Collaborative Research: Rhizosphere priming and C-N dynamics in grassland ecosystems in transition

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Rhizosphere priming, the focus of this study, is the process by which living roots affect the potential for soils to store and release carbon and nitrogen. On a global basis, soils store twice as much carbon as is in the atmosphere and regulate the nitrogen supply to maintain plant productivity while preventing excess nitrogen losses. Laboratory studies indicate that rhizosphere priming is likely a key control on soil CO2 emissions and the release of nitrogen from organic matter. However, the control of rhizosphere priming on soil carbon and nitrogen transformations in real ecosystems has been difficult to study and is not well understood. This is important because many environmental changes could alter rhizosphere priming, with potentially large consequences for carbon storage and nitrogen cycling. By measuring carbon and nitrogen isotope tracers in plants and soils, this study will follow the fate of different carbon and nitrogen sources and separate their contributions the functioning of the soil in grasslands of the central United States. This study also uses plants with different kinds of root characteristics to figure out the different influences plants can have on rhizosphere priming. Over three years, this study will address two main questions: (1) What is the magnitude of rhizosphere priming on the breakdown of organic matter under realistic soil conditions? and (2) How do different plant and soil characteristics affect priming across seasons, types of plants and different soils? This project is that start of a comprehensive effort to decipher and ground truth the important roles of of roots in actual grassland ecosystems.The results of this project will help us understand how changes in plants and environmental conditions affect air quality and the loss of nitrogen from soils. It will train nine undergraduate students, three graduate students, and a post-doctoral scientist. Recruitment of participants will focus on underrepresented groups and build on existing programs in California, Kansas and Oklahoma to increase the diversity of the project participants. Results will be incorporated into undergraduate and graduate courses in the three states and project data will be made available on a web site. This project will also help to enhance public education and awareness and to inform the general public of the importance of roots in providing essential services from our grasslands. Finally, the location and visibility of the experiment at the Konza Prairie Long-Term Ecological Research site in Kansas offers unique opportunities for public education, including development of modules for the schoolyard programs and other outreach activities.