EAPSI: Constraining the Isotope Effect of Denitrification to Improve Global Models of N Fluxes

Walker Rebecca H, Davis CA

Investigators

Abstract

This project will use modeling to quantify the amount of nitrogen lost from soils through denitrification, a key component of the nitrogen cycle. Quantifying denitrification is important because the gases produced during denitrification cause poor air quality that damages human health. Also, because nitrogen limits the ability of plants to grow, quantifying it will allow for better predictions about carbon storage. Denitrification is nearly impossible to measure directly, and as such, developing an accurate model is essential. This project will be conducted at the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia under the mentorship of Dr. Ying-Ping Wang. The collaboration provides access to the expertise and computing capacity at CSIRO. Denitrification removes biologically available nitrogen (N) from ecosystems, making it an important control over the biosphere's N balance, with implications for air quality, human health, and climate change. Despite its importance, estimates of the global soil denitrification flux remain highly uncertain. Major challenges lie in directly measuring the gaseous by-products of denitrification and scaling this complex microbial processes. Process-based models constrained by empirical isotopic evidence have emerged as a method to help overcome these challenges. However, the robustness of this method is limited by incomplete understanding of isotopic expression of denitrification and how it varies across known controls, such as carbon and nitrate availability and soil moisture and temperature. The project will determine how the isotopic expression of denitrification varies across a range of environmental controls and will incorporate this data into models of denitrification. Ultimately this model will be incorporated into the CASA-CNP, the global model of nutrient limitations on terrestrial carbon sequestration developed by scientists at CSIRO. This will reduce a key uncertainty in predictions of carbon sequestration. This award, under the East Asia and Pacific Summer Institutes program, supports summer research by a US graduate student and is jointly funded by NSF and the Australian Academy of Science.