Title: Shortgrass Steppe ecosystem dynamics and trace gas exchange under elevated CO2 (LT20)
A.R. Mosier, USDA/ARS; J.A. Morgan, USDA/ARS; D.G. Milchunas, Rangeland Ecosystem Science, Colo. St. Univ.; W.J. Parton, Natural Resource Ecology Laboratory, Colo. St. Univ. & D.S. Ojima, Natural Resource Ecology Laboratory, Colo. St. Univ.
TECO Grant Number: IBN-9524068
SUMMARY
During the past few decades the atmospheric concentration of CO2 has been increasing at historically unprecedented rates. Increasing CO2 concentrations will have a direct effect on plant production and plant communities and indirectly feed back into a number of soil biotic systems that influence long term ecosystem viability. The impact of elevated CO2 on the shortgrass steppe (SGS) which is used extensively for grazing has not been previously addressed.
Based on experiments with elevated CO2 in other ecosystems, elevated CO2 may induce changes in productivity and dominance of C4/C3 grasses in the SGS. Water use patterns will probably be altered and on the long term, soil N availability may be reduced. Alterations in C and N cycling in the soil induced by elevated CO2 may change soil N turnover rates which impacts nutrient availability to plants but also to soil microbes. Soil microbes produce NOx and N2O and consume atmospheric CH4. These atmospheric trace gases play important roles in ecosystem N availability and atmospheric chemistry and global climate change. These interactive feedbacks on the soil C and N cycles and their influence on trace gas fluxes have potentially important impacts on the global atmospheric budgets of the gases.
The research proposed couples use of large open top chamber CO2 enrichment in the field with soil N cycling and trace gas studies. Large open-top chambers, shown below, were constructed during 1996 and employed first during the 1997 growing season.
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Our overall objectives of this program are to determine the impact of
doubling CO2 in SGS mixed C3/C4 plant communities: (1) on
ecosystem dynamics; (2) on soil N and C cycles and the impact of changes on trace gas
flux; and (3) to incorporate the knowledge gained from these studies into simulation
models that will allow for realistic extrapolation through time and space. The
research proposed is primarily a field program that will be conducted at the USDA/ARS
Central Plains Experimental Range (CPER), within the shortgrass steppe in north central
Colorado on which is located the Shortgrass Steppe Long Term Ecological Research Site
(LTER). Close association and coordination will be maintained within the CPER and LTER
programs and the information gleaned from these studies will be used directly within both
long term programs. |
Research Objectives
Objective 1: Determine the impact of doubling CO2
in shortgrass steppe mixed C3/C4 plant
communities on:
a) net primary production
b) net ecosystem CO2/H2O exchange
c) C and N allocation both above and below ground
d) water and N use efficiency
Objective 2: Determine the impact of doubling CO2 on soil water and N dynamics on:
a) soil water content
b) C/N distribution in soil organic matter
c) changes in mineralizable N
d) NO and N2O emissions
e) CH4 consumption of atmospheric CH4
Objective 3: To incorporate the knowledge gained from these studies
into simulation models that
will allow for realistic extrapolation through time and space of:
a) soil moisture
b) nutrient cycling
c) plant productivity
03/21/02