination is proposed as a simple method sufficient to predict the early stages of beech decline at a biochemical level.