Collaborative Research: Elucidating unifying principles of soil carbon-nitrogen coupling using a continental-scale grassland experimental network

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Human activities such as fertilizer use on crops, cultivation of soybean crops, and fossil fuel burning are increasing the amount of nitrogen gas that is circulating in the atmosphere and coming down in rain and snow in what is known as nitrogen deposition. The full impacts of high amounts of nitrogen deposition on ecosystems around the world are not well known. In particular, how nitrogen deposition alters the amounts and forms of carbon in soils is very poorly understood. Yet, achieving better understanding of this so-called coupling between the nitrogen and carbon cycles is important for life on earth. Plants and soils exchange large amounts of carbon dioxide with the atmosphere each year and so small changes in the rate of that exchange could affect how fast carbon dioxide in the air is rising. This project will integrate results from extensive cross-site, coordinated field experiments with modeling to improve our mechanistic understanding of the coupling of belowground carbon and nitrogen in grassland ecosystems. This is a key knowledge gap for Earth system models used to predict the biogeochemical consequences of human-caused global environmental changes and to refine predictions of carbon cycle feedbacks to climate change. This project will also connect researchers with education and outreach programs of the Cedar Creek Long-Term Ecological Research project. These programs are aimed at training K-12 students and teachers and increasing participation and retention of women and members of other underrepresented groups in science, with a special focus on mentoring undergraduate Native Americans in research. Project investigators will also mentor graduate students and post-doctoral scholars. This research will use a network of decade-long nutrient addition experiments in North American grasslands, the Nutrient Network, to study how enhanced nitrogen inputs influence soil microbial dynamics, soil carbon cycling, and the release of carbon dioxide to the atmosphere. Results will be used to enhance the Microbial ENzyme Decomposition (MEND) model towards determining how nitrogen inputs affect: (1) biochemical stabilization of soil organic matter (SOM) by altering the quantity and quality of plant inputs to soils, and soil microbial community structure, stoichiometry, and functional potential; and (2) physicochemical stabilization of SOM by altering soil aggregate formation and SOM-mineral interactions. Results of computer simulation models of ecosystem carbon and nitrogen cycling will be made available to the scientific community at large through the Accelerated Climate Model for Energy program at the Department of Energy. All data generated from the proposed work will also be made publically available through the Nutrient Network research project and the Long-Term Ecological Research network.