Tuesday, November 14, 2006 - 11:10 AM

Effects of Increased Nitrogen Inputs on Soil Microbes: Implications for Decomposition and N Cycling.

Matthew D. Wallenstein, Colorado State Univ, 307 East Plum St, Fort Collins, CO 80524

The effects of increased N inputs (either through deposition or fertilization) on soil organic matter decomposition and most aspects of the N cycle are generally well understood, though the mechanisms behind these responses are more elusive and controversial.  Recent work in a number of ecosystems has begun to shed light on the response of the microbial and soil faunal communities that are responsible for decomposition and N cycling processes.  In some cases, connections between microbial communities and functions are direct.  For example, ammonia oxidizer populations are closely linked to nitrification rates, which tend to increase in response to chronic N inputs.  However, most soil decomposition processes, which in large part control N availability and cycling, are the result of extracellular enzyme activities.  Therefore, the response of heterotrophic microbes to increased N is mediated through the production and activity of extracellular enzymes.  I will present a framework for connecting observed responses of microbial communities to changes in decomposition and N-cycling processes, in an effort to better understand the mechanisms that underlie ecosystem-level responses to increased N.