Quantifying shoot and root biomass production and soil carbon under perennial bioenergy grasses in a subtropical environment

Highlights: • Giant reed, sweetcane, sugarcane, energycane, and elephantgrass were able to produce high shoot biomass in North Florida. • Giant miscanthus could not produce comparable shoot biomass with other species in the subtropical environment. • Sweetcane, energycane, and elephantgrass exhibited significant increases in soil C stock over four growing seasons. • Sweetcane, energycane, and elephantgrass are able to provide multiple ecosystem services rapidly following establishment. -- Abstract: Perennial bioenergy grasses can potentially replace fossil fuels and offset atmospheric CO₂ through soil C sequestration. However, limited information relevant to the impacts of bioenergy cropping on ecosystem services, especially above- and below-ground productivity and soil C sequestration is available for subtropical environments (e.g., southeastern USA). The objective of this study was to evaluate the impacts of perennial bioenergy cropping on C cycling and accumulation in the soil following four years of production in North Florida. Treatments consisted of six perennial grass species: giant reed, elephantgrass, energycane, sugarcane, sweetcane, and giant miscanthus. Elephantgrass, energycane, sweetcane, and sugarcane produced great shoot biomass (31–41 Mg ha⁻¹) when harvested once per year. Giant reed's shoot biomass responded favorably to two harvests per year (27–43 Mg ha⁻¹), whereas giant miscanthus did not perform well in any of the years (9–21 Mg ha⁻¹). Additionally, giant reed, sweetcane, and giant miscanthus produced greater root biomass (9–11 Mg ha⁻¹) compared with the other three species (2.5–3.2 Mg ha⁻¹). Among the six grasses, sweetcane, energycane, and elephantgrass resulted in increases in soil C stocks (~15 Mg ha⁻¹) relative to the initial level. Conversely, giant reed and giant miscanthus had no increase in soil C stock. Results suggested that interspecies differences observed in biomass yield among the six perennial bioenergy grasses could therefore affect soil C accumulation. High biomass yielding species such as sweetcane, energycane, and elephantgrass can effectively increase soil C within a few years following establishment in a subtropical environment.