Submitted to: Agriculture Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2001
Publication Date: N/A
Citation: N/A Interpretive Summary: Atmospheric carbon dioxide levels are increasing rapidly due to burning of fossil fuels and land use changes. Grasslands occupy a large area in the USA, but data is lacking on the role of grasslands as a sink for sequestering atmospheric carbon dioxide. The Bowen ratio energy balance technique was used to measure carbon dioxide fluxes over a mixed prairie grassland from 24 April to 26 October over 4 years. Dormant season soil carbon dioxide fluxes were estimated from soil temperatures. Four year growing season flux averaged 345 g carbon dioxide/m2, dormant period flux estimated form soil temperatures averaged -317 g CO2/m2 resulting in a net annual flux of 28 g carbon dioxide/m2/yr. These results suggest that Northern Great Plains mixed prairie grasslands can provide a small sink for atmospheric carbon dioxide, but overall the carbon cycle for the grassland studied was near equilibrium.
Technical Abstract: Temperate grassland ecosystems are an important component of the global carbon (C) cycle. The Bowen ratio/energy balance (BREB) technique was used to measure CO2 fluxes over a mixed prairie at Mandan, ND from 24 April to 26 October in 1996, 1997, 1998, and 1999. Above- ground biomass and leaf area index (LAI) were measured about every 21 days throughout the season. Root biomass and soil organic C and N content were determined to 110 cm depth in selected increments about mid-July each year. Peak above-ground biomass typically occurred between mid-July to early-August and ranged from 782 kg ha in 1998 to 1692 kg ha in 1996. Maximum LAI ranged from 0.34 in 1998 to 0.48 in 1999. Root biomass ranged from 12720 kg ha in 1996 to 16220 kg ha in 1997. Maximum CO2 fluxes generally coincided with periods of active above-ground biomass production. Short duration drought periods reduced CO2 fluxes. Total CO2 flux for the 24 April to 26 October period ranged from 181 g CO2 m2 in 1998 to 474 g CO2 m2 in 1999, while the four year average flux was 345 g CO2 m2. Fluxes during the non-measurement dormant season were estimated form soil temperatures and averaged -1.76 g CO2 m2 d. The sum of the growing season and dormant season fluxes ranged from -211 to 151 g CO2 m2 y and averaged 28 g CO2 m2 yr over the four year period. These results suggest that Northern Great Plains mixed prairie grasslands can provide a sink for atmospheric CO2, but overall the C cycle is probably near equilibrium.