Evidence for Fungal Dominance of Denitrification and Codenitrification in a Grassland Soil

Abstract

Fungi are capable of nitrification and denitrification and often dominate the microbial biomass of temperate grassland soils. We determined the contributions of bacteria and fungi to N2O and N2 production in a grassland soil from Northern Ireland by combining the substrate‐induced respiration inhibition method and the 15N gas‐flux method. Streptomycin (C21H39N7O12) was used as the bacterial inhibitor and cycloheximide (C15H23NO4) as the fungal inhibitor. By labeling the NH4 and NO3 pools, we tested the hypothesis that fungi produce N2O and N2 solely by the reduction of NO3 Cycloheximide decreased the flux of N2O by 89% and streptomycin decreased the flux by 23%, indicating that fungi were responsible for most of the N2O production. All of the N2O was derived from NO3 reduction. Labeled N2 was only detected in control and streptomycin treatments. The distribution of the 15N atoms in the labeled N2 indicated that the source of the labeling was predominantly the NO3 pool, but that the process of formation was not dominated by denitrification. Codenitrification, where a 15N atom from labeled nitrogen dioxide (NO2) combines with a 14N atom from a natural abundance source, was proposed as the process forming labeled N2 About 92% of the labeled N2 was estimated to be due to codenitrification and 8% due to denitrification. The flux of N2O was always greater than the flux of N2, the mole fraction of N2O averaging 0.7. Fungal denitrification could be of ecological significance because N2O is the dominant gaseous end product.

Effects of nitrogen deposition and fertilization on N transformations in forest soils: a review

“…Traditionally, heterotrophic denitrification and autotrophic nitrification are viewed as the main sources for N 2 O production in soils (Barnard et al 2005;Wrage et al 2001). In fact, processes such as heterotrophic nitrification by fungi (Eylar and Schmidt 1959), anaerobic oxidation of NH 4 + (Santoro et al 2011), and codenitrification by fungi and actinomycetes (Laughlin and Stevens 2002; have been identified to produce N 2 O. However, in humid environments, heterotrophic denitrification is widely accepted as the dominant source of N 2 O production, followed by autotrophic nitrification (Davidson et al 1986).…”

Response to Hypoxia, Reduction of Electron Acceptors, and Subsequent Survival by Filamentous Fungi

“…Although the main cast of the global nitrogen cycle is currently recognized in bacteria, recent studies have discovered fungal N 2 O production from soils. 36) This suggests a global role of fungal metabolism in preserving the nitrogen balance.…”

Anaerobic Metabolism: Linkages to Trace Gases and Aerobic Processes

“…There have been virtually no field studies of N0 3 -based metabolism by these organisms. However, Laughlin and Stevens (2002) selectively inhibited fungal activity using cycloheximide and observed a decrease in N 2 0 fluxes of 89% in a grassland soil; the antibiotic streptomycin decreased N 2 0 flux by 23%. Because fungi represent a large portion of the microbial biomass in soils (Ruzicka et al, 2000), they may be an important source of N 2 0 in some terrestrial ecosystems.…”