Switchgrass ecotypes alter microbial contribution to deep-soil C

Authors: Roosendaal, Damaris; Stewart, Catherine; DENEF, KAROLIEN - Colorado State University; FOLLETT, RONALD - Retired ARS Employee; Pruessner, Elizabeth; Comas, Louise; Varvel, Gary; SAATHOFF, AARON - Li-Cor, Inc; Palmer, Nathan - Nate; Sarath, Gautam; Jin, Virginia; Schmer, Marty; MADHAVAN, SOUNDARARAJAN - University Of Nebraska

Submitted to: Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2016
Publication Date: 5/10/2016
Citation: Roosendaal, D.L., Stewart, C.E., Denef, K., Follett, R., Pruessner, E.G., Comas, L.H., Varvel, G.E., Saathoff, A., Palmer, N.A., Sarath, G., Jin, V.L., Schmer, M.R., Madhavan, S. 2016. Switchgrass ecotypes alter microbial contribution to deep-soil C. Soil. SOIL 2, 185–197. doi:10.5194/soil-2-185-2016.

Interpretive Summary: Switchgrass (Panicum virgatum L.) is a C4, perennial grass that is being developed as a bioenergy crop for the United States. While aboveground biomass production is well documented for switchgrass ecotypes (lowland, upland), little is known about the impact of plant belowground productivity on microbial communities down deep in the soil profiles. Differences in root biomass and rooting characteristics of switchgrass ecotypes could lead to distinct differences in belowground microbial biomass and microbial community composition. We quantified root biomass and root architecture and the associated microbial abundance, composition and rhizodeposit C uptake for two switchgrass cultivars. Kanlow, a lowland cultivar with thicker roots, had greater plant biomass above- and belowground, greater root mass density, and lower specific root length compared to Summer, an upland cultivar with finer root architecture. Bacteria dominated microbial profiles for both Kanlow and Summer soils. The two ecotypes also had distinctly different microbial communities process rhizodeposit C; greater gram-negative bacteria under Kanlow and greater saprotrophic fungi Summer. For bioenergy production systems, variation between switchgrass ecotypes could alter microbial communities and impact C sequestration and storage as well as potentially other belowground processes.

Technical Abstract: Switchgrass (Panicum virgatum L.) is a C4, perennial grass that is being developed as a bioenergy crop for the United States. While aboveground biomass production is well documented for switchgrass ecotypes (lowland, upland), little is known about the impact of plant belowground productivity on microbial communities down deep in the soil profiles. Differences in root biomass and rooting characteristics of switchgrass ecotypes could lead to distinct differences in belowground microbial biomass and microbial community composition. We quantified root biomass and root architecture and the associated microbial abundance, composition and rhizodeposit C uptake for two switchgrass cultivars using stable isotope probing of microbial phospholipid fatty acids (PLFA) after 13CO2 pulse-chase labeling. Kanlow, a lowland cultivar with thicker roots, had greater plant biomass above- and belowground, greater root mass density, and lower specific root length compared to Summer, an upland cultivar with finer root architecture. The relative abundance of bacterial biomarkers dominated microbial PLFA profiles for both Kanlow and Summer soils (55.4% and 53.5%, respectively), with differences attributable to a greater relative abundance of gram-negative bacteria in Kanlow soils (18.1%) compared to Summer soils (16.3%). The two ecotypes also had distinctly different microbial communities process rhizodeposit C; greater relative atom % 13C excess in gram-negative bacteria (44.1 ± 2.3%) under the thicker roots of Kanlow and greater relative atom % 13C excess saprotrophic fungi under the thinner roots of Summer (48.5 ± 2.2%). For bioenergy production systems, variation between switchgrass ecotypes could alter microbial communities and impact C sequestration and storage as well as potentially other belowground processes.