Understanding the long-term fate of nitrate in terrestrial ecosystems: Organic N species
EMSL Project ID
50514
Abstract
We propose a series of experiments aimed at elucidating the mechanisms associated with the incorporation of nitrate (NO3-) into soil organic matter (SOM), with broad implications for the N biogeochemical cycle. Nitrate can be reduced to other N inorganic species via denitrification and/or incorporated into organic matter by immobilization. Immobilization is understood as a mechanism of NO3- transformation that entails the reduction of NO3- possibly to more reactive NO2- before immobilization into organic N. The overarching goal of this project is to understand the cycling of N in soils, specifically the incorporation of NO3- into natural organic matter (i.e., formation of Org-N species). To achieve this goal, we utilize a long-term field 15N tracer study (Arnot Forest), and laboratory-based mesocosm experiments with individual soil horizons (Oa, A, E, B). Our objectives are: Objective 1. Characterize the forms of N present in field-collected archive soil samples from a long-term (up to 10 years) whole-ecosystem 15N tracer study; and Objective 2. Elucidate N transformational pathways in individual Oa, A, E and B soil horizons from the Arnot experimental forest. Utilizing EMSL's advanced Nuclear Magnetic Resonance (NMR), Electron Paramagnetic Resonance (EPR), and 21T Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) capabilities, we will learn whether soils are capable of incorporating tracer 15N-NO3- into their structure to form soil organic nitrogen (SON) as well as dissolved organic nitrogen (DON) species. We will also follow the mechanisms of N immobilization by tracking and identifying N species present during time-resolved mesocosm incubations. The proposed work will be conducted in collaboration with Andrew Lipton, Eric Walter and Rosalie Chu, experts in advanced NMR, EPR, and FTICR-MS, respectively, approaches at EMSL. Coupling of advanced NMR, HYSCORE and high-resolution FTICR-MS analyses to study organic N species will aid in unraveling the molecular structures of organic N in soils (SON and DON). A self-consistent interpretation of the various NMR, EPR and FTICR-MS approaches is expected while an unequivocal interpretation could not be made from any individual technique. Consequently, the EPR, NMR and FTICR-MS experiments at EMSL are key analytical approaches that will provide the ability to resolve the dynamics of NO3- reactions in complex environmental matrices. The experiments we propose will provide molecular level understanding of macroscopic processes and are critical to understanding the character of N stored in terrestrial ecosystems and ultimately the release of this essential nutrient into plant-available forms. These experiments are also of great significance to understanding controls of nutrient losses that will improve water and air quality.
Project Details
Project type
Exploratory Research
Start Date
2018-10-21
End Date
2019-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
DiDonato N., C.S. Clendinen, A. Rivas-Ubach, N. Tolic, N. Sokol, D. Adhikari, and C. Martinez, et al. 09/15/2020. "Assessing soil organic matter features as detected with direct infusion high resolution mass spectrometry and LC-MS-MS feature based molecular networking." Abstract submitted to Metabolomics Association of North America (MANA), Online Conference, United States. PNNL-SA-155199.