Nitrogen mineralization and assimilation at millimeter scales

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 (NH4+)-N-15 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-N-15 across Si wafers in contact with the microcosms indicated strong gradients of (NH4+)-N-15 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 heterigeneities in soils. (c) 2006 Elsevier Ltd. All rights reserved.