Carbon dioxide and water fluxes from switchgrass managed for bioenergy production

Switchgrass (Panicum virgatum L.) is an important bioenergy crop with the potential to provide a reliable supply of renewable energy while also sequestering C in the soil. The purpose of this study was to quantify CO2 fluxes during the establishment and early production years of a young switchgrass stand in the northeastern USA. Switchgrass was sown in June 2004 and daily CO2 fluxes were measured for four years. Gross primary productivity (GPP) varied little among years, but ecosystem respiration (Re) decreased over time. The switchgrass generally began to take up CO2 in mid-May and continued until early-October, and was a net sink during a 98-day period from late-May through early-September. The rest of the year experienced a net loss of CO2 to the atmosphere. Harvested biomass increased each year and was not related to GPP. The switchgrass field was a net CO2 sink for the first three years, but became a source the final year due to increased removal of C as harvested biomass. This study suggests that in addition to their primary function as a source of renewable energy, switchgrass bioenergy crops in the northeastern USA can sequester CO2 for at least the first few years following establishment.