Date of Award


Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Plant, Soil, and Environmental Sciences


Ivan J. Fernandez

Second Committee Member

Lindsey Rustad

Third Committee Member

David B. Dail


Nitrogen is commonly thought of as the most limiting nutrient to plant growth, yet elevated N deposition can result in N accumulating in excess of biotic demand, a condition known as 'TI Saturation." Excess N can perturb soil microbial N transformations and may cause initial increases in net N mineralization rates followed by decreases in net N mineralization with concomitant increases in net nitrification. Along with increases in net nitrification and N loss, N saturation is often associated with a loss of forest productivity. Understanding nitrogen dynamics in soil under enhanced N deposition is key to predicting future forest health. We studied forest floor and mineral soils at the Bear Brook Watershed in Maine (BBWM), a paired watershed experiment with one watershed serving as a reference and another treated with (NH&SO4. We used both lab incubations and in situ measurements to evaluate net N mineralization and net nitrification in both watershed soils. Significantly higher net N mineralization and net nitrification rates were observed in the treated watershed by both methods. For example in situ net N mineralization was 4.25 mg kg" day" in the treated watershed compared to 3.00 mg kg-' day-' in the reference watershed. Soil under differing dominant forest types present in these watersheds resulted in different N cycling rates and different response to long-term N fertilization: hardwoods had higher N mineralization rates in the 0 horizons, however softwoods had higher rates in the mineral soils. Despite different N cycling rates, influenced by forest cover and treatment, input-output estimates suggested -80% N retention in treated watershed, despite the long-term N amendments to this watershed, and -96% N retention in the reference watershed.

Included in

Soil Science Commons