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Fertilizer production and fossil fuel combustion have altered the N cycle, increasing the amount of N atmospheric reactive compounds to double compared to preindustrial levels. In this context, experimental manipulations are crucial to elucidate forest ecosystem responses to increased N deposition, particularly forest N dynamics, ecosystems' C uptake capacity and tree ecophysiological responses. The AnaEE research platform FoR2N consists of long-term manipulative experiments that simulate elevated N atmospheric deposition in Italian forests across various sites and climatic conditions. Three sites are in the northeastern Alps (Quercus petraea and Fagus sylvatica forests), and one in the Central Apennines (Fagus sylvatica forest). In every site there are three control plots and three below-ground fertilizations are provided three times in each vegetative season starting from 2015. In three of the four sites, the role of canopies in intercepting atmospheric N inputs is evaluated by applying N also above the canopies, providing a realistic scenario about future N deposition on forest ecosystems. Recent FoR2N outcomes found no evidence of nutritional and physiological impairments in response to elevated N input [1] and highlight the prominent role of the canopy in intercepting considerable amounts of N from atmospheric deposition [2], revealing underrecognized processes that are essential for a deeper mechanistic understanding of the N cycle in forest ecosystems [2,3,4]. Further, species-specific altered wood densities of trees subjected to the above canopy fertilization were found [5], with potentially relevant implications for future forest management and timber production.
