Grantee Research Project Results

Management Impacts on Positive Feedbacks in Carbon and Nitrogen Cycles of Great Plains Grasslands

EPA Grant Number: U915622
Title: Management Impacts on Positive Feedbacks in Carbon and Nitrogen Cycles of Great Plains Grasslands
Investigators: Harris, Wylie N.
Institution: Texas A & M University
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 1999 through September 1, 2002
Project Amount: $85,968
RFA: STAR Graduate Fellowships (1999) RFA Text |  Recipients Lists
Research Category: Fellowship - Ecology , Ecological Indicators/Assessment/Restoration , Academic Fellowships

Objective:

The objectives of this research project are to: (1) evaluate impacts of herbivory and fire on carbon (C) and nitrogen (N) cycling; and (2) evaluate the modulatory effect of regional climate on that interaction in managed native grasslands of the Great Plains.

Approach:

The first part of the research project will focus on verifying predicted correlations between management history and plant-soil nutrient relations. Plants and soils will be sampled at an array of native prairie sites along a precipitation gradient in northern Texas. At the beginning and end of the growing season, leaves and roots will be sampled from five individuals of each biomass-dominant C3 and C4 graminoid species at each site, and soil cores will be taken from the edge of the root crown and from a point between plants. Soil organic matter (SOM) will be separated by density into three fractions (active, intermediate, and passive) using a silica-based suspension. Concentrations of C and N and the C:N ratio will be determined on plant tissues and SOM fractions. Microbial biomass C and N, and potential C and N mineralization rates, will be measured via laboratory incubations.

In the second part of the project, mechanistic linkages underlying the correlative phenomena will be assessed intensively by experimental manipulations at a mixed-grass prairie site in north Texas over a 2-year period. Treatments are replicated five times each in 36 m² plots and include: simulated grazing (clipping) at two levels of intensity (rotational and season-long), with and without manure amendments; burns at two seasons (summer and winter); and combinations of both burn treatments with the light grazing treatment. All measurements from the first part of the project (described in the paragraph above) will be duplicated in this part of the project, but at monthly intervals; in addition, laboratory incubations for potential C and N mineralization will be complemented by in situ IRGA soil respiration measurements (C) and resin core incubations (N).

In the third part of the project, regional climatic influences will be assessed by duplicating the sampling scheme described in the first part at an array of sites extending northward along a gradient of increasing temperature, from both extremes of the east-west precipitation gradient sampled in the first part of the project to a northern boundary of 52° N latitude.

An accurate assessment of the predicted consequences of grazing and burning, and the degree to which they are modulated by regional climatic variation, is essential for the development of sustainable resource management strategies and the quantification of global C and N budgets.

Supplemental Keywords:

fellowship, carbon and nitrogen cycles, Great Plains grasslands, soils, plants, soil organic matter, SOM, grazing, burning., Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Habitat, Ecology and Ecosystems, Environmental Monitoring, bunch grass, community composition, habitat dynamics, carbon allocation, land use effects, ecological consequences, community genetic diversity, grasslands, soil chemistry, grazing

Progress and Final Reports:

2000

2001

Final