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Mary Arthur


The study of biogeochemical cycles and their role in ecosystem function has helped to highlight the impacts of human activities on natural processes. However, our understanding of the effects of nitrogen (N) deposition on forested ecosystems remains limited due to the variable controls on N cycling. Soils, microclimate, and vegetation can influence rates and processes of N cycling, singly or in concert at multiple scales. Understanding how these factors influence N cycling across the landscape will help to elucidate the impacts of N deposition. The objectives of this study were to characterize variation in soils, microclimate and vegetation characteristics, and N cycling and decomposition dynamics across the landscape in a region impacted by N deposition. Relationships among these factors were explored to determine the main factors influencing N cycling and decomposition. Strong differences in net N mineralization and nitrification were found between forest stands with contrasting species composition and moisture availability. Nitrate production and leaching were related to sugar maple abundance, and base cation leaching was correlated with nitrate concentrations in soil solutions. Decomposition experiments were installed to examine the effects of substrate quality, microclimate and N availability on decay rates. Nitrogen amendments for the most part did not affect decomposition rates of wood and cellulose, and mass loss rates were correlated with microclimate and forest floor characteristics. In contrast, microclimate did not seem to affect leaf litter decay rates, and the results suggest that the presence of invertebrates may influence mass loss to a greater degree than moisture or litter quality. This work highlights the large degree of variability in N processing across the landscape and suggests that differences in microclimate and species composition may help to predict the impacts of chronic N deposition on N cycling and retention.