Abstract
In the light of expanding global air pollution levels, we have been engaged in better understanding the effects of increased Nitrogen (N) deposition rates on Carbon (C) sequestration in forest ecosystems. While most studies investigating N deposition have been using ground fertilization methods, those may not be the most representative of true deposition scenarios. Indeed, extensive research has demonstrated the complex relationship between atmospheric deposition and the tree canopy. Thus, in the current research an improved approach of above canopy N application was adopted, which may better simulate actual deposition effects. The experimental site is located in the Monticolo forest, Italy, where pure mature Sessile oak (Quercus petraea L.) plots have been treated since 2015 with N fertilizer applied to either the forest floor directly, or to the canopy, comparing the two methods alongside unfertilized control plots. However, until the start of the current PhD research, reports showed no effects of any of the N treatments on tree growth, after five years of continuous fertilization. Hence, a goal was set to explore whether possible productivity inhibition exists in the system. Elemental imbalances, such as Phosphorus (P) deficiencies, may play a crucial role in correctly assessing N deposition effects on plant productivity. Such nutrient imbalances may in fact stem from increased N inputs, and may shift ecosystems from N to other nutrimental limitations. Therefore, the first objective was to assess the state and availability of macro and micro elements in the system, with an emphasis on P, with the aim to gather whether our system may be depleted of certain essential nutrients, beyond N, or rather an inhibition due to toxic elemental overload may be present. is to assess. Furthermore, a second objective was to introduce additional growth traits that was not measured thus far in the form of ring widths and wood densities in order to detect potential underlying intrinsic effects under the different N application methodologies. A further experimental site under the Italian Nutrient Deposition Network (INDN), where a parallel canopy vs. understory N fertilization experiment has been performed on European beech (Fagus sylvatica L.), was incorporated in the second objective in order to provide a broader regional and species representation of the expected findings.