Annual variability of carbon exchanges over the bioenergy crops and standard row crops

How do bioenergy crops alter carbon sequestration under different climate conditions? Long-term monitoring of carbon fluxes is critical to answering this question and can reveal how crop biogeochemical cycles and climate interact to change these fluxes over time. Here we present findings from Iowa State University's Sustainable Advanced Bioeconomy Research (SABR) Farm where we compared carbon fluxes variation in standard row crops (corn and soybean) and bioenergy crops (miscanthus and sorghum) over time. Carbon fluxes were monitored using eddy covariance techniques (EC) for three growing seasons (2019-2021). Preliminary results indicate that the annual variation of cumulative net ecosystem carbon dioxide exchange (cumulativeNEE mean±stdev) was higher in sorghum (-496.3 ±405.2 g C m-2) than in miscanthus (-580.3 ±104.5 g C m-2), corn (-655.3 ±89 g C m-2) and soybean (-288 ±65.8 g C m-2). This high variation in sorghum was caused by high ecosystem respiration (Reco) in 2021 compared to 2019 and 2020, which led to a dramatic decrease in cumulativeNEE and near carbon neutrality. A structural model path analysis was used to understand driving forces of Reco. Path analysis indicated that SWC decrease greatly affected Reco for Sorghum more than other crops by showing an almost two-fold higher Reco at the lowest SWC year (2021). This study has importance for how long-term carbon flux monitoring in different crops is helpful to understand how carbon fluxes alter.