Variability and trends of atmospheric deposition, climate conditions, and radial tree growth in Romanian eLTER Sites

Atmospheric deposition plays a crucial role on forest ecosystems status, as it transports a range of micro- and macronutrients, along with pollutants, from the atmosphere to forest environment. As it’s well known, variations in climatic factors significantly influence tree growth. The amount of precipitation, which dissolves deposited elements and alters soil element concentrations, plays a determinate role in shaping tree growth. As a result, atmospheric inputs can be a substantial contributor to the annual nutrient supply required for tree growth. However, excessive nutrient and pollutant deposition can have negative effects on trees, soil quality, and water resources. Additionally, the combined impact of air pollution and climate change can suppress nutrient availability, soil moisture and finally, tree growth and forest productivity. This study evaluates the effects of atmospheric deposition and climatic factors, such as temperature and precipitation, on tree growth in four eLTER sites across Romania. It also examines the temporal variations of these parameters within these locations. The main objective is to analyse long-term monitoring data, i.e., radial growth of trees as an indicator of forest productivity in response to pollutants and atmospheric deposition. To achieve this, a quantitative assessment of atmospheric deposition flux has been carried out over the last decade by periodically collecting throughfall water in permanent research plots, followed by the determination of mineral ion concentrations. Radial tree growth was measured using band dendrometers. Principal Component Analysis was used to determine the relationships between tree growth, climate factors, and atmospheric deposition. The results indicate that, despite a decreasing trend in atmospheric deposition, they may still have a negative impact on tree growth. Furthermore, correlation matrix analysis of the studied parameters revealed that nitrate had the most significant influence on tree growth, followed by temperature, precipitation, and soil pH. Overall, preliminary results provide an overview of the temporal variability of atmospheric deposition across forest ecosystems in Romania.