Canopy structure, vertical radiation profile and photosynthetic function in a Quercus ilex evergreen forest

The studied evergreen forest dominated by Quercus ilex showed a leaf area Index (LAI) of 4.5, of which 61 % was accumulated within the tree layer, 30 % within the shrub layer, and 9 % within the herb layer. The leaves of all the species were +/- horizontally oriented (41 degrees), absorbing a relevant percentage of incident irradiance. The high LAI drastically modified the quality and quantity of solar radiation on the forest underground. The spectral distribution of the radiation under the forest was markedly deficient in blue and red wavelengths. The maximum absorption in these spectral bands was found in spring, when net photosynthetic rate (P-N) was at its maximum, and in summer, when new leaves reached 90 % of their definitive structure. The vertical radiation profile showed an evident reduction of the red-far red ratio (R/FR). Radiation quality and quantity influenced leaf physiology and morphology. Clear differences in leaf size, leaf water content per area (LWC) and specific leaf area (SLA) on the vertical profile of the forest were observed. All the shrub species showed similar SLA (12.02 m(2) kg(-1), mean value). The ability to increase SLA whilst simultaneously reducing leaf thickness maximized the carbon economy. The high chlorophyll (Chl) content of shrub layer leaves (1.41 g kg(-1) mean value) was an expression of shade adaptation. Both leaf morphology and leaf physiology expressed the phenotypic plasticity, Q. ilex, Phillyrea latifolia and Pistacia lentiscus of the forest shrub layer showed wide differences in leaf structure and function with respect to the same species developing under strong irradiance (low maquis): a 57 % mean increase of SLA and a 86 % mean decrease of P-N They showed high leaf plasticity. Leaf plasticity implies that the considered sclerophyllous species has an optimum developmental pattern achieving adaptation to environments.