Nitrogen Nutrition of Trees in the Northern Forest

The availability of soil nitrogen is one of the most important, limiting resources in the Northern Forest region. The current computer model for nitrogen cycling in the Northern Forest assumes that trees take up only inorganic nitrogen. However, recent studies show that plants also take up amino acids, an organic form of nitrogen from the soil.

Ecosystem structure and health are being altered by atmospheric nitrogen deposition, rising concentrations of atmospheric carbon dioxide and ozone, and climate change. For example, atmospheric nitrogen deposition changes the relative balance of inorganic and amino acid nitrogen in soil, which alters forest composition through a decline of tree and fungal species that rely on amino acids for nutrition. In the models used to predict forest responses to these environmental drivers, inorganic nitrogen is assumed to be the only plant-available pool of nitrogen. By excluding amino acids as a source of nitrogen for tree growth, it is unclear whether the current generation of biogeochemical models is capable of predicting ecosystem health in response to environmental change. Thus, the objective of this research is to understand the role of amino acids in sustaining ecosystem structure and health in the Northern Forest region. This will be achieved by examining the factors affecting amino acid production and turnover and the degree to which amino acids contribute to the nitrogen nutrition of trees.