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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Soil Management and Sugarbeet Research » Research » Publications at this Location » Publication #333808
Title: Seasonal switchgrass ecotype contributions to soil organic carbon, deep soil microbial community composition and rhizodeposit uptake during an extreme drought

Author
item Stewart, Catherine
item Roosendaal, Damaris
item DENEF, KAROLIEN - Colorado State University
item Pruessner, Elizabeth
item Comas, Louise
item Sarath, Gautam
item Jin, Virginia
item Schmer, Marty
item SOUNDARARAJAN, MADHAVAN - University Of Nebraska

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2017
Publication Date: 5/22/2017
Citation: Stewart, C.E., Roosendaal, D.L., Denef, K., Pruessner, E.G., Comas, L.H., Sarath, G., Jin, V.L., Schmer, M.R., Soundararajan, M. 2017. Seasonal switchgrass ecotype contributions to soil organic carbon, deep soil microbial community composition and rhizodeposit uptake during an extreme drought. Soil Biology and Biochemistry. 112:191-203. doi:10.1016/j.soilbio.2017.04.021.

Interpretive Summary: More than 50% of the world’s soil C stocks reside below 30 cm, but relatively little is known about the importance of rhizodeposit C and associated microbial communities in deep soil processes. Phenotypic variability in plant root biomass could impact C cycling through belowground plant allocation, rooting architecture and microbial community abundance and composition. The lowland ecotype had three times the root biomass with coarser architecture compared to the upland ecotype, Summer. Over the year, Kanlow lost 78% of its root biomass due to drought conditions, while Summer maintained its root biomass. Although the microbial communities associated with both ecotypes were similar, rhizodeposit uptake illustrated two different active microbial communities. The upland species, Summer, was associated with a more saprotrophic fungal community and the lowland species, Kanlow was associated with a more gram negative bacterial community. Rhizosphere soil 13C was slightly enriched at the end of the experiment, with no difference between the ecotypes. Root-derived C inputs drive soil C processes and these data suggest that plant-species specific interactions with the microbial community and climate variables could play an important role in the direction of C sequestration.

Technical Abstract: More than 50% of the world’s soil C stocks reside below 30 cm, but relatively little is known about the importance of rhizodeposit C and associated microbial communities in deep soil processes. Phenotypic variability in plant root biomass could impact C cycling through belowground plant allocation, rooting architecture and microbial community abundance and composition. We used a pulse-chase 13C labeling experiment with compound-specific stable-isotope probing to investigate the importance of rhizodeposit C to deep soil microbial biomass under two 3-yr old switchgrass ecotypes with distinct root architecture, Kanlow and Summer. We quantified root phenology, soil microbial biomass rhizodeposit uptake (13C-PLFAs) to a depth of 150 cm over one year. The lowland ecotype had three times the root biomass with coarser architecture compared to the upland ecotype, Summer. Over the year, Kanlow lost 78% of its root biomass due to drought conditions, while Summer maintained its root biomass. Although the microbial communities associated with both ecotypes were similar, rhizodeposit uptake illustrated two different active microbial communities. The upland species, Summer, was associated with a more saprotrophic fungal community and the lowland species, Kanlow was associated with a more gram negative bacterial community. Enriched communities converged over time. Although soil properties initially did not differ, rhizosphere soil C was greater one year later under Kanlow – presumably from unlabeled root death, since there was not greater 13C enrichment. Rhizosphere soil 13C was slightly enriched at the end of the experiment, with no difference between the ecotypes. Root-derived C inputs drive soil C processes and these data suggest that plant-species specific interactions with the microbial community and climate variables could play an important role in the direction of C sequestration.