Quantifying the carbon (C) uptake of the perennial grass, Miscanthus × giganteus (M × g), in both aboveground and belowground structures (e.g., net primary productivity (NPP)) and differences among methodological approaches is crucial. Many estimates of M × g productivity focus on aboveground harvestable yields and do not directly address belowground biomass in this perennial crop.
A study by researchers at the Center for Advanced Bioenergy and Bioproducts Innovation (CABBI), a Department of Energy-funded Bioenergy Research Center, set out to directly measure M × g NPP and to evaluate the effect of nitrogen fertilization, location, and method of rhizome biomass collection.
To more accurately constrain the amount of carbon taken up by M × g in both aboveground and belowground plant parts, CABBI researchers calculated the NPP of mature M × g at three sites with three nitrogen application rates using collections of aboveground and belowground biomass at two time points during the growing season.
Researchers found that aboveground M × g NPP ranged from 15.4 Mg DM ha–1 year–1 to 36.4 Mg DM ha–1 year–1 and belowground M × g NPP ranged from 4.4 Mg DM ha–1 year–1 to 19.6 Mg DM ha–1 year–1 . M × g NPP varied across sites, fertilization, and calculation assumptions. Aboveground NPP (yield) was on average 68.7% of the total NPP. Root-to-shoot ratios at peak biomass decreased with nitrogen application rate, from an average of 1.9 for 0 N plots to 0.89 for 224 N fertilized plots.
Overall, these results show that the range of mature M × g NPP is driven by aboveground productivity, influenced by nitrogen application and site. The results provide useful data to constrain agroecosystem models and provide crucial insights for future perennial belowground sampling. These estimates help improve our understanding of M × g carbon sequestration potential and will improve the representation of M × g in agroecosystem models.
