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Title: Carbon dioxide and water vapor fluxes in winter wheat and tallgrass prairie in central Oklahoma

Author
item BAJGAIN, RAJEN - University Of Oklahoma
item XIAO, XIANGMING - University Of Oklahoma
item BASARA, JEFFREY - University Of Oklahoma
item Wagle, Pradeep
item ZHOU, YUTING - University Of Oklahoma
item MAHAN, HAYDEN - University Of Oklahoma
item Gowda, Prasanna
item MCCARTHY, HEATHER - University Of Oklahoma
item Northup, Brian
item Neel, James
item Steiner, Jean

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2018
Publication Date: 7/23/2018
Citation: Bajgain, R., Xiao, X., Basara, J., Wagle, P., Zhou, Y., Mahan, H., Gowda, P., Mccarthy, H., Northup, B.K., Neel, J.P., Steiner, J.L. 2018. Carbon dioxide and water vapor fluxes in winter wheat and tallgrass prairie in central Oklahoma. Science of the Total Environment. 644: 1511-1524. https://doi.org/10.1016/j.scitotenv.2018.07.010.
DOI: https://doi.org/10.1016/j.scitotenv.2018.07.010

Interpretive Summary: Winter wheat and tallgrass prairie are common land cover types in the Southern Great Plains of the United States. In recent years, agricultural expansion into native grasslands has been extensive. This study measured the exchange of carbon dioxide and water vapor fluxes from two major ecosystems (winter wheat and tallgrass prairie) in the Southern Great Plains of the United States using the eddy covariance technique. The major objective was to compare and contrast carbon dioxide and water vapor fluxes between two ecosystems for providing insights on how the conversion of tallgrass prairie grassland to winter wheat could impact the carbon and water budgets of the region. Although both ecosystems were sinks of carbon (carbon gain is more than the release) during their respective growing seasons, the wheat ecosystem was a net source of carbon on an annual scale when fluxes from summer fallow period were considered. In contrast, the tallgrass prairie ecosystem was a net sink of carbon on an annual scale. The daily evapotranspiration (ET) reached seasonal maximum of 6.0 mm day-1 and 7.2 mm day-1in winter wheat and tallgrass prairie, respectively. Wheat was more water efficient than tallgrass prairie on seasonal scale, while tallgrass prairie was more water efficient on an annual scale. The study suggests that the differences in magnitudes and patterns of carbon dioxide and water vapor fluxes between winter wheat and tallgrass prairie can exert influence the carbon and water budgets of the whole region under land use change scenario.

Technical Abstract: Winter wheat (Triticum aestivum L.) and tallgrass prairie are common land cover types in the southern plains of the United States. During the last century, agricultural expansion into native grasslands has been extensive, particularly either managed pasture or dryland crops such as winter wheat. In this study, we measured carbon dioxide (CO2) and water vapor fluxes (H2O) from winter wheat and tallgrass prairie ecosystems in Central Oklahoma using the eddy covariance technique. The objective of this study was to compare and contrast CO2 and H2O fluxes between two ecosystems for providing insights on how the conversion of tallgrass prairie grassland to winter wheat could impact the carbon and water budgets of the region. Daily net ecosystem CO2 exchange (NEE) reached seasonal peaks of - 9.24 g C m-2 d-1 and - 6.23 g C m-2 d-1in winter wheat and tallgrass prairie, respectively. Both ecosystems were sinks of carbon during their respective growing seasons. At the annual scale, the wheat ecosystem was a net source of carbon (56 ± 13 g C m-2 yr-1) when fluxes from summer fallow period were considered. In contrast, the tallgrass prairie ecosystem was a net sink of carbon (-128 ± 69 g C m-2 yr-1). The daily ET reached seasonal peak values of 6.0 mm day-1 and 7.2 mm day-1in winter wheat and tallgrass prairie, respectively. Although, ecosystem water use efficiency (EWUE, the ratio of cumulative gross primary production (GPP) to evapotranspiration (ET)) was higher in wheat (13.1 g CO2 mm-1 ET) than in tallgrass prairie (7.6 g CO2 mm-1 ET) at the seasonal scale, it was slightly higher in tallgrass prairie (6.9 g CO2 mm-1 ET) than in wheat (6.2 g CO2 mm-1 ET) at the annual scale. Results suggest that the differences in magnitudes and patterns of CO2 and H2O fluxes between winter wheat and tallgrass prairie ecosystems can exert an influence on the carbon and water budgets of the whole region under land use change scenario.