Location: Soil Management and Sugarbeet ResearchTitle: Seasonal switchgrass ecotype contributions to soil organic carbon, deep soil microbial community composition and rhizodeposit uptake during an extreme drought
|DENEF, KAROLIEN - Colorado State University
|SOUNDARARAJAN, MADHAVAN - University Of Nebraska
Submitted to: Soil Ecology Society Conference
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2017
Publication Date: 9/1/2017
Citation: Stewart, C.E., Roosendaal, D.L., Denef, K., 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 Ecology Society Conference. 112:191-203. doi:10.1016/j.soilbio.2017.04.021.
Technical Abstract: The importance of rhizodeposit C and associated microbial communities in deep soil C stabilization is relatively unknown. 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 switchgrass ecotypes (Panicum virgatum L., Kanlow and Summer) with contrasting root morphology. We quantified root phenology, soil microbial biomass (phosopholipid fatty acids, PLFA), and microbial rhizodeposit uptake (13C-PLFAs) to 150 cm over one year during a severe drought. The lowland ecotype, Kanlow, had two times more root biomass with a coarser root system compared to the upland ecotype, Summer. Over the drought, Kanlow lost 78% of its root biomass, while Summer lost only 60%. Rhizosphere microbial communities associated with both ecotypes were similar. However, rhizodeposit uptake under Kanlow had a higher relative abundance of gram-negative bacteria (44.1%), and Summer rhizodeposit uptake was primarily in saprotrophic fungi (48.5%). Both microbial community composition and rhizodeposit uptake shifted over the drought into gram-positive communities. Rhizosphere soil C was greater one year later under Kanlow due to turnover of unlabeled structural root C. Despite a much greater root biomass under Kanlow, rhizosphere d13C was not significantly different between the two ecotypes, suggesting greater microbial C input under the finer rooted species, Summer, whose microbial associations were predominately saprotrophic fungi. Root-derived C inputs drive soil C processes and these data suggest that individual plant interactions with the microbial community and extreme drought events affect soil C sequestration.