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109. Intraspecific Differences in Plants Impact Soil Microbial Substrate Utilization

Lola M. Klamm, Megan Kelly-Slatten, Dr. Julie Jastrow, Dr. Marie-Anne de Graaff

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  • Increasing carbon (C) storage in the soil may help reduce atmospheric carbon dioxide (CO2) and mitigate climate change.
  • The C4 grasses Panicum virgatum (switchgrass) and Andropogon gerardii (big bluestem) are candidate biofuel species that can contribute to soil C accumulation.
  • We showed that soil C accumulation differs among these species and their cultivars (Adkins et al., 2019), but the mechanisms that explain these differences remain uncertain.
  • Differences in soil C accumulation may be driven by variation in microbial substrate utilization.

We ask: How does microbial substrate utilization differ among cultivars of big bluestem and switchgrass?

Sample Collection and Processing

  • Monocultures of big bluestem and switchgrass cultivars (Table 1) were established in 2008 at the Fermilab Environmental Research Park in Batavia, IL (Figure 1).
  • In 2018, 10 cm soil cores were collected and homogenized. Rocks, roots, and litter were removed.
Field site, photo
Figure 1: Study site in Batavia, IL.

Table 1: Cultivars of Andropogon gerardii and Panicum virgatum.

Big bluestem (BB)Switchgrass (SG)
Bonanza (BO)Cave-in-Rock (CR)
Southlow (SO1)Kanlow (KA)
Suther (ST)Southlow (SO2)

Analysis of Microbial Substrate Utilization

Using MicroRespTM, we amended soil with C substrates (Table 2), incubated for 6 hours, and measured CO2 respiration.

Table 2: C substrates used for MicroRespTM assay

Carbohydratesglucose, xylose, fructose, arabinose, mannose, sucrose
Amino Acidsalanine, arginine, lysine, n-acetyl-glucosamine, histidine, phenylalanine, glycine
Organic Acidsmalic acid, ?-ketoglutaric acid, ascorbic acid, fumaric acid, 3,4-dihydroxybenzoic acid, uric acid, citric acid
Otherpolysorbate 80, cellulose, xylan, chitin

Main Results

  • Substrate utilization by the soil microbial community was not significantly affected by plant species.
  • Significant differences in the utilization of a majority of substrates did occur among various cultivars within and between species.
Figure 2, graph
Figure 2: This bar graph shows the average amount of CO2 respired by the soil microbial community associated with each cultivar as measured in mg of CO2 per gram of air per gram of soil for each substrate guild. The CO2 respired by the cultivar Cave-in-Rock (SG CR) is significantly lower than the CO2 respired by Suther (BB ST) and Southlow (SG SO2) when the soil is exposed to C sources within amino acids, carbohydrates, and other guilds.

These differences in substrate utilization may affect the ability of different cultivars to sequester CO2 and contribute to climate change mitigation.

Infographic of process: Cultivar 1 leads to lower CO2 output than Cultivar 2

Funding and Resources

Funding and Resources received from the following institutions:

  • Boise Cascade Corporation
  • Boise State University
  • Argonne National Laboratory

Additional Information

For questions or comments about this research, contact Lola Klamm at