Project Number: 5409-11000-003-00
Project Type: Appropriated

Start Date: Dec 15, 2004
End Date: Dec 14, 2009

Objective:
Objective I: Assess/project changes in the structure and functioning of Great Plains grasslands due to the interactive effects of elevated CO2 and legume N on primary production, N and C cycling, and plant community dynamics, including invasive weeds. Objective II: Develop management strategies that optimize responses of semi-arid rangeland to global change and minimize emission of greenhouse gases (GHGs).

Approach:
We will use novel Free Air CO2 Enrichment (FACE) technology to expose the native northern mixed-grass prairie (NMP) to a gradient of CO2 concentrations from present ambient levels of approximately 370 to 670 parts per million. Within the CO2 gradient, plots consisting of native NMP and NMP inter-planted with combinations of legume and invasive weed species will evaluate how legume N interacts with CO2 to affect soil C and N cycling, trace gas fluxes, water relations, plant physiology/demography/phenology, reproductive and vegetative recruitment, weed invasion, and plant community dynamics. In a related modeling exercise, data from previous CO2 enrichment and flux experiments will be used to predict long-term weather and global change responses of Great Plains grasslands. A second objective will evaluate the impacts of management strategies on C and N cycling and land-atmosphere exchange of greenhouse gases. The responses of soil C and N dynamics to variable grazing intensity and seasonality will be determined. Inter-seeding legumes into rangeland will be evaluated for its potential to enhance biomass production, forage quality, and mitigate greenhouse gas emissions. This information will be used to develop new management practices that consider trace gas emissions, in addition to more traditional rangeland goods and services.