Date of Award


Degree Type


Degree Name

Master of Science




Dr. Hugh Henry


Winter climate plays a critical role in the cycling of nitrogen (N). Soils in temperate regions may be particularly vulnerable to freeze-thaw cycles since they remain close to freezing over much of winter. These systems are also experiencing high rates of atmospheric N deposition and the extent to which these added inputs can be retained has important implications for productivity and plant species composition. Warming treatments were applied year-round or exclusively during winter and were crossed with a N addition treatment. I examined the interactive effects of warming and N deposition on i) net N mineralization and leaching losses using in situ resin cores and lysimeters, and ii) the retention of N after the growing season and over winter using 15N added as a pulse during spring melt 2007. Warming treatments did not affect net N mineralization or leaching over winter 2007 or 2008, however warming over winter 2007 increased mineral N availability the following growing season. Changes in soil temperatures in early spring may have important carry over effects on growing season N dynamics. Likewise, warming over winter did not alter 15N retention. Year-round warming increased the recovery of excess 15N in plants to the extent that it equaled the reductions in plant excess 15N recovery caused by nitrogen fertilization. Nitrogen fertilization caused substantial soil 15N losses, which overwhelmed any warming effects on 15N plant recovery. Climate warming may only moderate the effects of N deposition on ecosystem N losses to a limited extent in this system, although more extreme responses to more intense warming cannot be ruled out.



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