Understanding Plant-Soil-Microbial Processes to Enhance Ecosystem Services in Low-Input Biofuel Feedstock Production: Increasing Inter-Specific and Intra-Specific Biodiversity.

Perhaps the most promising approach in producing C-negative bioenergy (maximizing feedstock production while sequestering C) utilizes mixed-species perennial ecosystems. Research on restored prairie communities indicates that, for low-input systems, long-term yields can be greater with higher plant diversity than with low diversity communities or monocultures. Diverse grassland plantings are better equipped to deal with annual variations in climate and typically have fewer problems with pathogen buildup than monocultures.  Also, including legumes in the mixture is a low-input alternative to N fertilization.  However, growing a feedstock consisting of several different grass species might complicate efforts to convert plant cellulose into ethanol.  Another source of complementarity to maximize biomass production and C sequestration that we are investigating is within species (intra-specific) genetic variation by combining multiple genotypes of switchgrass. Previous research has focused primarily on aboveground biomass production. Our research extends belowground to assess how plant-soil-microbe interactions will influence soil carbon dynamics and the potential for carbon sequestration.  Sustainability of feedstock production practices may be improved if breeders can better identify plant traits that reduce fertilizer inputs and increase the crop’s ability to sequester carbon in recalcitrant pools. Because mycorrhizal symbioses facilitate plant growth in infertile and droughty soil and also mediate soil C accrual, these plant-fungal associations need to be considered in the design of feedstock management practices. Our goal is to enhance belowground ecosystem services, such as soil C storage, without a loss in production. Our field data conducted at Fermilab indicates both inter-specific and intra-specific biodiversity produced equal or greater aboveground biomass than monocultures of switchgrass cultivars. Multiple genotypes of switchgrass had a greater annual production of arbuscular mycorrhizal fungi, compared to monocultures of switchgrass. Results of our study will inform plant breeders on feedstock management that decrease fertilizer inputs, improve aboveground ecosystem services, such as wildlife habitat, while also increasing belowgound services such as soil tilth and soil carbon sequestration, all without a loss in production.