LAUSR

Abstract Old world bluestem cultivar WW-B Dahl [Bothriochloa bladhii (Retz.), S. T. Blake] is a non-native perennial C4 bunch grass with biofuel production potential grown predominantly in the Southern U.S. Great Plains. Although this is a popular introduced grass cultivar, data on carbon fluxes and evapotranspiration (ET) from this warm-season grass is rare. In this study, the eddy covariance method was used to measure CO2 and ET from an established stand of bluestem for three years (2013–2015). Year 2015 had the highest gross primary production (GPP; 1358 ± 143 g C m−2) followed by 2014 (1250 ± 31 g C m−2) and 2013 (1024 ± 91 g C m−2). The average loss of GPP as ecosystem respiration (Reco) was 76%. Annual NEE sums were -302 ± 15 g C m−2 in 2013, -265 ± 41 g C m-2 in 2014, and -287 ± 32 g C m−2 in 2015. Results from this study show that the NEE in grasslands in years with normal precipitation that is well distributed may not vary from years with above-normal precipitation. This is because precipitation enhances Reco along with carbon uptake, which may result in lower net carbon uptake in perennial grasslands in higher precipitation years than normal precipitation years. Gross primary production showed a linear relationship with ET (R2 = 0.90) and above ground biomass (R2 = 0.74). Only 26% of the GPP was allocated to above ground biomass indicating a higher allocation of carbon to below ground biomass. The water use efficiency of bluestem (2.9 g C kg-1 of water) matched well with that of native prairies and other dedicated biomass crops grown in the Southern Great Plains. As the demand for cellulosic biofuels is increasing, results from field experiments quantifying seasonal changes in carbon fluxes and ET could be important in understanding the contributions of large-scale production of novel biomass crops to regional carbon and hydrologic cycles.