FY2010 - Oak Ridge National Laboratory

Director’s R&D Fund—
Systems Biology and the Environment
SYSTEMS BIOLOGY AND THE ENVIRONMENT
05133
Carbon Drivers of the Microbe–Switchgrass Rhizosphere Interface
Christopher W. Schadt, Hector F. Castro-Gonzalez, Marie Anne De Graaff, Charles T. Garten III, and
Aimee T. Classen
Project Description
Plants allocate a significant proportion of their carbon belowground as roots and root exudates. These
often-labile carbon substrates serve as the energy source for complex microbial communities that inhabit
the rhizosphere and stimulate ecosystem nutrient processes. In spite of its ecological importance, root
exudation is poorly understood and even less is known about how changes in the amount and type of root
exudate might alter the functions of the soil microbial community. Microbial functional group
composition in the rhizosphere is likely influenced directly and indirectly by a number of complex factors
that include interactions with the dominant plant species as well as interactions with other
microorganisms. Studies of the feedbacks between root exudation and microbial community function will
enable better understanding of how shifts in plant genetics (e.g., bioenergy crops) may alter soil carbon
cycles, crop sustainability, and carbon sequestration. In laboratory and greenhouse studies, we will merge
the power of two technologies— 13 C stable isotope probing (SIP) and DNA analysis—to link root exudate
quality and quantity with microbial community structure and function in the rhizosphere using
switchgrass as a model system.
Mission Relevance
Understanding of the rhizosphere interface supports DOE objectives in carbon cycling and the role of
soils in bioenergy crop sustainability. This project proposes an approach that could be used in several
ecosystems by further development of genomic tools for ecosystem research. This will benefit research
programs in the DOE Office of Science, Office of Energy Efficiency and Renewable Energy, other
federal agencies such as EPA and USDA, and state extension progams. Within the DOE Office of
Biological and Environmental Research (BER), this project will enhance the goals of the Program for
Ecosystem Research (PER) to understand and predict effects of environmental changes associated with
energy production on terrestrial ecosystems. The PER has encouraged explorations across levels of
biological organization and the use of genomics in ecology. This project will also fit the DOE Genomics
Science (formerly GTL) program goals to characterize the functional repertoire of microbial communities
in natural environments and position ORNL to compete for DOEs planned investment in Genomics
Science centers that focus on carbon cycling and climate change research.
Accomplishments
We successfully (1) designed microcosms enabling us to semi-hydroponically grow plants under anexic
conditions to collect, and accurately identify root exudates; (2) identified some of the major root exudates
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