Temporal variation in total leaf phenolics concentration of Quercus robur in forested and harvested stands in northwestern Spain

Abstract

Phenolic compounds show intraspecific variation and this may be important in resistance of plants to herbivory. Changes in total leaf phenolics concentration in young Quercus robur L. trees growing under pine canopies and those growing in recently tree harvested areas were studied for 3 years in northwestern Spain. The oaks from the felled areas had a greater leaf phenolics concentration than those under pine canopies and showed less variation between individuals from the population. The average leaf phenolics concentrations also varied significantly between study years. The variations during leaf development and growth are in accordance with the majority of hypotheses that explain investment in secondary metabolism compounds. Leaf phenolics concentrations decreased rapidly during leaf maturity and senescence, but this decrease depended on the time of leaf shedding, the concentration being substantially lower in the year when leaves had been attached longer to the tree. Variation of leaf phenolics concentration was greater in senescent leaves than in green leaves. Such high concentration variability represents a source of spatial and temporal heterogeneity not only for potential herbivores but also for the soil nitrogen cycle in terrestrial ecosystems.Key words: total phenolics, northwestern Spain, Quercus robur, Pinus pinaster, forest harvest, leaf senescence.