Cultivar-specific microbiomes may modulate switchgrass (Panicum virgatum) biomass yields on reclaimed mine sites in West Virginia.

Switchgrass (Panicum virgatum) has been supported by the U.S. Department of Energy as a “model bioenergy crop” due to its well-characterized growth in various soil types and climates. Its ability to withstand harsh environmental conditions and increase soil stability has incentivized the use of switchgrass as a reclamation crop in recent years as well. However, little is known regarding plant-microbe interactions among switchgrass systems within reclaimed mine lands. A study conducted in 2008 grew switchgrass on high- and low- quality reclaimed mine sites (Hampshire and Hobet, respectively) in West Virginia to examine the resilience of switchgrass as a reclamation-friendly bioenergy crop. Switchgrass yields at Hampshire were nearly an order of magnitude higher than Hobet (8.4 Mg ha−1 vs 1.0 Mg ha−1). Within Hampshire, the Cave-in-Rock cultivar yield was 70% greater than that of Shawnee (12.9 Mg ha-1 vs. 7.6 Mg ha-1) and 187% greater than that of Carthage (12.9 Mg ha-1 vs. 4.5 Mg ha-1). Here, I sought to illuminate plant-microbial interactions that may account for this drastic shift in cultivar yield by examining the root-associated and bulk soils underneath three switchgrass cultivars using enzymatic activity analyses and microbiome taxonomic identification. Specifically, I tested two hypotheses: (i) that the root-associated microbiome will have a functionally and compositionally unique microbiome compared to that of the bulk soil and (ii) that there will be a cultivar-specific root-associated microbiome that may drive previously observed greater, but differential yields across switchgrass cultivars at Hampshire. Hampshire soils showed significant increases in extracellular enzymes associated with the acquisition of C, N, and P compared to Hobet. Additionally, the root-associated microbiome had a greater activities associated with the acquisition of C, N, and P compared to the bulk soil. Further, diverse and taxonomically-unique microbiomes were found between sites and cultivars. While Together, this data suggests that the root-microbiome may contribute to overall aboveground biomass yields between sites, and cultivar-specific microbiomes were observed that may substantiate differential yield responses within Hampshire.