Grantee Research Project Results

Alternative Stable States in Nitrogen Fixer Abundance

EPA Grant Number: FP917815
Title: Alternative Stable States in Nitrogen Fixer Abundance
Investigators: Bytnerowicz, Thomas A
Institution: Columbia University in the City of New York
EPA Project Officer: Lee, Sonja
Project Period: September 1, 2015 through August 31, 2018
Project Amount: $132,000
RFA: STAR Graduate Fellowships (2015) RFA Text |  Recipients Lists
Research Category: Academic Fellowships

Objective:

The ability of forests to bounce back from disturbance and to sequester atmospheric CO₂ is highly dependent on the nitrogen supplied through the presence and activity of symbiotic nitrogen fixing trees. The fellow is using theoretical modeling along with greenhouse and field experiments to address the following questions: what environmental conditions are favorable for symbiotic nitrogen fixers and how will ecosystems respond to pressures from global change as indicated by the presence and activity of nitrogen fixers?

Approach:

I am developing ecosystem models to evaluate the plant traits and environmental characteristics that lead to alternative trajectories of forest succession. Model analysis is accomplished through a combination of analytical and simulation techniques. I am also conducting experiments to investigate how well nitrogen fixing plants are able to tune fixation to meet their demand for nitrogen. These experiments investigate the effects of temperature, taxonomic identity, and environmental adaptation.

Expected Results:

Preliminary model analysis suggests that as forests mature, conditions can arise where alternative stable states between nitrogen fixing and nonfixing plants are possible. These dynamics can occur when competing plants are limited by different resources and when each plant is a superior competitor for the resource that limits its own growth. Plant traits such as carbon and nitrogen stoichiometry can generate conditions for alternative stable states. Additionally, the ability of nitrogen fixing plants to regulate their fixation activity determines their ability to persist in forests. It appears that the regulation of nitrogen fixation is most rapid in nitrogen fixing plants at low latitudes. My research will determine to what degree this pattern is driven by species identity versus environmental conditions. As a result, experimental results will inform us of the physiological responses of nitrogen fixing plants to projected changes in climate.

Supplemental Keywords:

nitrogen fixation, nitrogen limitation, model, alternative stable states, succession

Progress and Final Reports:

2016

2017

Final