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Volume 2, issue 2
SOIL, 2, 185–197, 2016
https://doi.org/10.5194/soil-2-185-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
SOIL, 2, 185–197, 2016
https://doi.org/10.5194/soil-2-185-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Original research article 10 May 2016

Original research article | 10 May 2016

Switchgrass ecotypes alter microbial contribution to deep-soil C

Damaris Roosendaal1, Catherine E. Stewart1,2, Karolien Denef3, Ronald F. Follett1,a, Elizabeth Pruessner1, Louise H. Comas4, Gary E. Varvel5,a, Aaron Saathoff6, Nathan Palmer7, Gautam Sarath7, Virginia L. Jin5, Marty Schmer5, and Madhavan Soundararajan8 Damaris Roosendaal et al.
  • 1Soil-Plant-Nutrient Research Unit, United States Department of Agriculture-Agricultural Research Service, Suite 320, 2150 Centre Avenue, Building D, Fort Collins, CO 80526-8119, USA
  • 2Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523-1499, USA
  • 3Central Instrument Facility (CIF), Department of Chemistry, Colorado State University, Fort Collins, CO 80523-1872, USA
  • 4Water Management Research Unit, United States Department of Agriculture, Agricultural Research Service, Suite 100, 2150 Centre Avenue, Building D, Fort Collins, CO 80526-8119, USA
  • 5Agroecosystems Management Research Unit, USDA-ARS, 251 Filley Hall/Food Ind. Complex, University of Nebraska, Lincoln, NE 68583-0937, USA
  • 6LI-COR Biosciences, Lincoln, NE 68504, USA
  • 7Grain, Forage, and Bioenergy Research Unit, USDA-ARS, 251 Filley Hall/Food Ind. Complex, University of Nebraska, Lincoln, NE 68583-0937, USA
  • 8Department of Biochemistry, University of Nebraska, Lincoln, NE 68588-0664, USA
  • aretired

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. Microbial dynamics in deeper soils are likely to exert considerable control on ecosystem services, including C and nutrient cycles, due to their involvement in such processes as soil formation and ecosystem biogeochemistry. 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 abundance and root architecture and the associated microbial abundance, composition, and rhizodeposit C uptake for two switchgrass ecotypes using stable-isotope probing of microbial phospholipid fatty acids (PLFAs) after 13CO2 pulse–chase labeling. Kanlow, a lowland ecotype with thicker roots, had greater plant biomass above- and belowground (g m−2), greater root mass density (mg cm−3), and lower specific root length (m g−1) compared to Summer, an upland ecotype with finer root architecture. The relative abundance of bacterial biomarkers dominated microbial PLFA profiles for soils under both Kanlow and Summer (55.4 and 53.5 %, respectively; P  =  0.0367), with differences attributable to a greater relative abundance of Gram-negative bacteria in soils under Kanlow (18.1 %) compared to soils under Summer (16.3 %; P  =  0.0455). 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 in 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.

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Short summary
Switchgrass is a deep-rooted perennial grass bioenergy crop that can sequester soil C. Although switchgrass ecotypes vary in root biomass and architecture, little is known about their effect on soil microbial communities throughout the soil profile. By examining labeled root-C uptake in the microbial community, we found that ecotypes supported different microbial communities. The more fungal community associated with the upland ecotype could promote C sequestration by enhancing soil aggregation.
Switchgrass is a deep-rooted perennial grass bioenergy crop that can sequester soil C. Although...
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