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Contributed Poster

Session: Soil

PS 47-211 - Bioenergy crop selection matters: Species impacts microbial function and soil carbon accumulation across depths

Wednesday, August 9, 2023
5:00 PM – 6:30 PM PDT
Location: ESA Exhibit Hall
Abstract: Recent studies have indicated that the C4 perennial bioenergy crops switchgrass (Panicum virgatum) and big bluestem (Andropogon gerardii) accumulate significant amounts of soil carbon (C) owing to their extensive root systems. We have observed significant inter-and intra-specific variability in soil C accumulation under these crops particularly across soil depths. These differences may be linked to variability in microbial metabolism of root-derived C. With this study we asked how inter- and intra-specific variation in perennial bioenergy crops impacts microbial function across soil depths, and how this relates to soil C accumulation after 10 years of growth. We evaluated how six cultivars of switchgrass (Cave-in-Rock, Kanlow, Southlow) and big bluestem (Bonanza, Southlow, Suther) impacted the Shannon diversity and substrate utilization of the soil microbial communities, and then compared these findings with C associated with coarse and fine particulate organic matter (CPOM, FPOM) plus silt- and clay-sized fractions. Our experimental field site was established in June 2008 at Fermilab in Batavia, IL. In 2018, soil cores were collected (30cm depth; 4.8-cm diameter) next to the crown of all cultivars. C4 species were established on soils that supported C3 grassland for 36 years before planting, which allowed us to use differences in the natural abundance of stable C isotopes to quantify C4 plant-derived C. We measured substrate induced C utilization (i.e. water, glucose, sucrose, malic acid, citric acid, alanine, N-acetylglucosamine (NAG) and polysorbate 80 (POL)) using MicroResp and compared substrate respiration values and functional diversity for each cultivar at three different depths (0-10, 10-20, 20-30 cm). We found that species drive differences in microbial function across soil depths, and these species-depth patterns are consistent in plant-derived soil C accumulation. Within the 0-10 cm, big bluestem had higher microbial activity compared to switchgrass. This was related to a higher quantity of plant-derived C in the POM soil fractions relative to switchgrass, possibly suggesting more root-C incorporation into the more bioavailable soil fraction. In the 10-30 cm depth, switchgrass had higher microbial respiration and higher functional diversity compared to big bluestem, resulting in a greater incorporation of plant-derived C into the mineral-associated clay fraction compared to big bluestem. These results suggest that species selection of bioenergy crops can impact soil C accumulation via microbial function. Gaining a better understanding of soil C accumulation patterns in bioenergy crops can help increase efficiency of bioenergy production and belowground C storage.