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Evidence for Fungal Dominance of Denitrification and Codenitrification in a Grassland Soil
Author(s) -
Laughlin Ronald J.,
Stevens R. James
Publication year - 2002
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2002.1540
Subject(s) - denitrification , dominance (genetics) , nitrogen , nitrogen fixation , cycloheximide , chemistry , grassland , soil water , nitrification , streptomycin , botany , flux (metallurgy) , environmental chemistry , agronomy , biology , ecology , biochemistry , organic chemistry , gene , protein biosynthesis , antibiotics
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 N 2 O and N 2 production in a grassland soil from Northern Ireland by combining the substrate‐induced respiration inhibition method and the 15 N gas‐flux method. Streptomycin (C 21 H 39 N 7 O 12 ) was used as the bacterial inhibitor and cycloheximide (C 15 H 23 NO 4 ) as the fungal inhibitor. By labeling the NH 4 and NO 3 pools, we tested the hypothesis that fungi produce N 2 O and N 2 solely by the reduction of NO 3 Cycloheximide decreased the flux of N 2 O by 89% and streptomycin decreased the flux by 23%, indicating that fungi were responsible for most of the N 2 O production. All of the N 2 O was derived from NO 3 reduction. Labeled N 2 was only detected in control and streptomycin treatments. The distribution of the 15 N atoms in the labeled N 2 indicated that the source of the labeling was predominantly the NO 3 pool, but that the process of formation was not dominated by denitrification. Codenitrification, where a 15 N atom from labeled nitrogen dioxide (NO 2 ) combines with a 14 N atom from a natural abundance source, was proposed as the process forming labeled N 2 About 92% of the labeled N 2 was estimated to be due to codenitrification and 8% due to denitrification. The flux of N 2 O was always greater than the flux of N 2 , the mole fraction of N 2 O averaging 0.7. Fungal denitrification could be of ecological significance because N 2 O is the dominant gaseous end product.