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ABSTRACT
Grasslands have an underground biomass component that serves as a carbon (C) storage sink. Switchgrass (Panicum virgatum L.) has potential as a biofuel crop. Our objectives were to determine biomass and C partitioning in aboveground and belowground plant components and changes in soil organic C in switchgrass. Cultivars Sunburst and Dacotah were field grown over 3 yr at Mandan, ND. Aboveground biomass was sampled and separated into leaves, stems, senesced, and litter biomass. Root biomass to 1.1-m depth and soil organic C to 0.9-m depth was determined. Soil C loss from respiratory processes was determined by measuring CO2 flux from early May to late October. At seed ripe harvest, stem biomass accounted for 46% of total aboveground biomass, leaves 7%, senesced plant parts 43%, and litter 4%. Excluding crowns, root biomass averaged 27% of the total plant biomass and 84% when crown tissue was included with root biomass. Carbon partitioning among aboveground, crown, and root biomass showed that crown tissue contained approximately 50% of the total biomass C. Regression analysis indicated that soil organic C to 0.9-m depth increased at the rate of 1.01 kg C m^sup -2^ yr^sup -1^. Carbon lost through soil respiration processes was equal to 44% of the C content of the total plant biomass. Although an amount equal to nearly half of the C captured in plant biomass during a year is lost through soil respiration, these results suggest that northern Great Plains switchgrass plantings have potential for storing a significant quantity of soil C.
Abbreviations: C, carbon; N, nitrogen; LAI, leaf area index.
THE RAPID RATE of increase in atmospheric CO2 levels has placed emphasis on better understanding the role of agriculture in mitigating this increase. The vast area of perennial grasslands and the large C-laden root biomass associated with grasslands suggests that grassland agriculture can contribute to reducing atmospheric CO2 concentrations. Native grasslands contain large amounts of soil organic C mainly because of their large root biomass (Frank et al., 1995). Measurement of CO2 fluxes have shown grasslands are generally a net sink for atmospheric CO2 (Frank and Dugas, 2001; Frank et al, 2000; Sims and Bradford, 2001; Suyker and Verma, 2001). Some suggest native grasslands are at soil organic C equilibrium and that expecting...