The influence of terpenoids on decomposition and nitrogen cycling in forest ecosystems will be investigated. Terpenoids are volatile organic compounds naturally produced by many plants. The central idea is that they are produced in large enough quantities in forest ecosystems and persist long enough in forest soils to act as regulators of organic matter breakdown and key processes in the nitrogen cycle such as mineralization and nitrification; the former (mineralization) is the microbially mediated conversion of organically-bound nitrogen to inorganic nitrogen forms that can be taken up by plants, and the latter (nitrification) is the microbial transformation of ammonium to nitrate. The research will be conducted on ponderosa pine forests of New Mexico, although the results should have very general applicability. The four specific objectives of research are as follows: 1) identify the temporal variation in terpenoid levels within the soil profile of an undisturbed soil profile in a ponderosa pine forest in a field study; 2) correlate terpenoid variation in the soil profile with variation in decomposition and nitrogen dynamics in the soil in the laboratory; 3) identify the specific terpenoids acting as regulators of decay and nitrogen cycling in the laboratory; and 4) test the results of the laboratory investigations in the field through a manipulation experiment involving burning to volatilize the terpenoids and then adding known amounts of specific terpenoids back to the system and following decomposition and nitrogen dynamics. The significance of this research lies in its focus on a factor, terpenoid concentration, that can influence the nitrogen cycle in forest ecosystems. Nitrogen is often a limiting nutrient in forest ecosystems and understanding the cause(s) of this limitation would have important implications for forest management. Dr. White is a young and very promising researcher and he will receive strong support, both technical and intellectual, for his research at the University of New Mexico. The Ecosystem Studies Program recommends that this award be made.