Does the Response of Soil Carbon to Nitrogen Addition Depend on the Type of Soil Carbon Present?

EPA Grant Number: F6F10348
Title: Does the Response of Soil Carbon to Nitrogen Addition Depend on the Type of Soil Carbon Present?
Investigators: Weiss, Marissa
Institution: Cornell University
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $111,172
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Terrestrial Systems Ecology


Human production of biologically available nitrogen (N) now exceeds available N production by all natural processes combined. Soils contain the largest near-surface reservoir of carbon (C), yet we do not know whether N deposition will stimulate soil decomposition, contributing to rising atmospheric CO2 concentrations.
The goal of my research is to quantify the response of soil C to N fertilization at the landscape scale using empirical tests that I will apply to an ecosystem model. Specifically, I will address three hypotheses:

  1. Decomposition of labile C with fast turnover times (decadal time scale) will be stimulated with added N, increasing CO2 loss to the atmosphere from the labile pool.
  2. Recalcitrant C with slow turnover times (>100 years) will be stabilized with added N, decreasing CO2 loss to the atmosphere from the recalcitrant pool.
  3. The rate and magnitude of CO2 loss from soils will ultimately be a function of the size of the faster-cycling labile C pool; in soils with a large labile C pool, CO2 loss will exceed C storage, resulting in a net increase in atmospheric CO2 with added N.


I will test this hypothesis across nine existing N fertilization experiments at northeastern forested sites. Using density fractionation and 14C, I will determine the long-term fertilization response of soil C pools to N. Using a laboratory incubation with a 15N addition and extracellular enzyme assays, I will determine the transient response of soil C to N fertilization, and elucidate mechanisms underlying the response. I will apply my experimental results to an ecosystem model to integrate the results with other ecosystem processes.

Expected Results:

My project will contribute new information about the response of multiple soil C pools to N deposition across a network of nine northeastern forested sites, with applications for management and policy. I will apply the outcomes of this research to improve model predictions of soil carbon response to nitrogen deposition.

Supplemental Keywords:

Soil organic matter, nitrogen deposition, soil respiration, extracellular enzyme activities, density fractionation, northeastern forests,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Monitoring/Modeling, Environmental Monitoring, Ecology and Ecosystems, atmospheric dispersion models, environmental impact, ecological models, atmospheric chemistry, nitrogen

Progress and Final Reports:

  • 2007
  • 2008
  • Final