Collaborative Research: Organic Nitrogen Cycling in Northern Hardwood - Conifer Forests

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The current conceptual model for the nitrogen (N) cycle of northeastern US forests stresses the importance of inorganic N forms (i.e., ammonium and nitrate) for tree growth and forest productivity. However, organic forms of N are also be taken up by plants. The overall objective of this proposal is to quantify the importance of organic N as a nutrient source in temperate forest ecosystems of the northeastern U.S. To achieve this objective, the factors that affect the production and turnover of organic N in the soil will be studied, focusing specifically on amino acids and amino sugars. The balance between the production and turnover of organic N will be assessed to determine the types and forms of N taken up by dominant tree species. These objectives will be met by establishing plants in single-species stands on two types of soil parent materials in western Connecticut and Massachusetts. Field and laboratory studies will be used to measure the pools, fluxes and uptake of organic N in the soil. The availability of N in the soil limits the productivity of forest ecosystems and their capacity to sequester rising concentrations of carbon dioxide, a greenhouse gas. By understanding the factors that affect the form and the quantity of N taken up by forest trees, this proposal will shed light on the processes regulating the availability of a key growth limiting soil resource and the degree to which forest ecosystems can be relied upon to absorb CO2 from the earth's atmosphere.