title: Are nitrogen-fertilized forest soils sinks or sources of carbon?
abstract: We developed a simple conceptual model that tracks nitrogen and carbon jointly through an N fertilized forest ecosystem. The stimulation of growth increases the litterfall and imports substrate for soil microorganisms. Microbial biomass forms according to the supply of C and N. The formation of microbial biomass is accompanied by respiratory C losses. The quantity of CO2 efflux depends on the C use efficiency of microbes. When excess N is available, the microbial activity is accelerated and the demand for substrate is high. Litterfall supplies an insufficient amount of C to the soil. In such a case, labile soil C is mineralized and the net effect of N fertilization is a loss of soil C. A strong N fertilization effect on the aboveground biomass can offset the soil C loss. In the case of a low N dosage or high N losses due to leaching or emission of nitrogen oxides, the soil C loss is small. The conceptual model was applied to a case study. The field data, collected over a time span of several decades, could not support sound conclusions on the temporal trend of soil C because the spatial and temporal variability of the chemical data was high. The conceptual model allowed to give an evaluation of the fertilization effect on soil C based on reproducible principles.
authors.affiliation: Department of Wildland Resources, Utah State University, Logan, UT 84322-5230, USA. helgavm@cc.usu.edu
authors.forename: Helga
authors.initials: H
authors.lastname: Van Miegroet
authors.forename: Robert
authors.initials: R
authors.lastname: Jandl
mesh_terms: D018533:Biomass; D002244:Carbon / Q000032:analysis*; D005308:Fertilizers; D009584:Nitrogen / Q000032:analysis*; D012987:Soil; D012988:Soil Microbiology
chemical_list: D005308:Fertilizers; D012987:Soil; D002244:Carbon; D009584:Nitrogen