Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 28, 2002
Publication Date: July 1, 2002
Citation: FRANK, A.B., LIEBIG, M.A., HANSON, J.D. SOIL CARBON DIOXIDE FLUXES IN NORTHERN SEMIARID GRASSLANDS. SOIL BIOLOGY AND BIOCHEMISTRY. 2002. v. 34. p. 1235-1241. Interpretive Summary: Grassland soils are high in soil organic carbon and contain extensive fibrous root systems creating an environment ideal for soil microbial activity and carbon dioxide loss to the atmospheric. Grasslands occupy a large area that may be a source of atmospheric carbon dioxide, but data is lacking on the magnitude of this source. We used the dynamic method to quantify soil carbon dioxide fluxes for grazed mixed-grass prairie (GP), nongrazed mixed-grass prairie (NGP), and grazed western wheatgrass (WWG), and to evaluate the relationship between soil temperature, air temperature, soil water content, and soil CO2 flux. Daily soil flux during the growing period averaged 3.5, 4.3, and 4.0 g CO2-C m-2 d-1 for NGP, GP, and WWG, respectively. Dormant period fluxes for the GP averaged 0.48 g CO2-C m-2 d-1 . Growing period soil carbon dioxide flux averaged 728 g CO2-C m-2 and dormant period CO2 flux averaged 86 g CO2-C m-2. Soil temperature accounted for 65 percent of flux variability. A predictive relationship was developed using the minimum, maximum, and optimum soil temperatures for soil CO2 flux. The magnitude of soil carbon dioxide fluxes measured confirms the importance of quantifying annual soil carbon dioxide losses in developing a C budget for grasslands. A model was developed to reliably estimate these soil carbon dioxide fluxes.
Technical Abstract: The high indigenous organic carbon (C) content in prairie soils provide a source of carbon dioxide (CO2) that is an important component in the C budget of grasslands. Soil fluxes were measured on a grazed mixed-grass prairie (GP), nongrazed mixed-grass prairie (NGP), and grazed western wheatgrass (WWG) wheatgrass. Objectives were to quantify soil CO2 fluxes for each site and to determine the contribution of soil temperature, soil water content, and air temperature to soil flux. Soil fluxes were measured about every 21 days at 1300 h during the 25 April-27 October growing period from 1996-2000 and on the grazed prairie during the 28 October-26 April dormant period from 1999-2001. Fluxes were low in the spring and autumn and peaked concurrent with biomass in late June to mid-July. Maximum fluxes averaged 5.8 g CO2-C m-2 d-1 for NGP, 6.9 g CO2-C m-2 d-1 for GP, and 6.1 g CO2-C m-2 d-1 for WWG. Soil fluxes measured during the dormant period decreased to near zero during the months of December, January, and February and then increased rapidly in March as soil temperatures increased. Daily soil flux during the growing period averaged 3.5 g CO2-C m-2 d-1 for NGP, 4.3 g CO2-C m-2 d-1 for GP, and 4.0 g CO2-C m-2 d-1 for WWG. Dormant period fluxes for the GP averaged 0.48 g CO2-C m-2 d-1. Regression analysis indicated that soil temperature accounted for 65%, soil water content 5%, and air temperature 3% of flux variability. Growing period soil CO2 flux over years averaged 728 g CO2-C m-2 and dormant period CO2 flux averaged 86 g CO2-C m-2. A predictive relationship describing the response of soil CO2 flux to changes in soil temperature was developed using the minimum, maximum, and optimum soil temperatures for soil CO2 flux.