Plant community composition influences fine root production and biomass allocation in perennial bioenergy cropping systems of the upper Midwest, USA

Fine roots play a key role in the global carbon (C) cycle because much of the C accumulating in soil is the result of fine root production and turnover. Here we explore the effect of plant community composition and diversity on fine root production in surface soils and plant biomass allocation to fine roots in six perennial cropping systems differing in composition and diversity planted as biofuel feedstocks. The six systems were established in 2008 at both a high and a moderate fertility site located in the upper Midwest, USA and included: switchgrass (Panicum virgatum), miscanthus (Miscanthus × giganteus), hybrid poplar (Populus nigra × P. maximowiczii 'NM6), native grasses (a five-species assemblage of Andropogon gerardii, Elymus canadensis, P. virgatum, Schizachrium scoparium, and Sorghastrum nutans), an early successional system, and a restored prairie with 25 sown grass, legume, and forb species. For three years (2011-2013) at both sites ingrowth cores were deployed each spring; half were extracted at mid-season and the rest in late fall. Native grasses and restored prairie systems produced 31-77% more fine roots by mid-season compared to the other cropping systems at both sites. Miscanthus and hybrid poplars tended to have the lowest fine root production. The polyculture cropping systems allocated 39-94% more energy to the production of fine roots, with the exception of switchgrass at the low fertility site. Findings demonstrate a greater potential for diverse biofuel cropping systems to allocate C belowground to fine roots as compared to monocultures, with potential implications for soil C sequestration.