Project: Defining the Roles of Microbial Taxa in Soil Nitrogen Turnover

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Principal investigators: Dr. Jennifer Pett-Ridge, Lawrence Livermore National Laboratory; Dr. David Myrold, Oregon State University; Peter Bottomley, Oregon State University

Associated with: The National Science Foundation

Project Summary:

Switchgrass (SG; Panicum virgatum L.), a perennial grass native to the tallgrass prairie, is one of the most promising bioenergy crops in the U.S., with potential to provide high-yield biomass on marginal soils unsuitable for traditional agricultural crops. A persistent concern for bioenergy cultivation of SG, with low-input management, is improving seedling establishment and resistance to abiotic and biotic stresses. Our study investigates the role that the switchgrass rhizosphere microbial community plays in mediating successful establishment; as well the role switchgrass plays in structuring its own rhizosphere microbial community through the expression of proteins and the production of root exudates.

To this end, we have established field plots at two sites in Oklahoma where we are observing the succession of the rhizosphere microbial community associated with both high- and low-performing switchgrass genotypes through the course of establishment, and over multiple years post-establishment. In the future, we will be clonally propagating high- and low-performers into common gardens in both sites to isolate the effects of individual plant genotypes on observed rhizosphere community succession.

We are also performing a 13CO­2 pulse-chase labeling experiment with switchgrass in the greenhouse, where we can directly alter soil nutrient status and water availability. This study will allow us to track 13C fixed through photosynthesis into switchgrass root exudates, and from there into the RNA and DNA of the microbial community being directly supported by the consumption of plant-derived carbon compounds.

Finally, we are investigating the potential of various “beneficial partner” microbial symbionts that may enhance switchgrass establishment and growth, particularly in the face of nutrient or water stress. By growing switchgrass in mesocosms in the greenhouse both with and without potential microbial symbionts isolated from our field plots, we aim to determine whether certain microbial taxa, such as Serendipita vermifera, allow their switchgrass symbionts to better access nutrients or water in limiting conditions.