<p>Human activity has globally increased the amount of nitrogen (N) entering ecosystems, which could foster higher rates of C sequestration in the N-limited forests of the Northern Hemisphere.&nbsp; Presently, these ecosystems are a large global sink for atmospheric CO2, the magnitude of which could be influence<img alt="Study Site Map" src="/research/sites/default/files/GradientProject_studysites.png" style="margin: 5px; width: 150px; float: right; height: 191px" title="Map of Study Sites" />d by the input of human-derived N from the atmosphere.&nbsp; Nevertheless, empirical studies and simulation models suggest that anthropogenic N deposition could have either an important or inconsequential effect on C storage in forests of the Northern Hemisphere, a set of observations that continues to fuel scientific discourse (Magnini et al. 2007, deVries et al. 2008, Reay et al. 2008).&nbsp; Although a relatively simple set of physiological processes control the C balance of terrestrial ecosystems, we still fail to understand how these processes directly and indirectly respond to greater N availability in the environment.&nbsp; The uptake of anthropogenic N by N-limited forest trees and a subsequent enhancement of net primary productivity have been the primary mechanisms thought to increase ecosystem C storage in Northern Hemisphere forests.&nbsp; However, there are reasons to expect that anthropogenic N deposition could slow microbial activity in soil, decrease litter decay, and increase soil C storage.&nbsp; Fungi dominate the decay of plant detritus in forests and, under laboratory conditions, high inorganic N concentrations can repress the transcription of genes coding for enzymes which depolymerize lignin in plant detritus; this observation presents the possibility that anthropogenic N deposition could elicit a similar effect under field conditions.&nbsp;</p><p>In our 16-yr-long field experiment, we have been able to document that simulated N deposition, at a rate expected in the near future, resulted in a significant decline in cellulolytic and lignolytic microbial activity, slowed plant litter decay, and increased soil C storage (+10%); this response is not portrayed in any biogeochemical model simulating the effect of atmospheric N deposition on ecosystem C storage.&nbsp; Our preliminary results support the hypothesis that simulated N deposition has down-regulated the transcription of fungal genes encoding lignocellulolytic enzymes, thereby slowing litter decay and substantially increasing soil C storage over a relative short duration.&nbsp; <em>The objective of this proposal is to understand the molecular mechanisms and metabolic processes by which simulated N deposition has slowed microbial decay of plant detritus, thereby increasing soil C storage in the wide-spread and ecologically important northern forest ecosystem.</em>&nbsp; We address our research objective using a combination of transcriptomic and metatranscriptomic approaches in parallel with biogeochemical analyses of soil C cycling.&nbsp; By linking the environmental regulation of microbial genes to biogeochemical processes, we endeavor to understanding the enhanced accumulation of soil C in response to a wide-spread agent of global change.<br />&nbsp;</p>