Root traits of perennial C4 grasses contribute to cultivar variations in soil chemistry and species patterns in particulate and mineral-associated carbon pool formation

Authors: KELLY-SLATTEN, MEGAN - Boise State University; Stewart, Catherine; TFAILY, MALAK - University Of Arizona; JASTROW, JULIE - Argonne National Laboratory; SASSO, ABIGAIL - Boise State University; DEGRAAF, MARIE-ANNE - Boise State University

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2023
Publication Date: 2/16/2023
Citation: Kelly-Slatten, M., Stewart, C.E., Tfaily, M., Jastrow, J., Sasso, A., de Graaf, M. 2023. Root traits of perennial C4 grasses contribute to cultivar variations in soil chemistry and species patterns in particulate and mineral-associated carbon pool formation. Global Change Biology Bioenergy. 15(4):613-628. https://doi.org/10.1111/gcbb.13041.
DOI: https://doi.org/10.1111/gcbb.13041

Interpretive Summary: Deep rooted native perennial grasses can store soil carbon, supporting climate smart agriculture. However, this potential can vary greatly due to the specific rooting traits. Scientists from USDA’s Agricultural Research Service, Boise State University, Argonne National Laboratory and University of Arizona studied different cultivars of switchgrass, a deep rooted grass with high potential for significant soil carbon storage. Their work reveals how different switchgrass cultivars not only accumulate different amounts of soil carbon but also different fractions of soil carbon. This work is especially critical in understanding the longevity of carbon storage and the tradeoffs between increased root biomass and soil C storage.

Technical Abstract: Recent studies have indicated that the C4 perennial bioenergy crops switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerardii) accumulate significant amounts of soil C owing to their extensive root systems. Soil C accumulation rates under these grasses are likely driven by inter- and intraspecific variability in plant traits. However, the mechanisms that underpin this variability in soil C storage remain unresolved. In this study we evaluated how cultivars of switchgrass (Cave-in-Rock, Kanlow, Southlow) and big bluestem (Bonanza, Southlow, Suther) varied in root traits, impacting decadal changes in soil C pools using stable isotope techniques. Our experimental field site was established in June 2008 at Fermilab in Batavia, IL. In 2018, soil cores were collected (30 cm depth; 4.8-cm diameter) from the root zone of all cultivars. We measured root biomass, root diameter, specific root length, bulk soil C and C associated with coarse and fine particulate organic matter (CPOM, FPOM) plus silt- and clay-sized fractions. Cultivar monocultures of both 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 also measured organic matter chemical class composition in root-zone soil using high resolution FTICR mass spectrometry. We found that total soil C was similar between species, but species accumulated C through different mechanisms. Big bluestem cultivars had larger root systems that increased C4 plant-derived C in the POM-C pool, while switchgrass cultivars increased the C4 plant-derived C in the clay fraction via differences in root morphology and soil chemistry. This highlights the importance of both POM-C and mineral associated C in building soil carbon pools.