US EPA

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: Manty, Dale
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

Objective:

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.

Approach:

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