Photosynthetic efficiency of forest trees is influenced by ecological factors, stand structure and tree diversity in European forests

The functionality of forests depends largely from the health and physiological performances of singular trees. There is a large body of literature that evidences functional interaction (competition and/or facilitation) between neighboring trees of different species. These interactions may be at hypogeal (water and nutrient use) or epigeous (light use) level and can be assessed by means of foliar analysis. Among all the parameters retractable from leaves, the photosynthetic efficiency assessed with chlorophyll a fluorescence – ChlF, demonstrated to be very informative. Within the project FunDivEUROPE, ChlF parameters were assessed through two European tree diversity platforms, constituted respectively by experimental and explorative forests. The overall survey covers all the main vegetational and climatic conditions, from Mediterranean to boreal regions. The patterns of ChlF parameters in relation to tree diversity depended from ecological factors of sites and tree species. P. abies trees in the Northernmost explorative site decreased their photosynthetic efficiency with increasing diversity, but the opposite trend was observed at the Southern site. The role of climatic and structural factors is analyzed and discussed. P. abies responded differently also in two of the experimental sites. Opposite patterns were attributed to the competition for light at different state of development of the stands.