B094-0009
Mineral-mediated persistence of soil organic matter and its chemical dynamics in response to nitrogen fertilization in grassland soils
Tuesday, 15 December 2020
Poster
Qian Zhao1, Stephen Callister2, Allison Thompson1, Ravi K Kukkadapu3, Malak M Tfaily4, Lisa Bramer1, Nikolla P Qafoku1, Sheryl L Bell1, Sarah E Hobbie5, Eric W. Seabloom6, Elizabeth T. Borer7 and Kirsten S Hofmockel8, (1)Pacific Northwest National Laboratory, Richland, WA, United States, (2)Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA, United States, (3)Pacific Northwest National Lab, Richland, WA, United States, (4)University of Arizona, Tucson, AZ, United States, (5)University of Minnesota Twin Cities, Ecology, Evolution, and Behavior, Saint Paul, MN, United States, (6)University of Minnesota Twin Cities, Minneapolis, United States, (7)University of Minnesota Twin Cities, Minneapolis, MN, United States, (8)Pacific Northwest National Laboratory, Earth and Biological Sciences, Richland, WA, United States
Abstract:
Biogeochemical cycling of carbon (C) in grassland soils is crucial to global terrestrial-atmosphere C flux in C cycling models. The retention of soil organic matter (OM) is governed by interactions with minerals, which mediate the sorption of chemically diverse OM molecules via distinct surface areas and chemical functional group availabilities. A quantitative and mechanistic understanding of how mineralogy influences OM persistence remains challenging due to the multi-layered nature of biochemical-mineral interactions that contribute to soil C persistence. In addition, human impacts on grassland soils, such as increased nitrogen (N) deposition, can influence C biogeochemical cycling by altering OM chemistry and mineral-OM associations. Therefore, soil management to enhance the formation and persistence of soil OM is increasingly needed.
This study sought to understand how soil mineralogy as well as N enrichment regulate OM persistence in grassland soils and how the chemical composition of OM is altered during microbial decomposition. Using a multi-site grassland experiment, the Nutrient Network, we found that with increasing abundance of ferrihydrite (Fh), the mineral-associated, hydrophobic fraction of OM became more enriched in lipid- and protein-like compounds, whereas the water-extractable organic carbon (WEOC) became more enriched in lignin-like molecules. Nitrogen addition disrupted the accumulation of protein-like molecules in the mineral-associated hydrophobic fraction. Microorganisms preferentially decomposed energetically favorable compounds, such as amino sugars, carbohydrates, proteins, and lipids in most soils; however, these molecules were preserved in soils with high Fh content. The microbial decomposition resulted in an increased richness of lignin and tannin derivatives. Moreover, the chemical composition of OM across different soils was similar after 8-months of microbial decomposition. The changes in chemical composition of OM were not as pronounced with N addition. This study provides an advanced understanding of mineral-dependent OM persistence, OM chemical composition during the microbial decomposition and altered mineral-OM interactions in response to N inputs.
