Switchgrass Ecotype Impacts Deep Soil Microbial Community Composition and Rhizodeposit Uptake.

Perennial cellulosic bioenergy crops such as switchgrass (Panicum virgatum L.) can improve marginally productive cropland and sequester C deep in the soil profile. Phenotypic variability in switchgrass cultivars alters belowground plant allocation, rooting characteristics; and subsequently, could modify the microbial community abundance and composition. We  quantified microbial contributions to SOM over a growing season, to a depth of 150 cm using a pulse-chase ¹³C labeling experiment of two switchgrass cultivars, Kanlow and Summer.  Root characteristics were significantly different between species, with the lowland cultivar having significantly larger roots with less specific root length compared to the upland species. We also analyzed the active (¹³C-labelled phospholipid fatty acids) and total (16S/18S rRNA pyrosequencing) microbial community associated with the rhizosphere of each cultivar. Active microbial community composition and rhizodeposit C uptake were different between the two cultivars.  The microbial community associated with the thinner roots of Summer had rhizodeposit C uptake associated primarily with saprotrophic fungi, while the thicker roots of Kanlow’s rhizodeposit C was processed primarily by G- bacteria. Phylogenetic profiles of the 16S/18S libraries show that both cultivar and depth significantly influence community composition. For bioenergy production systems, variation between switchgrass ecotypes could impact C sequestration and storage as well as C cycling by altering microbial communities.