Abstract
Increasing atmospheric nitrogen (N) emission from human activities has emerged as one most serious global change problems. The anthropogenic input of N in forests could deeply transform phytocenosis and ecosystem functions. In N-limited ecosystems, N deposition may enhance plant growth and thus enhance carbon sequestration. Nevertheless, an excess of N could promote N saturation process and trigger forest decline. The consequences of increased N deposition on forests depend largely on the fate of N in the ecosystem compartments. To better simulate increasing N depositions, we will perform a long-term canopy N-fertilization in two temperate forests, willing to provide better understating of direct N plant uptake by canopy and soil NO3--N leaching, against traditional below-canopy fertilization performed by most of the studies so far. To describe the fate of the applied N, stable isotope techniques will be adopted: the forest sites will be fertilizer with NH4NO3, at a known isotopic signature, both below and above the forest canopy in 18 different plots, the ecosystem components (plant, soil and water) will be sampled periodically to determine the total N content and its isotopic signature. The δ15N values permit to calculate the recovery of N-fertilizer in tree canopy, soil and leaching-water. Comparing the two different fertilization strategies, I will verify the hypotheses that the canopy uptake under experimentally high N deposition, would be very high. This project will get insight into the effects of N depositions on forests, to develop scientific knowledge useful for future predictions of the response of these ecosystems to global change.