COS 253-3 - Measuring and modeling the ability of perennial bioenergy crops to enhance soil carbon

Abstract: Perennial bioenergy crops have the potential to reduce carbon emissions and restore soil carbon stocks that were depleted due to traditional agricultural. While the lack of tillage in perennial management is partly responsible for increases in soil C, the contribution of litter, root, and microbial traits remains unknown. To address this unknown, we performed an integrated suite of experiments to examine how these traits drive soil C formation in Miscanthus x. giganteus. We then used this data to improve a novel plant-microbial interaction model, FUN-BioCROP. On the empirical side, we found that there is a link between miscanthus litter chemistry, the ability of microbes to decompose miscanthus litter, and the formation of soil C. Lab incubations of ¹³C labeled litter showed that additions of miscanthus litters led to more particulate soil C than mineral associated soil C, primarily due to complex litter chemistry driving low microbial carbon use efficiency. In the field, miscanthus roots were found to preferentially mine nitrogen from ¹³C and ¹⁵N labeled particulate organic matter which may act to further stabilize carbon by driving microbial N limitation. When we examined how the ability of miscanthus to form soil C varied down to 1m, we found that the fate of miscanthus root inputs shifted from particulate soil C to mineral associated soil C at deeper depths, likely due to their ability to act as microbial hotspots. Using these measurements to improve model projections, we found that miscanthus formed more soil carbon than corn or other perennial feedstocks like switchgrass after 50 years. However, given that miscanthus preferentially forms particulate soil C, warming simulations show that this carbon is susceptible to loss with global change. Collectively, these results suggest that miscanthus production has the potential to meet this goal of generating a carbon neutral fuel while restoring soil C.