Document: JAC-3-30-29

Carbon dioxide fluxes on the Colorado shortgrass steppe and Wyoming northern mixed prairie.

MORGAN, J.A.* ¹, G.E.SCHUMAN ² and T.G.GILMANOV ³

USDA-ARS, Fort Collins, CO USA ¹
USDA-ARS Cheyenne, WY USA ²
South Dakota State University, Brookings, SD USA ³

Abstract:
As atmospheric CO₂ concentrations continue to rise and affect the global climate, there is a need to better understand the C cycle in order to understand and manage C fluxes in future CO₂ enriched atmospheres. Our interest in this study is with two grasslands which lie within 40 miles of each other and represent vast expanses of the Great Plains, the shortgrass steppe (SGS) and the northern mixed prairie (NMP). Two bowen ratio/energy balance stations were installed in late March 1998, one at the USDA ARS Central Plains Experimental Range, a SGS in northeastern Colorado, and the other at the USDA-ARS High Plains Grasslands Research Station, a NMP just west of Cheyenne, WY. Fluxes of CO₂ were measured for 20 minute intervals throughout the growing season and into the late autumn until stations were dismantled in late November. Although productivity of the NMP is approximately twice that of the SGS, aboveground peak standing phytomass was similar at both sites in 1998, averaging 131 g m^-2 on the NMP and 133 g m^-2 on the SGS. The total amount of C assimilated from late March through November was considerably higher on the SGS site, with 138 g C assimilated compared to only 49 g C assimilated on the NMP. Seasonal and site-related patterns of C assimilation were controlled to a large extent and are explained in terms of soil water dynamics.

Keywords: carbon, productivity, photosynthesis, grass, range

This abstract is being presented at: 8:15 AM in session:
Oral Session #43: Plant Community Responses to Climate Change.