Strong mineralogic control of soil organic matter composition in response to nutrient addition across diverse grassland sites

• Published in: The Science of the total environment Vol. 736; p. 137839
• Main Authors: Zhao, Qian, Callister, Stephen J., Thompson, Allison M., Kukkadapu, Ravi K., Tfaily, Malak M., Bramer, Lisa M., Qafoku, Nikolla P., Bell, Sheryl L., Hobbie, Sarah E., Seabloom, Eric W., Borer, Elizabeth T., Hofmockel, Kirsten S.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.09.2020
• Subjects: biogeochemistry; Chemical composition; clay fraction; Ecosystem service; ecosystems; ferrihydrite; Fertilization; grassland soils; grasslands; hydrophobicity; iron; lipids; mineral content; Mineralogy; moieties; nitrogen; Organo-mineral complex; soil aggregates; soil mineralogy; soil organic matter; sorption; Zonal structure; Chemical composition; Fertilization; Organo-mineral complex; Ecosystem service; Mineralogy; Zonal structure
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.137839

Soil organic matter (SOM) dynamics are central to soil biogeochemistry and fertility. The retention of SOM is governed initially by interactions with minerals, which mediate the sorption of chemically diverse organic matter (OM) molecules via distinct surface areas and chemical functional group availabilities. Unifying principles of mineral-OM interactions remain elusive because of the multi-layered nature of biochemical-mineral interactions that contribute to soil aggregate formation and the heterogeneous nature of soils among ecosystems. This study sought to understand how soil mineralogy as well as nitrogen (N) enrichment regulate OM composition in grassland soils. Using a multi-site grassland experiment, we demonstrate that the composition of mineral-associated OM depended on the clay content and specific mineral composition in soils across the sites. With increasing abundance of ferrihydrite (Fh) across six different grassland locations, OM in the hydrophobic zone became more enriched in lipid- and protein-like compounds, whereas the kinetic zone OM became more enriched in lignin-like molecules. These relationships suggest that the persistence of various classes of OM in soils may depend on soil iron mineralogy and provide experimental evidence to support conceptual models of zonal mineral-OM associations. Experimental N addition disrupted the accumulation of protein-like molecules in the hydrophobic zone and the positive correlation of lignin-like molecules in the kinetic zone with Fh content, compared to unfertilized soils. These data suggest that mineralogy and clay content together influence the chemical composition not only of mineral-associated OM, but also of soluble compounds within the soil matrix. If these relationships are prevalent over larger spatial and temporal scales, they provide a foundation for understanding SOM cycling and persistence under a variety of environmental contexts. [Display omitted] •Beyond clay content, mineralogy strongly controlled the composition of MAOM.•Ferrihydrite accumulated proteins and lipids in the hydrophobic zone of MAOM.•The mineral core influenced biochemical persistence of OM in the kinetic zone.•Nitrogen fertilization altered carbon chemistry and organo-mineral interactions.