Nitrogen mineralization and assimilation at millimeter scales |
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Authors: | John B. Cliff Peter J. Bottomley Daniel J. Gaspar |
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Affiliation: | a Department of Crop and Soil Science, Oregon State University, Agriculture Life Science Building 3017, Corvallis, OR 97331, USA b Department of Microbiology, Oregon State University, 220 Nash Hall, Corvallis, OR 97331, USA c Advanced Radioanalytical Chemistry, Pacific Northwest National Laboratory, Richland, WA 99352, USA d Willam R. Wiley Environmental Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, USA |
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Abstract: | This study used inoculated, artificial soil microcosms containing sand, clay, cellulose, and localized “hotspots” of highly labile, organic N-containing dead bacteria to study N mineralization and assimilation at millimeter scales. Labeling with 15NH4+ along with measurement of its assimilation into microbial biomass at the bulk scale allowed estimation of gross rates of ammonification and N assimilation using isotope dilution. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analyses of transects of organic-15N across Si wafers in contact with the microcosms indicated strong gradients of 15NH4+ assimilation as a function of proximity to the hotspots that were not apparent using bulk analyses. This combination of bulk and ToF-SIMS analyses represents a powerful approach to explore the physical and biochemical factors that affect N process heterogeneities in soils. |
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Keywords: | Ammonification Immobilization Isotope dilution Time-of-flight secondary ion mass spectrometry SIMS Nitrogen |
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