Chlorophyll fluorescence signature of European forests is affected by species specific features, latitude and tree species composition. Insights from a terrestrial survey.

A comprehensive assessment of the Chlorophyll a Fluorescence (ChlF) features in European forests was carried out in the years 2012-2013 within the European project FunDivEUROPE (7FP). This project was aimed at explore the functional role of the forest biodiversity along a latitudinal and ecological gradient in Europe (Finland, Poland, Germany, Romania, Italy, Spain). As part of this project, physiological and pathological responses of trees were assessed by means of foliar analysis on selected trees. The leaf parameters measured were: diffusion of pathogens and insects attacks on leaves, nitrogen content, carbon isotope composition and photosynthetic efficiency, detected by means of chlorophyll a fluorescence (ChlF) parameters (by using the prompt fluorescence analysis and the JIP-test). This presentation reports some results obtained with ChlF analysis at European scale pointing out the role of ecological and structural factors (including tree diversity) on the photosynthetic efficiency of tree species. ChlF parameters vary significantly across species: conifers showed the highest overall photosynthetic efficiency (measured by Performance Indices), whereas Mediterranean oaks had the /lowest ability to trap photons (measured by FV/FM). The Central European forests (Germany and Poland) showed higher Performance Indices values, with respect to the forests at the Southernmost and Northernmost edges. High solar radiation and temperature depress, at continental scale, the quantum yield efficiency (FV/FM) and PI on absorption basis (PIABS) but, at the same time, enhance the efficiency of the I-P phase of the fluorescence transient. PIABS was in general positively correlated with structural characteristics of the forest stand, such as basal are and leaf area index. The effects of tree diversity, however, was species-specific and site-specific. Picea abies, the most common tree species in the project sites, showed opposite patterns in Finland (negative correlation between PIABS and Shannon Index) and in Romania (positive correlation between the same parameters). In Quercus ilex (in Italy and Spain) PIABS is generally negatively correlated with Shannon Index. These results are discussed in terms of competition/ facilitation between different tree species in relation to their ability to exploit ecological resources. The outcomes for forest management is also discussed.