Carbon Control on Nitrogen Dynamics in the Forest Floor of an N-Enriched Deciduous Forest Ecosystem

Recent evidence from nitrogen (N) saturation studies indicates that forest floors in moderately impacted forests are the primary sink for atmospheric N inputs. Some researchers have suggested that the sink capacity of organic horizons is dependent on the amount of available carbon (C), which can be used for microbial N assimilation. To test the hypothesis that C limitation in forest floors exposed to chronic N deposition leads to an enhanced N leaching, a field C input manipulation experiment is under way in a deciduous forest. Since September 1999 aboveground C input has been doubled (by doubling litter input or by amending glucose) or excluded in replicated plots. Here we report the short-term response of concentrations of dissolved inorganic N (DIN: NO₃ ^?-N and NH₄ ⁺-N) in forest floor percolate to the C input manipulation. In autumn following the C input manipulation, DIN concentrations in forest floor percolate decreased in all plots except the No Litter plots compared to the pre-treatment summer concentrations. In contrast, the concentrations of DIN in the No Litter plots remained high. A different seasonal pattern of DIN leaching among treatments, along with measurements of microbial biomass C and potential nitrification rates of forest floor samples, indicates that seasonal N dynamics in the forest floor are largely regulated by C availability changes assoicated with litterfall C input.