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

Seasonal changes in all major and minor photosynthetic pigments and antioxi dants were studied in sun and shade in beech (Fagus sylvatica L.) leaves an d buds under Mediterranean conditions. Both sun and shade leaves differed p rogressively 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 an tioxidative system. Pigment content decreased progressively during summer i n sun leaves and remained stable in shade leaves. From July to September, t here 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 occurre d first in sun leaves. During this process, Chl was completely degraded, xa nthophylls were esterified with fatty acids, and violaxanthin was converted into zeaxanthin, while carotenes remained stable. One of the main indicato rs of tree decline and air pollution is accelerated leaf ageing, and this p rocess is characterised in beech leaves by tocopherol and pigment destructi on, so we have used these criteria to verify whether these parameters can b e used as early indicators of tree decline. All pigments and antioxidants ( including alpha -tocopherol) decreased with beech decline, except xanthophy ll cycle pigments. As reduction of these compounds is concomitant with a si milar level of Chl degradation, Chl determination is proposed as a simple m ethod sufficient to predict the early stages of beech decline at a biochemi cal level.